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The effect of chronic pain upon the response to noxious stimuli by psychiatric patients
Journal of Psychosomauc Research. 1965, Vol 8, pp 405 to 419. Pergamon Press Ltd
Printed m Northern Ireland
THE EFFECT OF CHRONIC PAIN UPON THE RESPONSE TO NOXIOUS STIMULI BY PSYCHIATRIC PATIENTS H.
MERSKEY*
(Recewed 14 December 1964)
Some common methods of assessing pain THERE is an extensive experimental literature on human responses to noxious or painful stimuh. The psychiatric and psychological section of this literature ha.s been well reviewed by Hall [1] and is also taken into account by Hardy et al. [2] and by Beecher [3] and will be the subject of a detailed report by the present writer [4]. The consensus of opinion from that literature holds that it is possible to measure a Pain Perception Threshold (P.P.T.), defined as the point at which an individual experiences pain when submitted to noxious stimuli. A Pain Reaction Threshold (P.R.T.) can also be measured. The latter is a point chosen according to some physiological or verbal indication of a response to the stimulus. In some cases, e.g. Chapman and Jones [5], it is measured by wincing or withdrawal and in others, e.g. Hazouri and Mueller [6], by a change in the pulse rate, or some other physiological variable. In those instances the P.R.T. can be recorded before the P.P.T. is reached. In most cases it represents a point at which the subject declares the pain to be severe. Such a point wall normally exceed the P.P.T. A third"type of measurement is to give a standard stimulus which will always be felt and to observe the response to it. The terminology used for these measures varies somewhat in different studies. Hall [1] spoke of Pare Perception Thresholds and Pain Reaction Thresholds, but changed his terminology later [7] to Verbal Report of Pain (V.R.P. equivalent to P.R.T.) and Pain Reaction Point. (P.R.P. equivalent to P.R.T.) The present writer and his colleagues [8, 9] have also used these several terms. Each of them has some disadvantages and for reasons given elsewhere [10] it is particularly confusing to talk of "Reactions to Pain". However the terms P.P.T. and P.R.T. are well estabhshed. They wdl therefore be used for the purpose of this discussion and the term P.P.T. will also be used in describing the present work, but the term P.R.T. will be discarded in the report of this investigation, the term Severe Pain Threshold (S.P T.) being preferred for what might otherwise have been called P.R,T. The most common types of stimulus used have been the Heat-Pain apparatus of Hardy et al. [11,7], pressure-pare and electric shock. All these methods have been severely criticised by Beecher [3] who claims to have shown from his considerable review of the literature and from hIs own investigations that pain thresholds assessed experimentally are unreliable and that the nature of the experimental situation leads to mistakes in the assessment of pain. The writer considers that Beecher has made a valid objection to the interpretation of many studies. Pain Perception Thresholds may vary, hke other thresholds, with distraction of the subject and with the experimental instructions and other conditions * Present address:
Saxondale Hospital, Radchffe-on-Trent, Nottingham. 405
406
H. MERSKEY
and this is even more true of Pain Reaction Thresholds. However there is adequate evidence that the heat-pain technique can be rehable [12-14] and pressure-pain, according to the method used here, has been found to be moderately reliable [9]. Further, although there are physical reasons why the threshold to electric shock may be very variable [15] this need not apply to the estimate of intensities above threshold level and Hill et al. [16] found that such estimates could be correlated with the wattage of the stimulus. The results with heat-pain measurement on which many of the common views are founded can therefore often be accepted, although some caution will be required in interpretation. The same applies to measurements of pressure-pain thresholds and of the response to electric shock reported in this work. Common findings on exper,nental pain tn psyehtatrlc pattents and others
Women are generally found to have lower P.P.T.s or P.R.T.s than men [17, 18, 5, 2, 19, 8, 20, 9]. Kennard [19] was able to show that this was not due to any significant difference in skin thickness. Hardy et al. [2] show variations with attitude, suggestion, fatigue and emotion. Age has no consistent effect. Sherman [18] found no effect with age, but later Sherman and Robilland [21] reported a decrease in sensitivity after the age of thirty in normal subjects. Hardy et al. [22] on the other hand found no evidence that P.P.T.s were related to age in normal subjects. Psychoneurotic patients are generally agreed to have lower thresholds than general medical patients. Schizophrenic patients and retarded depressives may have h~gher thresholds (see Hall's review, 1, 1953). Differences in various directions have been found between negroes and whites, Indians, Canadian "Office Patients" and Miners. These social or racial differences are almost certainly due to effects of attitude. Merskey and Spear [9] found no difference between male Afro-Asian and White medical students. Altogether the importance of atmude is made clear in a study by Schachter [23]. The same noxious stimuli were introduced to one group of subjects in a re-assuring way whilst to another they were described as painful. The groups showed different social responses, indicating more anxiety in the second situation. Thus sex, psychiatric diagnosis and attitude are amongst the most important factors affecting pain sensitivity or threshold level. The effects o f spontaneous pare
Pain is a common symptom in psychiatric illness [24, 25] There have been few studies specifically dealing w~th the P.P.T. and P.R.T. in patients w~th established pain, but many of the psychoneurotic and general medical patients studied by other authors must have had pain. In a series by Chapman et al. [26] on patients with neurocirculatory asthenia, figures were given which showed that almost all the patients complained of pain. This group had a psychoneurotic response pattern in the experimental situation. A study by Schilhng and Musser [27] on peptic ulcer patients showed a similar trend towards increased reactivity or lowered thresholds. Studies of P.P.T. and P.R.T. in the presence of chronic paln have been done in relation to leucotomy by King et al. [28] and Hardy et al. [2]. The first group found bilateral lowering of cutaneous Heat-Pain Perception Thresholds after leucotomy in 5 out of 6 patients, but the results were not significant. The data from Hardy et al. are scanty and less clear-cut, but tend to support King et al. Contrary to the findings with psychoneurotic patients therefore there is some suggestion that chronic pain may
Effect of chronic pain upon the response to noxious stimuli
407
raise thresholds which l e u c o t o m y later reduces. H a z o u r i a n d Mueller [6] reached a similar view in three p a t i e a t s with i n t r a c t a b l e r o o t - p a i n relieved b y c o r d o t o m y . P.P.T. a n d P . R . T . in n o r m a l areas o f skin fell strikingly after the o p e r a t i o n . Lastly K e n n a r d [19] studied 24 patients with chronic p a i n a n d 57 n o r m a l controls. T h e patients all h a d a focal source for their p a i n b u t h a d p r e v i o u s l y been labelled " o v e r - r e a c t o r s . " She f o u n d no d~fference between the g r o u p s with m e a s u r e m e n t o f thresholds to electric shock a n d with G . S . R . b u t b o t h these techniques are open to criticism on the g r o u n d s o f u n r e l i a b d i t y a n d insufficient v a h d a t i o n . O n the whole the p a p e r s on chronic pain, a l t h o u g h confined to a limited n u m b e r o f patients, suggest that where there is a substantial local o r organic cause for the p a i n this raises thresholds elsewhere in the b o d y whereas in the presence o f p s y c h o n e u r o s i s with pain, t h r e s h o l d s m a y fall. The present investigation was u n d e r t a k e n to d e t e r m i n e whether persistent " p s y c h o g e n i c " p a i n raised or lowered p a r e thresholds. The p r o v i s i o n a l hypothes~s was t h a t neurotic patients w o u l d be f o u n d to have lowered thresholds o r increased reactivity a n d t h a t the presence o r absence even o f severe p a i n w o u l d be relatively u n i m p o r t a n t . It was a n t i c i p a t e d that some depressive patients w o u l d have high thresholds a n d others low ones. MATERIAL A. The following experimental groups were studied: 1. Patients with pain, Groups WPM (males) and WPF (females) These were 90 psychiatric patients (37 males and 53 females) with a spontaneous complaint of pain of more than ~2 duration. Cases with prmlafacte "organic" pare were avoided from the outset, but the serms includes three patmnts in whom ~t was ultimately decided that an organic lesion was the principal factor causing pain and six m whom it was thought to be a possible subsidiary factor. 13 of these patients were short-stay in-patients or out-patients at a Mental Hospital (Cherry Knowle Hospital, Sunderland.). The remainder were short-stay m-patients, out-patients and day-patients In the Sheffield University Psychiatric Department. 63 patients described their pain as severe, 12 as moderate and 5 as mild or aching. 47 patients described the pain as continuous and m 13 more it occupmd most of the day. In 71 patients it was present throughout all their waking hours or on a majority of days of the week. In general, therefore, the patients studied complained of continuous severe pam. These patients with pain were d~vlded for certain purposes into sub-groups according to their main diagnosis, as follows:
Sub-Group Sub-Group Sub-Group Sub-Group Sub-Group Sub-Group
PAM PAF PHM PHF PDM PDF
14 Males with Anxiety Neurosis and Pain. 10 Females with Anxiety Neurosis and Paln 14 Males with Hysteria and Pain. 27 Females with Hysteria and Pain. 6 Males with Depression and Pain 13 Females w~th Depression and Pain.
There were also six pain patients with other diagnoses. 2. Patients without pain, Grottos A M and AF, DM and DF In these groups all the patients denied the presence of aches or pains. Groups AM and AF comprised 10 men and 11 women with anxiety neurosis (mainly phobic). Groups DM and DF comprised 10 men and 9 women with depression, mainly endogenous in type. 3. Hypochondriacal patients, Groups S M and SF These groups were included only m part of the study. They were a special set of 16 males and 20 females, selected as being grossly hypochondrlacal by Dr I. Pllowsky who was making a particular study of them. They were regarded as being markedly over-concerned with their physical health. They did not accept reassurance or only did so fleetingly and they tended to return to the same complaint and to produce new ones.
408
H. MERSKEY
4. Normal students, Groups CM and CF These consisted of 15 male and 20 female medical students who all denied aches or pains. The medical students were previously acquainted with the Investigator as were all the patients apart from groups SM and SF. Except for one who refused to take part, the students were a consecutlve series takmg thelr psychiatric clerkship at the time of testing. All the students and some of the patients were aware that they were serving as controls but some patients, despite explanation, beheved the tests were part of their treatment.
Techmques and Mode of Presentation The Maudsley Personality Inventory was given to all subjects who could read and follow the instructions, except for those m groups SM and SF The results with this test are not considered here except m respect of ~ts correlation w~th the other measures The subjects m all groups, except SM and SF, were then tested m order with. I Chnlcal estimates of the Response to Pro-Prick on palms, face and soles of the feet. it. Pare Perception Thresholds and Severe Pain Thresholds determined with the Pressure Algometer; and nl Electronic Recordmg of Finger-Movement m response to mild electric shocks. Those In Groups SM and SF only had mvesUgatlon (u). As a prehmmary all subjects were told that the tests were tests of sensitivity and not tests of endurance. The response to pm-pnck (Technique t) ~s a measure of the extent to which the subject, withdraws, winces or complains when pricked with a hypodermic needle in a standard fashion It has been described m full elsewhere [29, 8] and forms only a minor part of the present report The Pressure Algometer (Techmque i0 consists of a plunger mounted on a spring and bearing a calibrated scale. The end of the plunger is smooth, flat and circular, with a diameter of 0-5 cm and area of 0"196 cmL The plunger was held against the forehead of the subject who was again told that the test was a sensitivity test and not an endurance test. He was asked to say firstly, when he felt pain and then when it hurt a lot. After a prehmlnary trial the process was repeated 4 times, increasing the pressure as nearly as possible at a rate of 1"0 kg/sec. The figures at each level were averaged The lower level gives a measure of the Pain Perception Threshold (P.P.T), the upper level a measure of the Severe Pain Threshold (S.P.T). This techmque has been described and standardlsed by Merskey and Spear [9] and shown to give moderately consistent results. The S.P.T. corresponds to what has otherwise been called the Pain Reaction Threshold (P,R.T), or Pare Reaction Point (P.R.P). Finger-movement m response to electric shock (.Technique m) was recorded as follows The subject was asked to sit with his left forefinger resting steadily on a lever and to keep his hand steady. The lever, suitably damped, rested on the plezo-elecmc crystal from a microphone insert whose potential changes were fed into an E,E G. amphfier The rate of change of pressure by the finger could thus be recorded. The subject was told that he was being asked to take part m yet another test of sensltw~ty. It was emphas~sed that it was a research procedure, that the shocks were of todd to moderate severity, and that there was no danger He was then told that he would be given 3 pairs of shocks and asked to say in each pair which was the stronger or whether they were both the same The shocks were obtained by charging an 8 p F paper dielectric condenser from a 90 V battery and discharging the condenser through a potenttometer. The maximum discharge available, measured by an Avometer was 93V, 1"7 m Amp. through the electrodes used. q-he discharge was divisible in an approximately hnear fashion at nine settmgs of the potentlometer. It was delivered to the subject through circular monel-metal electrodes of 1" diameter apphed with Cambridge electrode jelly to the palmar and dorsal surfaces of the right hand. qhe strength of the individual shocks when taken across an mvometer was Pair 1 Volts mAmp
Paw 2
Pair 3
1
2
3
4
5
6
31 0'5
52 0.9
52 0.9
31 0-5
72 1"2
31 0 5
Thus shocks 1,4 and 6 were Identical in strength and the maximal shock was No. 5 Shocks of the same strength were included in this way at different points because it was suspected that the amount of finger-movement recorded at first would be related to anticipatory anxiety and might dlmlmsh subsequently The dehvery of each shock was registered manually on the E E.G paper, usually via an event-marker. The largest deflection within 1 sec after each shock was measured as an estimate
Effect of chromc pare upon the response to noxious stimuh •
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FiG. 1. Finger movement in response to electric shocks. Normal male medical student; Top line: Time-base: 1"5 cm/sec; 2nd Line: Finger-movement; 3rd Line: Eventmarker.
F.M. CALIB. IOOpv
Fie. 2. Finger-movement in response to electric shocks. Female patient with pain. Time-base as for F~g. 1: 1st Line: Finger-movement; 2nd Line: Event-marker; Both Figs. 1 and 2 show the typical relatively large response to the Ist shock followed by a decline with subsequent shocks and some increase again w~th the largest shock (No. 5). of the degree of reaction. Figures 1 and 2 show two typical sets of responses. The finger-movement test was always done last. Amongst the WPM and WPF groups many patients clearly failed to understand the explanation offered for the finger-movement test. Anyone who showed the least reluctance to undergo the test was not gwen it and no-one m any group who expressed unwdhngness was examined with it. RESULTS a. Ages o f the experimental groups The ages of the groups studied are shown in Table 1. It is clear that there are wide d~fferences m age between several of the groups. It wdl be ewdent from other tables (especially Table 2) that there is no consistent trend of response to the tests according to age, e.g. in a number of instances patients with depression who tend to be elderly, score most like young normal controls, and d~fferences between male and female subjects which will be demonstrated, occur qmte often at s~mdar ages. Further an intra-group exammatton of some results showed no significant trend with age. The influence of age on these results is therefore unlikely greatly to affect the other comparisons made.
b. The response to Pin-Prick The results are not presented in detad since the test d~d not discnm,nate patients from normals nor patient groups from each other and there was no consistent pattern of response according to diagnosis. Although the differences were not significant it was found that depressed patients with pain reacted more than those w~thout pain and this ~s of interest since simdar trends were obtained with the Algometer and Finger-movement Scores (Tables 2 and 3). It is also worth ment,onmg that a consistent sex difference was present. Every one of the six male groups studied reacted less than the corresponding female groups.
c. Pain Perception Threshold and Severe Pam Threshold The results obtained for the above measures using the pressure algometer are shown in Table 2. Nearly all the patients, except for the hypochondnacal ones, were assessed both for P.P.T. and S.P.T. There were 13 instances at the beginning of the study where only the S.P T. was sought. There are indications from other work [10] that th~s need not be, expected to affect the S.P.T One anxious male patient would only give P.P.T. scores and there were 3 patients m the pain series who were lost for this invest]gabon. The results indicate that m general P.P.T. and S.P.T vary together. The S.P T. results are more in accordance with expectation. For convenience of presentation the P.P.T. wdl be considered first. Both with P.P.T. and S.P.T. low scores indicate an early response to the stimulus, high scores a delayed one.
410
H. MERSKEY TABLE ] , - - A G E DISTRIBUTION OF THE EXPERIMENTAL GROUPS
G r o u p s W P M a n d W P F Include 6 patients with diagnoses o t h e r t h a n those of the p r m o p a l pain sub-groups
Group
No
M e a n age in years
S D
CM CF AM AF DM DF SM SF
Male students Female students Anxiety neurosfs: males Anxiety neurosis: females Depression : males Depression" females H y p o c h o n d r m c a l : males H y p o c h o n d r l a c a l : females
15 20 10 11 l0 9 16 20
2473 21 6 32 3 29 73 47 3 39 33 46 94 49 3
1 91 0 95 7 83 8 2 16 06 9 55 3 79 4 71
WPM SPF
W h o l e group males with pare W h o l e group females with pare
37 53
45 1 45-78
11 16 13 93
PAM PAF PHM PHF PDM PDF
Anxiety n e u r o s i s ' S u b - g r o u p males with pain Anxiety neurosis: S u b - g r o u p females with pain Hysteria: Sub-group males with p a m Hysteria: S u b - g r o u p females with pain Depression" Sub-group males with pain Depression" Sub-group females with p a m
14 10 14 27 6 13
41 9 37 9 45 8 45 6 545 53
11 65 9 74 1l 84 11 61 74 19 31
Ta, BLE 2.--ALGOMETER SCORES FOR PAIN PERCEPTION THRESHOLD (P.P T.) AND SEVERE PAIN THRESttOLD (S P . T ) IN KG/0-196 CM~
Pain Perception T h r e s h o l d Group No
Mean
CM CF SM SF AM AF DM DF
15 20 . . 10 10" 10 9
3 63 2 73 . .
WPM WPF PAM PAF PHM PHF PDM PDF other
Severe Pain T h r e s h o l d
S.D.
No.
Mean
b D.
5 75 4 41 4 49 3 29 4 46 3 56 4 69 493
1 28 0 91 1 75 0 91 0 73 0 78 1 09 1 35
2 85 26 3 18 381
0 98 0 60 0 51 1 17
15 20 16 20 9+ ll 10 9
32* 46*
324 32
1 15 1 35
36~ 51++
441 3 99
145 1 47
13 10 13 22 4 11 5
3 19 36 3 25 3 13 2 36 26
1 087 0 51 1-42 l 57 1 45 099
14 10 13 26 6 12 6
4 5 4 71 4 31 3 83 3 97 335
1 21 0 79 1 64 1 62 1 65 1 15
.
095 0 61
-
.
* P P T. refused or not sought in 12 pain patnents a n d one in group AF. i O n e patient refused S P.T test after s u b m i t t i n g to P.P T. test ~ S P T not obtained on 3 patmnts m the pain groups.
Effect of chronic pain upon the response to noxious stimuli
411
In evaluating the results with the pressure algometer four questions have to be considered, viz: (1) (2) (3) (4)
Do male groups score more than comparable female groups, as would be expected ? Similarly, do the students score more than the patients? Are there any major differences between different dmgnostlc groups ? Do comparable diagnostic groups with and without pain score in the same way or differently ?
Systematic comparisons have therefore been made between the appropriate groups in respect of each of these questions for the P P.T. and S.P.T. The method of doing th~s has been to perform t-tests on all those differences which, from inspection, might be thought to be sigmficant. The results of these t-tests are then set out for the groups compared. It should be noted that doing multiple t-tests in thTs way introduces a hkehhood of finding some differences which are significant at the 0-05 and even at the 0 01 level of probability and which are nevertheless due to chance variation. Having regard to the number of possible comparisons which might be made the level of probablhty for any one case which can be taken as reasonably likely not to be due to chance has therefore been set at p / 0.001. However there is also a substantml number of cases where probabdltles o f p /_ 0 05, p L 0'02, p /_ 0-01 emerge, m agreement w~th each other, in respect of particular questions such as (1) and (2) above. In these cases it can be shown that the sum of all the individual probabdities is such as to be unlikely to be due to chance and the trends have been interpreted accordmgly.
1. Pam Perception ThreshoM The following comparisons have been made:
i. Males with females In several pairs of groups females score less than males, i.e. females respond sooner to the stimulus, but there are two pairs (Groups D M and DF, P A M and PAF) where the reverse happens. None of the differences between males and females is significant. For the largest difference, that between Groups C M and CF t = 1"526,p L 0-2, N.S. Thus the P.P.T. is not a sensitive or consistent indicator of differences due to sex although the trend as for males to have higher scores, as expected. ii. Normal subjects with others Group CM CM CM CF CF
with with with with with
Group Group Group Group Group
AM, DM, PDM, DF, PAF,
t t t t t
1'985p 1'557p 2'269 p 3.23 p 3'863 p
/_ 0 1, N.S. / 0'3, N.S. ~ 0 05 Z. 0'005 Z_ 0 001
These results present a comphcated picture: male normal controls tend as expected to score higher than patient groups, but female normal controls tend to do the reverse--whether the patients are anxious or depressed. It will be seen later that the S.P.T. of the female controls is relatively higher than the P.P.T. and therefore it is hkely that whilst the "tolerance" of the normal female subjects is appropriately large their readiness to respond early or to detect a pare is also great. ill. Different diagnostic groups with each other Amongst the patients without pain the anxious respond first as expected. A significant difference occurs between groups A F and D F where t = 2"879, p /_ 0'02. This is probably meaningful since a s~mdar trend occurs with the S.P.T. There is a tendency for depressed patients with pare to score less than other patients with pain but the trend is not significant (on inspection and by comparison with the groups already tested). iv. Similar diagnostic groups w~th and without pain Group A F with Group PAF, t 4'09, p Z_ 0-001 D F with Group PDF, t 2"495, p / 0 025 Anxious patients wxth pare respond later than other anxious patients without pain. Depressed patients with pain respond sooner than other depressed patients.
CoolDTen t T h e P . P . T . so f a r h a s g i v e n r e s u l t s w h o s e i n t e r p r e t a t i o n is difficult a n d c o n f u s i n g . T h e r e is s o m e e v i d e n c e f r o m it, h o w e v e r , t h a t t h e p r e s e n c e o f e x i s t i n g p a i n is a s s o c i a t e d w i t h a rise i n t h e s t i m u l u s a c c e p t e d b y a n x i o u s p a t i e n t s a n d a d e c r e a s e i n t h a t a c c e p t e d
412
H. MERSKEY
by depressed patients. The effect with the anxious patients might be supposed to be due to those with pain having much concealed tension so that although anxious they would respond less to stimuli whilst in those without pain the anxiety was much more overt and the response to stimuli great too. It may be mentioned that the trends of the responses in the depressed patients and m the anxious male patients are similar both for this test and for the Pin-Pick tests. 2 Severe Pam ThreshoM
The following comparisons have been made. i. Males with females
Group CM SM AM DM WPM PHM PAM PDM
with Group CF, with Group SF, wnthGroupAF, with Group DF, with Group WPF, with Group PHF, wuth Group PAF, with Group PDF,
t 3-716p z5 0001 t 2 595 p z_' 0.01 t244 pL005 On inspection N S. t 1-373 p Z 0'2, N.S t 0 948p z_ 0 4, N S On inspection, N S On inspection, N.S
In the case of two paars males respond before females (Groups D M and D F and PAM and PAF) The differences are not significant although they are m the same direction as the P P.T results Otherwise males respond after females. 11. Normal subjects w~th others
GroupCMwnthGroupSM, CMwlthGroupAM, CM with G r o u p D M , CM with Group WPM, CM wLth G r o u p P A M CM with Group PHM, CF Vclth Group SF, CF with Group AF CF with G r o u p P D F , CF ~nth G r o u p P H F ,
t2276p :005 t 2 7 4 5 p ~_002 t2147p_005 t 2 505 p / 0 0 2 t2689p •002 t 2 603p ,~ 0 02 t 3914p_0001 t 2 605 p , 0 02 t2795p, 001 t 1 225p , 0 3
Normal males respond later than all other groups, usually significantly so. Normal females respond significantly later than most other female groups. Normal females responded slightly sooner than depressed females without pain and shghtly sooner than anxious females without pann but these latter differences are not s~gnnficant. The S.P.T. thus distinguishes clearly between normals and most dmgnostlc groups of the corresponding sex. As noted w~th the P.P.T. depressed patients without pann respond late and so do an-,lous patients ~ ith pare. Ul. Different thaffnostlc etou,o~ ittth GroupDM SF SV SV AI" I)F PAl-
each otlleJ x~ithGIoupWPM, x~uthGroup DF, v, J t h G r o u p W P F , ',~lth Group PAF, with Group DF, \~nth Group WPI-, ~ t h Group PDI~,
t057, p_ t 3 855,/'~ t072, p t 4 202, p t 2 838, p t I 7~3, p t 3 162, p
06, N S 0 001 05, N S 0 001 0 02 01, N S 0 005
The male diagnostic groups dJffer ,,err httle from each other Femalc hypochondrlac,d patients score markedly low and they differ ~ery sagnlficantly from groups DF and PAF Anxious female patients v,~thout pasta Stole in a ~ery smltlar x~ay to hypoc, hondrlacal female patients and respond early So
Effect of chronic pain upon the response to noxious stimuli
413
also do depressed female patients with pain. Depressed female patients without paln respond late as do anxious female patients with pain. The pattern here is again similar to the pattern with the P P.T. and with the Pin-Prick tests. iv. Similar diagnostic groups with and without pam Group D M with Group PDM, t 1.0212p Z_ 0 3 N.S. AF with Group PAF, t 3'352 t7 Z 0005 D F with Group PDF, t 2 903 p Z. 0.001 The tendency is again evident for anxious patients without pain and depressed patients with pain to respond early whilst the corresponding groups with and without pain respond late. With females the tendency is highly significant.
Comment O f the m e a s u r e s e m p l o y e d the S.P.T. a p p e a r s the m o s t i n f o r m a t i v e a n d useful. It gives s u b s t a n t i a l e v i d e n c e t h a t m a l e s u s u a l l y s c o r e h i g h e r t h a n f e m a l e s a n d t h a t normals
score high.
Hypochondriacal
female patients, anxious
female patients
w i t h o u t p a i n a n d d e p r e s s e d p a t i e n t s w i t h p a i n s c o r e low. A n x i o u s p a t i e n t s w i t h p a i n a n d d e p r e s s e d patients w i t h o u t pain score high. These patterns o f response are quite consistent. Patients with hysteria and pain occupy an intermediate position.
d. Finger movement lest There is evidence [23] that the response to electric shock will vary greatly depending upon the way it is presented. This is also obvious as an a priori consideration and was confirmed by casual visitors to the laboratory. Care was therefore taken to present the test in the same way to all subjects. The variation in size of shock delivered was planned to take this into account. It was anticipated that the early shocks in the series would give a measure of the anxiety of the subject when compared with later later shocks of the same s~ze. It was also expected that the largest shock being the fifth one the preceding sequence would have conditioned the subject so that the response to the fifth shock would tend to be a measure of the response to pain. These expectations were borne out to a considerable extent by the responses ehclted. In the section on methods the strength of the shocks was given and it is evident that, taken in order of presentation, they had approximately the following ratios of voltage: 3 ' 5 : 5 ' 3 ' 7 3, nos. l, 4 and 6 being equal to each other and nos 2 and 3 being equal to each other. In general it was found that the largest responses were to nos. l and 5, and the least responses to no. 6. The pattern was not uniform Occasionally there was a response to the first shock and almost no response thereafter. Some subjects gave almost no response to any shock A few responded most to the second. However expectations were confirmed in that the trend was as predicted for shocks l and 5 to produce the largest responses. Photographs of two representative records are given in Fig. l and Fig. 2 In Fig. 1 the response is shown of a male medical student who gave a moderate initial iesponse to Shock l and little thereafter Figure 2 shows the responses of a female patient with hysteria and pain who gave the largest response to the first shock and lower responses thereafter but a fairly marked one to the fifth shock These patterns are representative of all dmgnostic groups. In every group however there was a number of patients who gave minimal responses of 0 I mm or less and in certain groups especially group AM there were some who gave very large responses which exceeded the linear range of recording of the E E G pens The restilt of this is that the data are very abnormally distributed and can only be assessed by non-parametric statistics so that the Mann-Whitney U test has been employed. It may be noted that this is sa~d to have 95°o of the po~er of the t-test (30). In one instance for a very large nunaber of scores a Chi"- median test was used. The main results obtained are given in Table 3 Only about half the patmnts with pare accepted the test Almost all the other subjects accepted the test but two anxious female patients stopped after the first shock. Table 3 shows the marked tendency for the response to the fourth shock to be less than that to the first. Taking all the patients together a median test of these 2 sets of responses gives a value Chi 2 -- 6 748,p /_ 0 01. As indicated the values for the fifth response tend to rise again and to resemble those for the first. The total for all shocks also tends to follow the pattern for the individual shock in different groups. Comparisons between groups have been made as follows for the totals of all responses, taking the estimates of probability on a two-tail Mann-Whitney U test
414
H. MERSKEY TABLE 3 . - - F I N G E R
MOVEMENT TEST
M A X I M U M DEVIATION IN CM AFTER SHOCK I ( 3 1
V),
4(52 V) a n d 5 ( 7 2 V) AND TOTALS FOR RESPONSES TO ALL 6 SHOCKS Shocks Group
No.
1
4
5
Totals 1-6
Mean
Mean*
Mean*
Mean*
Medmn*
CM CF AM AF DM DF
15 20 9 11 9 9
051 0 5 1 37 0 95 07 0 63
031 0 31 0 99 0 45 04 04
04l 0 45 0 87 049 06 0 64
227 2 64 6'68 3 11 33 3 08
14 2 1 4 1 2.5 27 30
WPM WPF
26 25
0 58 06
0 53 0 53
0 44 0 59
3 02 3 27
18 35
PAM PAF PHM PHF PDM PDF
10 7 8 10 5 7
09 061 0 36 0-66 0 52 066
0 6 043 0 36 0 52 0.74 073
0 47 041 0 38 0 63 0 48 083
3 83 28l 2 25 3 19 3 34 4 11
2 45 18 16 3 1 37 40
* The number o f group A F for these columns ~s 9. (1) Males with females GroupCM AM PAM PHM
wlthGroupCF with G r o u p A F with G r o u p P A F wzth G r o u p P H F
p p p p
A 0 1 , N-S. _X01,N.S. ~ 0.1, N.S .X 0 1, N.S.
N o significant differences between sexes were found with this test, in some pmrs of diagnostic groups men score more than w o m e n and in others the reverse occurs and there ~s no well-marked trend (2) Nol mal subjects with others Group CM CM CM CM CF CF
with Group A M with G r o u p D M with G r o u p P M with G r o u p P D M wlthGroupPF with Group P D F
p ~002 p _~ 0-1, N.S. p ± 0 052, N S p A 0 1, N S p , , 00214 p ~ 0 1, N.S.
Normal subjects tend to score less than most patient groups and the results are s~gmficant in two instances as shown (3) Different dtaffnosttc ffroit]gs with each other Group A M with Group W P M p LL 0 06, l'q S. PHMwithGroupPHF p _X01, N S . P A F with G r o u p P D F p 2x01, N S There were no marked differences between the diagnostic groups. (4) Stroll(It chagnosttc~rouos with and without flain In the hght of the above results and on inspection of the data it is evident that there are no marked differences between groups with and without pare in this test.
Comment The test does not distlngmsh between the sexes or between different dlagnost~c groups although patients tend to score more highly than normals. It shows quite well
Effect of chronic pain upon the response to noxious stimuli
415
t h a t t h e r e is a r e d u c t i o n in t h e r e s p o n s e as t h e p a t i e n t b e c o m e s f a m i l i a r w i t h t h e s i t u a t i o n a n d after he has f o u n d t h a t the first shocks are at m o s t mildly painful. The test s h o w s s o m e c o r r e s p o n d e n c e in the t r e n d o f g r o u p results w i t h t h o s e o b t a i n e d in r e s p o n s e t o P i n - P r i c k , a l t h o u g h t h e c o r r e s p o n d e n c e is s m a l l a n d u n i m p r e s s i v e .
e. Test intercorrelations Scores were available on the Maudsley Personality Inventory as well as on the different physical tests. If these scores reflect similar functions then they should intercorrelate--at least to some extent. The appropriate correlation coefficients have therefore been calculated for females for a number of different measures. Group WPF was chosen for the calculation of r as being the largest single group. Group CF was chosen for the calculation of Tau for the finger-movement test as being the largest group in which all or most of the subjects accepted that test. The results are shown in Table 4 TABLE 4.--INTER-CORRELATIONS BETWEEN MEASURES OF THE RESPONSE TO STIMULI AND THE MAUDSLEY PERSONALITY INVENTORY
Product-moment correlation co-efficient:
N E Pro-prick P.P.T. S P.T. * p ~_ 0 05 1"p Z_ 0-025 1 p Z_ 0-01 §p L 0.001
Kendall's Tau
E
Pro-prick
P.P.T.
S.P.T.
Finger movement test
--0"347* -----
0"025 0 047 --.
--0 127 --0"019 --0 39 + -.
--0 077 --0 071 --0.416++ 0 915§ .
0 124 --0"12t 0 224 --0 322"~ 0 219
.
r---calculated for female patients with pain. Tau--calculated for 20 female medical students.
As is usual, there is a small negative lntercorrelatlon between the two scales of the M P I. but this test showed no significant correlations with the other measures. Significant correlations in the appropriate direction do appear however between the algometer measures and the response to pro-prick. This is in accordance with previous work [8]. Further the finger-movement test is significantly correlated with one of the algometer measures, the P.P T It has already been noticed that to some extent those two measures tended to vary together when different groups were compared. In addition as found in other work [9] there is a very high intercorrelation between the two measures obtained with the algometer. However this particular very high correlation must be, at least partially, a statistical artefact since the S.P T. figure always includes a part of the P.P.T. figure. Taken overall these findings show that the Maudsley Personality Inventory correlates very badly with the response to noxious stimuli in the experimental situation. However, they confirm the findings of Jarvik and Wolff [31] that there is a significant inter-correlation bet~een various sorts of measures of pain response.
f. The relationship o f headache to the Pain Perception ThreshoM and the Severe Pain Threshold. In the Group WPM there were 12 men who did not complain of headache and in Group WPF there were 19 women. In diagnosis these no-headache sub-groups were similar to the full Pain Groups. Thus the females comprised 5 with anxiety, 8 with hysteria, 5 with depression and 1 other, whilst the males comprised 4 with anxiety, 5 with hysteria, 2 with depression and 1 schtzophremc The responses of the male and female no-headache groups (Table 5) can therefore be compared with those of the remainder of the patients with pain. In particular it ts of interest to compare them in respect of the P P.T. and S P T. since these measures were taken from the forehead There were some slight trends which may be mentioned although they were not significant; the No-Headache group of men tended to have smaller N scores, and higher E scores than the whole W P.M. group, whdst Pin-Prick and Finger-movement test scores tended to be low. There are some indications therefore that the males without headache tend to have a less neurotic pattern on the M P I. and to respond to stimuli less This last feature is also apparent with the P.P.T and S P.T. scores which in each case are higher than those in the general group (Table 2). The difference is most
416
H. MERSKEY
marked with S.P.T but is not quite significant. Comparing the males without headache with the remaining males t ~ 2 005, p /_ 0.1, N.S With these male patients therefore it can be said that those with headache tend to react more but that despite this a s~gnlficant difference could not be demonstrated at the site (forehead) where many of them had pain and where the other group did not. The actual presence of pain at the site of the stimulus d,d not produce a significant trend even in a group which appeared on several tests to be slightly more responsive than its control group. With the female patients the results in all tests are very similar, both for the headache and the noheadache groups with pain All scores, including the P.P.T. and S P T are so close to those of the whole group that they can show no significant d,fference. For example, comparing these two halves of the WPF group for P.R.T., t ~ 1-04,p Z_ 0-4, N.S Thus again the presence of headache did not produce a significantly earlier response to forehead stlmulat,on. It IS concluded that at least with respect to headache, psychogenic pain does not usually have more than a slight effect on the response to noxious stimuli at the site of the complaint. T A B L E 5 . - - P A T I E N T S W I T H PAIN BUT NO HEADACHE
MEAN SCORES IN T W O TESTS
Age
P.P T
S.P T.
Finger movement (Total 1-6)
Males
Score No
46-16 12
3 66 11
5'16 11
2 77 7
Females
Score No
48 52 19
3 29 16
4 26 17
3 36 9
DISCUSSION W h e n the whole group of patients with pain is c o m p a r e d with the other groups it is evident that in general those with pain resemble the other patients a n d differ from the n o r m a l subjects. The m a n n e r of response by psychiatric patients with pain to noxious stimuli is thus seen to be principally influenced by the type of c o n d i t i o n they have. Diagnosis therefore seems of as m u c h i m p o r t a n c e as the presence of pain in determining the response in the tests used. This conclusion emerges particularly from the present study. A n u m b e r of others also emerge which are well supported by the literature. Thus as expected, w o m e n react more t h a n men, the anxious usually react more t h a n n o r m a l s and other patients a n d n o r m a l subjects react less t h a n most patients. The findings are qualified to the extent that they distinguish groups a n d not l n d w i d u a l s - - a l t h o u g h there were very few patients who reached the higher ranges of scores with the algometer and such scores were often reached by the n o r m a l students. It must also be acknowledged that work of this sort may have, as Beecher [3] insists, only a limited bearing on chnlcal problems of pain. Still, these experimental measurements do offer some positive information, a n d the finding of significant group differences a n d significant test-intercorrelations gives support to the view that there are aspects of the h u m a n response to noxious stimuli which can be illuminated, if only a little, in this way. A further qualification might be that the results were obtained by only one investigator a n d although the measurements themselves are reasonably reliable and objective it is always possible that unconscious bias by the experimenter could affect the performance of different groups. It can be said in this respect that every effort was made to present the stimuli in a u n i f o r m way. In addition it is worth n o t i n g that m a n y of the depressed patients were thought to show considerable signs of tension as well as
Effect of chrontc pain upon the response to
noxious
stimuli
417
retardation so that the marked difference between their responses and those of the patients with anxiety was not expected but nevertheless emerged. A point of interest which appears from consideration of the sub-groups with pain and without pain is the opposite effect that pare might be thought to have in raising thresholds where there is anxiety and in reducing them where there is depression. It must be remarked here that it remains uncertain whether the differences In testresponse between anxious and depressed patients with and without pain were directly related to the presence or absence of that complaint. It has been accepted that diagnosis is of importance in predicting the response of different groups. There were however other clinical differences between the groups with and without pain but with similar diagnoses. These were found in a clinical study contemporaneous with the present one. Therefore it cannot be argued that the relative decrease in the response to noxious stimuli in anxious patients with pain and the relative increase in the response in depressed patients with pain are directly related to the presence or absence of pain. This conclusion is also inevitable on logical or a priori grounds; a significant association does not imply a casual one. What has been shown is that these assocIations exist and as they exist it may be relevant to take them into account m certgin situations. With regard to the effects of "organic" and "psychogenic" pain on pain-thresholds it is difficult to make a reliable comparison. It has been claimed that "organic" pain raises thresholds [6]. The findings reported here for the response to noxious stimuli in patients with pain and with different diagnoses make it seem possible that groups of "organic" patients, with differen~ attitudes to their wounds or dlnesses, might also react variously during measurement of experimental pain thresholds in the same way as happened with the psychiatric patients in this study. Certainly "psychogenic" pain as such appears to have no uniform effect on pain thresholds although psychiatric patients in general tend to have low thresholds for pain and high reactivity. Lastly it may be stressed that his own spontaneous pain matters more to the patient than extraneous stimuli. Just as patients with neurotic anxiety may show a normal attitude to objective difficulties but excessive concern with their neurotic ones, so in psychogenic pain the external noxious stimulus may be treated much more lightly than the internal painful but non-noxious disturbance. SUMMARY The literature on the exper,mental response to noxious stimuli in patients with chronic pain has been reviewed and it has been shown that there are very few studies in this field either of "psychogenic" or "organic" pain. The results are then reported of investigations of the response to pin-prick, of thresholds obtained with the pressure algometer and of the response to electric shock measured by electronic recording of finger-movement. The pressure algometer was the most sensitive test-instrument employed, it showed a tendency for females to react more than males and for normal subjects to react less than patients. A special group of very hypochondrlacal patients reacted earliest and most. There was a tendency for anxious patients without pain to react more than depressed patients without pain, and in fact depressed patients without pain reacted relatively late. On the other hand anxious patients with pain responded late to the algometer and depressed patients with pare responded to it relatively early. 5
418
H
MERSKEY
Patients w i t h h y s t e r i a a n d p a r e o c c u p i e d an i n t e r m e d i a t e p o s i t i o n b e t w e e n o t h e r diagnostic groups. A test o f f i n g e r - m o v e m e n t in r e s p o n s e to e l e c m c s h o c k g a v e clear e v i d e n c e t h a t p a r t o f the r e s p o n s e was related to a n x i e t y in the test s i t u a t i o n a n d p a r t to the unp l e a s a n t n a t u r e o f the stimulus. It did n o t distinguish well b e t w e e n g r o u p s b u t did i n d i c a t e t h a t n o r m a l subjects r e a c t e d less t h a n p a t i e n t s w i t h a n x i e t y o r w i t h pain. W h i l s t the a l g o m e t e r was the m o s t effective i n d i c a t o r o f differences b e t w e e n g r o u p s in the r e s p o n s e to n o x i o u s stimuli t h e r e were several significant l n t e r c o r r e l a t i o n s w i t h o t h e r test m e a s u r e s . T h u s the t w o a l g o m e t e r m e a s u r e s o f P . P . T . a n d S.P.T. w e r e b o t h significantly c o r r e l a t e d w i t h the r e s p o n s e to pin prick. F u r t h e r , the fingerm o v e m e n t test s h o w e d a s i g m f i c a n t c o r r e l a t i o n w i t h the P.P.T., so t h a t it seems as if these tests m e a s u r e d a c o m m o n p a r a m e t e r o f response. Lastly, w h e n the r e s p o n s e s a s s o c i a t e d w i t h a p a r t i c u l a r site w e r e c o n s i d e r e d It was s h o w n t h a t p s y c h i a t r i c p a t i e n t s w i t h o u t h e a d a c h e were i n c h n e d to react slightly less t h a n t h o s e w i t h h e a d a c h e . H o w e v e r , there was no s l g m f i c a n t difference b e t w e e n t h e m and o t h e r p s y c h i a t r i c p a t i e n t s w i t h p a i n - - e v e n w i t h the a l g o m e t e r tests w h i c h i n v o l v e d p a r e on the f o r e h e a d . T h u s , m at least this instance, there was no significant effect o f local p s y c h o g e n i c p a r e u p o n the r e s p o n s e to t r a u m a at the s a m e site. Acknowledgements--This work has depended greatly upon the wllhngness of students and patients
to undergo the tests and my thanks are due to all my subjects It is a pleasure also to thank the many colleagues who have given assistance and advice Mr W. Troupe made the pressure algometer and Mr. A Troupe constructed the electric shock apparatus from a design by Mr. W. H. Stanton. The patients were under the care of Drs. G Fitzpatrick, A Gllhs and C F. Lascelles and Professor E Stengel and Dr W L. Tonge I am grateful to all these colleagues and to Mr. P R F Clarke and Drs I Pdowsky and F. G. Spear for encouragement and helpful discussions. Mr. G. Mascas gave valuable statistical advice This work was part of a D M. Thesis accepted by Oxford University REFERENCES 1 HALLK R L. Studies of cutaneous pain- a survey of research since 1940. Brtt J Psychol 44, 281 (1953). 2. HARDYJ O,, WOLFF H G. and GOODeLL H Pain sensations and reactions Wllhams & WiIktns, Baltimore (1952). 3 BEECHER H K Measurement of subjectwe responses. Quantitative effect of drugs Oxford Umverslty Press, New York (1959). 4. MERSKEYH. To be published 5 CHAPMAN W. P, and JONES C
6 7
9 10 II 12 13 14 15 16
M. Varmtions m cutaneous and visceral pare sensmvlty in
normal subjects J CIm. Incest 23, 81 (1944) HAZOUR1L A and MUELLERA D Pain threshold studies on paraplegic patients 4tch Neitrol Psychtat 64, 607 (1950) HALL K R L and STRmE E The varying response to pain m psychiatric disorders A study tn abnormal psychology Brtt J Med Psvchol 27, 46 (1954) MERSKEY H , GILLIS A and MARSZALEKK. S. A clinical mvest~gat~on of reactions to pain J Ment Scl. 108, 347 (1962) MERSKEY H and SPEAR F G The rehablhty of the pressure algometer BJlt J Soc Chn Ps),chol. 3, 130 (1964) MERSKEYH and SPEAR F G The concept of pare (To be pubhshed) HARDYJ D ,WOLFF H. G and GOODELL H Studies in pain A new method for mcasurmg pare threshold" observations on spatml summation of pare J Clin Invest 19, 649 (1940) EDWARDSW. Recent research on pare perception P~ych Bull 47, 449 (1950) KUTSCHeR A H. and KUTSCHERN. W Evaluation of the H-W-G pain threshold apparatus and technique lnt Rec Med 170, 202 (1957) MCKENNA A E The experimental approach to pare J ,4Dpl Ph$ stol 13, 449 ~1958) MUELLeRE E , LOEFeLt R and MEAD S Skin impedance m relz(t~on to pare tlarcshold testing by electrical means J Appl Phvstol 5, 746 (1953) HILL H E , KORNETSKYG , FLANARYH G and WIKLERA Effects ol anxiety and morphine on dl~cnmmatmn of mtensmes of pamful sttmuh J Chn Incest 31,473 (1952)
Effect of chronic pain upon the response to noxious stimuli
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17. WILDER R. M. JR. Sensitivity to pain. Proc. Mayo Clinic 15, 551 (1940). 18. SHERMANE. D. Sensitivity to pare. Canad. Med. Ass. J. 41t, 437 (1943). 19. KENNARD M . A . Responses to painful stimuli of patients with severe chromc painful conditions. J. Clin. Invest. 31, 245 (1952). 20. DUNDEE J. W. and MOORE J. Alterations in response to somatic pain associated with anaest h e s i a - I : An evaluation of a method of analgeslmetry. Brit. J. Anaesth. 32, 396 (1960) 21. SHERMANE. D. and ROBILLARD E. Sensitivity to pare in the aged Canad. Med. Ass. J 83, 944 (1960). 22. HARDY J. D , WOLFF H. G. and GOODELLH. Relation of attitude and suggestion to the perception of and reaction to pain. Res. Publ. Ass. Nerv. Ment. Dis. 23, 434 (1943). 23. SCHACHTER S. The psychology of affiliation--experimental studies of the sources of gregariousness. pp. 141, Tavistock Publications, London (1959). 24. KEEL G. O., OZELIS S., GREENBERG I. and GALLANT L. J. Pain and other somatic complaints in a psychiatric clinic. Maryland Med. J. 8, 188 (1959). 25. SPEARF. G. A study of pare as a symptom in psychiatric dlness. M.D. Thesis, Bristol UmversJty (1964). 26. CHAPMAN W. P., COHEN M. E. and Coaa S. Pain in neuroorculatory asthema, combat fatigue and anxiety neurosis. J. Chn. Invest 25, 890 (1946). 27. SCHILLING R. F. and MUSSER M. J. Pain reaction thresholds in patients with peptic ulcer. Amer. J. M e d Sct. 219, 207 (1949) 28. KIr~o H. E., CLAUSEN J. and SCARrr J. E. Cutaneous thresholds for pain before and after prefrontal lobotomy. J. Nerv. Ment. Dis. 112, 93 (1950). 29. STENGEL E , OLDHAM A. J. and EnRENaERG A. S. C. Reactions to pare in various abnormal mental states J. Ment. Sct. 101, 52 (1955). 30. SIEGEL S. Non-parametric statistics for the behavloural sciences. McGraw-Hall, New York (1956). 31. JARVIK M. E. and WoLff B. B. Differences between deep pain responses to hypertomc and hypotomc sahne solutions. J. Appk Physiol. 17, 641 (1962).
Printed m Northern Ireland
THE EFFECT OF CHRONIC PAIN UPON THE RESPONSE TO NOXIOUS STIMULI BY PSYCHIATRIC PATIENTS H.
MERSKEY*
(Recewed 14 December 1964)
Some common methods of assessing pain THERE is an extensive experimental literature on human responses to noxious or painful stimuh. The psychiatric and psychological section of this literature ha.s been well reviewed by Hall [1] and is also taken into account by Hardy et al. [2] and by Beecher [3] and will be the subject of a detailed report by the present writer [4]. The consensus of opinion from that literature holds that it is possible to measure a Pain Perception Threshold (P.P.T.), defined as the point at which an individual experiences pain when submitted to noxious stimuli. A Pain Reaction Threshold (P.R.T.) can also be measured. The latter is a point chosen according to some physiological or verbal indication of a response to the stimulus. In some cases, e.g. Chapman and Jones [5], it is measured by wincing or withdrawal and in others, e.g. Hazouri and Mueller [6], by a change in the pulse rate, or some other physiological variable. In those instances the P.R.T. can be recorded before the P.P.T. is reached. In most cases it represents a point at which the subject declares the pain to be severe. Such a point wall normally exceed the P.P.T. A third"type of measurement is to give a standard stimulus which will always be felt and to observe the response to it. The terminology used for these measures varies somewhat in different studies. Hall [1] spoke of Pare Perception Thresholds and Pain Reaction Thresholds, but changed his terminology later [7] to Verbal Report of Pain (V.R.P. equivalent to P.R.T.) and Pain Reaction Point. (P.R.P. equivalent to P.R.T.) The present writer and his colleagues [8, 9] have also used these several terms. Each of them has some disadvantages and for reasons given elsewhere [10] it is particularly confusing to talk of "Reactions to Pain". However the terms P.P.T. and P.R.T. are well estabhshed. They wdl therefore be used for the purpose of this discussion and the term P.P.T. will also be used in describing the present work, but the term P.R.T. will be discarded in the report of this investigation, the term Severe Pain Threshold (S.P T.) being preferred for what might otherwise have been called P.R,T. The most common types of stimulus used have been the Heat-Pain apparatus of Hardy et al. [11,7], pressure-pare and electric shock. All these methods have been severely criticised by Beecher [3] who claims to have shown from his considerable review of the literature and from hIs own investigations that pain thresholds assessed experimentally are unreliable and that the nature of the experimental situation leads to mistakes in the assessment of pain. The writer considers that Beecher has made a valid objection to the interpretation of many studies. Pain Perception Thresholds may vary, hke other thresholds, with distraction of the subject and with the experimental instructions and other conditions * Present address:
Saxondale Hospital, Radchffe-on-Trent, Nottingham. 405
406
H. MERSKEY
and this is even more true of Pain Reaction Thresholds. However there is adequate evidence that the heat-pain technique can be rehable [12-14] and pressure-pain, according to the method used here, has been found to be moderately reliable [9]. Further, although there are physical reasons why the threshold to electric shock may be very variable [15] this need not apply to the estimate of intensities above threshold level and Hill et al. [16] found that such estimates could be correlated with the wattage of the stimulus. The results with heat-pain measurement on which many of the common views are founded can therefore often be accepted, although some caution will be required in interpretation. The same applies to measurements of pressure-pain thresholds and of the response to electric shock reported in this work. Common findings on exper,nental pain tn psyehtatrlc pattents and others
Women are generally found to have lower P.P.T.s or P.R.T.s than men [17, 18, 5, 2, 19, 8, 20, 9]. Kennard [19] was able to show that this was not due to any significant difference in skin thickness. Hardy et al. [2] show variations with attitude, suggestion, fatigue and emotion. Age has no consistent effect. Sherman [18] found no effect with age, but later Sherman and Robilland [21] reported a decrease in sensitivity after the age of thirty in normal subjects. Hardy et al. [22] on the other hand found no evidence that P.P.T.s were related to age in normal subjects. Psychoneurotic patients are generally agreed to have lower thresholds than general medical patients. Schizophrenic patients and retarded depressives may have h~gher thresholds (see Hall's review, 1, 1953). Differences in various directions have been found between negroes and whites, Indians, Canadian "Office Patients" and Miners. These social or racial differences are almost certainly due to effects of attitude. Merskey and Spear [9] found no difference between male Afro-Asian and White medical students. Altogether the importance of atmude is made clear in a study by Schachter [23]. The same noxious stimuli were introduced to one group of subjects in a re-assuring way whilst to another they were described as painful. The groups showed different social responses, indicating more anxiety in the second situation. Thus sex, psychiatric diagnosis and attitude are amongst the most important factors affecting pain sensitivity or threshold level. The effects o f spontaneous pare
Pain is a common symptom in psychiatric illness [24, 25] There have been few studies specifically dealing w~th the P.P.T. and P.R.T. in patients w~th established pain, but many of the psychoneurotic and general medical patients studied by other authors must have had pain. In a series by Chapman et al. [26] on patients with neurocirculatory asthenia, figures were given which showed that almost all the patients complained of pain. This group had a psychoneurotic response pattern in the experimental situation. A study by Schilhng and Musser [27] on peptic ulcer patients showed a similar trend towards increased reactivity or lowered thresholds. Studies of P.P.T. and P.R.T. in the presence of chronic paln have been done in relation to leucotomy by King et al. [28] and Hardy et al. [2]. The first group found bilateral lowering of cutaneous Heat-Pain Perception Thresholds after leucotomy in 5 out of 6 patients, but the results were not significant. The data from Hardy et al. are scanty and less clear-cut, but tend to support King et al. Contrary to the findings with psychoneurotic patients therefore there is some suggestion that chronic pain may
Effect of chronic pain upon the response to noxious stimuli
407
raise thresholds which l e u c o t o m y later reduces. H a z o u r i a n d Mueller [6] reached a similar view in three p a t i e a t s with i n t r a c t a b l e r o o t - p a i n relieved b y c o r d o t o m y . P.P.T. a n d P . R . T . in n o r m a l areas o f skin fell strikingly after the o p e r a t i o n . Lastly K e n n a r d [19] studied 24 patients with chronic p a i n a n d 57 n o r m a l controls. T h e patients all h a d a focal source for their p a i n b u t h a d p r e v i o u s l y been labelled " o v e r - r e a c t o r s . " She f o u n d no d~fference between the g r o u p s with m e a s u r e m e n t o f thresholds to electric shock a n d with G . S . R . b u t b o t h these techniques are open to criticism on the g r o u n d s o f u n r e l i a b d i t y a n d insufficient v a h d a t i o n . O n the whole the p a p e r s on chronic pain, a l t h o u g h confined to a limited n u m b e r o f patients, suggest that where there is a substantial local o r organic cause for the p a i n this raises thresholds elsewhere in the b o d y whereas in the presence o f p s y c h o n e u r o s i s with pain, t h r e s h o l d s m a y fall. The present investigation was u n d e r t a k e n to d e t e r m i n e whether persistent " p s y c h o g e n i c " p a i n raised or lowered p a r e thresholds. The p r o v i s i o n a l hypothes~s was t h a t neurotic patients w o u l d be f o u n d to have lowered thresholds o r increased reactivity a n d t h a t the presence o r absence even o f severe p a i n w o u l d be relatively u n i m p o r t a n t . It was a n t i c i p a t e d that some depressive patients w o u l d have high thresholds a n d others low ones. MATERIAL A. The following experimental groups were studied: 1. Patients with pain, Groups WPM (males) and WPF (females) These were 90 psychiatric patients (37 males and 53 females) with a spontaneous complaint of pain of more than ~2 duration. Cases with prmlafacte "organic" pare were avoided from the outset, but the serms includes three patmnts in whom ~t was ultimately decided that an organic lesion was the principal factor causing pain and six m whom it was thought to be a possible subsidiary factor. 13 of these patients were short-stay in-patients or out-patients at a Mental Hospital (Cherry Knowle Hospital, Sunderland.). The remainder were short-stay m-patients, out-patients and day-patients In the Sheffield University Psychiatric Department. 63 patients described their pain as severe, 12 as moderate and 5 as mild or aching. 47 patients described the pain as continuous and m 13 more it occupmd most of the day. In 71 patients it was present throughout all their waking hours or on a majority of days of the week. In general, therefore, the patients studied complained of continuous severe pam. These patients with pain were d~vlded for certain purposes into sub-groups according to their main diagnosis, as follows:
Sub-Group Sub-Group Sub-Group Sub-Group Sub-Group Sub-Group
PAM PAF PHM PHF PDM PDF
14 Males with Anxiety Neurosis and Pain. 10 Females with Anxiety Neurosis and Paln 14 Males with Hysteria and Pain. 27 Females with Hysteria and Pain. 6 Males with Depression and Pain 13 Females w~th Depression and Pain.
There were also six pain patients with other diagnoses. 2. Patients without pain, Grottos A M and AF, DM and DF In these groups all the patients denied the presence of aches or pains. Groups AM and AF comprised 10 men and 11 women with anxiety neurosis (mainly phobic). Groups DM and DF comprised 10 men and 9 women with depression, mainly endogenous in type. 3. Hypochondriacal patients, Groups S M and SF These groups were included only m part of the study. They were a special set of 16 males and 20 females, selected as being grossly hypochondrlacal by Dr I. Pllowsky who was making a particular study of them. They were regarded as being markedly over-concerned with their physical health. They did not accept reassurance or only did so fleetingly and they tended to return to the same complaint and to produce new ones.
408
H. MERSKEY
4. Normal students, Groups CM and CF These consisted of 15 male and 20 female medical students who all denied aches or pains. The medical students were previously acquainted with the Investigator as were all the patients apart from groups SM and SF. Except for one who refused to take part, the students were a consecutlve series takmg thelr psychiatric clerkship at the time of testing. All the students and some of the patients were aware that they were serving as controls but some patients, despite explanation, beheved the tests were part of their treatment.
Techmques and Mode of Presentation The Maudsley Personality Inventory was given to all subjects who could read and follow the instructions, except for those m groups SM and SF The results with this test are not considered here except m respect of ~ts correlation w~th the other measures The subjects m all groups, except SM and SF, were then tested m order with. I Chnlcal estimates of the Response to Pro-Prick on palms, face and soles of the feet. it. Pare Perception Thresholds and Severe Pain Thresholds determined with the Pressure Algometer; and nl Electronic Recordmg of Finger-Movement m response to mild electric shocks. Those In Groups SM and SF only had mvesUgatlon (u). As a prehmmary all subjects were told that the tests were tests of sensitivity and not tests of endurance. The response to pm-pnck (Technique t) ~s a measure of the extent to which the subject, withdraws, winces or complains when pricked with a hypodermic needle in a standard fashion It has been described m full elsewhere [29, 8] and forms only a minor part of the present report The Pressure Algometer (Techmque i0 consists of a plunger mounted on a spring and bearing a calibrated scale. The end of the plunger is smooth, flat and circular, with a diameter of 0-5 cm and area of 0"196 cmL The plunger was held against the forehead of the subject who was again told that the test was a sensitivity test and not an endurance test. He was asked to say firstly, when he felt pain and then when it hurt a lot. After a prehmlnary trial the process was repeated 4 times, increasing the pressure as nearly as possible at a rate of 1"0 kg/sec. The figures at each level were averaged The lower level gives a measure of the Pain Perception Threshold (P.P.T), the upper level a measure of the Severe Pain Threshold (S.P.T). This techmque has been described and standardlsed by Merskey and Spear [9] and shown to give moderately consistent results. The S.P.T. corresponds to what has otherwise been called the Pain Reaction Threshold (P,R.T), or Pare Reaction Point (P.R.P). Finger-movement m response to electric shock (.Technique m) was recorded as follows The subject was asked to sit with his left forefinger resting steadily on a lever and to keep his hand steady. The lever, suitably damped, rested on the plezo-elecmc crystal from a microphone insert whose potential changes were fed into an E,E G. amphfier The rate of change of pressure by the finger could thus be recorded. The subject was told that he was being asked to take part m yet another test of sensltw~ty. It was emphas~sed that it was a research procedure, that the shocks were of todd to moderate severity, and that there was no danger He was then told that he would be given 3 pairs of shocks and asked to say in each pair which was the stronger or whether they were both the same The shocks were obtained by charging an 8 p F paper dielectric condenser from a 90 V battery and discharging the condenser through a potenttometer. The maximum discharge available, measured by an Avometer was 93V, 1"7 m Amp. through the electrodes used. q-he discharge was divisible in an approximately hnear fashion at nine settmgs of the potentlometer. It was delivered to the subject through circular monel-metal electrodes of 1" diameter apphed with Cambridge electrode jelly to the palmar and dorsal surfaces of the right hand. qhe strength of the individual shocks when taken across an mvometer was Pair 1 Volts mAmp
Paw 2
Pair 3
1
2
3
4
5
6
31 0'5
52 0.9
52 0.9
31 0-5
72 1"2
31 0 5
Thus shocks 1,4 and 6 were Identical in strength and the maximal shock was No. 5 Shocks of the same strength were included in this way at different points because it was suspected that the amount of finger-movement recorded at first would be related to anticipatory anxiety and might dlmlmsh subsequently The dehvery of each shock was registered manually on the E E.G paper, usually via an event-marker. The largest deflection within 1 sec after each shock was measured as an estimate
Effect of chromc pare upon the response to noxious stimuh •
•
D.P.
•
,
aJ ~ ; . ~ r
• CALl|. IOOp'.
~
.~lb..__.a~c.d~,._ L .
A , A ....
409 I .n.--..d~.....a..__A
2
"'
"%.
,'
~
-----,-J
"l
- -
~
FiG. 1. Finger movement in response to electric shocks. Normal male medical student; Top line: Time-base: 1"5 cm/sec; 2nd Line: Finger-movement; 3rd Line: Eventmarker.
F.M. CALIB. IOOpv
Fie. 2. Finger-movement in response to electric shocks. Female patient with pain. Time-base as for F~g. 1: 1st Line: Finger-movement; 2nd Line: Event-marker; Both Figs. 1 and 2 show the typical relatively large response to the Ist shock followed by a decline with subsequent shocks and some increase again w~th the largest shock (No. 5). of the degree of reaction. Figures 1 and 2 show two typical sets of responses. The finger-movement test was always done last. Amongst the WPM and WPF groups many patients clearly failed to understand the explanation offered for the finger-movement test. Anyone who showed the least reluctance to undergo the test was not gwen it and no-one m any group who expressed unwdhngness was examined with it. RESULTS a. Ages o f the experimental groups The ages of the groups studied are shown in Table 1. It is clear that there are wide d~fferences m age between several of the groups. It wdl be ewdent from other tables (especially Table 2) that there is no consistent trend of response to the tests according to age, e.g. in a number of instances patients with depression who tend to be elderly, score most like young normal controls, and d~fferences between male and female subjects which will be demonstrated, occur qmte often at s~mdar ages. Further an intra-group exammatton of some results showed no significant trend with age. The influence of age on these results is therefore unlikely greatly to affect the other comparisons made.
b. The response to Pin-Prick The results are not presented in detad since the test d~d not discnm,nate patients from normals nor patient groups from each other and there was no consistent pattern of response according to diagnosis. Although the differences were not significant it was found that depressed patients with pain reacted more than those w~thout pain and this ~s of interest since simdar trends were obtained with the Algometer and Finger-movement Scores (Tables 2 and 3). It is also worth ment,onmg that a consistent sex difference was present. Every one of the six male groups studied reacted less than the corresponding female groups.
c. Pain Perception Threshold and Severe Pam Threshold The results obtained for the above measures using the pressure algometer are shown in Table 2. Nearly all the patients, except for the hypochondnacal ones, were assessed both for P.P.T. and S.P.T. There were 13 instances at the beginning of the study where only the S.P T. was sought. There are indications from other work [10] that th~s need not be, expected to affect the S.P.T One anxious male patient would only give P.P.T. scores and there were 3 patients m the pain series who were lost for this invest]gabon. The results indicate that m general P.P.T. and S.P.T vary together. The S.P T. results are more in accordance with expectation. For convenience of presentation the P.P.T. wdl be considered first. Both with P.P.T. and S.P.T. low scores indicate an early response to the stimulus, high scores a delayed one.
410
H. MERSKEY TABLE ] , - - A G E DISTRIBUTION OF THE EXPERIMENTAL GROUPS
G r o u p s W P M a n d W P F Include 6 patients with diagnoses o t h e r t h a n those of the p r m o p a l pain sub-groups
Group
No
M e a n age in years
S D
CM CF AM AF DM DF SM SF
Male students Female students Anxiety neurosfs: males Anxiety neurosis: females Depression : males Depression" females H y p o c h o n d r m c a l : males H y p o c h o n d r l a c a l : females
15 20 10 11 l0 9 16 20
2473 21 6 32 3 29 73 47 3 39 33 46 94 49 3
1 91 0 95 7 83 8 2 16 06 9 55 3 79 4 71
WPM SPF
W h o l e group males with pare W h o l e group females with pare
37 53
45 1 45-78
11 16 13 93
PAM PAF PHM PHF PDM PDF
Anxiety n e u r o s i s ' S u b - g r o u p males with pain Anxiety neurosis: S u b - g r o u p females with pain Hysteria: Sub-group males with p a m Hysteria: S u b - g r o u p females with pain Depression" Sub-group males with pain Depression" Sub-group females with p a m
14 10 14 27 6 13
41 9 37 9 45 8 45 6 545 53
11 65 9 74 1l 84 11 61 74 19 31
Ta, BLE 2.--ALGOMETER SCORES FOR PAIN PERCEPTION THRESHOLD (P.P T.) AND SEVERE PAIN THRESttOLD (S P . T ) IN KG/0-196 CM~
Pain Perception T h r e s h o l d Group No
Mean
CM CF SM SF AM AF DM DF
15 20 . . 10 10" 10 9
3 63 2 73 . .
WPM WPF PAM PAF PHM PHF PDM PDF other
Severe Pain T h r e s h o l d
S.D.
No.
Mean
b D.
5 75 4 41 4 49 3 29 4 46 3 56 4 69 493
1 28 0 91 1 75 0 91 0 73 0 78 1 09 1 35
2 85 26 3 18 381
0 98 0 60 0 51 1 17
15 20 16 20 9+ ll 10 9
32* 46*
324 32
1 15 1 35
36~ 51++
441 3 99
145 1 47
13 10 13 22 4 11 5
3 19 36 3 25 3 13 2 36 26
1 087 0 51 1-42 l 57 1 45 099
14 10 13 26 6 12 6
4 5 4 71 4 31 3 83 3 97 335
1 21 0 79 1 64 1 62 1 65 1 15
.
095 0 61
-
.
* P P T. refused or not sought in 12 pain patnents a n d one in group AF. i O n e patient refused S P.T test after s u b m i t t i n g to P.P T. test ~ S P T not obtained on 3 patmnts m the pain groups.
Effect of chronic pain upon the response to noxious stimuli
411
In evaluating the results with the pressure algometer four questions have to be considered, viz: (1) (2) (3) (4)
Do male groups score more than comparable female groups, as would be expected ? Similarly, do the students score more than the patients? Are there any major differences between different dmgnostlc groups ? Do comparable diagnostic groups with and without pain score in the same way or differently ?
Systematic comparisons have therefore been made between the appropriate groups in respect of each of these questions for the P P.T. and S.P.T. The method of doing th~s has been to perform t-tests on all those differences which, from inspection, might be thought to be sigmficant. The results of these t-tests are then set out for the groups compared. It should be noted that doing multiple t-tests in thTs way introduces a hkehhood of finding some differences which are significant at the 0-05 and even at the 0 01 level of probability and which are nevertheless due to chance variation. Having regard to the number of possible comparisons which might be made the level of probablhty for any one case which can be taken as reasonably likely not to be due to chance has therefore been set at p / 0.001. However there is also a substantml number of cases where probabdltles o f p /_ 0 05, p L 0'02, p /_ 0-01 emerge, m agreement w~th each other, in respect of particular questions such as (1) and (2) above. In these cases it can be shown that the sum of all the individual probabdities is such as to be unlikely to be due to chance and the trends have been interpreted accordmgly.
1. Pam Perception ThreshoM The following comparisons have been made:
i. Males with females In several pairs of groups females score less than males, i.e. females respond sooner to the stimulus, but there are two pairs (Groups D M and DF, P A M and PAF) where the reverse happens. None of the differences between males and females is significant. For the largest difference, that between Groups C M and CF t = 1"526,p L 0-2, N.S. Thus the P.P.T. is not a sensitive or consistent indicator of differences due to sex although the trend as for males to have higher scores, as expected. ii. Normal subjects with others Group CM CM CM CF CF
with with with with with
Group Group Group Group Group
AM, DM, PDM, DF, PAF,
t t t t t
1'985p 1'557p 2'269 p 3.23 p 3'863 p
/_ 0 1, N.S. / 0'3, N.S. ~ 0 05 Z. 0'005 Z_ 0 001
These results present a comphcated picture: male normal controls tend as expected to score higher than patient groups, but female normal controls tend to do the reverse--whether the patients are anxious or depressed. It will be seen later that the S.P.T. of the female controls is relatively higher than the P.P.T. and therefore it is hkely that whilst the "tolerance" of the normal female subjects is appropriately large their readiness to respond early or to detect a pare is also great. ill. Different diagnostic groups with each other Amongst the patients without pain the anxious respond first as expected. A significant difference occurs between groups A F and D F where t = 2"879, p /_ 0'02. This is probably meaningful since a s~mdar trend occurs with the S.P.T. There is a tendency for depressed patients with pare to score less than other patients with pain but the trend is not significant (on inspection and by comparison with the groups already tested). iv. Similar diagnostic groups w~th and without pain Group A F with Group PAF, t 4'09, p Z_ 0-001 D F with Group PDF, t 2"495, p / 0 025 Anxious patients wxth pare respond later than other anxious patients without pain. Depressed patients with pain respond sooner than other depressed patients.
CoolDTen t T h e P . P . T . so f a r h a s g i v e n r e s u l t s w h o s e i n t e r p r e t a t i o n is difficult a n d c o n f u s i n g . T h e r e is s o m e e v i d e n c e f r o m it, h o w e v e r , t h a t t h e p r e s e n c e o f e x i s t i n g p a i n is a s s o c i a t e d w i t h a rise i n t h e s t i m u l u s a c c e p t e d b y a n x i o u s p a t i e n t s a n d a d e c r e a s e i n t h a t a c c e p t e d
412
H. MERSKEY
by depressed patients. The effect with the anxious patients might be supposed to be due to those with pain having much concealed tension so that although anxious they would respond less to stimuli whilst in those without pain the anxiety was much more overt and the response to stimuli great too. It may be mentioned that the trends of the responses in the depressed patients and m the anxious male patients are similar both for this test and for the Pin-Pick tests. 2 Severe Pam ThreshoM
The following comparisons have been made. i. Males with females
Group CM SM AM DM WPM PHM PAM PDM
with Group CF, with Group SF, wnthGroupAF, with Group DF, with Group WPF, with Group PHF, wuth Group PAF, with Group PDF,
t 3-716p z5 0001 t 2 595 p z_' 0.01 t244 pL005 On inspection N S. t 1-373 p Z 0'2, N.S t 0 948p z_ 0 4, N S On inspection, N S On inspection, N.S
In the case of two paars males respond before females (Groups D M and D F and PAM and PAF) The differences are not significant although they are m the same direction as the P P.T results Otherwise males respond after females. 11. Normal subjects w~th others
GroupCMwnthGroupSM, CMwlthGroupAM, CM with G r o u p D M , CM with Group WPM, CM wLth G r o u p P A M CM with Group PHM, CF Vclth Group SF, CF with Group AF CF with G r o u p P D F , CF ~nth G r o u p P H F ,
t2276p :005 t 2 7 4 5 p ~_002 t2147p_005 t 2 505 p / 0 0 2 t2689p •002 t 2 603p ,~ 0 02 t 3914p_0001 t 2 605 p , 0 02 t2795p, 001 t 1 225p , 0 3
Normal males respond later than all other groups, usually significantly so. Normal females respond significantly later than most other female groups. Normal females responded slightly sooner than depressed females without pain and shghtly sooner than anxious females without pann but these latter differences are not s~gnnficant. The S.P.T. thus distinguishes clearly between normals and most dmgnostlc groups of the corresponding sex. As noted w~th the P.P.T. depressed patients without pann respond late and so do an-,lous patients ~ ith pare. Ul. Different thaffnostlc etou,o~ ittth GroupDM SF SV SV AI" I)F PAl-
each otlleJ x~ithGIoupWPM, x~uthGroup DF, v, J t h G r o u p W P F , ',~lth Group PAF, with Group DF, \~nth Group WPI-, ~ t h Group PDI~,
t057, p_ t 3 855,/'~ t072, p t 4 202, p t 2 838, p t I 7~3, p t 3 162, p
06, N S 0 001 05, N S 0 001 0 02 01, N S 0 005
The male diagnostic groups dJffer ,,err httle from each other Femalc hypochondrlac,d patients score markedly low and they differ ~ery sagnlficantly from groups DF and PAF Anxious female patients v,~thout pasta Stole in a ~ery smltlar x~ay to hypoc, hondrlacal female patients and respond early So
Effect of chronic pain upon the response to noxious stimuli
413
also do depressed female patients with pain. Depressed female patients without paln respond late as do anxious female patients with pain. The pattern here is again similar to the pattern with the P P.T. and with the Pin-Prick tests. iv. Similar diagnostic groups with and without pam Group D M with Group PDM, t 1.0212p Z_ 0 3 N.S. AF with Group PAF, t 3'352 t7 Z 0005 D F with Group PDF, t 2 903 p Z. 0.001 The tendency is again evident for anxious patients without pain and depressed patients with pain to respond early whilst the corresponding groups with and without pain respond late. With females the tendency is highly significant.
Comment O f the m e a s u r e s e m p l o y e d the S.P.T. a p p e a r s the m o s t i n f o r m a t i v e a n d useful. It gives s u b s t a n t i a l e v i d e n c e t h a t m a l e s u s u a l l y s c o r e h i g h e r t h a n f e m a l e s a n d t h a t normals
score high.
Hypochondriacal
female patients, anxious
female patients
w i t h o u t p a i n a n d d e p r e s s e d p a t i e n t s w i t h p a i n s c o r e low. A n x i o u s p a t i e n t s w i t h p a i n a n d d e p r e s s e d patients w i t h o u t pain score high. These patterns o f response are quite consistent. Patients with hysteria and pain occupy an intermediate position.
d. Finger movement lest There is evidence [23] that the response to electric shock will vary greatly depending upon the way it is presented. This is also obvious as an a priori consideration and was confirmed by casual visitors to the laboratory. Care was therefore taken to present the test in the same way to all subjects. The variation in size of shock delivered was planned to take this into account. It was anticipated that the early shocks in the series would give a measure of the anxiety of the subject when compared with later later shocks of the same s~ze. It was also expected that the largest shock being the fifth one the preceding sequence would have conditioned the subject so that the response to the fifth shock would tend to be a measure of the response to pain. These expectations were borne out to a considerable extent by the responses ehclted. In the section on methods the strength of the shocks was given and it is evident that, taken in order of presentation, they had approximately the following ratios of voltage: 3 ' 5 : 5 ' 3 ' 7 3, nos. l, 4 and 6 being equal to each other and nos 2 and 3 being equal to each other. In general it was found that the largest responses were to nos. l and 5, and the least responses to no. 6. The pattern was not uniform Occasionally there was a response to the first shock and almost no response thereafter. Some subjects gave almost no response to any shock A few responded most to the second. However expectations were confirmed in that the trend was as predicted for shocks l and 5 to produce the largest responses. Photographs of two representative records are given in Fig. l and Fig. 2 In Fig. 1 the response is shown of a male medical student who gave a moderate initial iesponse to Shock l and little thereafter Figure 2 shows the responses of a female patient with hysteria and pain who gave the largest response to the first shock and lower responses thereafter but a fairly marked one to the fifth shock These patterns are representative of all dmgnostic groups. In every group however there was a number of patients who gave minimal responses of 0 I mm or less and in certain groups especially group AM there were some who gave very large responses which exceeded the linear range of recording of the E E G pens The restilt of this is that the data are very abnormally distributed and can only be assessed by non-parametric statistics so that the Mann-Whitney U test has been employed. It may be noted that this is sa~d to have 95°o of the po~er of the t-test (30). In one instance for a very large nunaber of scores a Chi"- median test was used. The main results obtained are given in Table 3 Only about half the patmnts with pare accepted the test Almost all the other subjects accepted the test but two anxious female patients stopped after the first shock. Table 3 shows the marked tendency for the response to the fourth shock to be less than that to the first. Taking all the patients together a median test of these 2 sets of responses gives a value Chi 2 -- 6 748,p /_ 0 01. As indicated the values for the fifth response tend to rise again and to resemble those for the first. The total for all shocks also tends to follow the pattern for the individual shock in different groups. Comparisons between groups have been made as follows for the totals of all responses, taking the estimates of probability on a two-tail Mann-Whitney U test
414
H. MERSKEY TABLE 3 . - - F I N G E R
MOVEMENT TEST
M A X I M U M DEVIATION IN CM AFTER SHOCK I ( 3 1
V),
4(52 V) a n d 5 ( 7 2 V) AND TOTALS FOR RESPONSES TO ALL 6 SHOCKS Shocks Group
No.
1
4
5
Totals 1-6
Mean
Mean*
Mean*
Mean*
Medmn*
CM CF AM AF DM DF
15 20 9 11 9 9
051 0 5 1 37 0 95 07 0 63
031 0 31 0 99 0 45 04 04
04l 0 45 0 87 049 06 0 64
227 2 64 6'68 3 11 33 3 08
14 2 1 4 1 2.5 27 30
WPM WPF
26 25
0 58 06
0 53 0 53
0 44 0 59
3 02 3 27
18 35
PAM PAF PHM PHF PDM PDF
10 7 8 10 5 7
09 061 0 36 0-66 0 52 066
0 6 043 0 36 0 52 0.74 073
0 47 041 0 38 0 63 0 48 083
3 83 28l 2 25 3 19 3 34 4 11
2 45 18 16 3 1 37 40
* The number o f group A F for these columns ~s 9. (1) Males with females GroupCM AM PAM PHM
wlthGroupCF with G r o u p A F with G r o u p P A F wzth G r o u p P H F
p p p p
A 0 1 , N-S. _X01,N.S. ~ 0.1, N.S .X 0 1, N.S.
N o significant differences between sexes were found with this test, in some pmrs of diagnostic groups men score more than w o m e n and in others the reverse occurs and there ~s no well-marked trend (2) Nol mal subjects with others Group CM CM CM CM CF CF
with Group A M with G r o u p D M with G r o u p P M with G r o u p P D M wlthGroupPF with Group P D F
p ~002 p _~ 0-1, N.S. p ± 0 052, N S p A 0 1, N S p , , 00214 p ~ 0 1, N.S.
Normal subjects tend to score less than most patient groups and the results are s~gmficant in two instances as shown (3) Different dtaffnosttc ffroit]gs with each other Group A M with Group W P M p LL 0 06, l'q S. PHMwithGroupPHF p _X01, N S . P A F with G r o u p P D F p 2x01, N S There were no marked differences between the diagnostic groups. (4) Stroll(It chagnosttc~rouos with and without flain In the hght of the above results and on inspection of the data it is evident that there are no marked differences between groups with and without pare in this test.
Comment The test does not distlngmsh between the sexes or between different dlagnost~c groups although patients tend to score more highly than normals. It shows quite well
Effect of chronic pain upon the response to noxious stimuli
415
t h a t t h e r e is a r e d u c t i o n in t h e r e s p o n s e as t h e p a t i e n t b e c o m e s f a m i l i a r w i t h t h e s i t u a t i o n a n d after he has f o u n d t h a t the first shocks are at m o s t mildly painful. The test s h o w s s o m e c o r r e s p o n d e n c e in the t r e n d o f g r o u p results w i t h t h o s e o b t a i n e d in r e s p o n s e t o P i n - P r i c k , a l t h o u g h t h e c o r r e s p o n d e n c e is s m a l l a n d u n i m p r e s s i v e .
e. Test intercorrelations Scores were available on the Maudsley Personality Inventory as well as on the different physical tests. If these scores reflect similar functions then they should intercorrelate--at least to some extent. The appropriate correlation coefficients have therefore been calculated for females for a number of different measures. Group WPF was chosen for the calculation of r as being the largest single group. Group CF was chosen for the calculation of Tau for the finger-movement test as being the largest group in which all or most of the subjects accepted that test. The results are shown in Table 4 TABLE 4.--INTER-CORRELATIONS BETWEEN MEASURES OF THE RESPONSE TO STIMULI AND THE MAUDSLEY PERSONALITY INVENTORY
Product-moment correlation co-efficient:
N E Pro-prick P.P.T. S P.T. * p ~_ 0 05 1"p Z_ 0-025 1 p Z_ 0-01 §p L 0.001
Kendall's Tau
E
Pro-prick
P.P.T.
S.P.T.
Finger movement test
--0"347* -----
0"025 0 047 --.
--0 127 --0"019 --0 39 + -.
--0 077 --0 071 --0.416++ 0 915§ .
0 124 --0"12t 0 224 --0 322"~ 0 219
.
r---calculated for female patients with pain. Tau--calculated for 20 female medical students.
As is usual, there is a small negative lntercorrelatlon between the two scales of the M P I. but this test showed no significant correlations with the other measures. Significant correlations in the appropriate direction do appear however between the algometer measures and the response to pro-prick. This is in accordance with previous work [8]. Further the finger-movement test is significantly correlated with one of the algometer measures, the P.P T It has already been noticed that to some extent those two measures tended to vary together when different groups were compared. In addition as found in other work [9] there is a very high intercorrelation between the two measures obtained with the algometer. However this particular very high correlation must be, at least partially, a statistical artefact since the S.P T. figure always includes a part of the P.P.T. figure. Taken overall these findings show that the Maudsley Personality Inventory correlates very badly with the response to noxious stimuli in the experimental situation. However, they confirm the findings of Jarvik and Wolff [31] that there is a significant inter-correlation bet~een various sorts of measures of pain response.
f. The relationship o f headache to the Pain Perception ThreshoM and the Severe Pain Threshold. In the Group WPM there were 12 men who did not complain of headache and in Group WPF there were 19 women. In diagnosis these no-headache sub-groups were similar to the full Pain Groups. Thus the females comprised 5 with anxiety, 8 with hysteria, 5 with depression and 1 other, whilst the males comprised 4 with anxiety, 5 with hysteria, 2 with depression and 1 schtzophremc The responses of the male and female no-headache groups (Table 5) can therefore be compared with those of the remainder of the patients with pain. In particular it ts of interest to compare them in respect of the P P.T. and S P T. since these measures were taken from the forehead There were some slight trends which may be mentioned although they were not significant; the No-Headache group of men tended to have smaller N scores, and higher E scores than the whole W P.M. group, whdst Pin-Prick and Finger-movement test scores tended to be low. There are some indications therefore that the males without headache tend to have a less neurotic pattern on the M P I. and to respond to stimuli less This last feature is also apparent with the P.P.T and S P.T. scores which in each case are higher than those in the general group (Table 2). The difference is most
416
H. MERSKEY
marked with S.P.T but is not quite significant. Comparing the males without headache with the remaining males t ~ 2 005, p /_ 0.1, N.S With these male patients therefore it can be said that those with headache tend to react more but that despite this a s~gnlficant difference could not be demonstrated at the site (forehead) where many of them had pain and where the other group did not. The actual presence of pain at the site of the stimulus d,d not produce a significant trend even in a group which appeared on several tests to be slightly more responsive than its control group. With the female patients the results in all tests are very similar, both for the headache and the noheadache groups with pain All scores, including the P.P.T. and S P T are so close to those of the whole group that they can show no significant d,fference. For example, comparing these two halves of the WPF group for P.R.T., t ~ 1-04,p Z_ 0-4, N.S Thus again the presence of headache did not produce a significantly earlier response to forehead stlmulat,on. It IS concluded that at least with respect to headache, psychogenic pain does not usually have more than a slight effect on the response to noxious stimuli at the site of the complaint. T A B L E 5 . - - P A T I E N T S W I T H PAIN BUT NO HEADACHE
MEAN SCORES IN T W O TESTS
Age
P.P T
S.P T.
Finger movement (Total 1-6)
Males
Score No
46-16 12
3 66 11
5'16 11
2 77 7
Females
Score No
48 52 19
3 29 16
4 26 17
3 36 9
DISCUSSION W h e n the whole group of patients with pain is c o m p a r e d with the other groups it is evident that in general those with pain resemble the other patients a n d differ from the n o r m a l subjects. The m a n n e r of response by psychiatric patients with pain to noxious stimuli is thus seen to be principally influenced by the type of c o n d i t i o n they have. Diagnosis therefore seems of as m u c h i m p o r t a n c e as the presence of pain in determining the response in the tests used. This conclusion emerges particularly from the present study. A n u m b e r of others also emerge which are well supported by the literature. Thus as expected, w o m e n react more t h a n men, the anxious usually react more t h a n n o r m a l s and other patients a n d n o r m a l subjects react less t h a n most patients. The findings are qualified to the extent that they distinguish groups a n d not l n d w i d u a l s - - a l t h o u g h there were very few patients who reached the higher ranges of scores with the algometer and such scores were often reached by the n o r m a l students. It must also be acknowledged that work of this sort may have, as Beecher [3] insists, only a limited bearing on chnlcal problems of pain. Still, these experimental measurements do offer some positive information, a n d the finding of significant group differences a n d significant test-intercorrelations gives support to the view that there are aspects of the h u m a n response to noxious stimuli which can be illuminated, if only a little, in this way. A further qualification might be that the results were obtained by only one investigator a n d although the measurements themselves are reasonably reliable and objective it is always possible that unconscious bias by the experimenter could affect the performance of different groups. It can be said in this respect that every effort was made to present the stimuli in a u n i f o r m way. In addition it is worth n o t i n g that m a n y of the depressed patients were thought to show considerable signs of tension as well as
Effect of chrontc pain upon the response to
noxious
stimuli
417
retardation so that the marked difference between their responses and those of the patients with anxiety was not expected but nevertheless emerged. A point of interest which appears from consideration of the sub-groups with pain and without pain is the opposite effect that pare might be thought to have in raising thresholds where there is anxiety and in reducing them where there is depression. It must be remarked here that it remains uncertain whether the differences In testresponse between anxious and depressed patients with and without pain were directly related to the presence or absence of that complaint. It has been accepted that diagnosis is of importance in predicting the response of different groups. There were however other clinical differences between the groups with and without pain but with similar diagnoses. These were found in a clinical study contemporaneous with the present one. Therefore it cannot be argued that the relative decrease in the response to noxious stimuli in anxious patients with pain and the relative increase in the response in depressed patients with pain are directly related to the presence or absence of pain. This conclusion is also inevitable on logical or a priori grounds; a significant association does not imply a casual one. What has been shown is that these assocIations exist and as they exist it may be relevant to take them into account m certgin situations. With regard to the effects of "organic" and "psychogenic" pain on pain-thresholds it is difficult to make a reliable comparison. It has been claimed that "organic" pain raises thresholds [6]. The findings reported here for the response to noxious stimuli in patients with pain and with different diagnoses make it seem possible that groups of "organic" patients, with differen~ attitudes to their wounds or dlnesses, might also react variously during measurement of experimental pain thresholds in the same way as happened with the psychiatric patients in this study. Certainly "psychogenic" pain as such appears to have no uniform effect on pain thresholds although psychiatric patients in general tend to have low thresholds for pain and high reactivity. Lastly it may be stressed that his own spontaneous pain matters more to the patient than extraneous stimuli. Just as patients with neurotic anxiety may show a normal attitude to objective difficulties but excessive concern with their neurotic ones, so in psychogenic pain the external noxious stimulus may be treated much more lightly than the internal painful but non-noxious disturbance. SUMMARY The literature on the exper,mental response to noxious stimuli in patients with chronic pain has been reviewed and it has been shown that there are very few studies in this field either of "psychogenic" or "organic" pain. The results are then reported of investigations of the response to pin-prick, of thresholds obtained with the pressure algometer and of the response to electric shock measured by electronic recording of finger-movement. The pressure algometer was the most sensitive test-instrument employed, it showed a tendency for females to react more than males and for normal subjects to react less than patients. A special group of very hypochondrlacal patients reacted earliest and most. There was a tendency for anxious patients without pain to react more than depressed patients without pain, and in fact depressed patients without pain reacted relatively late. On the other hand anxious patients with pain responded late to the algometer and depressed patients with pare responded to it relatively early. 5
418
H
MERSKEY
Patients w i t h h y s t e r i a a n d p a r e o c c u p i e d an i n t e r m e d i a t e p o s i t i o n b e t w e e n o t h e r diagnostic groups. A test o f f i n g e r - m o v e m e n t in r e s p o n s e to e l e c m c s h o c k g a v e clear e v i d e n c e t h a t p a r t o f the r e s p o n s e was related to a n x i e t y in the test s i t u a t i o n a n d p a r t to the unp l e a s a n t n a t u r e o f the stimulus. It did n o t distinguish well b e t w e e n g r o u p s b u t did i n d i c a t e t h a t n o r m a l subjects r e a c t e d less t h a n p a t i e n t s w i t h a n x i e t y o r w i t h pain. W h i l s t the a l g o m e t e r was the m o s t effective i n d i c a t o r o f differences b e t w e e n g r o u p s in the r e s p o n s e to n o x i o u s stimuli t h e r e were several significant l n t e r c o r r e l a t i o n s w i t h o t h e r test m e a s u r e s . T h u s the t w o a l g o m e t e r m e a s u r e s o f P . P . T . a n d S.P.T. w e r e b o t h significantly c o r r e l a t e d w i t h the r e s p o n s e to pin prick. F u r t h e r , the fingerm o v e m e n t test s h o w e d a s i g m f i c a n t c o r r e l a t i o n w i t h the P.P.T., so t h a t it seems as if these tests m e a s u r e d a c o m m o n p a r a m e t e r o f response. Lastly, w h e n the r e s p o n s e s a s s o c i a t e d w i t h a p a r t i c u l a r site w e r e c o n s i d e r e d It was s h o w n t h a t p s y c h i a t r i c p a t i e n t s w i t h o u t h e a d a c h e were i n c h n e d to react slightly less t h a n t h o s e w i t h h e a d a c h e . H o w e v e r , there was no s l g m f i c a n t difference b e t w e e n t h e m and o t h e r p s y c h i a t r i c p a t i e n t s w i t h p a i n - - e v e n w i t h the a l g o m e t e r tests w h i c h i n v o l v e d p a r e on the f o r e h e a d . T h u s , m at least this instance, there was no significant effect o f local p s y c h o g e n i c p a r e u p o n the r e s p o n s e to t r a u m a at the s a m e site. Acknowledgements--This work has depended greatly upon the wllhngness of students and patients
to undergo the tests and my thanks are due to all my subjects It is a pleasure also to thank the many colleagues who have given assistance and advice Mr W. Troupe made the pressure algometer and Mr. A Troupe constructed the electric shock apparatus from a design by Mr. W. H. Stanton. The patients were under the care of Drs. G Fitzpatrick, A Gllhs and C F. Lascelles and Professor E Stengel and Dr W L. Tonge I am grateful to all these colleagues and to Mr. P R F Clarke and Drs I Pdowsky and F. G. Spear for encouragement and helpful discussions. Mr. G. Mascas gave valuable statistical advice This work was part of a D M. Thesis accepted by Oxford University REFERENCES 1 HALLK R L. Studies of cutaneous pain- a survey of research since 1940. Brtt J Psychol 44, 281 (1953). 2. HARDYJ O,, WOLFF H G. and GOODeLL H Pain sensations and reactions Wllhams & WiIktns, Baltimore (1952). 3 BEECHER H K Measurement of subjectwe responses. Quantitative effect of drugs Oxford Umverslty Press, New York (1959). 4. MERSKEYH. To be published 5 CHAPMAN W. P, and JONES C
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M. Varmtions m cutaneous and visceral pare sensmvlty in
normal subjects J CIm. Incest 23, 81 (1944) HAZOUR1L A and MUELLERA D Pain threshold studies on paraplegic patients 4tch Neitrol Psychtat 64, 607 (1950) HALL K R L and STRmE E The varying response to pain m psychiatric disorders A study tn abnormal psychology Brtt J Med Psvchol 27, 46 (1954) MERSKEY H , GILLIS A and MARSZALEKK. S. A clinical mvest~gat~on of reactions to pain J Ment Scl. 108, 347 (1962) MERSKEY H and SPEAR F G The rehablhty of the pressure algometer BJlt J Soc Chn Ps),chol. 3, 130 (1964) MERSKEYH and SPEAR F G The concept of pare (To be pubhshed) HARDYJ D ,WOLFF H. G and GOODELL H Studies in pain A new method for mcasurmg pare threshold" observations on spatml summation of pare J Clin Invest 19, 649 (1940) EDWARDSW. Recent research on pare perception P~ych Bull 47, 449 (1950) KUTSCHeR A H. and KUTSCHERN. W Evaluation of the H-W-G pain threshold apparatus and technique lnt Rec Med 170, 202 (1957) MCKENNA A E The experimental approach to pare J ,4Dpl Ph$ stol 13, 449 ~1958) MUELLeRE E , LOEFeLt R and MEAD S Skin impedance m relz(t~on to pare tlarcshold testing by electrical means J Appl Phvstol 5, 746 (1953) HILL H E , KORNETSKYG , FLANARYH G and WIKLERA Effects ol anxiety and morphine on dl~cnmmatmn of mtensmes of pamful sttmuh J Chn Incest 31,473 (1952)
Effect of chronic pain upon the response to noxious stimuli
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