- Email: [email protected]
Information effect on the perception of pain during electromyography
671
Information Effect on the Perception of Pain During Electromyography James K. Richardson, MD, Jeffrey E. Evans, PhD, John H. Warner, MA ABSTRACT. Richardson JK, Evans JE, Warner JH. Information effect on the perception of pain during electromyography. Arch Phys Med Rehabil 1994;75:671-5. a Pain during the performance of electromyography (EMG) is an important clinical problem because pain distresses the patient and can interfere with diagnostic accuracy. We hypothesized that anxiety and pain perception associated with EMG would decrease if patients received written material describing the EMG before examination. Forty-two subjects received written material and 30 did not. Information before the test significantly decreased pain perception for women during the nerve conduction studies (p = &OS), but not during the needle examination. A similar effect was not identified for the men. Other results indicate that women perceive the test as more painful than do men, older subjects perceive more pain and experience greater anxiety than do younger subjects, and all subjects perceive greater pain during the performance of (concentric, bipolar) needle electromyography than during the nerve conduction studies. 0 1994 bv the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Y
I
Rehabilitkion Pain during the performance of electromyography (EMG) is an important clinical problem. It distresses the patient and can limit diagnostic accuracy by preventing the test from being performed thoroughly. Previous studies have suggested that increased pain perception during EMG is associated with females,’ needle characteristics,* anxiety level, and self-assessment of pain before the examination.3 Despite awareness of the problem, few efforts at decreasing pain perception during EMG have been reported. LaJoie4 found that analgesia was produced by a combination of barbiturate and narcotic, whereas Spence and Guyton’ suggested that pain perception decreased when auditory input was provided during the examination. Pain reduction has also been produced through behavior modification and relaxation techniques used before the EMG exam.’ However, each of these techniques has drawbacks. Drugs are impractical for persons who must go to work or drive themselves home after the procedure, and auditory input prevents the patient from easily following examiner directions. The routine teaching of behavior modification or relaxation techniques is time-consuming and expensive because of the relative brevity of the EMG exam. Giving information to patients before medical procedures can be practical and inexpensive. Furthermore, there is precedent for the idea that information reduces stress before medical procedures. For example, Johnson and colleagues’ found less disruption of function in a group of subjects who From the Department of Physical Medicine and Rehabilitation (Drs. Richardson, Evans), Umversity of Michigan Medical Center; and Center for Statistical Consultation and Research (Mr. Warner), University of Michigan, Ann Arbor. MI. Submitted for publication May 6, 1993. Accepted in revised form October 14. 1993. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organizations with which the authors are associated. Reprint requests to James Richardson, MD, Department of PM&R, University of Michigan Medical Center ID204, Ann Arbor, MI 48109-0042. 0 1994 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003.9993/94/7506-0132$3.00/O
received information regarding radiation for prostate carcinoma compared with a group who did not receive such information. Leventhal and coworkers’ found that women who underwent Lamaze training reported less fear, pain, and fatigue associated with childbirth compared with women who had not received such training. Stewart’ noted that women with dysplastic Pap smears who had been mailed informational brochures reported less distress and had less fear of cancer than patients with similar Pap results who had not received the information. Finally, a meta-analysis of studies that provided information before a variety of noxious medical procedures, including endoscopy, cast removal, and dental work, found that sensory information in particular tended to reduce pain and distress.” High anxiety regarding the EMG examination is also associated with increased perception of pain. Patients coming to EMG have high levels of anxiety that might be “decreased by prior information . . . about the test.“? We therefore tested the hypothesis that written information provided to patients before their EMG examination would decrease patient anxiety and retrospective pain perception. Secondarily. we explored the relationship between age and sex and the retrospective perception of pain during EMG. METHODS
Study subjects were ambulatory outpatients referred for electromyographic evaluation of musculoskeletal problems such as radiculopathy and carpal tunnel syndrome. Subjects were included if they were more than 18 years of age, had no previous EMG experience, could speak and understand English and were willing to participate. All subjects were ambulatory outpatients in generally good health. Before the EMG, a pamphlet that explained the test was sent to one half of the subject population. Subjects received a pamphlet if the 5th digit of their g-digit hospital identification number was even (the informed group), but not if it was odd (the uninformed group). Office personnel enclosed the pamphlet with appointment slips that were delivered to the patient 7
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672
to 10 days before the EMG appointment. The physicians and technicians who performed the EMG and administered the pain and anxiety questionnaires were unaware that any subjects had received information about the EMG. The physicians and technicians were led to believe only that pain and anxiety were being measured in patients undergoing EMG. The pamphlet, which was written by the authors, describes the purpose and importance of the EMG in common terms and the sensations the patient might experience during the nerve conduction studies and the needle examination. The pamphlet’s tone was meant to be informative and reassuring but frank. The text of the pamphlet is as follows: Your physician has referred you to the University of Michigan Medical Center for an electromyogram (EMG). The EMG can give you and your physician information about the health of your nerves and muscles that no other test, such as an xray, scan, or blood test, can give. You may have heard about the EMG, or you may know nothing about it. The purpose of this pamphlet is to explain the purpose of the test, and to inform you about what you will experience when you have the test. As you may know, the brain and spinal cord control muscle movements and receive information from the body through a network of nerves. These nerves travel through your arms, legs and body. Information is transmitted along these nerves by small electric impulses. The EMG is a way to measure the ability of your nerves to carry these electrical messages. The test itself has two parts: 1) nerve conduction studies and 2) needle electromyography. In the first part, a nerve is stimulated by sending a mild, brief shock to the skin near the nerve. Then the speed and strength of the nerve’s response to the stimulus is measured through small discs that are taped to your skin. The physicians and technicians working with you know what normal nerve responses should be and can tell the health of the nerve being tested. The electric impulses are in no way dangerous to you, even if you have a pacemaker. The physician or technician will tell you when to expect a stimulus, but it still may feel sudden and annoying. Despite this, most patients find the nerve conduction studies tolerable, especially because of their importance in determining your diagnosis. The second part of the test is the needle electromyography. This part of the test is the most accurate and sensitive test known to determine if there is any damage to the nerves that supply your muscles. In this part a thin needle is inserted into a muscle. The electric signals in your muscles are then transmitted onto a screen where the physicians can see and hear them. For most people the discomfort or pain is less than when they get blood drawn for a lab test. Again, most of our patients tolerate the test well. Of course, each needle is used only once and then thrown away, so there is no possibility of transmitting disease through the needle. When the EMG is completed the physician will look at the results of the two parts of the study and write a report that will be sent to your doctor. If the test shows a problem, then your doctor can discuss with you what should be done. If the test is normal then you can rest assured that your nerves. muscles and the connections between them are healthy. We hope this pamphlet has answered some of your questions, but if you have more please ask us when you come in for your test. We look forward to working with you so that we can supply you and your physician with the information you need.
Arch Phys Med Rehabil Vol75,
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AND EMG, Richardson Before the EMG, basic demographic data including age, sex, present occupation, and level of education achieved, was recorded for each subject. Then a 20-statement instrument designed to measure state anxiety was completed by the subjects (the State-Trait Anxiety Inventory [STAI]).” The STAI is a questionnaire designed to measure both situationexperienced at the moment, ally specific “state anxiety” and anxiety which is a personal characteristic or trait that tends to manifest across situations and over time. We were interested in anxiety at the time of the impending EMG exam and our ability to modify it. We also were concerned with minimizing the length of time necessary to complete our questionnaires. We therefore administered only the state anxiety questions of the STAI. Test-retest reliability (stability) of the STAI state scale is low as would be expected for a scale designed to measure transient changes in level of anxiety. Internal consistency measured by the alpha coefficient was good, ranging from 0.83 to 0.92 for the state questionnaire, depending on the state of the subjects. Item-reminder correlations for high school and college students were good. Concurrent validity is high for both student subject and neuropsychiatric patient samples when compared to the IPAT Anxiety scale and the Taylor Manifest Anxiety Scale (Y > 0.75). Construct validity assessed for college students was good. lo After the EMG, subjects filled out a part four of the McGill Pain Questionnaire (MPQ)” and a Visual Analogue Scale (VAS)12 of pain intensity for both the nerve conduction studies and the needle examination. The MPQ is a comprehensive inventory of pain characteristics. We used questions that asked for a numerical rating of the pain experienced on the EMG and of the worst pain they had ever experienced. Subtracting the scores for the nerve conduction study and for the needle exam from the “worst pain” scores yielded scores corrected for the patient’s tendency to rate pain at the low or high ends of the scale. Evaluation of the MPQ suggests that it “provides valid indices of some, at least, of the dimensions of pain, and can be used to determine the effects of different therapeutic manipulations.“” The VAS asks patients to put a vertical line through a 1Ocm horizontal line at the point which best represents the intensity of pain on each exam. The left margin of the scale represents “no pain” and the right margin “the worst pain imaginable.” Price and coworkers” report high between-session reliability of the VAS measure of experimental pain (Y = 0.97). For clinical pain, internal consistency was shown for most patients with pain. In addition VAS responses were correlated +0.70 with physician’s ratings of patients’ improvement. The last question asked subjects if they had received and read the information sent to them in the mail about the EMG. If there was discordance between a subject’s response to that question, and what actually occurred based on the hospital identification number code, then the data were excluded from analysis. In this way only subjects who received and read the information were included in the informed group. Statistical analyses were performed using the Systat statistical program package.13 A multivariate generalized linear model was computed to determine the importance of age and sex, in addition to informational status, to our analysis.
INFORMATION/PAIN
AND EMG, Richardson
Table 1: Mean Age and Standard Deviation for Each Experimental Group by Sex Sex
Not Informed
(SD)
Informed
48.0 ( 12.5) n = 13 39.4 c13.4) n = I7
Male Female
Table 3: Probability Values for Analysis of Covariance Sex-
46.0 ( 13.3) n = 13 44.0 ( 12.8) n = 29
RESULTS Ninety-one patients filled out questionnaires before and after the EMG. Seventy-six knew whether they had received and read information before the test. Four subjects were excluded because of missing data; 72 were included in the analysis. Of the 72, 42 received the information and 30 did not. The characteristics of each group with respect to mean age and sex are shown in table 1. There was no significant differences between the two groups with respect to age or educational level. Differences between the sexes with regard to age and education were not computed and this constitutes a limitation of the analysis. The distribution of information had no effect on the number of patients who did not arrive for their scheduled EMG appointments. During the 3 months of the study the “no-show” rate averaged 4.3%, whereas 1 month before and 2 months after the study, the “no-show” rate averaged 5%. Table 2 shows means of test scores for informed and uninformed subjects and for each sex. Table 3 shows levels of significance from an analysis of covariance (ANCOVA). Inspection of means across all subjects (table 2) shows virtually no difference between informed and uninformed subjects in their reports of pre-EMG anxiety (STAI) or in their MPQ reports of pain perception after the nerve conduction study or after the needle exam. However, the VAS shows, in informed subjects, a trend toward decrease in pain perception on the nerve conduction study (p = .07). When sex
Test State anxiely
Nerve conduction pain (visual) Needle exam pain (McGill) Needle pain
exam (visual)
Sex
Information
State anxiety Nerve conduction pain (McGill) Nerve conduction pain (visual) Needle exam pain (McGill) Needle exam pain (visual) Total
0.176
0.896
0.746
0.53 1
0.963
0.205
O.S7(i
0.070”~
0.008”‘Y
0.22 I
o.s44
0.935
0.3 I R
0. IO6
0.003”’ <0.001*
0. I x7 o.s71
0.850 0.096”
0.002~” ’ <0.001 t i
Means and Standard
<0.001**
* Very significant. ’ Older with increased anxiety +Women with increased pain. ” Trend n Uninformed
Information
Age ~0.001
*’
and pain.
with increased pain.
is added as a covariate, the interaction between sex and information for the VAS on the nerve conduction study is significant (p = .008). Inspection of means shows that on that measure women, but not men, report far less pain if they received the information designed to educate them about the EMG exam. The means for the MPQ are in the same direction for women, but the differences are not statistically significant. Modeling these results by the method of least squares regression shows that both sex and age, but not level of education, account for a significant amount of the variance across 3 of the 5 tests of anxiety and pain perception performed (table 3). Results for age show that across all tests older persons reported more anxiety and pain than did younger persons, significantly so for state anxiety (II < .OO1) and for the needle exam (p = .002). In addition, all women, regardless of informational status, reported significantly more pain than men on the visual analogue scale for the needle exam (p = ,003) as well as for the nerve conduction study (p < .OOl). Finally, table 2 also shows that the needle examination was perceived to be more painful than the nerve conduction studies by both men and women. Probability values for analysis of covariance are shown
Errors for Test Scores Holding Age Constant
All Females
All Informed
3h.41
39.95
38.02
38.25
35.83
37.00
40.20
39.70
1157)
(I.701
(1.X8)
12.83)
(7.M)
(1.89)
(2.51)
~0.095)
02x0
-6.64 (0.74)
-7.09 (0.49)
--6.71 (0.65)
--O.OII (0.015)
0.04I
18.25
4x.99
(3.38)
(4.4X)
-0.210 IO. 170)
0.30X
All Uninformed
Male Informed
-
All Males
(2.01t Nerve conduction pain (McGill)
Test
(SD)
An analysis of covariance was performed to determine the statistical significance of each of those variables and interactions between them on subjects’ responses on each of the five tests of anxiety or pain perception.
Table 2: Adjusted
673
-6.23 IO..521
-6.65 (0.41)
(0.44)
(0.48)
(0.73)
30.96 (3.601
3X.62
25.62
33.96
23.00
(2.81)
(3.04)
(3.35)
CT.061
-5.79 10.60)
-5.32
36.06
5
(3.85)
(0.46)
I.37
(3.00)
-6.45
-5.52
-6.42
-s.s9
-.5X.?
Male Uninformed
I X.93 (5. IO)
Female Informed
Female Uninformed
Age
R2
-0.436
-.5.3X (0.84)
-6.20 (0.84)
m-S.67 (O.Sh)
-4.97 (0.74)
-0.046 (WI23)
0.00x
46.92
33.29
3X.X1
(3.58)
(5.40)
(5.44)
47.63 (3.61)
55.01 (4.79)
-0.582 (O.I82)
02x0
Arch Phys bled Rehabil Vol75,
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(0.50)
(0.55)
40.46 (3.75)
Standard error in parenthesis.
674
INFORMATION/PAIN
in table 3 for the main effects of information, sex, age, and for the interaction between sex and information.
AND
EMG, Richardson
caused by common complaints such as headache and musculoskeletal pain as compared with a group of college students. The elderly have been noted to perceive less pain in medical settings as well. Elderly persons with duodenal ulcer and DISCUSSION acute myocardial infarction reported a decreased perception The results suggest that written information describing the of pain as compared with younger patients with the same EMG and its purpose may decrease retrospective evaluations diagnoses.** Furthermore, Schocken and coworkers*’ found of severity of pain for women. The results are only suggesless state anxiety in elderly, as compared with younger pative because a statistically significant reduction in pain pertients, 12 to 18 hours before undergoing cardiac catheterizaception with information was achieved only for the VAS tion. Clearly, previous research does not supply clues as to measurement of pain on the nerve conduction studies. Howwhy the elderly apparently find the EMG more anxietyever, the fact that the informed women’s scores on the other provoking and painful than the young in this study. three pain scales were in the direction of reduced pain perIf information has decreased pain perception, then this ception suggests that this significant finding did not occur study parallels other studies that have suggested that inforby chance. In addition to other research, which has found mation before medical procedures can favorably alter pain that women perceive the EMG as more painful than men,1*3 perception and recovery. Information has been beneficial in studies of experimental pain have usually shown lower pain reducing anxiety and/or enhancing recovery in gastrointestithresholds for women.‘4,‘5 In addition, sex differences in pain nal endoscopic procedures,“4 abdominal surgery,25 and dental modulation have been noted in animal models.16 Therefore procedures.26 Suls and Wan’ suggested that providing both the VAS data, which showed an increased pain perception in women in this study whereas the MPQ did not, are com- sensory and procedural information, that is information repatible with previous research. This agreement with other garding the anticipated subjective experiences and the proceresearch, coupled with a previous finding that the VAS is dural mechanics, were most likely to favorably influence the patient. Other studies have suggested that the success of more sensitive to subtle differences in the subjective experience of pain,” suggests that the VAS may have been the the intervention partially depends on the subjects’ intrinsic superior pain assessment instrument in this study. This lends coping styles.26,27Although our intervention did attempt to provide both sensory and procedural information, no attempt strength to our finding that the VAS data reflect reduced was made to differentiate coping styles and/or tailor the pain perception in women who received information before intervention based on coping style. However, the recent work the EMG. of Buckelew and colleagues*’ showed that coping strategies How should we explain the finding that only the women showed decreased pain perception after being supplied with that involved reinterpreting pain were associated with deinformation? It may be that the women in this study paid creased pain perception during EMG. This finding supports more attention to the information sent to them. Other studies the use of educational materials because an effect of educahave suggested that women have “greater interest in and tion is to modify the way people interpret their experience. In the present study there is apparently no difference in concern with health matters.“” Therefore, although great care was taken in the study design to only evaluate those the level of anxiety before the EMG examination between subjects who had read the information sent to them, the the group that received information and the group that did women may have read the information more carefully and not. Previous research has tied pain perception during EMG to two unalterable variables, female sex, and pre-examinabetter prepared themselves for the EMG. Another possibility is that the gender of the EMG technicians (all women) influ- tion self-assessment of pain, and anxiety, a presumably modifiable variable.‘,3 We assumed that any positive affect this enced this study’s outcome. Levine and De Simone18 found that men, but not women, reported less pain in response to study might show, given the well known association between an experimentally induced painful stimulus when the stimu- anxiety and pain, would be through a reduction in anxiety. lus and pain assessment instrument was administered by a However this was not shown. This could be because of the state anxiety instrument being insensitive to the mild changes member of the opposite sex. Because the nerve conduction in anxiety produced by the information. Another explanation studies (one of the painful stimuli) and the pain assessment instruments were given by women in our study, men may could be that the information did not reduce anxiety just before the test because the information had confirmed that have underreported pain whether or not they received information. This may have produced a floor effect so that the there was going to be some pain or discomfort during the information could not decrease measured pain perception in examination. During the procedure the subjects’ anxiety may have lessened as the events reassuringly corresponded with the men. Our findings for age suggest that older people are both the information they had received. Finally, it simply could more anxious before the procedure and experience more pain be that the information did not alter anxiety levels at any time during the examination. It is hard to reconcile this on the needle exam, at least as suggested by the reportedly more sensitive visual analogue scale. This is at odds with conclusion with the apparent reduction in pain perception in other research in this area. Neri and Agazzani” and Tucker at least some members of the group that received informaand colleagues*’ found that experimentally induced pain tion. thresholds increased with age. Roy and coworkers*’ noted This study does have limitations that have to be taken that elderly persons reported significantly less regular pain into account when conclusions are made. In particular, the
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INFORMATION/PAIN
women could have had group characteristics in age or educational level that were different from those of the men, and this difference might have influenced the results. In addition, the results may not be a direct result of the information that the subjects were given. As an example, it may have been that the subjects who received the information asked the physicians and technicians more questions before and during the study. As a result the subjects who received more information also received more attention during the examinations, felt more at ease. and perceived less pain. This study cannot clarify whether such an indirect mechanism is responsible for the effect observed; however, the potential clinical use of the intervention remains regardless of the actual mechanism of effect. The results contradict a previous study’ that found that nerve conduction studies were perceived as more painful than the needle examination. In this study needle electromyography was perceived as more painful than the nerve conduction studies for both sexes on both pain scales. This may be explained by the fact that a monopolar needle was used in the other study, whereas a concentric bipolar needle was used in this one. Another finding of practical importance is that the number of patients who missed appointments for their EMG did not change during the 3-month study when compared to the months immediately before and after the study. The information was sent to half of all the patients who underwent EMG during those 3 months. We were alert to the possibility that the information might frighten patients and increase the “noshow” rate, but this did not occur. In summary it seems that a written document that provides procedural and sensory information about EMG may reduce patient perception of pain during the examination, particularly for women during the nerve conductive studies. The men may not have responded to the information because they did not read it as carefully as the women, because they underreported their pain in response to the women technicians who administered both the nerve conduction studies and the pain assessment instruments, or because the intervention was simply not effective for them. Finally, the women reported greater pain related to the EMG than did the men, and the elderly reported more EMG-related pain and anxiety than did the young. Future research could investigate the differential response of the sexes to information, and possibly include coping style as a variable. The finding that the elderly experience more pain during the EMG needs to be confirmed, and interventions developed to assist a group that seems more resilient to other medical procedures. Acknowledgment. The authors thank Barbara Kramer, Susan Nalepa. Kathleen Ryan, and Teresa Spiegelberg whose advice and tenacious assistance made this studv possible. We would also like to thank Deborah Zolot. BS for her help with ;he data.
AND
6. I.
8.
9.
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27. References I. Gans BM, Kraft GH. Pain perception Arch Phys Med Rehabil 1977~58: 13-6
in clinical
electromyography.
EMG, Richardson
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Spence WR, Guyton JD. Control of pain during electromyography. Arch Phvs Med Rehabil 1966:47:771-4. Khoshbin S. Hallet M. Lunbeck R. Predictors of patients’ experience of pain in EMG. Muscle Nerve 1987: 10:629-3? _. La.Joie WJ: Analgesia in electromyogrdphy. Arch Phys Med Rehahil 1%3:44:42-4. Kaplan RM, Metzger G. Jablecki C. Brief cognitive and relaxation training increases tolerance for a painful clinical electromyographic examination. Psychosom Med 1983;45: 155-62. Johnson JE. Lauver DR. Nail LM. Process of coping with radiation therapy. J Consult Clin Psycho1 1989;57:358-64. Leventhal EA. Leventhal H, Shacham S. Easterling OV. Active coping reduces reports of pain from childbirth. J Consult Clin Psycho1 1989;57:365-71. Stewart 0. The effect of educational brochure:. on knowledge and emotional distress in women with abnormal Papanicolaou smears. Ohstet Gynecol 1993; 8 I :280-2. Suls J. Wan CK. Effects of sensory and procedural information on coping with stressful medical procedures and pain: a meta-analysis. J Consult Clin Psvchol 1989;57:372-9. Spielberger CD:Gorsuch RL. Lushene RE. State-Trait Anxiety Inventory Manual. Palo Alto. CA: Consulting Psychologist Press, Inc, 1970. Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain 1975; I :277-99. Price DD. McGrath PA, Rafii A. Buckingham B. The validation Ibf visual analogue scales as ratio scale measures for chronic and experimental pain. Pain 1983; l7:45-56. Wilkins&t L. Systat: the system for statistics. Evanston (IL): Systat. Inc. 1987. Otto MW. Dougher MJ. Sex differences and personality factors tn responsivity to pain. Percept Mot Skills 1985;61:383-90. Weisenberg M. Pain and pain control. Psycho1 Bull 1977;84: 1008-44. Kepler KL, Kest D, Kiefel JM, Cooper ML. Bodnar RJ. Roles of gender, gonadectomy and estrous phase m the analgesic effects of intracerebroventricular morphine in rats. Pharmacol Biochem Behav 1989;34:1 19-27. Council on Ethical and Judicial Affairs, American Medical Association: gender disparities in clinical decision making. JAMA I99 I ; 366:55’)62 Levine FM. DeSimone LL. The effects of gender on pain report m male and female subjects. Pain I99 I ;44:69-72. Neri M. Agazzini E..’Aging and right-left asymmetry in experimental pain measurement. Pain 1984: 19:43-8. Tucker MA, Andrew MF. Ogle SJ. Davison JG. Age-associated change in pain threshold measured by transcutaneous ncuronal electrical stimulation. Age Aging 1989; 18:241-6. Roy R. Thomas M. Makerenko P. A comparative study of pain contplaints in a non-clinical Canadian population of university students and seniors. Pain Clin 1990;3:213-22. Scapa E, Horowitz M. Avtalion J, Waron M, Eschar J. Appreciation of pain in the elderly. Isr J Med Sci 1992:28:94-6 _. Schocken DD, Greene AF, Worden TJ. Harrison EE. Spielberger CD. Effects of age and gender on the relationship between anxiety and coronary artery disease. Psychosom Med l987;49: I 18-26. Wilson JF. Moore RW. Randolph S, Hanson BJ. Behavioral preparation of patients for gastrointestinal endoscopy: information. relaxation. and coping style. J Hum Stress 1987~8: 13-23. Sime MA. Relationship of preoperative fear. type of coping, and information received about surgery to recovery from surgery. J Pers Sr)c Psycho1 1976:34:716-24. Auerhach SM. Kendall PC. Cuttler HF. Levitt NR. Anxiety. focus of control, type of preparatory information, and adjustment to dental surgery. J Consult Clin Psycho] 1976:44:809-18. Buckelew SP. Conway RC, Shutty MS. Lawrence JA, Grating MR. Anderson SK. et al. Spontaneous coping strategies to manage acute pam and anxiety during electrodiagnostic studies. Arch Phys Med Rehabil 1993;73:594-8.
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Information Effect on the Perception of Pain During Electromyography James K. Richardson, MD, Jeffrey E. Evans, PhD, John H. Warner, MA ABSTRACT. Richardson JK, Evans JE, Warner JH. Information effect on the perception of pain during electromyography. Arch Phys Med Rehabil 1994;75:671-5. a Pain during the performance of electromyography (EMG) is an important clinical problem because pain distresses the patient and can interfere with diagnostic accuracy. We hypothesized that anxiety and pain perception associated with EMG would decrease if patients received written material describing the EMG before examination. Forty-two subjects received written material and 30 did not. Information before the test significantly decreased pain perception for women during the nerve conduction studies (p = &OS), but not during the needle examination. A similar effect was not identified for the men. Other results indicate that women perceive the test as more painful than do men, older subjects perceive more pain and experience greater anxiety than do younger subjects, and all subjects perceive greater pain during the performance of (concentric, bipolar) needle electromyography than during the nerve conduction studies. 0 1994 bv the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Y
I
Rehabilitkion Pain during the performance of electromyography (EMG) is an important clinical problem. It distresses the patient and can limit diagnostic accuracy by preventing the test from being performed thoroughly. Previous studies have suggested that increased pain perception during EMG is associated with females,’ needle characteristics,* anxiety level, and self-assessment of pain before the examination.3 Despite awareness of the problem, few efforts at decreasing pain perception during EMG have been reported. LaJoie4 found that analgesia was produced by a combination of barbiturate and narcotic, whereas Spence and Guyton’ suggested that pain perception decreased when auditory input was provided during the examination. Pain reduction has also been produced through behavior modification and relaxation techniques used before the EMG exam.’ However, each of these techniques has drawbacks. Drugs are impractical for persons who must go to work or drive themselves home after the procedure, and auditory input prevents the patient from easily following examiner directions. The routine teaching of behavior modification or relaxation techniques is time-consuming and expensive because of the relative brevity of the EMG exam. Giving information to patients before medical procedures can be practical and inexpensive. Furthermore, there is precedent for the idea that information reduces stress before medical procedures. For example, Johnson and colleagues’ found less disruption of function in a group of subjects who From the Department of Physical Medicine and Rehabilitation (Drs. Richardson, Evans), Umversity of Michigan Medical Center; and Center for Statistical Consultation and Research (Mr. Warner), University of Michigan, Ann Arbor. MI. Submitted for publication May 6, 1993. Accepted in revised form October 14. 1993. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organizations with which the authors are associated. Reprint requests to James Richardson, MD, Department of PM&R, University of Michigan Medical Center ID204, Ann Arbor, MI 48109-0042. 0 1994 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation 0003.9993/94/7506-0132$3.00/O
received information regarding radiation for prostate carcinoma compared with a group who did not receive such information. Leventhal and coworkers’ found that women who underwent Lamaze training reported less fear, pain, and fatigue associated with childbirth compared with women who had not received such training. Stewart’ noted that women with dysplastic Pap smears who had been mailed informational brochures reported less distress and had less fear of cancer than patients with similar Pap results who had not received the information. Finally, a meta-analysis of studies that provided information before a variety of noxious medical procedures, including endoscopy, cast removal, and dental work, found that sensory information in particular tended to reduce pain and distress.” High anxiety regarding the EMG examination is also associated with increased perception of pain. Patients coming to EMG have high levels of anxiety that might be “decreased by prior information . . . about the test.“? We therefore tested the hypothesis that written information provided to patients before their EMG examination would decrease patient anxiety and retrospective pain perception. Secondarily. we explored the relationship between age and sex and the retrospective perception of pain during EMG. METHODS
Study subjects were ambulatory outpatients referred for electromyographic evaluation of musculoskeletal problems such as radiculopathy and carpal tunnel syndrome. Subjects were included if they were more than 18 years of age, had no previous EMG experience, could speak and understand English and were willing to participate. All subjects were ambulatory outpatients in generally good health. Before the EMG, a pamphlet that explained the test was sent to one half of the subject population. Subjects received a pamphlet if the 5th digit of their g-digit hospital identification number was even (the informed group), but not if it was odd (the uninformed group). Office personnel enclosed the pamphlet with appointment slips that were delivered to the patient 7
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672
to 10 days before the EMG appointment. The physicians and technicians who performed the EMG and administered the pain and anxiety questionnaires were unaware that any subjects had received information about the EMG. The physicians and technicians were led to believe only that pain and anxiety were being measured in patients undergoing EMG. The pamphlet, which was written by the authors, describes the purpose and importance of the EMG in common terms and the sensations the patient might experience during the nerve conduction studies and the needle examination. The pamphlet’s tone was meant to be informative and reassuring but frank. The text of the pamphlet is as follows: Your physician has referred you to the University of Michigan Medical Center for an electromyogram (EMG). The EMG can give you and your physician information about the health of your nerves and muscles that no other test, such as an xray, scan, or blood test, can give. You may have heard about the EMG, or you may know nothing about it. The purpose of this pamphlet is to explain the purpose of the test, and to inform you about what you will experience when you have the test. As you may know, the brain and spinal cord control muscle movements and receive information from the body through a network of nerves. These nerves travel through your arms, legs and body. Information is transmitted along these nerves by small electric impulses. The EMG is a way to measure the ability of your nerves to carry these electrical messages. The test itself has two parts: 1) nerve conduction studies and 2) needle electromyography. In the first part, a nerve is stimulated by sending a mild, brief shock to the skin near the nerve. Then the speed and strength of the nerve’s response to the stimulus is measured through small discs that are taped to your skin. The physicians and technicians working with you know what normal nerve responses should be and can tell the health of the nerve being tested. The electric impulses are in no way dangerous to you, even if you have a pacemaker. The physician or technician will tell you when to expect a stimulus, but it still may feel sudden and annoying. Despite this, most patients find the nerve conduction studies tolerable, especially because of their importance in determining your diagnosis. The second part of the test is the needle electromyography. This part of the test is the most accurate and sensitive test known to determine if there is any damage to the nerves that supply your muscles. In this part a thin needle is inserted into a muscle. The electric signals in your muscles are then transmitted onto a screen where the physicians can see and hear them. For most people the discomfort or pain is less than when they get blood drawn for a lab test. Again, most of our patients tolerate the test well. Of course, each needle is used only once and then thrown away, so there is no possibility of transmitting disease through the needle. When the EMG is completed the physician will look at the results of the two parts of the study and write a report that will be sent to your doctor. If the test shows a problem, then your doctor can discuss with you what should be done. If the test is normal then you can rest assured that your nerves. muscles and the connections between them are healthy. We hope this pamphlet has answered some of your questions, but if you have more please ask us when you come in for your test. We look forward to working with you so that we can supply you and your physician with the information you need.
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AND EMG, Richardson Before the EMG, basic demographic data including age, sex, present occupation, and level of education achieved, was recorded for each subject. Then a 20-statement instrument designed to measure state anxiety was completed by the subjects (the State-Trait Anxiety Inventory [STAI]).” The STAI is a questionnaire designed to measure both situationexperienced at the moment, ally specific “state anxiety” and anxiety which is a personal characteristic or trait that tends to manifest across situations and over time. We were interested in anxiety at the time of the impending EMG exam and our ability to modify it. We also were concerned with minimizing the length of time necessary to complete our questionnaires. We therefore administered only the state anxiety questions of the STAI. Test-retest reliability (stability) of the STAI state scale is low as would be expected for a scale designed to measure transient changes in level of anxiety. Internal consistency measured by the alpha coefficient was good, ranging from 0.83 to 0.92 for the state questionnaire, depending on the state of the subjects. Item-reminder correlations for high school and college students were good. Concurrent validity is high for both student subject and neuropsychiatric patient samples when compared to the IPAT Anxiety scale and the Taylor Manifest Anxiety Scale (Y > 0.75). Construct validity assessed for college students was good. lo After the EMG, subjects filled out a part four of the McGill Pain Questionnaire (MPQ)” and a Visual Analogue Scale (VAS)12 of pain intensity for both the nerve conduction studies and the needle examination. The MPQ is a comprehensive inventory of pain characteristics. We used questions that asked for a numerical rating of the pain experienced on the EMG and of the worst pain they had ever experienced. Subtracting the scores for the nerve conduction study and for the needle exam from the “worst pain” scores yielded scores corrected for the patient’s tendency to rate pain at the low or high ends of the scale. Evaluation of the MPQ suggests that it “provides valid indices of some, at least, of the dimensions of pain, and can be used to determine the effects of different therapeutic manipulations.“” The VAS asks patients to put a vertical line through a 1Ocm horizontal line at the point which best represents the intensity of pain on each exam. The left margin of the scale represents “no pain” and the right margin “the worst pain imaginable.” Price and coworkers” report high between-session reliability of the VAS measure of experimental pain (Y = 0.97). For clinical pain, internal consistency was shown for most patients with pain. In addition VAS responses were correlated +0.70 with physician’s ratings of patients’ improvement. The last question asked subjects if they had received and read the information sent to them in the mail about the EMG. If there was discordance between a subject’s response to that question, and what actually occurred based on the hospital identification number code, then the data were excluded from analysis. In this way only subjects who received and read the information were included in the informed group. Statistical analyses were performed using the Systat statistical program package.13 A multivariate generalized linear model was computed to determine the importance of age and sex, in addition to informational status, to our analysis.
INFORMATION/PAIN
AND EMG, Richardson
Table 1: Mean Age and Standard Deviation for Each Experimental Group by Sex Sex
Not Informed
(SD)
Informed
48.0 ( 12.5) n = 13 39.4 c13.4) n = I7
Male Female
Table 3: Probability Values for Analysis of Covariance Sex-
46.0 ( 13.3) n = 13 44.0 ( 12.8) n = 29
RESULTS Ninety-one patients filled out questionnaires before and after the EMG. Seventy-six knew whether they had received and read information before the test. Four subjects were excluded because of missing data; 72 were included in the analysis. Of the 72, 42 received the information and 30 did not. The characteristics of each group with respect to mean age and sex are shown in table 1. There was no significant differences between the two groups with respect to age or educational level. Differences between the sexes with regard to age and education were not computed and this constitutes a limitation of the analysis. The distribution of information had no effect on the number of patients who did not arrive for their scheduled EMG appointments. During the 3 months of the study the “no-show” rate averaged 4.3%, whereas 1 month before and 2 months after the study, the “no-show” rate averaged 5%. Table 2 shows means of test scores for informed and uninformed subjects and for each sex. Table 3 shows levels of significance from an analysis of covariance (ANCOVA). Inspection of means across all subjects (table 2) shows virtually no difference between informed and uninformed subjects in their reports of pre-EMG anxiety (STAI) or in their MPQ reports of pain perception after the nerve conduction study or after the needle exam. However, the VAS shows, in informed subjects, a trend toward decrease in pain perception on the nerve conduction study (p = .07). When sex
Test State anxiely
Nerve conduction pain (visual) Needle exam pain (McGill) Needle pain
exam (visual)
Sex
Information
State anxiety Nerve conduction pain (McGill) Nerve conduction pain (visual) Needle exam pain (McGill) Needle exam pain (visual) Total
0.176
0.896
0.746
0.53 1
0.963
0.205
O.S7(i
0.070”~
0.008”‘Y
0.22 I
o.s44
0.935
0.3 I R
0. IO6
0.003”’ <0.001*
0. I x7 o.s71
0.850 0.096”
0.002~” ’ <0.001 t i
Means and Standard
<0.001**
* Very significant. ’ Older with increased anxiety +Women with increased pain. ” Trend n Uninformed
Information
Age ~0.001
*’
and pain.
with increased pain.
is added as a covariate, the interaction between sex and information for the VAS on the nerve conduction study is significant (p = .008). Inspection of means shows that on that measure women, but not men, report far less pain if they received the information designed to educate them about the EMG exam. The means for the MPQ are in the same direction for women, but the differences are not statistically significant. Modeling these results by the method of least squares regression shows that both sex and age, but not level of education, account for a significant amount of the variance across 3 of the 5 tests of anxiety and pain perception performed (table 3). Results for age show that across all tests older persons reported more anxiety and pain than did younger persons, significantly so for state anxiety (II < .OO1) and for the needle exam (p = .002). In addition, all women, regardless of informational status, reported significantly more pain than men on the visual analogue scale for the needle exam (p = ,003) as well as for the nerve conduction study (p < .OOl). Finally, table 2 also shows that the needle examination was perceived to be more painful than the nerve conduction studies by both men and women. Probability values for analysis of covariance are shown
Errors for Test Scores Holding Age Constant
All Females
All Informed
3h.41
39.95
38.02
38.25
35.83
37.00
40.20
39.70
1157)
(I.701
(1.X8)
12.83)
(7.M)
(1.89)
(2.51)
~0.095)
02x0
-6.64 (0.74)
-7.09 (0.49)
--6.71 (0.65)
--O.OII (0.015)
0.04I
18.25
4x.99
(3.38)
(4.4X)
-0.210 IO. 170)
0.30X
All Uninformed
Male Informed
-
All Males
(2.01t Nerve conduction pain (McGill)
Test
(SD)
An analysis of covariance was performed to determine the statistical significance of each of those variables and interactions between them on subjects’ responses on each of the five tests of anxiety or pain perception.
Table 2: Adjusted
673
-6.23 IO..521
-6.65 (0.41)
(0.44)
(0.48)
(0.73)
30.96 (3.601
3X.62
25.62
33.96
23.00
(2.81)
(3.04)
(3.35)
CT.061
-5.79 10.60)
-5.32
36.06
5
(3.85)
(0.46)
I.37
(3.00)
-6.45
-5.52
-6.42
-s.s9
-.5X.?
Male Uninformed
I X.93 (5. IO)
Female Informed
Female Uninformed
Age
R2
-0.436
-.5.3X (0.84)
-6.20 (0.84)
m-S.67 (O.Sh)
-4.97 (0.74)
-0.046 (WI23)
0.00x
46.92
33.29
3X.X1
(3.58)
(5.40)
(5.44)
47.63 (3.61)
55.01 (4.79)
-0.582 (O.I82)
02x0
Arch Phys bled Rehabil Vol75,
June 1994
(0.50)
(0.55)
40.46 (3.75)
Standard error in parenthesis.
674
INFORMATION/PAIN
in table 3 for the main effects of information, sex, age, and for the interaction between sex and information.
AND
EMG, Richardson
caused by common complaints such as headache and musculoskeletal pain as compared with a group of college students. The elderly have been noted to perceive less pain in medical settings as well. Elderly persons with duodenal ulcer and DISCUSSION acute myocardial infarction reported a decreased perception The results suggest that written information describing the of pain as compared with younger patients with the same EMG and its purpose may decrease retrospective evaluations diagnoses.** Furthermore, Schocken and coworkers*’ found of severity of pain for women. The results are only suggesless state anxiety in elderly, as compared with younger pative because a statistically significant reduction in pain pertients, 12 to 18 hours before undergoing cardiac catheterizaception with information was achieved only for the VAS tion. Clearly, previous research does not supply clues as to measurement of pain on the nerve conduction studies. Howwhy the elderly apparently find the EMG more anxietyever, the fact that the informed women’s scores on the other provoking and painful than the young in this study. three pain scales were in the direction of reduced pain perIf information has decreased pain perception, then this ception suggests that this significant finding did not occur study parallels other studies that have suggested that inforby chance. In addition to other research, which has found mation before medical procedures can favorably alter pain that women perceive the EMG as more painful than men,1*3 perception and recovery. Information has been beneficial in studies of experimental pain have usually shown lower pain reducing anxiety and/or enhancing recovery in gastrointestithresholds for women.‘4,‘5 In addition, sex differences in pain nal endoscopic procedures,“4 abdominal surgery,25 and dental modulation have been noted in animal models.16 Therefore procedures.26 Suls and Wan’ suggested that providing both the VAS data, which showed an increased pain perception in women in this study whereas the MPQ did not, are com- sensory and procedural information, that is information repatible with previous research. This agreement with other garding the anticipated subjective experiences and the proceresearch, coupled with a previous finding that the VAS is dural mechanics, were most likely to favorably influence the patient. Other studies have suggested that the success of more sensitive to subtle differences in the subjective experience of pain,” suggests that the VAS may have been the the intervention partially depends on the subjects’ intrinsic superior pain assessment instrument in this study. This lends coping styles.26,27Although our intervention did attempt to provide both sensory and procedural information, no attempt strength to our finding that the VAS data reflect reduced was made to differentiate coping styles and/or tailor the pain perception in women who received information before intervention based on coping style. However, the recent work the EMG. of Buckelew and colleagues*’ showed that coping strategies How should we explain the finding that only the women showed decreased pain perception after being supplied with that involved reinterpreting pain were associated with deinformation? It may be that the women in this study paid creased pain perception during EMG. This finding supports more attention to the information sent to them. Other studies the use of educational materials because an effect of educahave suggested that women have “greater interest in and tion is to modify the way people interpret their experience. In the present study there is apparently no difference in concern with health matters.“” Therefore, although great care was taken in the study design to only evaluate those the level of anxiety before the EMG examination between subjects who had read the information sent to them, the the group that received information and the group that did women may have read the information more carefully and not. Previous research has tied pain perception during EMG to two unalterable variables, female sex, and pre-examinabetter prepared themselves for the EMG. Another possibility is that the gender of the EMG technicians (all women) influ- tion self-assessment of pain, and anxiety, a presumably modifiable variable.‘,3 We assumed that any positive affect this enced this study’s outcome. Levine and De Simone18 found that men, but not women, reported less pain in response to study might show, given the well known association between an experimentally induced painful stimulus when the stimu- anxiety and pain, would be through a reduction in anxiety. lus and pain assessment instrument was administered by a However this was not shown. This could be because of the state anxiety instrument being insensitive to the mild changes member of the opposite sex. Because the nerve conduction in anxiety produced by the information. Another explanation studies (one of the painful stimuli) and the pain assessment instruments were given by women in our study, men may could be that the information did not reduce anxiety just before the test because the information had confirmed that have underreported pain whether or not they received information. This may have produced a floor effect so that the there was going to be some pain or discomfort during the information could not decrease measured pain perception in examination. During the procedure the subjects’ anxiety may have lessened as the events reassuringly corresponded with the men. Our findings for age suggest that older people are both the information they had received. Finally, it simply could more anxious before the procedure and experience more pain be that the information did not alter anxiety levels at any time during the examination. It is hard to reconcile this on the needle exam, at least as suggested by the reportedly more sensitive visual analogue scale. This is at odds with conclusion with the apparent reduction in pain perception in other research in this area. Neri and Agazzani” and Tucker at least some members of the group that received informaand colleagues*’ found that experimentally induced pain tion. thresholds increased with age. Roy and coworkers*’ noted This study does have limitations that have to be taken that elderly persons reported significantly less regular pain into account when conclusions are made. In particular, the
Arch Phys Med Rehabil Vol75,
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INFORMATION/PAIN
women could have had group characteristics in age or educational level that were different from those of the men, and this difference might have influenced the results. In addition, the results may not be a direct result of the information that the subjects were given. As an example, it may have been that the subjects who received the information asked the physicians and technicians more questions before and during the study. As a result the subjects who received more information also received more attention during the examinations, felt more at ease. and perceived less pain. This study cannot clarify whether such an indirect mechanism is responsible for the effect observed; however, the potential clinical use of the intervention remains regardless of the actual mechanism of effect. The results contradict a previous study’ that found that nerve conduction studies were perceived as more painful than the needle examination. In this study needle electromyography was perceived as more painful than the nerve conduction studies for both sexes on both pain scales. This may be explained by the fact that a monopolar needle was used in the other study, whereas a concentric bipolar needle was used in this one. Another finding of practical importance is that the number of patients who missed appointments for their EMG did not change during the 3-month study when compared to the months immediately before and after the study. The information was sent to half of all the patients who underwent EMG during those 3 months. We were alert to the possibility that the information might frighten patients and increase the “noshow” rate, but this did not occur. In summary it seems that a written document that provides procedural and sensory information about EMG may reduce patient perception of pain during the examination, particularly for women during the nerve conductive studies. The men may not have responded to the information because they did not read it as carefully as the women, because they underreported their pain in response to the women technicians who administered both the nerve conduction studies and the pain assessment instruments, or because the intervention was simply not effective for them. Finally, the women reported greater pain related to the EMG than did the men, and the elderly reported more EMG-related pain and anxiety than did the young. Future research could investigate the differential response of the sexes to information, and possibly include coping style as a variable. The finding that the elderly experience more pain during the EMG needs to be confirmed, and interventions developed to assist a group that seems more resilient to other medical procedures. Acknowledgment. The authors thank Barbara Kramer, Susan Nalepa. Kathleen Ryan, and Teresa Spiegelberg whose advice and tenacious assistance made this studv possible. We would also like to thank Deborah Zolot. BS for her help with ;he data.
AND
6. I.
8.
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IO. I I. 12.
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27. References I. Gans BM, Kraft GH. Pain perception Arch Phys Med Rehabil 1977~58: 13-6
in clinical
electromyography.
EMG, Richardson
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