Validity of the general health questionnaire (GHQ) in detecting psychiatric disturbance in amputees with phantom pain

Journal of Psychosomorrc Printed in Great Britain.

VALIDITY

Research,

Vol.

30, No. 3, PP. 277-281,

OF THE GENERAL

(GHQ) IN DETECTING IN AMPUTEES

0022-3999186 $3.00+ .oO Pergamon Journals Ltd.

1986.

HEALTH

PSYCHIATRIC WITH

JAMES

QUESTIONNAIRE DISTURBANCE

PHANTOM

PAIN

LINDESAY *

(Received 25 June 1985; accepted in revised form 2 September 1985) Abstract-The 28-item General Health Questionnaire (GHQ) was validated against the PSE-derived Index of Definition in a sample of amputees with long-standing phantom and stump pain attending a Limb Fitting Centre. This form of the GHQ is a sensitive identifier of overt psychiatric disorder in this setting.

INTRODUCTION

THE LOSSof a limb, for whatever reason, is a major event with profound implications, and psychiatric disorder may ensue either as an acute post-amputation reaction [ 11, or as more chronic disturbance [ 2, 31. Cases of post-operative psychiatric disorder are usually detected and treated in hospital, but psychiatric disturbance in established amputees is more difficult to identify. Frank et al. [ 41 have suggested that a significant proportion of U.S. amputees succumb to depression only after they have left the medical system, and they argue that routine follow-up may need to be extended beyond the time required for physical rehabilitation in order to allow identification of cases requiring psychiatric intervention. In the United Kingdom, the supra-regional Limb Fitting Centres provide a suitable focus for the psychiatric screening of amputees. These Centres remain in regular contact with their clients until they have been fitted with definitive prostheses, and this contact is maintained on an ad hoc basis as further adjustment, repair and replacement become necessary. There is a dichotomy in the population of amputees that continue to attend Limb Fitting Centres following receipt of their definitive prostheses, and this is of some importance with regard to screening for psychiatric disorder. Unlike most clinic populations, a proportion of the attenders are fit, well-adjusted individuals leading active lives, and it is heavy use of their prostheses that brings them to the clinic for repairs. Another group come because they have a complaint, usually about the performance of the prosthesis, or the condition of the stump; in particular, those that complain of enduring phantom or stump pain without any obvious local cause find their way back to the clinic in search of a cause and a cure. Pain complaints of long standing are associated with psychiatric disturbance [ 5, 61, and give surgeons and prosthetists most cause for concern in this respect [7, 81. It is upon this group of patients that any screening exercise should concentrate. Screening for psychiatric disorder by interview is expensive and time-consuming, and would be unnecessary if a first-stage self-rating instrument could be shown to provide a useful alternative. The General Health Questionnaire (GHQ) [ 91 is a selfadministered schedule designed to detect changes in a subject’s emotional state, and its validity and reliability as a screening instrument for conspicuous *Division of Psychiatry, United Medical & Dental Schools, Guy’s Hospital, 271

London,

SE1 9RT, U.K.

JAMES LINDESAY

278

non-organic and non-psychotic psychiatric disturbance have been examined in various hospital, general practice and community settings [ 10-121. This study looks at the validity of the GHQ in detecting psychiatric disturbance in a group of amputees complaining of phantom or stump pain attending a Limb Fitting Centre.

METHODS

Subjects The subjects were 35 amputees attending the Roehampton Limb Fitting Centre. This study formed part of a wider-ranging survey of amputees with and without significant phantom and stump pain. The sample for this study comprised 31 subjects who had been participants in a recently-completed drug trial for postamputation pain problems. They were drawn from the population attending the limb fitting clinics at Roehampton, and represented those who had made significant complaints to the staff of phantom or stump pain. The other four subjects also complained of long-standing episodic or chronic post-amputation pain, and were drawn from the same clinics as were the drug trial participants, but they had not actually taken part in the trial. All subjects continued to complain of pain at the time of interview for this study, and in all cases, no local cause for the pain was apparent. The criteria for inclusion in the overall survey were: unilateral amputation of an arm or leg; at least six months post-amputation; aged between 16 and 75 yr; no evidence of memory loss or dementia; and no other major disability, such as severe neurological impairment following a stroke. There were 27 men and 8 women in this sample, and the mean age of the subjects was 55.2+ 13.1 yr.

Procedure All subjects completed the 28.item GHQ, and responses were scored using the conventional O-O-1-1 method [ 131. The 9th edition of the Present State Examination (PSE) [ 141 was also administered (blind to the GHQ scores), and an Index of Definition (ID) derived from the total score [ 151. The validity coefficients used in this study are as defined in Tarnopolsky et al. [ 161.

RESULTS

The case-identification

data are set out in Table

TABLE I.-CASE-IDENTIFICATION

BY

I.

AND GHQ

IN AMPUTEES

GHQ Index of Definition

I

-

2/3 4 5/6/7

~ -

no symptoms non-specific symptoms specific symptoms cases

O-3

4

5

6

20 2

I

1

1

7

8

91

1 1

1 I

1

5

An ID of 5 or more implies that sufficient PSE symptoms are present for the CATEGO program to assign a likely ICD-8 diagnosis [ 151, and was taken as a threshold of ‘caseness’ in this validation. This is, however, a stringent criterion against which to validate the GHQ; the presence of specific symptoms (ID level 4) is also clinically significant, since this may represent a developing disorder. In view of this, validity co-efficients have been calculated for various cut-off scores on the GHQ at both ID thresholds (3/4 and 415); they are given in Table II. Changing the ID threshold did not affect the total number of false negatives and false positives over the range of GHQ cut-offs examined; the mis-classification rates are therefore identical for both ID thresholds at any given GHQ cut-off. The total PSE score is correlated with the GHQ score (r= 0.88; p < O.OOl), which

GHQ

TABLE II.-CO-EFFICIENTS GHQ AT

validity

with amputees

279

OF VALIDITYFOR SIX CUT-OFF VALUESOF THE 28-1~~~ ID THRESHOLDS(ID 3/4 AN,, 4/5)

TWO

314 85%

ID 3/4:

specificity sensitivity mis-classification rate positive predictive value negative predictive value

ID 4/5:

specificity sensitivity mis-classification rate positive predictive value negative predictive value

82% 100% 14% 0.58 0.0

89% 14% 0.67 0.04

4/5

GHQ cut-offs 5/6 617 92%

7/a

8/9

11% 0.78 0.08

96% 67% 11% 0.86 0.11

96% 100% 67% 67% 9% I 1% 1.0 0.86 0.10 0.11

89% 86% 11% 0.67 0.04

93% 71% 11% 0.71 0.07

93%

88% 89%

78%

11% 0.73 0.04 86% 100% 11% 0.64 0.0

71%

11% 0.71 0.07

suggests that this score is useful as an index of severity of any psychiatric present.

96% 71% 9% 0.83 0.07

disturbance

Diagnosis In all seven cases where the ID was 5 or more, an ICD-8 diagnosis of neurotic depression (300.4) was assigned. Two of these also received a possible differential diagnosis of endogenous depression (296.2). Only one of the seven cases was receiving any psychiatric treatment at the time of interview, suggesting that much psychiatric disorder in this population is going undetected.

DISCUSSION

It is now recognised that the GHQ should not be used uncritically as an estimator or indicator of psychiatric morbidity in settings where its validity is unproven [ 161. Various factors may confound the ability of the GHQ to detect psychiatric illness; false negatives may arise from subjects with chronic psychiatric illness giving ‘same as usual’ responses to the items, and conversely, social dysfunction and physical symptoms may increase GHQ scores in the absence of significant psychiatric illness, leading to false positives [ 171. Furthermore, any validation exercise that uses an interview schedule as its criterion must also leave open the possibility that a proportion of the ‘true negatives’ in fact have undisclosed psychiatric disorders that remain undetected either by questionnnaire or by interview. As regards amputees, it has been suggested that phantom pain represents in some way a ‘depressive equivalent’; Parkes [ 181 found that phantom pain persisting at one year post-operatively was associated with a rigid and compulsively self-reliant personality, and he attributed the apparently low rate of emotional disturbance in this group to their stoic denial. Any covert psychiatric disorder that is not detected by the validating PSE interview lies outside the scope of the present study, so these findings should not be taken as an index of the total prevalence of psychiatric disorder in amputees complaining of phantom pain. This study has investigated the behaviour of the GHQ in a fairly small sample of

JAMES LINDESAY

280

amputees with long-standing pain complaints; assuming that this sample is representative, these results validate the GHQ as an identifier and a measure of the manifest psychiatric morbidity in this group. It may be seen from Table II that the best discrimination between cases and non-cases is achieved using an ID threshold of 41.5 and a GHQ cut-off of 4/S. Under these circumstances, sensitivity was maximal at loo%, and the specificity of the test was 86%. The predictive values and the total mis-classification rate of the GHQ depend upon the expected prevalance of psychiatric cases in the population to be screened; below a prevalance of about 1 l%, the probability that a high GHQ score identifies a case (the positive predictive value) drops rapidly [ 191. There are no comparable studies of the prevalence of psychiatric disorder in amputees with post-amputation pain, but assuming that this sample is representative and that the prevalence is about 20070, then the positive and negative predictive values and the total mis-classification rate of the GHQ found here are meaningful. Using a cut-off of 4/5, the GHQ detected all of the cases that exceeded the ID 5 + threshold, and only two of the false positives were completely asymptomatic on the PSE. These subjects scored highly on the ‘social dysfunction’ (C) scale of the 28-item GHQ which, unlike its other three scales, does not ask about the presence of specific psycho-pathological symptoms, and so taps an area of dis-ease not covered by the PSE. This need not present a clinical screening problem; if certain amputees are vulnerable to significant social impairment in the absence of other evidence of psychiatric disorder, they should be identifiable by examination of their scores on the various sub-scales of the 28-item GHQ. For the clinician, the sensitivity of a first-stage screening instrument is more important than its specificity; a small number of false positives is acceptable so long as the net result is the detection of all true cases. The GHQ appears to perform adequately in this respect when applied to this sample. The 28-item version used here is easy to administer and to score, and its sub-scales may be of value in determining the clinical significance of an elevated score [ 131. Moreover, it appears to be perfectly acceptable; there were no refusals in this study, a gratifying finding that reflects the good compliance and esprit de corps prevalent among amputees. Further research is required to determine whether cases detected by the GHQ in this setting would benefit from psychological or psychiatric treatment.

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Oxford

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