depression and the chronic pain experience

8
Pain, 46 (1991) 177-184 0 1991 Elsevier Science Publishers B.V. 0304-3959/91/$03.50 ADONIS 030439599100172LJ 177 PAIN 01822 Depression and the chronic pain experience Jennifer A. Haythornthwaite a, William J. Sieber b and Robert D. Kerns ’ a National Institute on Aging, Baltimore, MD 21224 (U.S.A.), ’ Yale Urkersity, New Hawn, CT 06520 (U.S.A.i und (’ Yale Unkersity School of Medicine and West HaL,en Veterans Affairs Medical Center, Psychology Sewice, West Harem CT 06516 (U.S.A.) (Received 26 February 1990, revision received 14 November 1990, accepted 20 November 19901 Summary The present study examined the relationship between depression and a constellation of pain-re- lated variables that describe the experience of chronic pain patients. Thirty-seven depressed and 32 non-depressed heterogeneous chronic pain patients were identified through structured interviews, use of standardized criteria and scores on the Beck Depression Inventory (BDI). The 2 groups were compared on demographic variables and scores on the Marlowe-Crowne Social Desirability scale (MC), as well as measures of disability and medication use, pain severity, interference due to pain and reported pain behaviors. The depressed group was found to be younger and to score lower on the MC than the non-depressed group. Multivariate analyses of covariance (MANCOVA), using age and MC as covariates, reveaIed that depressed chronic pain patients, relative to their non-depressed counterparts, reported greater pain intensity, greater interference due to pain and more pain behaviors. There were no group differences on the measures of disability and use of medications. The results provide further support for the importance of incorporating depression into clinical and theoretical formulations of chronic pain. Future use of structured interviews and standardized criteria for diagnosing depression may clarify some of the inconsistencies found in the literature. Key words: Chronic pain; Depression; Depression diagnosis; Pain intensity; Activity; Pain behaviors Introduction An apparently high rate of depression among chronic pain patients has spurred increased attention to this problem in both clinical and theoretical formulations of chronic pain. Although the exact nature of the relationship between pain and depression remains somewhat controversial, depression has been demon- strated to have a substantial effect on both clinical presentation [14,21,25,401 and treatment response 13,111. Progress has recently been made in identifying as- pects of the pain experience that differentiate de- pressed and non-depressed chronic pain patients; how- ever, many inconsistencies remain when results are compared across studies. Demographic variables, such as sex and level of education, and medical history Correspondence too: Jennifer A. Haythornthwaite, National Insti- tute on Aging, 4940 Eastern Avenue, Baltimore, MD 21224. U.S.A. variables, such as duration of pain, type of pain and number of operations, generahy have not been found to differentiate these 2 groups. Two studies have re- ported opposite findings when comparing the age of depressed and non-depressed pain patients [8,491, and 2 recent studies indicated that depressed pain patients were more likely than non-depressed pain patients to receive a variety of medications, including sedative/ hypnotics and narcotics [211 and antidepressants and anxiolitics [6]. Comparisons of depressed and non-depressed chronic pain patients on variables related to the experi- ence of pain, such as pain intensity, activity impairment and pain behaviors, have yielded inconsistent findings. Some studies have reported a positive relationship between depression and pain intensity ratings E6,10,11,21,331 whereas other studies reported no reli- able relationship [25,34,39,481. On the other hand, de- pressed chronic pain patients have been consistently found to be less active than their non-depressed coun- terparts [6,10,17,21,25]. Although Keefe and his col-

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Pain, 46 (1991) 177-184 0 1991 Elsevier Science Publishers B.V. 0304-3959/91/$03.50 ADONIS 030439599100172LJ

177

PAIN 01822

Depression and the chronic pain experience

Jennifer A. Haythornthwaite a, William J. Sieber b and Robert D. Kerns ’ a National Institute on Aging, Baltimore, MD 21224 (U.S.A.), ’ Yale Urkersity, New Hawn, CT 06520 (U.S.A.i

und (’ Yale Unkersity School of Medicine and West HaL,en Veterans Affairs Medical Center, Psychology Sewice, West Harem CT 06516 (U.S.A.)

(Received 26 February 1990, revision received 14 November 1990, accepted 20 November 19901

Summary The present study examined the relationship between depression and a constellation of pain-re- lated variables that describe the experience of chronic pain patients. Thirty-seven depressed and 32 non-depressed heterogeneous chronic pain patients were identified through structured interviews, use of standardized criteria and scores on the Beck Depression Inventory (BDI). The 2 groups were compared on demographic variables and scores on the Marlowe-Crowne Social Desirability scale (MC), as well as measures of disability and medication use, pain severity, interference due to pain and reported pain behaviors. The depressed group was found to be younger and to score lower on the MC than the non-depressed group. Multivariate analyses of covariance (MANCOVA), using age and MC as covariates, reveaIed that depressed chronic pain patients, relative to their non-depressed counterparts, reported greater pain intensity, greater interference due to pain and more pain behaviors. There were no group differences on the measures of disability and use of medications. The results provide further support for the importance of incorporating depression into clinical and theoretical formulations of chronic pain. Future use of structured interviews and standardized criteria for diagnosing depression may clarify some of the inconsistencies found in the literature.

Key words: Chronic pain; Depression; Depression diagnosis; Pain intensity; Activity; Pain behaviors

Introduction

An apparently high rate of depression among chronic pain patients has spurred increased attention to this problem in both clinical and theoretical formulations of chronic pain. Although the exact nature of the relationship between pain and depression remains somewhat controversial, depression has been demon- strated to have a substantial effect on both clinical presentation [14,21,25,401 and treatment response 13,111.

Progress has recently been made in identifying as- pects of the pain experience that differentiate de- pressed and non-depressed chronic pain patients; how- ever, many inconsistencies remain when results are compared across studies. Demographic variables, such as sex and level of education, and medical history

Correspondence too: Jennifer A. Haythornthwaite, National Insti- tute on Aging, 4940 Eastern Avenue, Baltimore, MD 21224. U.S.A.

variables, such as duration of pain, type of pain and number of operations, generahy have not been found to differentiate these 2 groups. Two studies have re- ported opposite findings when comparing the age of depressed and non-depressed pain patients [8,491, and 2 recent studies indicated that depressed pain patients were more likely than non-depressed pain patients to receive a variety of medications, including sedative/ hypnotics and narcotics [211 and antidepressants and anxiolitics [6].

Comparisons of depressed and non-depressed chronic pain patients on variables related to the experi- ence of pain, such as pain intensity, activity impairment and pain behaviors, have yielded inconsistent findings. Some studies have reported a positive relationship between depression and pain intensity ratings E6,10,11,21,331 whereas other studies reported no reli- able relationship [25,34,39,481. On the other hand, de- pressed chronic pain patients have been consistently found to be less active than their non-depressed coun- terparts [6,10,17,21,25]. Although Keefe and his col-

17s

leagues ]2 l] reported that depression reliably predicted a variety of pain behaviors. an earlier study did not demonstrate a relationship between depressed mood and observed pain behaviors [35].

The inconsistencies across studies may bo due to the wide range of methods used to identify depression, a practice which has hampered progress in this area [X,42]. There is clearly a need to incorporate structured assessment and criteria into the measurement of de- pression among chronic pain patients (421. After re- viewing the use of self-report instruments that assess depression, such as the Beck Depression Inventory (BDIJ [21. a group of prominent investigators [23] re- cently expressed concern over the reliance upon self- report measures when studying depression. These au- thors cautioned that careful diagnostic procedures arc necessary in order to identify depression that is not confounded by other psychopathology and emphasized the need to employ multiple methods for assessment.

While the BDI has been demonstrated to be a useful index of depression among chronic pain patients [49]. a recent study denlonstr~tt~d high correlations between the BDI and measures of general psychologi- cal distress [lo]. This type of finding, also found among community samples [38], raises issues about the psy- chopathological specificity of the BDI [22]. At issue is the extent to which high scores on the BDI indicate clinical depression and not depressed mood of a tran- sient nature or some other psychopathological state.

The use of multiple methods for assessing dcpres- sion, including structured interviews and diagnostic criteria, has generally been limited to studies of preva- lence of depression among chronic pain patients [3 1,32] and biogenetic factors shared by these 2 disorders [8,15,16.50]. Studies examining cognitive and behav- ioral characteristics that discriminate depressed from non-depressed pain patients have rarely used standard- ized methods to diagnose depression. Structured inter- views and diagnostic criteria have the benefit of identi- fying chronic pain patients whose complaints of de- pression are clinically significant and not of a transient nature and allow comparison of findings across studies.

The impact of response style, for example social desirability, on self-reports of pain has also rarely been examined. Beck and Beamesderfer [l] observed that depressed patients described themselves in an unfavor- able way, even in response to questions not addressing their depressive symptomatology. These authors sug- gested that a socially undesirable response style was a distinguishing characteristic of depression. Given this description of depression, chronic pain patients who are also depressed would be expected to portray them- selves in an unfavorable way even in response to ques- tions about areas other than their affective state, such as questions about their experience of pain.

The present study was designed to delineate reliable

differences in the experience of chronic pain between groups of patients with and without coexisting depres- sion. Three methodological strengths extend previous findings. First. diagnostic interviewing. standardized criteria and a self-report measure were used to identify depression. The patients who met diagnostic criteria for major depression and presented with at least ;I mildly depressed score on the BDI [22] were included in the depressed group: patients who did not meet criteria for major depression and presented with i-l normal score on the BDI were included in the non-de- pressed group. Second, multivariate statistical procc- dures were used to examine multiple aspects of the pain experience, including disability and use of mcdica- [ions, ratings of pain severity. frequency of pain behav- iors and impairment of daily activities. And third. ;L frequently used mcasurc of social desirability, the Mar- lowe-Crowne Social Desirability scale. was used to examine the intluence of this response style on the experience of pain.

Method

.Su&ect.s

Subjects were obtained from consecutive admissions to an interdisciplinary pain rehabilitation program and met the following criteria: (a) pain of at least 6 months duration, (b) pain not related to malignancies, and tc) no evidcncc of active psychosis or acute risk of suicide. Only subjects who completed structured interviewing and all questionnaire measures were included in the analyses.

Two criteria were used to identify groups of de- pressed and non-depressed subjects. First, the Schcd- ule for Affective Disorders and Schizophrenia (SADS) [ 131. a structured psychiatric interview. was used to establish a diagnosis based on the Research Diagnostic Criteria (RDC) [l&46]. SADS interviews were con- ducted by 3 interviewers (advanced doctoral level psy- chology students1 who received extensive training in administering the SADS and using the RDC from II research psychiatrist. Training consisted of watching experienced interviewers conduct the SADS interview while trainees simultaneously rated patients’ responses. then of participating in the interviews conducted by trained interviewers and finally of conducting intcr- views with trained interviewers watching and supervis- ing. Upon completion of each SADS interview, RDC were used to determine a diagnosis of major depres- sion, minor depression or no depression. A sample of 12 interviews were selected for computing inter-rate] reliability. The agreement between raters for diagnosis of major depression, minor depression or no deprcs- sion was 100%.

Since diagnoses were based on the patient’s descrip-

179

tion of the worst week of the identified episode, a second criterion was used to reflect the severity of s~ptoms of depression at the time of evaluation. A BDI score of 11 was used to identify at least a mild level of current depressive symptomatology [22]. Using both criteria, 37 patients were classified as depressed; these pain patients were diagnosed with major depres- sion using the RDC and scored 11 or higher on the BDI. Thirty-two patients were classified as non-de- pressed; these pain patients were diagnosed as having either minor depression or no depression based on the RDC and scored 10 or less on the BDI. Twenty-two patients were excluded using the double criteria.

The sample, including the depressed and the non- depressed groups, ranged in age from 26 to 78 years (M = 49.3, S.D. = 13.6) and had attained a mean edu- cational level of 12.1 years (S.D. = 2.2). Eighty-four percent were males and 59% were married. The most common pain complaint was low back pain (49%), with neck and shoulder musculoskeletal pain (14%) and other musculoskeletal pain (16%) comprising the ma- jority of the remaining complaints. The average dura- tion of pain was just over 8 years (S.D. = 7.2 years), with 48% of the patients reporting at least one surgery for their pain prior to the evaIuation. Only 20% of the subjects were actively employed, and 5170 of all pa- tients were receiving some form of compensation for their pain.

Questionnaire and interview data were grouped into 4 theoretically derived constructs relevant to a compre- hensive pain assessment. These constructs induded disability and use of medications, pain severity, inter- ference due to pain and pain behaviors. Empirical support for these constructs is based in part on the published factorial validity of the West Haven-Yale Multidimensional Pain Inventory (WHYMPII [291. Each construct was measured by multiple scales which are described below.

Disability and medication use. Six variables derived from a semi-structured pain assessment interview were used to index pain-related disability and patients’ use of medications. Use of medications for pain, including narcotic and non-narcotic analgesics and use of antide- pressant medications were each coded as present or absent, The chronic@ of the pain problem was coded in months. Previous surgery for the pain complaint, compensation for pain and current employment were also coded as present or absent for each patient.

Pain secerity. Two measures were used to measure pain severity: the Pain Rating Index (PRI) [36] from the McGill Pain Questionnaire and the Pain Severity scale from the WHYMPI [29]. Both scales have been demonstrated to have good psychometric properties.

Interference. This construct assessed the degree of

interference caused by pain and the frequency with which patients engaged in a variety of common activi- ties that may be affected by chronic pain. Five sub- scales from the WHYMPI were included to measure this construct, including Interference, Social Activities, Outdoor Activities, Activities Away From Home and Household Activities. These scales have shown good internal consistency and test-retest reliability 1291.

Pain behaviors. The Pain Behavior Checklist (PBCL) [26] was used as a measure of self-reported pain behav- ior. Patients rated how often they engaged in 17 differ- ent behaviors on 7-point scales (0 = not at all; 6 = almost all the time). These items have been previously factor analyzed into 4 reliable scales: Distorted Ambu- lation (e.g., walking in a protective fashion), Facial/ Audible Expressions (e.g., grimacing, clenching teeth), Affective Distress (e.g., becoming irritable or angry), and Seeking Help (asking someone to do something to help the pain). The 4 scales have been shown to have good internal consistency and stability. The scales have been validated against observed pain behaviors and other self-report measures of the pain experience [26].

Social desirability. The Marlowe-Crowne Social De- sirability scale (MC) [9] consisted of 33 true-false items. Work done on the MC since its original develop- ment indicates that the scale measures affect inhibi- tion, defensiveness and presenting oneself in a positive light. The scale has been demonstrated to have good internal consistency and stability [9].

Procedure Subjects completed the SADS and pain interviews

and questionnaires as part of a comprehensive assess- ment protocol that preceded the implementation of the rehabilitation program. The assessment protocol has been described elsewhere [24,28].

Results

As a first step in the analyses, demographic vari- ables and MC scores were compared between the groups of depressed and non-depressed patients. Next, simple correlations between variables which differed between the 2 groups and the measures of pain inten- sity, interference and pain behaviors were examined. Since 5 of the 6 measures of disability and medication use were dichotomous scores, these measures were not included in the correlational analysis. Since univariate analyses (chi-square and analysis of covariance) were used to examine group differences on disability and use of medications, the alpha for these tests was adjusted (0.008) using the Bonferroni method (alpha/number of univariate tests) to maintain the familywise error rate. Multivariate analyses of covariance (MANCOVA) with age and social desirability as the covariates were used

IS0

to examine group differences on the constructs of pain intensity, interference and pain behaviors. Eta-squared was computed as an estimate of the strength of associa- tion in the population between depression and the pain experience constructs [5]. When multivariate analyses were significant, univariate analyses of covariance (ANCOVA) were conducted on individual measures.

A l-way muItivariate analysis of variance was per- formed comparing the 2 groups on age and education. A multivariate main effect of group (F (2, 65) = 6.63, P < 0.0 1) was found with univariate analyses to be due to the younger mean age of the depressed patients compared to the non-depressed patients t F (1, 66)= 12.71. P < 0.001; see Table I). There was no significant difference on education. Chi-square analyses showed no significant differences between groups on type of pain, gender or marital status (Ps > 0.10). A l-way ANOVA between groups (F (1. 66) = 9.61. P < 0.01) revealed that non-depressed patients scored signifi- cantly higher than did depressed patients on the Mar- lowe-Crowne (M = 22.0 (S.D. = 5.4) and M = 17.4 (SD. = 6.7). respectively). The 2 variables found to be significantly different between the 2 groups, age and Marlowe-Crowne, were used as covariates for the analyses of pain intensity, interference and pain behav- iors.

Simple correlations between age and MC and the measures of pain intensity, interference and pain be- haviors were examined next. Significant relationships were found between age and the McGilI Pain Ques- tionnaire (f. = -0.31, P < 0.01; see Table II), the In- terference scale from the WHYMPI (I = --(1.29, t” c( 0.05). the Outdoor Activity scale from the WHYMPI (r = 0.26, P < 0.05) and the Affective Distress scale from the PBCL (r = -0.28. P < 0.05). Marlowe-

TABLE I

DESCRIPTIVE STATISTICS FOR DEPRESSED AND NON-DE-

PRESSED PATIENTS ON BACKGROUND VARIABLES

Vnriahle Depressed Non-depressed

N = 37 N = 32

Age * Mean

S.D.

Education

Mean

S.W.

Gender (52 male)

Marital status

(c: married)

Type of pain (r’r 1

Low back pain

Neck/shoulder

Other muscul~sekeltai

Other pain

44.3

11.4

12.3

‘.O 81

55.0 13.x

11.x

2.4 8X

hfl

37 0

IY

75

TABLE II

CORRELATION BETWEEN AGE. SOCIAL DESIRABILITY

AND PAIN MEASURES

Pain measure Age Social desirability - ._.~ --

Pain severity

McGill pain questionnaire (,..j * .i * - 0.07 WHYMPI-I’S O.Oh 0.13

Interference ~I~YMPI-lnterferencc 0.70 * -- 0.15 Activities away from home 0.12 ‘^I 0. I I Social activilies 0. I5 O.Ijf, Outdoor activities 0.x + 0.23 Ilousehold activities 0.03 - 0.01~

Pain behavior>

Distorted arnbul~itjon -~. I),iP 0.0x Facial expressions -~ 0. 19 ci..w *-* Affective d&treks -. ().‘X :* * _ 0.43 % *

Seeking help -- 0. I fl -- I). I2 --. _-

c I’ c 0.05: * ,b P c O.()l,

Crowne scores correlated significantly with 2 of the PBCL subscales, Facial Expressions (P = - 0.30, P < 0.01) and Affective Distress (r = -0.43, 1’ < 0.01).

The first pain construct examined was disability and medication use. A l-way ANCOVA, using age and MC as covariates, showed no difference between the groups of depressed and non-depressed pain patients on dura- tion of the pain. Chi-square analyses showed no group differences in the likelihood of receiving pain medica- tions, anti-depressant medications, whether the patient was receiving compensation for pain, whether the pa- tient had received surgery for the pain complaint or employment status iail Ps < 0.01). These results arc presented in Table III.

A l-way MANCOVA on the pain intensity mea- sures yielded a significant effect of group (F (2. 04) = 0.23. P < 0.01: see Table IV). Depression diagnosis accounted for 14% of the variance in pain intensity

TABLE III

DESCRIPTIVE STATISTICS FOR DEPRESSED AND NON-DE-

PRESSED PATIENTS ON MEASURES OF DISABILITY AND

PREDICATION USE

--- Measure

Duration (years)

Mean

SD.

Using pain medication ic? ) Using anti-depressant

medication (3)

Surgery for pain

complaint(S)

Receiving compensation

for pain (%)

E,mployment status (Q)

Depressed

N = 31

?,‘)

7.11

9.5

13.3

59.5

61.1

if>.?

______ Non-depressed

N = 31 _~

x2

7.6

75.0

21.0

34.3

4O.h

75 .o

181

TABLE IV

MEANS AND STANDARD DEVIATIONS FOR DEPRESSED AND NON-DEPRESSED PATIENTS ON MEASURES OF PAIN INTEN- SITY, INTERFERENCE AND PAIN BEHAVIORS

construct

Intensity McGill Pain Questionnaire

Mean S.D,

WHYMPI-PS Mean S.D.

hrerference WHYMPI-Interference

Mean SD.

Activities away from home Mean S.D.

Social actities Mean

S.D. Outdoor activities

Mean SD.

Household activities Mean S.D.

Pain behal?ors

Distorted ambulation Mean S.D.

Facial expressions Mean S.D.

Affective distress Mean S.D.

Seeking help Mean S.D.

Depressed Non-depressed

N = 37 N = 32

0.47 0.27 0.20 0.18

4.41 4.29 0.86 1.09

4.80 3.64 0.90 1.26

1.91 2.62 1.10 1.11

1.97 2.60

1.11 1.27

0.95 1.86 1.31 1.63

2.65 3.26 1.20 1.46

2.99 2.64 1.29 1.57

3.61 2.27 1.68 1.74

3.87 2.09 1.22 1.38

3.05 2.86 1.60 1.38

F df Eta ’

6.23 ** 2,64 0.14 7.04 *** 365

1.84 365

4.25 ** 5.61 0.20 6.96 ** 3,65

3.96 * 3,65

1.65 3.65

3.02 * 3,65

1.42 3.65

5.86 *** 4,62 0.22 <l 3,65

4.44 ** 3.65

13.42 *** 3,65

<I 3.65

* P < 0.05; **p<o.o1; *** P<O.OOl.

measures. Separate ANCOVAs revealed that de- pressed patients reported significantly higher pain in- tensity as measured by the PRI (F (3, 65) = 7.04, P < 0.01) but not on the WHYMPI Pain Severity scale (F (3, 65) = 1.84, P > 0.10).

A l-way MANCOVA on the interference and activ- ity measures revealed a significant main effect of group (F (5, 61) = 4.25, P < 0.01). Depression diagnosis ac- counted for 20% of the variance in the measures of interference. A series of ANCOVAs revealed that the amount of time spent Away From Home (F (3, 65) = 3.96, P < 0.011, in Outdoor Activities (F (3, 65) = 3.02, P < O.OS>, and the amount of reported overall Interfer- ence in activities (F (3, 65) = 6.96, P < 0.001) were

significantly different for the 2 groups. As can be seen in Table IV the depressed patients reported less activ- ity and more interference than the non-depressed pa- tients.

Finally, a l-way MANCOVA revealed a significant main effect of group on pain behaviors (F (4,62) = 5.86, P < 0.001; see Table IV). Depression diagnosis ac- counted for 22% of the variance in pain behaviors. Univariate ANCOVAs revealed that the depressed pain patients reported more Affective Distress pain behav- iors (F (3, 65) = 13.42, P < 0.0011 and Facial Expres- sions (F (3, 65) = 4.44, P < 0.01). There were no signif- icant differences between groups on Distortions in Ambulation or in Seeking Help.

Discussion

This study demonstrated reliable differences be- tween depressed and non-depressed chronic pain pa-

tients on a constellation of pain-related variables that

broadly reflect the experience of pain. The depressed

pain patients reported greater pain intensity. greater interference due to pain and more pain behaviors.

However. depressed pain patients were similar to non- depressed patients in the type of chronic pain experi-

enced, their use of medications and their disability due to pain.

Response style was found to be an important char- acteristic that distinguished depressed patients from

their non-depressed counterparts. As would be pre-

dicted from the depression literature [l]. depressed chronic pain patients endorsed more socially ztndesir- able statements when describing themselves than did

non-depressed pain patients. The mean for the non-de- pressed group on the MC was in the upper quartile (above 19) of the normative distribution for the scale

[8], indicating that these patients as a group showed high levels of affective inhibition and defensiveness, a response style similar to that described previously by Blumer and Heilbronn [4, p. 3861 as “solid citizens.”

However, the method used to identify the 2 groups of patients does not support a conceptualization of the experience of chronic pain as a “masked” depressed mood [4] or depression as an inevitable response to

chronic pain [47]. Patients who were classified as non- depressed did not report symptoms of depression on a commonly used self-report measure of depression and did not meet criteria for depression when administered a structured psychiatric interview. The observation that these patients reported lower levels of pain intensity, less interference due to pain and fewer pain behaviors demonstrates that this is an identifiable subgroup of chronic pain patients whose pain experience is less

severe than their depressed counterparts. The findings provide further information about

characteristics that are shared by the 2 groups, as well as characteristics that differentiate the 2 groups. Al- though correlational, these findings provide partial support for 2 prominent theoretical models of the development of depression among chronic pain pa- tients. The greater pain severity experienced by the depressed pain patients provides partial support for biological models, which propose a common neuroen- docrine substrate to chronic pain and depression [SO]. The relationship between greater interference due to

pain and depression provides partial support for a cognitive-behavioral mediational model of the devel- opment of depression, suggesting that depression de- velops only in those patients whose experience of pain interferes with instrumental activities [25].

Inconsistencies between previous studies on the cor-

relation between depression and pain severity may

have been due to the wide range of methods used to measure depression. including single, self-report mea-

sures of symptoms of depression or measures of de-

pressed mood. The present study had the advantage of using structured interviews and RDC diagnoses, in

addition to the BDI, to identify clinically significant depression. thus avoiding the inclusion of patients with transiently depressed mood.

Previous research using the McGill Pain Question-

naire has demonstrated associations between depres- sion and affective pain descriptors [30], although a

more recent study did not confirm this finding [lOI. Unlike the Pain Severity scale from the WHYMPI, the

Pain Rating Index (PRI) from the McGill Pain Ques- tionnaire contains an affective component which corre-

lates with total PRI scores [36]. The differential rela- tionship between depression and the 2 pain severity scales used in the present study suggest that the affec- tive component of the PRI contributed to its significant association with depression.

Contrasting with previous findings [6,10,21], de- pressed patients in the present study were not more likely to be taking analgesic medications, did not have a longer duration of their pain and were not more likely to have had an operation for their pain com- plaint. Surprisingly, depressed patients were also not more likely than the non-depressed patients to be taking anti-depressant medications. The low rate for the depressed group (about 13%) of receiving anti-de- pressant medications suggests that, for many depressed patients. the referring physicians did not recognize the patients’ depression. Stud& addressing the ability 01 medical practitioners to identify depression in theit patients indicate that the severity or presence of de- pression is frequently unrecognized [7,37,43,451. Alter- natively, the depressed patients may have been previ- ously treated unsuccessfully with anti-depressant medi- cations, with discontinuation of this therapy prior to referral for pain management. Although not assessed in the current study, this is unlikely since Doan and Wadden [IO] recently reported that few of the de- pressed pain patients in their sample had received treatment for depression. although many reported symptoms of depression. A third interpretation of this finding is that the non-depressed patients taking anti- depressants (almost 22%) included patients who had been depressed prior to referral to the program, treated with antidepressant therapy, experienced relief from their symptoms of depression and were being main-

tained on this effective intervention. Although depressed patients did not have a shortet

duration of pain complaint compared to the non-de- pressed patients, depressed patients were younger. The ages of the 2 groups, combined with the relatively equal duration of the pain complaint, suggests that

183

patients who develop chronic pain earlier in the life- span (in their thirties) experience more depression than patients who develop chronic pain later in the lifespan (in their forties). The inverse relationship be- tween age and depression among chronic pain patients is similar to epidemiological studies of depression in the community [41] and deserves further attention. Clearly longitudinal studies are needed to establish causal relationships between age of onset of pain and the development of depression.

Some cautionary notes are warranted. First, the sample employed may limit the generalizability of the results. Both groups of patients studied were predomi- nantly male, which may limit the applicability of the findings to female pain patients. Additionally, the pain patients were patients at a Veterans Affairs Medical Center, which might not be representative of the gen- eral population of pain patients. However, with the exception of gender, Holzman and colleagues [20] demonstrated that pain patients seen in 2 VAMC pain clinics were similar on demographic and treatment variables to patients seen in 2 non-VA pain clinics.

A second shortcoming of the study is the reliance upon the self-reports of patients. While there is some evidence that the state of depression may influence some self-report measures [l&19], the evidence is not consistent [231. In the present study, the relationships between depression and aspects of the pain experience were independent of effects that a response style, such as social desirability, may have on self-report. The differential effects of depression on the self-report measures, such that not all measures of the pain expe- rience were associated with depression, also minimizes the importance of this criticism.

The results of this study underscore the importance of depression as a psychological condition that affects the pain experience of the chronic pain patient. Future use of standardized interviews and criteria to identify depressed chronic pain patients in studies examining the experience of pain and cognitive and behavioral correlates of depression may clarify inconsistencies in the literature and may lead to further development of conceptual models of chronic pain and depression.

Acknowledgements

This work was supported by VA Merit Review re- search funds awarded to the third author.

The authors would like to express appreciation to Mary Casey Jacob and Allison Milburn for assistance in performing diagnostic interviews and to Roberta Rosenberg for assistance in performing statistical anal- yses.

References

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ments in Psychopharmacology, Karger, Basel, 1974, pp. 151-169.

2 Beck, A.T., Ward, C.H., Mendelson, M., Mock, J. and Erbaugh,

J., An inventory for measuring depression, Arch. Gen. Psychiat..

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