Longitudinal Relationships Among Pain, Sleep Problems, and Depression in Rheumatoid Arthritis

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1 Journal of Abnormal Psychology 1992, Vol. 101, No. 3, Copyright 1992 by the American Psychological Association Inc 002t-843X/92/$3.00 Longitudinal Relationships Among Pain, Sleep Problems, and Depression in Rheumatoid Arthritis Perry M. Nicassio California School of Professional Psychology, San Diego, and Department of Psychiatry, University of California, San Diego Kenneth A. Wallston School of Nursing Vanderbilt University This research evaluated the relationship between pain and sleep problems, and the role of pain and sleep problems in depression, in a sample of 242 patients who had been diagnosed with definite or classical rheumatoid arthritis (RA). Patients completed the Pain scale of the Arthritis Impact Measurement Scales, the Center for Epidemiological Studies Depression Scale, and self-reports of sleep disturbance at two data waves over a 2-year interval. Cross-sectional multiple regression analysis revealed that the sleep problems variable was independently associated with depression at Time 1. Longitudinal multiple regression analyses demonstrated that prior pain predicted subsequent adverse changes in sleep problems, whereas sleep problems did not affect pain over time, and prior pain and the interaction of high pain and high sleep problems were independently associated with depression from Time 1 to Time 2. These data suggest that pain may exacerbate sleeping difficulty in RA patients, and that both factors may contribute to depression over time. Clinical observations and empirical research indicate that reports of sleep disturbance are common in patients with chronic pain syndromes (e.g., Moldofsky, Scarisbrick, England, & Smythe, 1975; Pilowsky, Crettenden, & Townley, 1985). For example, in a study of 100 consecutive chronic pain patients who had been referred for evaluation and treatment at a hospital-based pain clinic in England, 70% reported sleeping poorly (cf. Pilowsky et al, 1985). Compared with chronic pain patients who reported sleeping normally, poor sleepers reported fewer hours slept, more hours spent reclining during the day, and a significantly higher degree of pain intensity and affective disturbance. Although the nature of the sleep disturbance was not delineated in this study, the report of poor sleep served as a benchmark for poorer psychological adjustment, greater difficulty with pain, and a higher degree of illness behavior. Sleep disturbance also appears to be a prevalent complaint among patients with rheumatoid arthritis (RA). As many as two thirds of RA patients have reported chronic sleeping difficulty (Wright, 1985). Survey data (Hart, Taylor, & Huskisson, 1970) indicate that the majority of RA patients have difficulty maintaining sleep, whereas fewer have difficulty initiating sleep. Awakening during the night is often accompanied by arising to "loosen up" to attenuate joint stiffness that has occurred during sleep. In a study that evaluated self-reports of sleep disturbance in patients diagnosed with RA, osteoarthritis, seronegative spondarthritis, and other medical conditions, Leigh, Bird, Hindmarch, and Wright (1987) did not find a higher incidence This research was supported by Grant 5R01 NR01007 to Kenneth A. Wallston from the National Center for Nursing Research, National Institutes of Health. Correspondence concerning this article should be addressed to Perry M. Nicassio, California School of Professional Psychology, San Diego Campus, 6212 Ferris Square, San Diego, California of sleeping difficulty in patients with rheumatic disorders; however, rheumatic patients cited pain much more frequently as a problem that interfered with their sleep than patients with other medical problems. Because the uncontrollable, episodic pain of R A is the most troublesome symptom of this condition (Skevington, 1987), it is not surprising that patients would attribute their sleeping difficulty to pain. The authors suggested that pain may cause sleep disturbance in RA, but the design of their research did not permit such a conclusion. Causal Relationship Between Chronic Pain and Sleep Disturbance An important question to address is whether there is a causal relationship between pain and sleep disturbance in RA and to ascertain the nature and direction of this relationship. This relationship may have significant implications for the etiology and treatment of this condition. If the pain of RA exacerbates sleep disturbance and other difficult symptoms, then efforts should be made at regulating pain as a primary therapeutic target. In contrast, if insomnia or a structural sleep abnormality contributes to pain and other disease-related symptoms, then attention should focus on the treatment of primary sleep pathology in RA. It also is possible that pain and sleep disturbance are both consequences of underlying pathophysiology and, although interdependent, bear no causal relationship to one another. Moldofsky (1989) postulated that the alpha electroencephalogram (EEG) nonrapid eye movement (NREM) sleep anomaly may exacerbate pain, joint tenderness, and fatigue in patients with RA and fibromyalgia, a chronic pain syndrome of unknown organic etiology. This irregularity, which disrupts sleep continuity, is characterized by the intrusion of alpha activity (7.5 to 11.0 Hz) into both lighter stages (1 and 2) and deeper stages (3 and 4) of NREM sleep, and is interpreted to reflect

2 PAIN, SLEEP PROBLEMS, AND DEPRESSION 515 evidence of an arousal disorder within sleep. Viewed as a biological marker of nonrestorative sleep, this sleep disturbance is strongly associated with awakening unrefreshed and with reports of poor sleep quality. In a study of the sleep physiology and morning symptoms of 15 patients with acute classical R A (Moldofsky, Lue, & Smythe, 1983), objective evidence of this sleep abnormality was found in all patients, with associated symptomatology involving increased joint tenderness and fatigue. A variety of noxious influences, including stressful events and flare-up activity, have been offered as possible causes of this sleep abnormality, which, in turn, may aggravate disease symptoms. A recent investigation by Mahowald, Mahowald, Bundlie, and Ytterberg (1989) used all-night polysomnographic recording in a sleep laboratory to study the sleep of 16 patients who had been diagnosed as having definite or classical RA. Although no control group was used, the findings of this descriptive study are particularly noteworthy. The authors found no objective evidence of sleep deprivation from measures of sleeponset latency, sleep efficiency, and sleep distribution; however, all subjects experienced a high frequency of EEG-defined awakenings and arousals per hour of sleep, which markedly interfered with sleep continuity. Although multiple sleep latency testing indicated extensive daytime sleepiness, self-reports of sleep length, degree of interruption, and restlessness revealed little subjective awareness of the degree to which sleep had been objectively disrupted the preceding night. Experimental evidence on the potential etiologic significance of R A in sleep disturbance in rats has been provided by Landis, Levine, and Robinson (1989). These investigators induced adjuvant arthritis through the intradermal injection of myobacterium butyricum and compared experimental and control rats on objective sleep parameters. After 2 weeks had elapsed postinjection, arthritic rats had more episodes of wakefulness and light sleep than controls, and shorter periods of deeper sleep. Moreover, scores assessing the severity of arthritis were associated with a greater percentage of time spent in light sleep. These data suggest that experimentally induced arthritis causes sleep fragmentation similar to that found in the Mahowald et al. (1989) clinical study. These studies do not clarify whether pain or other systemic disease processes are triggering the sleep disruption found in R A, and therefore provide no conclusive evidence on the nature or the direction of the pain-sleep disturbance relationship. Nonetheless, this research supports the existence of objective, verifiable abnormalities in sleep physiology that appear to be associated with the disorder itself. Pain, Depression, and Sleep Disturbance in RA In addition to the presence of aberrations in sleep physiology, a high incidence of dysphoric mood and other symptoms of depression is found in RA patients (Brown, 1990; Frank et al., 1988; Gardiner, 1980). Forty-two percent of a sample of 137 R A clinic patients were found to meet research diagnostic criteria for either major depression or dysthymic disorder (Frank et al., 1988). Although depression in these patients is likely to be affected by multiple factors, including aspects of the disease itself, the relationship between chronic pain and depressive symptoms in RA (Brown, 1990) and other chronic pain conditions (Romano & Turner, 1985) has been the subject of considerable theoretical and research interest. Using structural equation modeling methods, Brown (1990) investigated the causal relationship between chronic pain and depression in a sample of 243 RA patients in a prospective design. No evidence in this analysis was found for depression affecting subsequent pain, but modest support was found for the causal impact of pain on subsequent depressive symptoms over a 12-month period. Other psychosocial variables may contribute to depressive symptoms in R A independently of pain, or may moderate the pain-depression relationship. Cognitive variables such as helplessness beliefs about the controllability of arthritis (Nicassio, Wallston, Callahan, Herbert, & Pincus, 1985) and the tendency to "catastrophize" about pain (Keefe, Brown, Wallston, & Caldwell, 1989) correlate with higher reports of depressive symptoms. Passive pain coping strategies and lower levels of perceived emotional support are associated with higher concurrent depression and exacerbations of depression over time after controlling for prior pain and disease activity variables (Brown, Nicassio, & Wallston, 1989; Brown, Wallston, & Nicassio, 1989). Moreover, the interaction of pain and passive coping and the combination of pain and lack of emotional support have both been shown to contribute independent variance to depressive symptoms in the studies just mentioned. As is the relationship between pain and sleep disturbance, the relationship between pain and depression in R A is complex and subject to different causal interpretations. A related question that has not been investigated in this area of research is the impact of sleep disturbance on subsequent depression in R A patients. Although sleep maintenance problems and early morning awakenings may be symptoms of major depressive disorder (American Psychiatric Association, 1987, p. 224), arousals from sleep and other sources of sleep fragmentation can increase sleepiness, dysphoria, anergia, and other mood problems independently of pain and disease processes (Bonnet, 1985). Disturbed sleep may interfere with efforts to cope effectively with pain and functional disability, thus leading to a downward spiral of functioning in RA patients. Such reasoning, however, is hypothetical and in need of empirical evaluation. To shed light on these issues, we addressed three major questions in the present research: (a) What are the cross-sectional relationships between pain and reports of sleep disturbance and depression in a large population of RA patients? (b) Is there greater evidence for prior pain predicting exacerbations of sleep disturbance, or does prior sleep disturbance contribute to worsening of pain? and (c) Does prior sleep disturbance play an independent role in exacerbating depressive symptoms, or does it interact with pain in producing such consequences? The design of this research has both cross-sectional and prospective components in which data on pain, depression, and sleep disturbance were examined at two data waves over a 2-year period. Subjects Method The subjects for the present analyses included 242 patients (75% female) who were diagnosed with definite or classical RA by a practicing rheumatologist and who furnished data at two particular waves (3

3 516 PERRY M. NICASSIO AND KENNETH A. WALLSTON and 7) of a multiwave longitudinal study. These two waves were 24 months apart. At the time of study onset, 12 months prior to Wave 3 (Time 1 [Tl]), the mean age for this subsample was 52 years (SD = 13.3), and the mean duration of illness since time of diagnosis was 3.3 years (SD = 2.23). Ninety-six percent of the subjects were Caucasian and 77% were married. Twenty percent of the subsample reported having less than a high school education, and 39% reported having additional education beyond high school. At Wave 3 (Tl), 47% reported being employed full- or part-time, 15.3% were retired, and 13.2% reported being unemployed and on disability payments. In response to a question concerning the degree to which arthritis affected their functioning, 9% at Wave 3 (Tl) indicated that they could do everything they wanted to do, 46% indicated that they could do most things but had some limitations, 39% indicated that they could do some of the things they wanted to do and had some limitations, and 6% indicated that they could hardly do any of the things they wanted to do. Overall, these data reflect a moderate degree of impairment in the sample. Ninety-three percent of the patients were on some form of prescribed medication for their arthritis. 1 Procedure All data for this study were obtained by self-report responses to mailed questionnaires (see Brown, Nicassio, & Wallston, 1989, and Brown, Wallston, & Nicassio, 1989, for further details about the methods used in this study). Measures Pain. The four pain items from the Arthritis Impact Measurement Scales (AIMS; Meenan, Gertman, & Mason, 1980; Meenan, Gertman, Mason, & Dunaif, 1982) were used to assess the severity and frequency of painful episodes, the length of morning stiffness, and the frequency of pain in two or more joints during the previous month. Specifically, patients answered the following questions on 5-point scales: (a) "During the past month, how would you describe the arthritis pain you usually have?" (0 = noneto 5 = severe)', (b) "During the past month, how often have you had severe pain from your arthritis?" (0 = never to 5 = always); (c) "During the past month, how long has your morning stiffness usually lasted from the time you wake up?" (0 = do not have morning stiffness to 5 = over four hours); and (d) "During the past month, how often have you had pain in two or more joints at the same time?" (0 = never to 5 = always). The internal consistency (Cronbach's alpha) of this four-item scale was.87 at Tl and.88 at Time 2 (T2). Sleep problems. The degree of difficulty sleeping was assessed by responses to three items: (a) "To what extent has your arthritis interfered with your sleep?" (answered on a scale ranging from no interference [0] to very severe interference [5]); (b) "To what extent are you experiencing stress in the area of sleep, not due to arthritis?" (answered on a scale ranging from no stress [0] to very severe stress [5]); and (c) "During the past week, my sleep was restless" (answered on a scale ranging from rarely or none of the time [1 ] to most or all of the time [4]. (This last item was originally part of the Center for Epidemiological Studies Depression Scale [CES-D], discussed below.) Cronbach's alpha for this three-item index of sleep difficulty was.82 at Tl and.86 at T2. Depression. Depressive symptomatology was measured with 19 of the 20 items that remained on the CES-D (Radloff, 1977) once the item pertaining to restless sleep was removed. Radloff and her colleagues (see Radloff & Locke, 1986; Radloff & Teri, 1986) have thoroughly reviewed evidence confirming the reliability and validity of the CES- D. Cronbach's alpha for the slightly amended version used in these analyses was.91 at Tl and.92 at T2. Functional disability. Physical functional impairment was assessed by two items each from five scales of the AIMS: mobility, household activities, dexterity, physical activities, and activities of daily living. Evidence for the reliability and validity of this shortened version of the AIMS has been presented elsewhere (Wallston, Brown, Stein, & Dobbins, 1989). At Tl, these 10 items had a Cronbach's alpha of.85. Results Prevalence of Sleep Complaints At Tl, individual items of the sleep problems measure were examined to ascertain the degree to which subjects reported disturbed sleep. In response to the item on frequency of restless sleep during the previous week, 57% reported that their sleep was restless most of the time. Sixty percent of the sample reported that arthritis interfered with their sleep from a mild to moderate degree, and 14% indicated severe or very severe interference. In response to the item on the extent to which factors other than arthritis interfered with sleep, 46% reported mild to moderate interference and 7% reported severe to very severe interference. These data demonstrate that the vast majority of R A patients reported at least some degree of sleep disturbance, and that they were more likely to attribute their sleeping difficulty to arthritis than to other factors. Cross-Sectional Findings Data from Tl were analyzed to evaluate the static relationship between AIMS pain and sleep problems, and then to determine the potential contribution of pain and sleep problems to current depression. The zero-order correlation between pain and sleep problems was highly significant (r =.60, p <.001), and the relationship between these variables remained significant (r =.41, p <.001), after partialing out the effects of age, education, duration of illness, and degree of functional impairment. Thus, reports of greater arthritis pain were associated with a higher degree of reported sleep disturbance. A hierarchical multiple regression analysis (Cohen & Cohen, 1983) was conducted to evaluate the independent effects of pain and sleep problems on depression. In this regression procedure, the dependent variable is a residualized score created after the removal of the variance accounted for by demographic variables and functional impairment. Predictor variables were entered into the equation in the following order: (a) demographic and disease history variables (age, education, and duration of illness) and functional impairment, (b) AIMS pain and sleep problems, and (c) the interaction between AIMS pain and sleep problems. The rationale for including this interaction was to examine the potentially deleterious impact of the combination of high pain and high sleep problems on current depressive symptoms. To avoid the problem of multicollinearity of the main effects of these variables with their interaction using raw scores, the interaction term was derived by creating deviation scores for each variable (X M x ) and then multiplying the deviation scores (Cronbach, 1987). Table 1, which summarizes the results of this analysis, reveals that as a group, age, education, duration of illness, and functional impairment accounted for 25% of the variance in depression, but univariate tests showed that only functional impair- 1 The majority of the patients were on multiple medications to manage their RA. The most common medications in descending order of use were aspirin; nonsteroidal, anti-inflammatory drugs; steroids; gold; and immunosuppressive drugs. Although individual reactions to these drugs may vary considerably across patients, at typical therapeutic dosages for R A they are not known to impair sleep (Michael Weisman, personal communication, November 13,1991).

4 PAIN, SLEEP PROBLEMS, AND DEPRESSION 517 Table 1 Cross-Sectional Hierarchical Multiple Regression Analysis of Time I Predictor Variables on Depression at Time 1 Time 1 predictor Age, education, duration of illness, and functional impairment Pain and sleep problems Pain X sleep problems Step F* 19.32* 24.77* 21.27* dfo 4,227 6,225 7,224 change F change 1 " 26.91* 0.49 dfo 1,225 1,224 ' F test of the overall significance of the regression equation including all independent variables entered up to that point in the analysis. b F test of the change in accounted for by the entry of independent variables at that step of the regression equation. *p<.001. ment proved to be a significant, independent predictor, t(221) = 1.52, p <.001. On the second step of the analysis, the combination of AIMS pain and sleep problems contributed 14% unique variance to depression. Of the two variables, however, univariate tests revealed sleep problems to have a highly significant effect on residualized depression, f(225) = 6.49, p <.001, whereas pain did not contribute to residualized depression, (225) = The interaction of pain and sleep problems, which was entered on the third step of the equation, did not add unique variance to residualized depression beyond that contributed by the variables at Steps 1 and 2. Thus, greater sleep problems and functional impairment were significantly associated with higher concurrent depression in this analysis. Longitudinal Analyses Although a positive bivariate relationship was found between pain and sleep problems in cross-sectional analyses, the nature of this relationship was explored further to determine whether prior pain predicted exacerbations of sleep problems from Tl to T2, or vice versa. Two separate multiple regression analyses were conducted to examine this question. In both of these analyses, demographic and disease history variables were entered on Step 1, whereas Tl depression, pain, functional impairment, and sleep problems were introduced into the equation on Step 2 (see Tables 2 and 3). In the first analysis, T2 sleep problems served as the criterion variable, in the second analysis, T2 pain Table 2 Means and Standard Deviations for Study Variables by Time Period Time 1 Time 2 Variable M SD M SD Pain 8 Sleep problems'" Depression' * Arthritis Impact Measurement Scales Pain scale. b Three-item index, including one item from the Center for Epidemiological Studies Depression Scale (CES-D). c Nineteen-item version of the CES-D. was the criterion variable. These analyses evaluated the predictive effects of either prior pain or sleep problems on subsequent residualized pain or sleep problems scores after the autoregressive effects of these variables and the effects of prior depression and functional impairment had been statistically controlled. In the first analysis, demographic and disease history variables accounted for 6% of the variance in T2 sleep problems, but only education was found to be uniquely negatively related to sleep problems, (210) = -2.63, p <.01. On Step 2, the combination of Tl depression, pain, functional impairment, and sleep problems contributed 36% unique variance to T2 sleep problems. Of this group of variables, prior sleep problems, /(206) = 7.03, p <.001, and prior pain, (206) = 2.61, p <.01, independently predicted sleep problems at T2. In the second analysis, which focused on T2 pain as the criterion variable, demographic and disease history variables also accounted for 6% of the variance in T2 pain, with education emerging again as the only significant individual predictor, t(210) = 2.99, p <.01. Tl depression, pain, functional impairment, and sleep problems also contributed 36% unique variance to T2 pain, but in this case only Tl pain proved to be significantly predictive of T2 pain, (206) = 8.21, p <.001. These analyses provide support for two conclusions. First, significant autoregressive effects of prior pain and sleep problems were found over time. Second, significant evidence was found for prior pain exacerbating T2 sleep, whereas no evidence was found to suggest that prior sleep problems affected subsequent pain. A final hierarchical multiple regression analysis was executed to evaluate the main effects of Tl pain and sleep problems and their interaction on changes in depression at T2 after controlling for demographic and disease history variables as well as prior depression and functional impairment (see Table 4). As in the cross-sectional analysis, pain, sleep problems, and their interaction entered the regression equation after all other variables to determine their independent contribution to changes in depression. At Step 1, demographic and disease history variables accounted for 9% of the variance in T2 depression. Of this group, education proved to be a significant, negative predictor of depression, t(210) = -3.82, p <.001. The entry into the equation of Tl depression, pain, functional impairment, and sleep problems at Step 2 accounted for an additional

5 518 PERRY M. NICASSIO AND KENNETH A. WALLSTON Table 3 Longitudinal Hierarchical Multiple Regression Analysis of the Effects of Time 1 Predictor Variables on Sleep Problems at Time 2 F Time 1 predictor Step F* dfa change change 11 dfo Age, education, and duration of illness Depression, functional impairment, pain, and sleep problems * 32.25** 3,210 7, ** 1, 206 " Ftest of the overall significance of the regression equation including all independent variables entered up to that point in the analysis. b F test of the change in accounted for by the entry of independent variables at that step of the regression equation. *p<.01. **p< % of the variance in T2 residualized depression. Of this set of variables, Tl depression, f(206) = 7.27, p <.001, and Tl pain, /(206) = 2.87, p <.01, independently predicted T2 residualized depression. In contrast to cross-sectional findings, a main effect of sleep problems was not found on residualized depression, but the interaction of Tl pain and sleep problems, which was entered on the final step of the analysis, was significant, (205) = 2.87, p <.01, accounting for 2% unique variance in residualized depression at T2. The nature of this interaction is depicted in Figure 1, which presents standardized residualized CES-D scores that were derived through regression analysis by removing the effects of demographic and disease history variables, Tl depression, functional impairment, and the main effects of Tl pain and sleep problems from T2 depression scores. Tl pain and sleep problems were dichotomized into high and low groups for the purpose of depicting the interaction. These data illustrate two major points. First, subjects who initially were low in pain and high in sleep problems declined in depression over time; second, subjects who reported both high pain and high sleep problems at Tl increased in depression over time and were markedly more depressed at T2 than subjects who initially reported low pain and high sleep problems. Thus, level of pain substantially altered the manner in which sleep problems affected depression over time. Discussion This research has provided additional evidence that sleep disturbance is both a prevalent and significant clinical problem for RA patients. The finding that the majority of patients reported that R A interfered with their sleep converges with prior survey data (Hart et al., 1970; Wright, 1985) as well as sleep laboratory findings by Mahowald et al. (1989) that documented extensive sleep fragmentation in a small sample of RA patients. Because RA patients may be unaware of their sleep abnormalities, and may therefore not report sleep disturbance when objective irregularities are found (Mahowald et al., 1989), these findings assume added significance. Moreover, when the RA patients we studied reported sleep disturbance, they tended to attribute it more to their RA than to other sources of stress in their lives. Patients were not queried about the specific aspects of their medical condition that contributed to their sleep disturbance, but evidence was presented in both cross-sectional and longitudinal findings that degree of sleep disturbance was related to Table 4 Longitudinal Hierarchical Multiple Regression Analysis of the Effects of Time 1 Predictor Variables on Depression at Time 2 Time 1 predictor Age, education, and duration of illness Depression, pain, functional impairment, and sleep problems Pain X sleep problem Step F* 6.72* 25.15* 23.81* djs 3,210 7,206 8,205 change F change 1 " 35.65* 8.22* dfe 1,206 1,205 F test of the overall significance of the regression equation including all independent variables entered up to that point in the analysis. b F test of the change in accounted for by the entry of independent variables at that step of the regression equation. *p<.00l.

6 PAIN, SLEEP PROBLEMS, AND DEPRESSION 519 Depression T2 High Pain T Low Sleep Problems High Figure 1. Interaction of pain and sleep problems at Time 1 (Tl) on standardized residualized Center for Epidemiological Studies Depression Scale scores at Time 2 (T2). arthritis pain. In other research, RA patients have cited pain as the main factor interfering with their sleep (Leigh et al., 1987), and it also has been found that chronic pain patients who report sleeping poorly have higher pain levels than patients who report sleeping normally (Pilowsky et al., 1985). The present study extended these findings by addressing the potential causal relationship between pain and sleep disturbance. From longitudinal regression analyses, it was found that arthritis pain predicted exacerbations in sleep 2 years later, whereas prior sleep disturbance had no impact on subsequent pain. These findings are particularly noteworthy in that demographic variables, prior functional impairment, depression, and either pain or sleep problems were statistically controlled in a sample of patients whose level of pain and sleep problems remained quite stable over the study period. Cross-sectional and longitudinal analyses both documented the pain-sleep disturbance association independently of other potentially confounding variables, thus reducing the likelihood that the relationship was the artifactual result of a negative reporting bias. It also is significant that these findings are in agreement with those of the Landis et al. (1989) experimental study on adjuvant arthritis in rats in which disease symptoms were associated with objective sleep measures reflecting a lower depth of sleep and greater sleep fragmentation. Although prospective in nature, because our study provided only correlational evidence, the relationship between pain and sleep is not directly amenable to causal interpretation. Nevertheless, it can be said that RA patients who report high pain may be at risk for developing sleep disturbance. Furthermore, although sleep disturbance appears to be aggravated by prior pain, its existence may contribute to subsequent mood disturbance. Significant daytime sleepiness and symptoms of depressed mood also have been found in normal subjects submitted to experimental disruption and awakening from sleep (Bonnet, 1985; Stepanski, Lamphere, Badia, Zorick, & Roth, 1984). In the present study, cross-sectional multiple regression analysis revealed an association between sleep problems and depression that was independent of pain, functional impairment, and other demographic variables. Pain, in fact, did not contribute unique variance to depression at Tl. However, findings suggest that disturbance in sleep may partly account for, and complement the understanding of, the pain-depression relationship. Longitudinal multiple regression analysis did reveal a significant main effect of prior pain on subsequent depression, confirming the importance of pain as a possible etiological factor in depression (see Brown, 1990); yet, its interaction with current sleep problems also was significant. Sleep problems did not independently exacerbate depressive symptoms over time, but did so for those patients reporting a high level of pain. At this time, the mechanisms linking sleep

7 520 PERRY M. NICASSIO AND KENNETH A. WALLSTON problems to depression in persons with high pain are not understood. However, the combination of high pain and high sleep disturbance may produce anergia, motivational deficits, or a higher level of passive coping (e.g., Brown, Nicassio, & Wallston, 1989), which exacerbates depression. On the other hand, this combination may affect depression physiologically by contributing to underlying disease processes or disrupting serotonergic mechanisms associated with the regulation of mood (Beutler, Engle, Oro-Beutler, Daldrup, & Meredith, 1986; Magni,I987). In conclusion, evidence has been presented on the nature of the pain-sleep disturbance relationship that has illustrated the role of these variables in contributing to subsequent mood disturbance in a large sample of R A patients. Further investigation into the role of sleep disturbance in RA would benefit from a more specific identification of the nature of the sleep disturbance reported through the use of daily sleep diary measures that have been profitably used in insomnia research (Lacks, 1987). Daily measures of sleep-onset latency and sleep quality could then be studied in conjunction with measures of pain and mood to determine their relationship in a manner that more clearly reflects the everyday functioning of RA patients. The current study, though, points to the need for the continued development and implementation of behavioral interventions that have proven effective in reducing RA pain (Bradley et al., 1987) and insomnia (e.g., Bootzin, 1972; Nicassio & Bootzin, 1974) for those patients afflicted with a high degree of sleep disturbance and high levels of pain with RA. References American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (Rev. 3rd ed.). 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