Both depression and chronic pain are common conditions

Transcription

1 Gender Differences in Depression and Chronic Pain Conditions in a National Epidemiologic Survey SARAH E.P. MUNCE, M.SC. DONNA E. STEWART, M.D., FRCPC The authors explored gender differences in the prevalence of depression in four chronic pain conditions and pain severity indices in a national database. In 131,535 adults, the prevalence of depression in women (9.1%) was almost twice that of men (5%). One-third (32.8%) had a chronic pain condition (fibromyalgia, arthritis/rheumatism, back problems, and migraine headaches). The prevalence of depression in individuals with chronic pain conditions was 11.3%, versus 5.3% in those without. Women reported higher rates of chronic pain conditions and depression and higher pain severity than men. Depression and chronic pain conditions represent significant sources of disability, especially for women. (Psychosomatics 2007; 48: ) Both depression and chronic pain are common conditions in medical and psychiatric practice. Nowhere is this more obvious than in general-hospital psychosomatic services. Although depression and chronic pain may occur independently, they are often comorbid. For example, in chronic-pain patients, the prevalence of depression has been reported as ranging from 31% to 100%, 1,2 and pain complaints in depressed individuals range from 34% to 66%. 3 These findings are of particular concern for women because they suffer from major depression at twice the prevalence rate of men. 4,5 Rates of depression and chronic pain are likely to be lower in the general population than in clinical samples, 6 but how frequent are they in the community, and how often do they occur together? One household survey in the United States found that whereas depression occurred in 8% of the population, this rate rose to 18% in people who also had chronic pain. 7 Specific chronic pain conditions Received September 12, 2005; revised May 2, 2006; accepted May 24, From the University Health Network, Women s Health Program, University of Toronto, Toronto, Ontario, Canada. Send correspondence and reprint requests to Sarah Munce, M.Sc., University Health Network, Women s Health Program, 200 Elizabeth St., Toronto, Ontario, Canada M5G 2C4. sarah.munce@uhn.on.ca 2007 The Academy of Psychosomatic Medicine may have different rates of depression. In a Canadian study, the population rate for depression was 5.9% in pain-free individuals, and 19.8% in those who suffered from chronic low back pain. 8 Not surprisingly, when the etiology of the pain condition is considered, studies of more defined pain disorders (e.g., peripheral neuropathy) report lower cooccurrence of depression than do studies of medically unexplained pain. 9 Other studies have examined how the risk of depression increases with the severity, frequency, duration, and number of pain symptoms. 10 In the International Association for the Study of Pain s Classification of Chronic Pain, 11 there are approximately twice as many pain disorders with a higher prevalence in women than those with a higher prevalence in men. Among the most common of these are headaches, orofacial pain, and musculoskeletal pain. 12 Growing evidence suggests that the comorbidity of depression and chronic pain is also proportionately higher in women than men, 12,13 although there is some indication that the characteristics of pain may be different between men and women, with one prospective study demonstrating that the reported severity of pain was related to depression in women, whereas, for men, it was functional impairment that was related to depression. 14 Thus, the purpose of this study was to compare the prevalence of depression and pain-severity indices by Psychosomatics 48:5, September-October 2007

2 Munce and Stewart gender, in four chronic pain conditions. In doing this, we used the Canadian Community Health Survey Cycle 1.1 (CCHS 1.1), a national epidemiological database. TABLE 1. Variable METHOD The CCHS 1.1 The CCHS 1.1 was carried out by Statistics Canada in 2001, with the primary objective of providing crosssectional estimates of health determinants, health status, and health-system utilization across Canada. Data collection took place in 2000 and 2001, with a response rate of 85%. (See Table 1.) The target population included individuals age 12 or older, living in private dwellings in the 10 provinces and 3 territories, excluding those living on Indian Reserves or Crown lands, institutionalized residents, full-time members of the military, and residents of certain remote areas. To provide reliable estimates for all health regions, a net sample of 134,000 consenting respondents was needed. With few exceptions, every health region had at least 500 respondents. 15 The survey used multistaged, stratified random-sampling procedures and was administered by trained interviewers, using the computerassisted personal or telephone interviewing method. 15 Informed consent was obtained by Statistics Canada. Characteristics of the CCHS 1.1 Population Prevalence, Percent Gender Men 49.2 Women 50.8 Marital status Married/common-law 57.9 Widowed/separated/divorced/single 42.0 Income adequacy Lowest 3.4 Lower-middle 6.9 Middle 19.9 Upper-middle 31.7 Highest 27.4 Education Secondary 29.3 Secondary graduate 18.5 Some post-secondary 8.2 Post-secondary graduate 43.2 Race Caucasian 85.0 Other 14.2 Mean age, years 42.1 CCHS 1.1: Canadian Community Health Survey Cycle 1.1, a national epidemiological database. Chronic Pain Separate chronic pain conditions included selfdisclosure of fibromyalgia, arthritis/rheumatism, back problems, and migraine headaches. The definition of these chronic pain conditions included two criteria: 1) the condition was reported to have been diagnosed by a healthcare professional; and, 2) it had lasted for at least 6 months. Individuals who responded Yes to having at least one of these conditions were included in the chronic-pain group. The respondents age at diagnosis was also recorded. Three questions regarding pain and discomfort were included. First, respondents were asked whether or not they were usually free from discomfort (Yes or No), the usual intensity of their pain or discomfort (Mild, Moderate, or Severe), and the number of activities that their pain or discomfort prevented (None, A Few, Some, or Most). Depression The World Health Organization s (WHO) Composite International Diagnostic Interview Short Form for Major Depression (CIDI SFMD) 16 was used to measure major depressive episodes (MDE) in this survey and was administered by trained interviewers. The full version of the CIDI was specifically developed by WHO to measure depression in epidemiological studies and is based on DSM IV criteria for major depression. The interview schedule was developed and validated by Kessler and colleagues 17 and has been used in many epidemiological studies of depression, in samples ranging in age from 12 years to over 60 years. 6,18 The CIDI underwent extensive field-testing on individuals age 15 years and older during the U.S. National Comorbidity Study (NCS). 17,19 The diagnostic accuracy of the CIDI depression module has shown to be good in adolescents, 20 elderly subjects, 21 and medically ill populations. 22 The CIDI SFMD uses a 90% predictive cut-point to represent an MDE. In order to report caseness of an MDE, this 90% cut-point is used and corresponds to reporting five of the eight depression symptoms (depressed mood, loss of interest, fatigue, difficulties in sleeping and concentration, weight gain or loss, feelings of worthlessness, and suicidal ideation) in the same 2-week period over the past 12 months, at least one of which must be depressed mood or loss of interest. This choice of a cutoff is not only justified by its face validity for DSM IV criteria, 23 but also because of its high sensitivity (90%) and specificity (94%), when compared against the full version of the CIDI. 24 The overall classification accuracy of the CIDI SFMD in identifying an MDE is 93%. 24 Psychosomatics 48:5, September-October

3 Gender, Depression, and Pain Statistical Analysis Because the CCHS 1.1 used a complex sampling design, estimates of prevalence must take into consideration the sampling and design effects. In this analysis, estimates of prevalence were calculated using the sampling weights provided by Statistics Canada. 25 Reported percentages, therefore, are weighted, whereas reported sample sizes are the actual number of observed subjects. Because of missing data for some variables, subgroup sample sizes can vary from comparison to comparison. SPSS Version 12.0 software (SPSS, 2003) was used to perform the analyses. Thus, the design of our study is a retrospective analysis of a national random probably sample, and, in order to meet the objective of our study, associations between categorical data were analyzed with the nonparametric chi-square test. RESULTS Overall The sample consisted of 131,535 individuals from the general population, with a mean age of 42.1 years, and an approximately equal proportion of men and women. Approximately 7% of this sample had depression, and 32.8% had at least one of the specified chronic pain conditions (i.e., fibromyalgia [1.1%], arthritis/rheumatism [15.2%], back problems [17.6%], and migraine headaches [9.1%]). The prevalence of depression in individuals with a chronic pain condition was 11.3%, versus 5.3% in those without. When examining the overall prevalence of depression by chronic pain condition, the rates were the following: 22.3% for fibromyalgia (v 2 [1] 93, , p 0.000), 10% for arthritis/rheumatism (v 2 [1] 53, , p 0.000), 12.6% for back problems (v 2 [1] 232,375.95, p 0.000), and 17.3% for migraine headaches (v 2 [1] 375,182.39, p 0.000). Chronic Pain As expected, women reported a higher prevalence of almost all chronic pain conditions. Overall, 38.4% of women, versus 27.1% of men, reported having at least one chronic pain condition. This difference represented a statistically significant sex chronic pain condition association (v 2 [1] 375,182.39, p 0.000). In terms of the individual chronic pain conditions, all of the conditions (except back problems) had a much higher prevalence in women. In all cases, there was a significant sex condition association: 1.8% of women, versus 0.3% of men, had fibromyalgia (v 2 [1] 134,489.40, p 0.000); 19.0% of women, versus 11.4% of men, had arthritis/rheumatism (v 2 [1] 283,084.78, p 0.000); 18.3% of women, versus 16.8% of men, had back problems (v 2 [1] 9, , p 0.000); and 13.2% of women, versus 5.0% of men, had migraine headaches (v 2 [1] 529,341.97, p 0.000). For comparison, the prevalence rates of the various chronic pain conditions have been reported by gender in both depressed and non-depressed samples (Table 2). TABLE 2. Depression The prevalence of depression in women was in accordance with previous psychiatric epidemiology that has shown depression to occur twice as often in women as men. Women with fibromyalgia reported the highest rate of depression. The prevalence rates of depression in the other chronic pain conditions were also significantly higher in women (see Table 3). As expected, there was a linear association between pain severity and the proportion of individuals with major depression. Consistent with the other trends in this study, a greater proportion of depressed women versus depressed men rated their pain severity as severe. Last, depressed women reported a slightly higher number of chronic conditions than did depressed men. DISCUSSION This cross-sectional study revealed that more women than men suffered from major depression, as well as fibro- Percent Prevalence Rates of Chronic Conditions in Various Groups (By Gender) Variable Men Women Chronic pain in general population At least one condition Fibromyalgia Arthritis/rheumatism Back problems Migraine headaches Chronic pain conditions in depression sample At least one condition Fibromyalgia Arthritis/rheumatism Back problems Migraine headaches Chronic pain conditions in no-depression sample At least one condition Fibromyalgia Arthritis/rheumatism Back problems Migraine headaches Psychosomatics 48:5, September-October 2007

4 Munce and Stewart myalgia, arthritis/rheumatism, back problems, and migraine headaches. The findings of this study are consistent with previous psychiatric epidemiological studies 4,5 demonstrating that women suffer from major depression at twice the prevalence rate of men. Also, in each of the four chronic pain conditions, the prevalence rate of depression was more elevated in women than in their male counterparts. Moreover, there were a greater proportion of depressed women than men who rated their pain as severe, and they reported more chronic conditions. Certainly, the findings of this study support previous findings of a higher prevalence of chronic pain conditions among women than men. 11,12 All of the chronic pain conditions carried an elevated rate of depression, as compared with the overall rates of depression in men and women. The prevalence of depression in each of the four chronic pain conditions was considerably higher in women than men. This trend was particularly notable for fibromyalgia: women with fibromyalgia reported a prevalence of depression of almost 24%, considerably higher than the overall 9% prevalence of depression in women. Given the ambiguous etiology of fibromyalgia, this finding corresponds with previous studies suggesting that more defined pain disorders (e.g., peripheral neuropathy) are associated with TABLE 3. Variable Various Prevalence Rates of Chronic Conditions by Gender, Percent Men Women Chronic pain condition Fibromyalgia Arthritis/rheumatism Back problems Migraine headaches Condition Chronic pain Depression Rates of depression by chronic pain condition Fibromyalgia Arthritis/rheumatism Back problems Migraine headaches Rates of depression by pain severity Mild Moderate Severe Rates of depression by number of activities prevented None A few Some Most Number of chronic conditions by depression status No depression Depression a lower occurrence of depression than studies of medically unexplained pain. 9 This increased prevalence of depression in chronic pain conditions may be indicative of the dynamic and bidirectional association between pain and depression. Symptoms of depression have been associated with a number of processes thought to increase pain, including cognitive distortions, lower levels of positive reinforcement, 26 helplessness, 27 and a relative lack of positive affect. 28 In turn, these processes contribute to inadequate coping in the face of stressful life events and increasing pain, thereby demonstrating how depression can propagate and intensify the stress pain stress cycle. 19 Given this phenomenon, and since women consistently report elevated rates of depression, the associated higher prevalence rates of chronic pain conditions as compared with men can be explained. The stress pain stress cycle also raises the important issue of cognition in pain perception. Given that the proportion of depressed individuals increased proportionally with pain severity, and the finding that more depressed women than depressed men rated their pain as severe, it is possible that gender differences in pain perception are associated with the increased prevalence of chronic pain conditions among women, and, in turn, the elevated rates of depression in women. These findings also indirectly support biological theories of the comorbidity of chronic pain and depression, namely the role of 5-hydroxytryptamine and norepinephrine in the pathogenesis of depression and the perception of pain, and their key role as modulatory neurotransmitters in the descending spinal inhibitory pathway and as part of the body s endogenous analgesic system. 29,30 Moreover, the role of estrogen in the observed higher prevalence of comorbid depression and chronic pain in women is an active topic of research. 31 Although some of these findings have been reported or alluded to in clinical samples, 1,2,7 limited data have been available on population-based chronic pain conditions and depression, and this study offers several strengths as compared with previous epidemiological investigations in this area. For example, this large epidemiologic database was nationally representative and reported a response rate of 85%, which is higher than most studies (cf. Kessler et al. 6 ). Furthermore, the definition of chronic pain required a duration of at least 6 months. This specification is closer to the accepted medical criterion 32 than the 1-month duration used in Magni et al. 7 or the 1-day criterion used in Von Korff et al. 33 Psychosomatics 48:5, September-October

5 Gender, Depression, and Pain Limitations A major limitation of the present study, and cross-sectional analysis in general, is its inability to establish cause and effect. In this case, there is no way to determine whether major depression is the result of chronic pain, a causative factor, or if both may be caused by a common biological process. As with all research that studies the association between chronic pain conditions and depression, the issue of criterion contamination exists. 34 Although the prevalence of depression in this study may be inflated because of the somatic symptoms, it should also be underscored that the CIDI has performed well in detecting depression in medically-ill populations. 22 Despite this fact, the CCHS 1.1 used the abbreviated version of the full diagnostic interview, which contained no probe questions to determine the source of the symptoms. Furthermore, depression was measured by use of a dichotomous variable (Yes/No). Therefore, it may have been worthwhile to use a more liberal definition of depression (e.g., number of depressive symptoms) or even distress, as in the study by Mausner-Dorch and Eaton. 35 The assessment of chronic pain was also limited in the CCHS 1.1. Information on diagnosis and duration was based on self-disclosure, although the respondents had to have had their condition diagnosed by a healthcare professional. Another limitation of such an epidemiological survey is the consideration that, because the sample is so large, even small differences can emerge as statistically significant. These limitations are typical of epidemiological surveys that focus on general health rather than specific disorders, as Currie and Wang, 8 who also used the CCHS 1.1 database, noted in their study on chronic back pain and depression. CONCLUSION This study provides evidence from a large population sample that women suffer from both depression and chronic pain conditions at approximately twice the prevalence of men. This study also provided evidence that depression rates among those with chronic pain conditions are considerably higher than rates of depression in the general population. Increased pain severity may play a particularly significant role for women, leading to further distress and further pain. Given that women with chronic pain conditions experience particularly elevated rates of depression, as compared with men, and women suffer from depression at twice the prevalence rate of men, depression, whether alone, or especially in the presence of a comorbid pain condition, represents a substantial source of distress and disability for women. The research and data analyses were carried out at Statistics Canada. However, the opinions and views do not represent those of Statistics Canada. References 1. 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