Associations Between Arthritis and a Broad Range of Psychiatric Disorders: Findings From a Nationally Representative Sample

The Journal of Pain, Vol 9, No 1 (January), 2008: pp 37-44 Available online at www.sciencedirect.com

Associations Between Arthritis and a Broad Range of Psychiatric Disorders: Findings From a Nationally Representative Sample Lachlan A. McWilliams,* Ian P. Clara,† Paul D. J. Murphy,* Brian J. Cox,† and Jitender Sareen† *Department of Psychology, Acadia University, Wolfville, Nova Scotia, Canada. † Department of Psychiatry, University of Manitoba, Winnipeg, Manitoba, Canada.

Abstract: Data from the National Epidemiological Study of Alcoholism and Related Conditions (NESARC) were used to investigate associations between arthritis and a wide range of psychiatric disorders in a large sample (n ⴝ 43,093) representative of the adult population of the United States. NESARC participants completed the Alcohol Use Disorder and Associated Disabilities Interview Schedule – DSM-IV Version and provided reports regarding medical conditions, including arthritis, experienced over the past year. Logistic regression analyses that adjusted for potential confounding variables (ie, gender, marital status, age, income, and other health conditions) indicated that arthritis had significant positive associations with each of the 7 personality disorders included in the NESARC (ie, avoidant, dependent, obsessive-compulsive, paranoid, schizoid, histrionic, and antisocial). Arthritis also had significant positive associations with mood and anxiety disorders. In contrast to several recent studies indicating arthritis may have relatively larger associations with anxiety disorders than with major depression, the magnitudes of the associations involving anxiety disorders were not particularly large compared with those regarding depressive disorders. Alcohol- and substancerelated disorders had negative associations with arthritis. However, additional analyses indicated that age was a confounding variable in these relationships and revealed that arthritis was not associated with either alcohol- or substance-related disorders. Perspective: This article presents the first study to investigate associations between arthritis and personality disorders and is the first study to investigate relationships between a condition characterized by pain and personality disorders using a community sample. It may prompt research and clinical attention to the role of personality disorders in arthritis. © 2008 by the American Pain Society Key words: Arthritis, mood disorders, anxiety disorders, personality disorders, nationally representative sample.

N Received June 15, 2007; Revised July 30, 2007; Accepted August 7, 2007. The National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) was supported by the National Institute on Alcohol Abuse and Alcoholism and the National Institute on Drug Abuse. The NESARC data was provided by the Substance Abuse and Mental Health Data Archive and the Interuniversity Consortium for Political and Social Research. This research was partially funded by a grant awarded to Dr. McWilliams from the Acadia University Research Fund. Dr. Jitender Sareen was supported by a Canadian Institutes of Health Research New Investigator Award, and Dr. Brian Cox was supported by the Canada Research Chairs Program. Address reprint requests to Dr. Lachlan McWilliams, Department of Psychology, Acadia University, Wolfville, NS, Canada B4P 2R6. E-mail: Lachlan. [email protected] 1526-5900/$34.00 © 2008 by the American Pain Society doi:10.1016/j.jpain.2007.08.002

umerous studies have demonstrated that pain conditions and psychiatric disorders are positively associated.9 Consistent with this pattern of findings, arthritis has also been found to be positively associated with psychopathology in both clinical23 and community samples.35 This pattern is noteworthy because comorbid arthritis and psychopathology have been linked to increased disability,22,36 reduced quality of life,29,11 and increased health care utilization.37 Research regarding pain and psychopathology conducted with clinical samples has emphasized depression.6 However, recent epidemiological research has drawn attention to the possibility that anxiety disorders are also positively associated with painful medical conditions. For example, using data from the National Comorbidity Survey (NCS),21 McWilliams et al25 found that anx37

38 iety disorders were positively associated with “severe arthritis, rheumatism, or another bone or joint disease” and that this type of pain had larger associations with several anxiety disorders than with major depression. McWilliams et al26 obtained a similar pattern of findings regarding arthritis when utilizing data from the Midlife Development in the United States Survey and also found relatively large associations between anxiety disorders and both back pain and migraine headaches. In light of these recent findings, anxiety disorders warrant further attention in relation to arthritis and other conditions involving pain. The diagnostic term personality disorder refers to a stable pattern of behavior and inner experience that leads to distress or impairment. For a personality disorder to be diagnosed, these behavioral and emotional traits must differ substantially from societal and cultural expectations, be inflexible, and have an early onset (ie, adolescence or early adulthood).3 For example, paranoid personality disorder refers to a pattern characterized by suspiciousness and distrust (eg, interpreting benign remarks as having a hidden and threatening meaning, or having an unjustified preoccupation with the trustworthiness of friends). Research has not yet investigated associations between arthritis and personality disorders. However, research with chronic pain samples is suggestive of an association between the experience of pain and personality disorders. For example, in the first study to apply personality disorder criteria from the DSM-III1 to a chronic pain sample, Reich et al32 found 47% of the 43 patients met the criteria for a personality disorder; the most common personality disorders were histrionic and dependent. In a more recent study that applied DSMIII-R2 criteria, Polatin et al31 found that 51% of a large chronic low back pain sample met the criteria for at least 1 personality disorder. The most common of these were paranoid (33%), borderline (15%), and avoidant (14%). Although neither of these studies used a control group, these rates are clearly much higher than those found in the general population. However, these studies utilized treatment-seeking samples that are more likely to have comorbid conditions, so they likely overestimated the prevalence of personality disorders amongst those with chronic pain.5 To date, research has not investigated relationships between any medical condition characterized by pain and personality disorders using a community sample representative of the general population. The present study used data from the National Epidemiologic Survey on Alcoholism and Related Conditions (NESARC)16 to investigate associations between arthritis and a wide range of psychiatric disorders. The main objectives were to (1) investigate associations between arthritis and personality disorders using a representative community sample and (2) determine whether earlier research indicating that there are strong positive associations between arthritis and anxiety disorders could be replicated. Although alcohol- and substance-related disorders are not commonly investigated with regard to

Arthritis and Psychopathology arthritis and other conditions involving pain, they were also considered in the present study.

Materials and Methods Subjects and Procedures The data used were from the 2001-2002 NESARC. It involved a representative sample of the noninstitutionalized civilian population aged 18 and older residing in the United States. Participants were administered faceto-face computerized personal interviews. There were 43,093 respondents with an overall response rate of 81%. The sample was weighted to adjust for probabilities of selection, nonresponse, and oversampling. Weighted data were then adjusted to approximate the United States population on a variety of sociodemographic factors (ie, region, age, sex, race, ethnicity). All participants provided informed consent prior to being interviewed. The entire NESARC protocol received full ethical review and approval from the U.S. Census Bureau and the United States Office of Management and Budget.

Diagnostic Assessment Mental health disorders were diagnosed using the National Institude on Alcohol Abuse and Alcoholism’s Alcohol Use Disorder and Associated Disabilities Interview Schedule – DSM-IV Version (AUDADIS-IV).12 The AUDADIS-IV includes DSM-IV3 Axis-I and Axis II disorders. The Axis-I disorders examined in the present study included depressive disorders (viz, major depression, and dysthymia) and anxiety disorders (viz, panic with agoraphobia, panic without agoraphobia, social phobia, simple phobia, and generalized anxiety disorder). Composite variables representing alcohol-related conditions (viz, alcohol abuse or dependence) and abuse or dependence related to other types of drugs (viz, sedatives, tranquilizers, opiates, stimulants, hallucinogens, cannabis, cocaine, and inhalants/solvents) were also used. The AUDADIS-IV assesses disorders on a lifetime and pastyear basis, and allows for the exclusion of cases in which the disorder is caused by a medical condition, substance abuse, or in the case of major depression, bereavement. Data for the present study involved past-year diagnoses with the exclusion criteria applied. AUDADIS-IV measures of DSM-IV Axis-I disorders have been found to have fair to good test re-test reliability with ␬ values for diagnoses considered in the present study ranging from 0.40 (specific phobia) to 0.74 (alcohol abuse).13 The main approach to establishing the validity of the mood and anxiety disorder modules of the AUDADIS-IV was to examine associations between diagnoses of these disorders and mental disability scores on the Short Form12v2,39 a reliable and valid quality of life measure for use in large population surveys, which was included as part of the NESARC interview. These analyses demonstrated that each mood and anxiety disorder assessed in the NESARC was a highly significant predictor of the social functioning, role emotional function, mental health, and mental health component summary scores on the Short

ORIGINAL REPORT/McWilliams et al 14

Form-12v2. Additionally, the construct validity of the substance- and alcohol-related disorders modules has been supported by studies indicating high levels of concordance between AUDADIS-IV diagnoses of these conditions and those of other structured interviews.38 Findings obtained with the Spanish version of the AUDADIS-IV are also supportive of the validity of the AUDADIS-IV. This research7 indicated that there was a high level of agreement between several Axis-I disorders diagnoses obtained with lay interviewer administration of the AUDADIS-IV and diagnoses obtained with administration of the AUDADIS-IV by a psychiatrist in which probing of interviewees’ responses was also allowed. The ␬ values for alcohol abuse or dependence, drug abuse or dependence, and major depression (.75, .66, and .64) indicated adequate levels of agreement regarding these disorders. This research did not evaluate other components of the interview relevant to the present study (eg, past-year dysthymia and anxiety disorders). The AUDADIS-IV also included seven personality disorders (viz, antisocial, avoidant, dependent, obsessive compulsive, paranoid, schizoid, and histrionic). The AUDADIS-IV section related to personality disorders involved a series of personal symptom questions concerning participants’ usual feelings and actions, excluding times when they were depressed, manic, anxious, under the influence of drugs or alcohol, experiencing withdrawal, or physically ill. To be classified as having a particular personality disorder, respondents had to endorse the appropriate number of positive symptoms for the disorder, and at least one endorsed symptom had to result in social or occupational dysfunction. Grant et al10 demonstrated good test re-test reliability of the AUDADIS-IV as a measure of DSM-IV personality disorders with ␬ coefficients ranging from 0.40 (histrionic personality disorder) to 0.67 (antisocial personality disorder). The validity of the AUDADIS-IV personality disorder diagnoses were also examined by assessing their associations with Short Form12v2 scores. With the exception of histrionic personality disorder, each personality disorder had a statistically significant positive association with mental health component summary scores on the Short Form-12v2 after adjusting for age, other personality disorders, and Axis-I disorders.15

Health Conditions The presence of arthritis was determined on the basis of 2 questions. Participants were first asked whether they “had arthritis in the last 12 months”; those responding in the affirmative were also asked whether this diagnosis had been confirmed by a doctor or other health professional. Those responding “yes” to both questions were categorized as having past-year arthritis (0 ⫽ absent, 1 ⫽ present). Those who reported that arthritis had not been confirmed by a doctor or other health professional were categorized as not having arthritis. While this self-report method does not posses the validity that would be provided by a medical examination of each participant, the follow-up item regarding confirmation

39 of the diagnosis would ensure that self-reported diagnoses would match closely with clinical diagnoses. A procedure similar to that described above was used to assess 10 other health conditions including hardening of the arteries or arteriosclerosis, high blood pressure, cirrhosis of the liver, other liver disease, chest pain or angina pectoris, rapid heartbeat or tachycardia, heart attack or myocardial infarction, other forms of heart disease, stomach ulcer, and gastritis. A variable indicating the presence of 1 or more health condition other than arthritis was created for the present study (0 ⫽ none, 1 ⫽ one or more condition other than arthritis).

Demographic Variables The sociodemographic variables utilized in the present study were gender (0 ⫽ male; 1 ⫽ female), age (in years of age; 0 ⫽ 65 and above, 1 ⫽ less than 65), marital status (0 ⫽ married, living as if married, or never married, 1 ⫽ widowed, divorced, or separated), and personal income (in dollars/year; 0 ⫽ 20,000 and above, 1 ⫽ 19,999 or less). Each of these variables has been found to be associated with psychopathology in previous research utilizing the NESARC data set,17 and each was coded such that a score of 1 on the variable generally represented a risk factor for psychopathology. For example, age was treated as a categorical variable in which being under 65 years of age was risk factor because Hasin et al17 determined that those in the younger age cohorts (18 –29, 30 – 44, and 45– 64 years of age) of the NESARC were more likely to have a lifetime history of major depression than those in the oldest age cohort (65 years of age or older). Moreover, other epidemiological research has consistently indicated similar age-related effects with regard to anxiety,18 alcoholrelated,8 and substance-related disorders.4

Results All inferential statistics were calculated using the SUDAAN Software for the Statistical Analysis of Correlated Data. Due to the complex sample design and weighting, the SUDAAN software is required to estimate the standard errors, which is done using the Taylor series linearization method and the stratification information available in the NESARC data set. Arthritis (confirmed by a health professional) was endorsed by 17.0% (unweighted n ⫽ 7876) of the sample. Those with arthritis were significantly more likely to report one or more other health condition (27.5%) than those without arthritis (7.0%; ␹2 ⫽ 166.63, P ⬍ .01). When the sociodemographic variables were considered, those with arthritis were more likely to belong to the categories that were positively associated with psychopathology in the Hasin et al17 research with the NESARC. Specifically, in comparison to those without arthritis, those with arthritis were more likely to be female (49.7% vs 63.5%; ␹2 ⫽ 121.69, P ⬍ .01), to be widowed, divorced, or separated (14.7% vs 31.1%; ␹2 ⫽ 151.22, P ⬍ .01), and to be in the low income category (45.1% vs 58.0%; ␹2 ⫽ 108.91, P ⬍ .01). An exception to this pattern was the age variable. Although Hasin et al found those in the 65 and

40 Table 1.

Arthritis and Psychopathology

Past-Year Axis I Disorders: Prevalence Rates and Associations With Arthritis PREVALENCE

NONARTHRITIS DISORDER Mood disorders Major depression Dysthymia Anxiety disorders Panic with agoraphobia Panic without agoraphobia Social phobia Simple phobia Generalized anxiety Substance-related disorders Alcohol abuse or dependence Substance abuse or dependence

ODDS RATIOS (95% CONFIDENCE INTERVALS PARENTHESES)

ARTHRITIS

IN

%

N

%

N

BIVARIATE

ADJUSTED

6.50 1.60

2386 586

9.80 3.00

733 257

1.57 (1.39–1.78)† 1.94 (1.57–2.40)†

1.63 (1.43–1.87)† 1.63 (1.30–2.04)†

0.50 1.30 2.60 6.70 1.80

186 461 879 2347 620

0.80 2.60 3.60 9.40 3.50

68 192 261 726 274

1.67 (1.21–2.29)† 1.99 (1.60–2.47)† 1.40 (1.18–1.67)† 1.45 (1.29–1.63)† 2.06 (1.70–2.49)†

1.53 (1.11–2.11)* 1.84 (1.42–2.37)† 1.41 (1.16–1.71)† 1.45 (1.26–1.66)† 1.90 (1.52–2.37)†

9.20 2.10

3008 693

4.80 1.30

319 84

0.49 (0.43–0.57)† 0.60 (0.45–0.81)†

0.77 (0.67–0.90)† 0.88 (0.65–1.18)

NOTE: Percentages are based on weighted data and n values are based on unweighted data. Odds ratios adjusted for gender, marital status, income, age, and the presence of 1 or more health conditions other than arthritis. *P ⬍ .05. †P ⬍ .01.

greater years of age group were less likely to experience psychopathology, this group was far more likely to report arthritis (44.8%) than those in the younger age group (11.7%; ␹2 ⫽ 175.96, P ⬍ .01). Table 1 presents between group comparisons (viz, arthritis vs no arthritis) regarding the prevalence of each Axis I psychiatric disorder. Bivariate logistic regression analyses were used to examine the associations between arthritis and each of the Axis I disorders. Arthritis had significant positive associations with each mood and anxiety disorder. Consistent with the emphasis on depression in pain research, major depression was the most prevalent of the depressive and anxiety disorders in the arthritis subsample (9.8%). Two significant negative associations were also found. Those with arthritis were less likely than those without arthritis to report abuse or dependence of alcohol or drugs. To statistically account for other variables that may have independent effects on psychopathology, a series of multiple logistic regressions were used to calculate odds ratios that adjusted for gender, marital status, income, age, and the presence of a health condition other than arthritis. These findings are also reported in Table 1. The pattern of findings regarding mood and anxiety disorders was similar to those found with the bivariate logistic regressions. However, the adjusted odds ratios revealed a slightly different pattern with regard to the substance-related disorders. Specifically, the negative association between arthritis and substance abuse or dependence was no longer statistically significant. Psychiatric disorders are positively associated with each other.24 Therefore it was surprising that arthritis did not also have a positive association with the alcohol- and substance-related disorders. As noted above, individuals

in the older age group (⬎65 years of age) had higher rates of arthritis than those in the younger age group (⬍65 years of age; 44.8% vs 11.7%). Older individuals also had significantly lower rates of alcohol-related conditions (1.5% vs 9.8%; ␹2 ⫽ 202.53, P ⬍ .01) and substancerelated conditions (0.1% vs 2.4%; ␹2 ⫽ 127.84, P ⬍ .01) relative to those in the younger age group. Given these findings and previous research indicating alcohol problems have a negative association with arthritis amongst the elderly,6 it is possible that age may have been a confounding variable that could not be adequately adjusted for in the original multivariate logistic regressions investigating alcohol- and substance-related conditions. To address the possibility that age was a confound, associations between arthritis and alcohol- and substance-related conditions were investigated using stratified analyses involving 4 age-based subsamples. These subsamples were based on the age categories used in previous studies with the NESARC.17 Participants were categorized as 18 to 29 (21.8%), 30 to 44 (30.9%), 45 to 64 (31.1%), or 65 years of age or older (16.2%). Bivariate analyses regarding alcohol abuse or dependence within these 4 groups revealed a pattern consistent with the notion that the relationship between arthritis and alcohol abuse or dependence varies across age groups. There were positive associations (odds ratios in parentheses) between arthritis and alcohol abuse or dependence in the 18 to 29 age group (1.32) and in the 30 to 44 age group (1.21), but there were negative associations in the 45 to 64 age group (.87) and in the 65 and older age group (.88). However, none of these associations were statistically significant. Similar analyses were used to investigate the association between arthritis and substance abuse or depen-

ORIGINAL REPORT/McWilliams et al Table 2.

41

Personality Disorders: Prevalence Rates and Associations With Arthritis PREVALENCE NONARTHRITIS

ARTHRITIS

ODDS RATIOS (95% CONFIDENCE INTERVALS

IN

PARENTHESES)

PERSONALITY DISORDER

%

n

%

n

BIVARIATE

ADJUSTED-MODEL 1

ADJUSTED-MODEL 2

Antisocial Avoidant Dependent Obsessive-compulsive Paranoid Schizoid Histrionic

3.50 2.10 0.40 7.40 4.20 2.80 1.80

1156 737 148 2498 1643 1068 645

4.10 3.50 0.90 10.30 5.60 4.70 2.20

266 258 60 763 462 357 163

1.18 (1.01–1.37)* 1.68 (1.40–2.02)† 2.18 (1.45–3.29)† 1.44 (1.28–1.61)† 1.35 (1.18–1.55)† 1.73 (1.47–2.02)† 1.25 (1.01–1.54)*

2.46 (2.04–2.97)† 2.31 (1.80–2.97)† 2.25 (1.19–4.25)* 1.67 (1.44–1.92)† 1.86 (1.55–2.24)† 2.31 (1.90–2.81)† 2.39 (1.78–3.22)†

2.06 (1.72–2.48)† 1.62 (1.27–2.06)† 1.49 (0.82–2.70) 1.41 (1.23–1.62)† 1.40 (1.17–1.67)† 1.79 (1.48–2.17)† 1.80 (1.36–2.39)†

NOTE: Percentages are based on weighted data and n values are based on unweighted data. Model 1 odds ratios adjusted for gender, marital status, income, age, and the presence of 1 or more health conditions other than arthritis. Model 2 odds ratios adjusted for the variables included in model 1 as well as 3 additional variables representing the presence of 1 or more past-year depressive disorders, 1 or more past-year anxiety-disorders, and 1 or more past-year alcohol- or substance-related disorders. *P ⬍ .05. †P ⬍ .01.

dence. The associations between these conditions were not statistically significant in the youngest age group (1.68) or the oldest age group (.94). There were significant positive associations between these conditions in the 30 to 44 age group (1.74, P ⬍ .05) and in the 45 to 64 age group (2.21, P ⬍.01). However, further multivariate analyses that adjusted for gender, marital status, income, and the presence of a health condition other than arthritis revealed nonsignificant associations between arthritis and substance abuse or dependence in both the 30 to 44 age group (1.46) and the 45 to 64 age group (1.67). Table 2 presents between-group comparisons regarding the prevalence of each personality disorder. Each personality disorder was more common in the arthritis subsample than in the nonarthritis subsample. The bivariate logistic regression analyses presented in Table 2 indicated that arthritis had significant positive associations with each personality disorder. Two series of adjusted odds ratios were also conducted. The first of these was based on the approach used when investigating the Axis I disorders, and included variables that may have independent effects on psychopathology (ie, sociodemographic variables and the health condition variable). The results of these analyses were consistent with the findings of the bivariate analyses and indicated that arthritis was associated with each personality disorder. The second series of adjusted odds ratios was designed to examine associations between arthritis and personality disorders in a manner that also adjusted for recent emotional distress. This was done by including as covariates 3 composite variables representing the presence of one or more: (a) Depressive disorders, (b) anxiety disorders, and/or (c) alcohol- or substance-related conditions. Each of these composite variables included only past-year diagnoses. These analyses revealed a similar pattern, but the association between arthritis and dependent personality disorder was no longer statistically significant.

Discussion The primary aim of the study was to provide the first epidemiological investigation of associations between arthritis and personality disorders using a representative community sample. Those with arthritis had significantly higher rates of each personality disorder included in the NESARC. Each of these associations remained statistically significant after adjusting for relevant sociodemographic variables and the presence of a health condition other than arthritis. This pattern is suggestive of a nonspecific association between arthritis and personality disorders. These conditions may be associated because of a shared vulnerability factor. This explanation is plausible as there is evidence that childhood adversities, such as psychological trauma, are associated with both arthritis28 and adult psychopathology.20 Weisberg and Keefe’s40 diathesis-stress model regarding chronic pain and personality disorders provides a second potential explanation for the present findings. They suggested that “premorbid character pathology” could be exacerbated by the “stress of persistent pain” and result in a presentation consistent with a personality disorder. Unfortunately, the NESARC’s lack of information regarding childhood adversities and its cross-sectional nature precluded either of these explanations from being investigated. It is also possible that recent emotional distress associated with an Axis I disorder could have influenced participants’ reports of personality disorder symptoms and led to an exaggerated assessment of the prevalence of personality disorders. For example, those with a current (or recent) major depressive disorder may endorse some statements from the personality disorders sections of the AUDADIS-IV that are consistent with their current affective state (eg, from the schizoid section “Are there really very few things that give you pleasure?”) even though the statements are not accurate reflections of their typical affective states and behavior. Additional analyses

42 investigated whether the associations between arthritis and personality disorders would remain after adjusting for past-year Axis I disorders. With 1 exception, the findings of these analyses were consistent with the initial findings. Thus, it appears that the relationship between arthritis and personality disorders is not simply the result of the increased emotional distress associated with Axis I disorders. The 1 exception noted above was that the positive association between arthritis and dependent personality disorder was no longer statistically significant when the past-year Axis I disorders were included as covariates. It is possible that the earlier positive findings may have been obtained because those with arthritis have higher levels of distress (ie, Axis I disorders) and as a result inaccurately reported more symptoms of dependent personality disorder. However, it is important to note that the final adjusted odds ratios involved an extremely stringent test of association (ie, 8 covariates). As well, the bivariate odds ratios indicated that those with arthritis were more than twice as likely to be classified as having dependent personality disorder than those without arthritis. Given this situation and the cross-sectional nature of the study, it would be premature to conclude the association between arthritis and dependent personality disorder was due solely to the increased distress associated with Axis I disorders. Several recent studies have indicated that arthritis may have relatively larger associations with anxiety disorders than with major depression.25,26 Another main objective of the present study was to determine whether these findings could be replicated. Although major depressive disorder, dysthymia, and each anxiety disorder had a significant positive association with arthritis, the magnitudes of these associations were smaller than those found in previous research by McWilliams et al.25 As well, the associations involving anxiety disorders were not particularly large relative to those found with major depression and dysthymia. Two methodological features of the present study may be responsible for the smaller than anticipated associations above noted. First, the current study used the AUDADIS-IV whereas McWilliams et al’s25 study was based on data from the NCS, which utilized the Composite International Diagnostic Interview (CIDI).41 The AUDADIS-IV operationalizes DSM-IV criteria, whereas the version of the CIDI used in the study by McWilliams et al was based on DSM-III-R criteria. Perhaps more importantly, unlike the CIDI, the AUDADIS-IV provides diagnoses in which several exclusionary criteria can be applied (eg, not due to a medical condition or substance abuse). The current application of these exclusionary criteria might have led to relatively smaller associations because in some instances those with psychopathology related to a medical condition, which were more common amongst those with arthritis, would not have been classified as having a pastyear psychiatric disorder despite experiencing symptoms. Second, in the current study, arthritis was considered to be present only when respondents indicated that a doctor or a healthcare professional had confirmed the diag-

Arthritis and Psychopathology nosis. This method is advantageous because it eliminated some cases involving inaccurate self-diagnoses of arthritis. McWilliams et al’s study used a simpler self-report of arthritis that also included “rheumatism and other bone and joint disease,” so it is possible that some reporting this condition in their study may have had a condition other than arthritis or simple nonspecific joint pain. Given those with higher levels of psychological distress are more prone to reporting physical symptoms,30 the associations obtained by McWilliams et al may have been inflated because those with a mood or anxiety disorder were more likely to have joint pain and as a result may have inaccurately reported having arthritis. Alcohol-related conditions and substance use conditions were also investigated. The initial finding of negative associations between arthritis and alcohol abuse or dependence was counterintuitive. Given that those in the oldest age group (⬎65 years of age) reported high rates of arthritis and very low rates of alcohol abuse or dependence, the possibility that age may have been a confounding variable was explored. Additional analyses conducted in 4 age-based subsamples indicated that the direction of the association between arthritis and alcohol-related conditions varied across age groups. However, none of these associations were statistically significant. Similar analyses were conducted regarding substance abuse or dependence. Positive associations were found in 2 of the age groups, but these associations were not significant in the multivariate analyses. Overall, these follow-up analyses suggested that the significant negative associations initially found between arthritis and the alcohol- and substance-related conditions were obtained because age was a confounding variable. These null findings are also consistent with recent epidemiological research conducted with data from the National Comorbidity Survey Replication.36 One implication of the present findings and those of a few other studies19,27 is that epidemiological investigations regarding health conditions and psychopathology would be strengthened by assessing personality disorders. In terms of clinical practice, personality-related psychopathology has long been recognized as relevant when working with chronic pain patients.10 However, the importance of anxiety disorders and personality variables that could potentially complicate treatment have not generally been recognized with regard to arthritis. For example, an issue of Arthritis Care and Research that focused on assessment issues included articles on depression34 and other measures of psychological well-being,33 but did not include articles devoted to either anxiety or personality disorders. Thus, expanding the assessment of psychopathology beyond an almost exclusive focus on depression would be warranted. Several limitations of the present study should be noted. First, as previously discussed, the assessment of arthritis was brief. The requirement that a healthcare professional had to confirm this diagnosis in order for a classification of arthritis to be made in the current study may represent an improvement relative to a single item self-report of arthritis. However, this methodology likely

ORIGINAL REPORT/McWilliams et al identified a highly heterogeneous subsample of individuals with arthritis because the term arthritis actually refers to a large number of conditions (eg, relatively mild conditions, such as bursitis, to more severe and systemic conditions, such as rheumatoid arthritis). It would be expected that those with the most severe forms of arthritis would be the most likely to experience psychopathology. However, this possibility could not be investigated because information about the frequency, severity, and chronicity of the pain associated with arthritis was not collected. Another limitation was that a few personality disorders (ie, schizotypal, narcissistic, and borderline) were not assessed in the NESARC. The findings suggested that there is a nonspecific association between personality disorders and arthritis, but without including the entire range of personality disorders this conclusion cannot be reached definitely. Nonetheless, it is important to note that disorders from each personality disorder cluster were assessed, so a broad range of personality disorders was investigated. As well, a similar study concerning cardiovascular diseases27 also supported the nonspecific-

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43 ity of association between personality disorders and health conditions. In summary, this was the first epidemiological study to investigate associations between arthritis and personality disorders. Arthritis had a significant positive association with each personality disorder assessed in the NESARC. Arthritis had significant positive associations with each depressive and anxiety disorder, but the magnitudes of these associations were smaller than those found in several previous studies. Alcohol- and substance-related conditions were initially found to have significant negative associations with arthritis. However, additional analyses based on the possibility that age was a confounding variable indicated that arthritis was not associated with either alcohol- or substance-related disorders.

Acknowledgments The authors thank 2 anonymous reviewers and Kate Saldanha for providing valuable suggestions for improving this manuscript.

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