Comorbidity burden and its impact on psychosocial morbidity in depressed outpatients

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Background: Many studies have examined the co-occurrence of depression and one or two nondepressive disorders; however, little research has looked at broad spectrum comorbidity (i.e., comorbidity across several diagnostic categories) in depressed patients. Research on diagnostic practices in routine clinical settings – in which unstructured interviewing is the norm – suggests that comorbid conditions are often not detected [Zimmerman, M., Mattia, J. 1999. Psychiatric diagnosis in clinical practice: Is comorbidity being missed? Compr. Psychiatry, 40, 182–191]. In this study we examined the independent impact of different comorbid diagnostic categories on psychosocial morbidity in psychiatric outpatients with Major Depressive Disorder (MDD). Methods: Participants were drawn from a pool of 1000 psychiatric outpatients interviewed with the Structured Clinical Interview for DSM-IV diagnoses (SCID-IV; [First, M.B., Spitzer, R.L., Williams, J.B.W., Gibbon, M., 1995. Structured Clinical Interview for DSM-IV (SCID). American Psychiatric Association, Washington, D.C.]). We compared the demographics, clinical characteristics, and psychosocial functioning of depressed outpatients with and without different axis I comorbidities, then conducted multivariate analyses to determine the respective impact of comorbid axis I disorders. Results: Three hundred and seventy-three patients had a principal diagnosis of unipolar MDD. One hundred twenty-nine (34.6%) were diagnosed with MDD only, and 244 (65.4%) had MDD and at least one other axis I disorder. Comorbidity was associated with longer duration of index episode, more psychiatric morbidity, and more social and occupational impairment. There was also a significant relationship between increasing number of comorbid axis I disorders and greater psychiatric and psychosocial impairment. In regression analyses, comorbidity burden (i.e., the number of comorbid axis I disorders) showed the strongest relation to psychiatric and psychosocial impairment. Limitations: This is not a random sample of depressed outpatients and, thus, may not be generalizable to all outpatients with depression. Second, Axes II and III comorbidity were not assessed. Conclusions: Comorbidity burden showed the strongest relation to impairment over and above the presence of any particular class of disorders.