Comorbidity burden and its impact on psychosocial morbidity in depressed outpatients

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).

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.

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.

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.

Comorbidity burden showed the strongest relation to impairment over and above the presence of any particular class of disorders.