Background: Research on the long-term course of major depressive disorder (MDD) is hindered by the absence of established course criteria and by idiosyncratic definitions of chronicity. The aims of this study were to derive an empirical index of MDD course, to examine its predictive validity, and to identify the adulthood outcomes associated with a chronic course.
Method: Indicators for a MDD course factor were rationally selected and subjected to principal components (PCA) and confirmatory factor analyses (CFA) among 426 subjects with a lifetime history of MDD by age 30. Scores on the index prior to age 19 were examined as predictors of course from age 19 to 30. Associations between the index and outcomes of interest at age 30 were examined.
Results: Three indicators loaded highly on a chronic course index and displayed adequate internal consistency: early onset age, number of episodes, and duration of ill time. Predictive validity of the index was supported. A more chronic course was associated with greater symptom severity, greater likelihood of treatment utilization, and greater psychosocial impairment in multiple domains. Treatment utilization interacted with chronicity to predict relatively few outcomes and did not reduce the negative impact of a chronic course.
Conclusions: The course of MDD through early adulthood is best represented by a composite of early onset age, number of episodes, and duration of ill time. A chronic course through early adulthood is associated with numerous indicators of psychosocial impairment. Mental health treatment utilization in a naturalistic setting does not appear to reduce the negative impact of chronic MDD.