Heterogeneity of depression. Classification of depressive subtypes by longitudinal course

This paper describes the application of prospective longitudinal data from an epidemiological sample of young adults to define subtypes of major depression. Depression was classified on a spectrum from subthreshold manifestation of symptoms and duration at one end, to cases with recurrent episodes of depression meeting duration criteria for major depressive episodes at the other. There was a direct relationship between the severity of depression over the longitudinal course and both duration and recurrence of depressive episodes. The subgroup of depression with recurrence of both brief and longer duration episodes could be discriminated on most of the indicators of validity including symptoms, impairment, family history, and suicide attempts. In light of the young age of this cohort, the strong history of suicide attempts and other complications of depression among the subjects with recurrent depression was striking. These findings underscore the importance of employing course as a classification criterion of depression, and the inclusion of subthreshold episodes of depression in the characterization of course.