Single episode of major depressive disorder. First episode of recurrent mood disorder or distinct subtype of late-onset depression?

Of 687 consecutive inpatients and outpatients with primary major depressive illness, 213 (31%) were categorized as single episode (SE) by DSM-III-R criteria. Systematic evaluation of familial, sociodemographic, temperamental and symptomatological characteristics permitted the nearly equal division of SE into two categories: a. early-onset (< 45 years) "first episode" superimposed on either depressive or hyperthymic temperaments (against a bipolar and unipolar familial background), more severe depression, higher rates of suicide attempts, greater anxiety-somatization and psychotic tendencies, and with the potential for recurrence; b. late-onset (> or = 45 years) isolated episode (against an unipolar familial background) with greater life stressors, pursuing a protracted course with less likelihood of recurrence. In most other respects, early-onset SE was intermediate between recurrent major depression and late-onset SE. The implications of these findings for the now largely abandoned category of "involutional melancholia" are discussed.