THE LONG-TERM STABILITY OF DEPRESSIVE SUBTYPES

Objective: This study used the concept of diagnostic stability to exam ine the validity of three subtypes of major depression. Method: Patien ts with major depressive disorder (N=424) were assigned baseline diagn oses according to structured interviews and the Research Diagnostic Cr iteria. Follow-up evaluations took place at 6-month intervals over the next 5 years and annually for an additional 3 years. During. this per iod 424, 246, 163, and 96 of the patients who had recovered from the i ndex episode had one, two, three, and four recurrences, respectively, of major depressive disorder. The kappa statistic was used to quantify the likelihood that patients with the psychotic, agitated/retarded, o r endogenous subtype of depression in a given episode would again mani fest that subtype in subsequent episodes. Results: The psychotic subty pe showed the most enduring diagnostic stability across multiple subse quent episodes. Evert after three intervening episodes, patients with baseline psychotic major depression were five times more likely to dev elop a psychotic depression than were other depressed patients. For al l three subtypes, diagnostic stability was greater for contiguous epis odes than for noncontiguous episodes. Psychotic, agitated/retarded and endogenous subtypes showed significant stability after control for th e bipolar/unipolar and primary/secondary distinctions. The endogenous subtype was stable among patients with primary depression but not amon g those with secondary depression. Conclusions: The psychotic subtype was the most valid of the subtypes tested from the perspective of diag nostic stability. The fact that stability across adjacent episodes exc eeded stability across more distantly spaced episodes may reflect stat e-dependent determinants, and these are likely to vary by subtype.