Delineating the longitudinal structure of depressive illness: Beyond clinical subtypes and duration thresholds

Through the use of polysomnographic, epidemiologic, and prospective clinica l follow-up studies, the authors document that the course of major depressi ve disorder (MDD) is expressed by fluctuating symptoms in which depressive subtypes included in official diagnostic systems do not represent discrete disorders, but are stages along a dimensional continuum of symptomatic seve rity. Depressive symptoms at the major, minor, dysthymic or otherwise subth reshold levels are all integral components of the longitudinal clinical str ucture of MDD with each symptom level representing a different phase of ill ness intensity, activity and severity. Detailed analyses indicate that pati ents are symptomatic 60% of the time, much of it at the minor, dysthymic or subthreshold level. The symptomatic phases of illness activity are intersp ersed sporadically with inactive phases, when patients are asymptomatic. Th ese findings are pertinent to both clinical cohorts and community-based epi demiologic samples. Each level of depressive symptom severity is associated with significant psychosocial impairment; such impairment increases progre ssively with each stepwise increment in symptom severity, When patients are asymptomatic their psychosocial functioning returns to good or very good l evels. Residual subthreshold symptoms in the course of MDD are associated w ith high risk for early episode relapse and a significantly more chronic co urse of illness, Asymptomatic recovery from MDD is associated with signific ant delays in episode relapse and recurrence and a more benign course of il lness. We submit that, as in the case of chronic medical conditions, the go al of treating unipolar depressive illness should optimally be to return th e patient to as asymptomatic a level as is feasible by all available therap eutic means.