THE ROLE AND CLINICAL-SIGNIFICANCE OF SUBSYNDROMAL DEPRESSIVE SYMPTOMS (SSD) IN UNIPOLAR MAJOR DEPRESSIVE DISORDER

Analyses conducted in 10 526 community respondents investigated by the NIMH Epidemiological Catchment Area (EGA) Program, revealed the 1-mon th point prevalence of depressive symptoms and disorders in the genera l population, at the first ECA interview (Wave 1) to be 10%, as follow s: 2.3% major depressive disorder (MDD); 2.3% dysthymic disorder (DD); 1.5% minor depressive disorder (MinD); and 3.9% subsyndromal depressi ve symptoms (SSD, defined as two or more depressive symptoms beneath t he diagnostic threshold of MinD, DD or MDD). There appears to be two c lasses of SSD in this community sample: first, SSD, which occurred as an integral component of the course of unipolar major depressive disor der (MDD); and, second, SSD occurring spontaneously in non-unipolar de pressed community subjects. In the first instance, SSD was frequently prodromal to episodes of MinD or MDD or residual to resolving episodes . Analyses also support the conclusion that SSD is a clinically signif icant, interepisode, depressive subtype of unipolar MDD, since SSD is associated with harmful dysfunction in five of six measures of adverse outcome, has a significantly increased prevalence of past histories o f major depressive episodes, and an elevated lifetime prevalence of su icide attempts. Comparison of subsyndromal depressive symptomatology o r depressive disorder diagnoses at Wave 1 with diagnoses obtained, 1 y ear later, at the Wave 2 interview, confirm the persistent and chronic nature of depression in this large representative sample of community respondents, in which 71% of subjects with depressive symptoms or dis orders at Wave 1 continued to be symptomatic at Wave 2. In addition, s ubjects experienced a surprising degree of change in depressive sympto m and disorder diagnoses during the I-year observational window betwee n Wave 1 and Wave 2, in which a remarkable percentage of individuals, who began the year in a depressive symptom or disorder diagnostic cate gory, ended the year in another. This has led us to hypothesize that t he typical clinical picture of unipolar MDD is dynamic and pleomorphic in nature, characterized by substantial symptomatic fluidity, in whic h patients frequently change diagnoses from one depressive subtype to another during their course of illness. (C) 1997 Elsevier Science B.V.