Course and outcome of depressive episodes: comparison between bipolar, unipolar and subthreshold depression

Abstract

It is pragmatically important to know the comparative prognoses of bipolar, unipolar and subthreshold depressions after they present to clinical attention. Previous studies focusing on bipolar and/or unipolar depressions have questionable generalizability because of overrepresentation of inpatients and/or refractory patients, and no study has yet focused on the length of subthreshold depression. The Group for Longitudinal Affective Disorders Study (GLADS) in Japan is conducting a prospective, serial follow-up study of broadly defined mood disorder patients, who had not received treatment for their index episode before study entry. The median time to recovery for bipolar depression was 2.0 months (95%CI: 0.9-3.1), that for unipolar depression 3.0 (2.5-3.6), and that for subthreshold depression 3.2 (0-12.3). Survival analyses revealed no statistically significant difference among the three. Neither was the total time unwell significantly different among the three: on average, these patients were symptomatic with two or more significant affective symptoms for 9.5 (8.0-10.9) months out of the initial 24 months of follow-up. The bipolar depressed patients tended to present with graver functional impairment at intake, but thereafter there was no statistically significant difference in the global functioning of these three diagnostic subgroups. In our sample, patients with depressive disorder not otherwise specified appeared to suffer both symptomatologically and functionally as much as patients with major mood disorders.