Stability of symptoms across major depressive episodes in bipolar disorder

The DSM-IV includes subtypes, or illness specifiers, for major depressive episodes such as atypical and melancholic, which have been suggested to have predictive validity (1, 2). That is, depressive features may be informative about outcome or diagnosis (3). In particular, some investigators have reported that atypical depressive symptoms, most notably reversed neurovegetative symptoms, and melancholic features are more characteristic (and perhaps a hallmark) of bipolar disorder compared to major depressive disorder (MDD) (4-6). This literature makes the implicit, but important, assumption that depressive features are stable across episodes, an assumption rarely examined prospectively in large cohorts. In the only study to examine more than one depressive recurrence, Coryell and colleagues (7) found some stability for psychotic, agitated versus retarded, and ‘endogenous’ depression; this cohort included ~120 subjects with bipolar disorder. Smaller studies in MDD identified modest correlation for neurovegetative symptoms (8), groups of ‘endogenous’ or anxious symptoms (9, 10), melancholia (11), and suicidality (10). To our knowledge, no study has specifically examined stability of these symptoms in bipolar depression, and only one study considered more than one depressive episode. Beyond refining psychiatric nosology, understanding temporal stability may facilitate biological studies by clarifying ‘core’ symptoms of depression in mood disorders. It may also guide clinical practice if certain symptoms such as suicidality demonstrate stability from episode to episode. We therefore examined data from the multicenter Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) cohort study of bipolar disorder, utilizing the subset of individuals with up to three prospectively observed depressive episodes. We attempted to confirm the stability of neurovegetative symptoms and suicidality between episodes and explore the broader stability of mood symptoms.