Does hypomania distinguish bipolar II disorder from major depressive disorder?

Recent epidemiological/clinical studies have not found clear boundaries between bipolar II disorder (BP-II) and major depressive disorder (MDD), as subsyndromalhypomanic episodes were more common than syndromalhypomania. The aim of the study was to test if hypomania could still be used to split categorically BP-II and MDD.

274 consecutive remitted BP-II and 129 MDD outpatients were interviewed by the Structured Clinical Interview for DSM-IV on the most common symptoms and duration of hypomanic episodes (lasting at least 2 days, having at least 2 symptoms), in a private practice.

As expected by definition, BP-II versus MDD had significantly more episodic hypomanic symptoms. However, MDD had episodes of subsyndromalhypomanic symptoms (median number of symptoms 3). In the entire sample, frequency of episodes of hypomanic symptoms, according to the number of symptoms per episode, was normally, not bimodally,distributed. A grading(r = 0.57, p < 0.001) of the number of episodic hypomanic symptoms was found.

Findings question the splitting of BP-II and MDD based on hypomania, as hypomania (at least as defined by DSM-IV) seems more a dimensional than a categorical disorder.