The course of bipolar II disorder can follow several distinct trajectories, with a major depressive episode (MDE) being the most common presenting feature, a study of Japanese patients suggests.
The findings highlight the heterogeneity of the disorder in clinical practice, say Akeo Kurumaji and co-authors, from Tokyo Medical and Dental University Graduate School, in the Journal of Affective Disorders.
Kurumaji’s group recruited 128 consecutive individuals who were admitted to hospital with a diagnosis of bipolar II disorder. Based on reports by patients and their family members, patients were divided into four groups according to the nature of their first-ever initial mood disorder: MDE (n=91), hypomanic episode (n=18), dysthymic disorder (n=8) or cyclothymic disorder (n=11).
There were several important differences among the groups, report Kurumaji et al. Patients in the cyclothymia group were significantly younger, on average, than those in the MDE group, at 42.0 versus 47.7 years, and had a much earlier age at onset of mood disorder, at 23.5 versus 37.1 years.
The cyclothymia group also had a significantly higher rate of suicidal behaviours, at 72.3%, versus 22.2%, 34.4% and 62.5% in the hypomanic, MDE and dysthymic groups, respectively.
Among patients whose first mood disorder was a MDE, 44 patients experienced a first hypomanic episode after just one MDE, 19 after two MDEs, 17 after three and 11 after more than three MDEs.
A first hypomanic episode most commonly occurred within 1 year of the initial MDE; however, there was a wide distribution in the interval between first MDE and first hypomanic episode, with more than 15 years elapsing in several patients.
Interestingly, three-quarters of patients were taking antidepressant medication when they developed their first hypomanic episode.
Also, around 23% of patients developed a comorbid psychiatric illness after the onset of their mood disorder; anxiety disorder was the most prevalent comorbidity, followed by alcohol-related disorders, personality disorders, somatoform disorders and eating disorders.
And around 33% of patients had a psychiatric diagnosis that preceded the onset of the mood disorder; these were most often anxiety disorders, adjustment disorders and eating disorders.
The researchers summarise that MDE is the most common first mood episode in patients with bipolar II disorder, reported by around 70% of patients in this Japanese sample. The first episode of hypomania emerged after the first MDE in around half of the cohort, most often within 1 year, while patients are typically taking antidepressant medication.
These observations suggest that “special attention be paid to the emergence of the hypomanic episode during the clinical treatment of the first episode of the major depressive disorder, with the accurate assessment of the physiological effects of the treatment”, the researchers write.
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