Background: Patients with bipolar disorder (BD) differ in their relative predominance of types of episodes, yielding predominant polarity, which has important treatment implications. However, few prospective studies of predominant polarity exist.
Methods: In the Jorvi Bipolar Study (JoBS), a regionally representative cohort of 191 BD I and BD II in- and outpatients was followed for five years using life-chart methodology. Differences between depressive (DP), manic (MP), and no predominant polarity (NP) groups were examined regarding time ill, incidence of suicide attempts, and comorbidity.
Results: At baseline, 16% of patients had MP, 36% DP, and 48% NP. During the follow-up the MP group spent significantly more time euthymic, less time in major depressive episodes, and more time in manic states than the DP and NP groups. The MP group had significantly lower incidence of suicide attempts than the DP and NP group, lower prevalence of comorbid anxiety disorders but more psychotic symptoms lifetime and more often (hypo)manic first phase of the illness than the DP group. Classification of predominant polarity was influenced by the timeframe used.
Limitations: The retrospective counting of former phases is vulnerable to recall bias. Assignment of dominant polarity may necessitate a sufficient number of illness phases.
Conclusions: Predominant polarity has predictive value in predicting group differences in course of illness, but individual patients' classification may change over time. Patients with manic polarity may represent a more distinct subgroup than the two others regarding illness course, suicide attempts, and psychiatric comorbidity.
Keywords: Bipolar disorder; Outcome; Predominant polarity; Suicide attempts.
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