Comparison of Rapid-Cycling and Non-Rapid-Cycling Bipolar Disorder Based on Prospective Mood Ratings in 539 Outpatients

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Abstract
To detect risk factors for rapid cycling in bipolar disorder, the authors compared characteristics of rapid-cycling and non-rapid-cycling patients both from a categorical and a dimensional perspective. Outpatients with bipolar I disorder (N=419), bipolar II disorder (N=104), and bipolar disorder not otherwise specified (N=16) were prospectively evaluated with daily mood ratings for 1 year. Subjects were classified as having rapid cycling (defined by the DSM-IV criterion of four or more manic or depressive episodes within 1 year) or not having rapid cycling, and the two groups' demographic and retrospective and prospective illness characteristics were compared. Associated factors were also evaluated in relationship to episode frequency. Patients with rapid cycling (N=206; 38.2%) significantly differed from those without rapid cycling (N=333) with respect to the following independent variables: history of childhood physical and/or sexual abuse, bipolar I disorder subtype, number of lifetime manic or depressive episodes, history of rapid cycling, and history of drug abuse. The prevalence of these characteristics increased progressively with episode frequency. The proportion of women was greater than the proportion of men only among patients with eight or more episodes per year. The average time spent manic/hypomanic increased as a function of episode frequency, but the average time spent depressed was comparable in patients with one episode and in those with more than one episode. Brief episodes were as frequent as full-duration DSM-IV-defined episodes. A number of heterogeneous risk factors were progressively associated with increasing episode frequency. Depression predominated in all bipolar disorder patients, but patients with rapid cycling were more likely to be characterized by manic features. The findings overall suggest that rapid cycling is a dimensional course specifier arbitrarily defined on a continuum of episode frequency.