Issues in Estimating the Course of Rapid-Cycling Bipolar Disorder

To the Editor: We found the article by Christopher D. Schneck, M.D. et al. (1), published in the March 2008 issue of the Journal, to be very informative and useful. The authors presented an excellent real-world naturalistic study, which is difficult to design with regard to methodology. However, we would like to present several inquiries regarding the method and interpretation of the study.

First, we noted that among those patients who completed 1 year of treatment (N=1,191), only 5% (N=58) had four or more episodes at the 1-year follow-up. However, the significant number of dropouts (N=551) may raise concerns, since most of the patients who discontinue therapy are rapid-cycling patients and it is possible that the actual number of these individuals in the study might have been greater than what was observed. It is also possible that the initially enrolled patients and informants could have displayed a recall bias (2), which is reflected by the initial high percentage of rapid-cycling patients. Therefore, at the end of 1 year, the reduction in the percentage of rapid-cycling patients might possibly have been overestimated as a result of these influences.

Second, we would like to suggest that there may have been an influence of comorbidities, such as substance abuse or general medical conditions, which can affect the course of bipolar disorder, including rapid cycling (3) .