A longitudinal mirror-image assessment of morbidity in bipolar disorder

Background Evidence about the clinical course of bipolar disorder is inconsistent and limited. The aim of this study was to assess changes in morbidity in patients with bipolar disorder along a mean follow-up period of 80 months. Methods Based on a mirror-image design, the follow-up period of each patient was divided into two halves. Then, three measures of morbidity — number of affective episodes, time spent ill, and cycle length — were recorded and compared between each half of the follow-up period. Results On average, there was a trend to a smaller amount of time spent with subclinical symptomatology during the second half of the follow-up period. In contrast, there were no differences in terms of number of episodes, time spent with clinical symptoms, or cycle length between the first and second half of the follow-up period. A subgroup analysis identified 21.9% of patients with consistent data of a worsening during follow-up. Conclusions The results suggest that, on average, there is stability or slight improvement of clinical morbidity over the course of BD. Then, worsening of the clinical course may be a feature of a subgroup of patients rather than an inherent characteristic of the disorder. These subgroups or patient profiles could represent an opportunity for further studies to assess clinical, pathophysiologic, and therapeutic features associated with them.