Free interval duration: Clinical evidence of the primary role of excitement in bipolar disorder

Background: Cyclicity is the essential feature of Bipolar disorder, but the effect of different cycle patterns on the clinical features is poorly understood. Moreover, no studies investigated the relationship between mania and depression inside the manic-depressive cycle. Objective: The aim of this study is to verify the presence of a relationship between the manic and the depressive phase during the course of bipolar disorder Method: 160 consecutive patients with BD type I were recruited and followed for a mean period of 10 years. During the follow-up period, four types of euthymic phases were collected: free intervals present between a depressive and a manic/hypomanic episode (D-M); free intervals present between a manic/hypomanic and a depressive episode (M-D); free intervals present between two depressive episodes (D-D); free intervals present between two manic/hypomanic episodes (M-M). One-way ANOVA using the groups as independent variable and the duration of the free intervals as dependent variables was used. Furthermore, ANOVA was followed by Fisher's Protected Least Significant Difference post-hoc test to measure between-group differences. Results: M-D-free interval phases were shorter than D-M-free intervals. M-D intervals were the shortest ones, the D-D and D-M did not differ, and the M-M were the longest. Conclusion: The strict temporal link between manic and depressive phases supports the idea that the manic-depressive cycle usually begins with a manic episode, and that the subsequent depression is often the consequence of subsiding mania.