Objective: It is generally accepted that one of the most important predictors of recurrence in depressive and bipolar disorders is the number of previous episodes. However, very few studies have considered the individual tendency toward recurrence in analyses of the effect of the number of episodes on the risk of subsequent recurrence in affective disorder.
Method: Frailty models were used to estimate the effect of the number of episodes on the rate of recurrence taking into account the individual frailty toward recurrence. The study base consisted of 406 patients, 186 patients with depressive disorder and 220 patients with bipolar disorder, who were admitted between 1959 and 1963 to the Psychiatric Hospital University of Zurich with an affective episode and followed up to 1997.
Results: The individual rate of subsequent recurrence was found to increase with the number of episodes even when the effect was adjusted for the individual frailty toward recurrence. The effect of episodes was the same in depressive and bipolar disorders and for men and women.
Conclusion: It seems increasingly valid that in depressive and bipolar disorders, the risk of subsequent recurrence increases with the number of episodes.