Comorbidity of mood disorders: a longitudinal prospective study.

From the Zurich cohort study (n = 591), the association of major depressive episodes and recurrent brief depression (RBD) with other psychiatric disorders is presented cross-sectionally at age 28 and 30 years, and over ten years (age 20 to 30 years). Longitudinally, the odds ratios of major depression are highest with dysthymia (4.4), generalised anxiety disorder (4.4), panic disorder (2.7), hypomania and agoraphobia (2.6), and social phobia (2.4). There is a significant association with cannabis consumption and smoking. Follow-up data over nine years are available for 41 patients with a major depressive disorder (MDD) and 62 with RBD: approximately 20% of MDD patients did not receive a diagnosis during follow-up. Major depression reoccurred in 32%, became bipolar in 24%, or developed into RBD in 24%. RBD remitted in 41%, reoccurred in 35%, turned into major depression in 22%, and became bipolar in only 7%. Longitudinally, MDD and RBD show a symmetrical diagnostic change in a quarter of the cases. There is no substantial development of MDD or RBD into minor depression or generalised anxiety disorder. Thirteen per cent of those with RBD later developed panic disorder.