Objectives: Significant questions remain regarding both the incidence patterns of mood episodes in adolescents and young adults from the community and the conversion rate from unipolar to bipolar disorders. We addressed these issues by examining data from a prospective longitudinal community study to (i) determine the cumulative incidence of mood episodes and disorders in the first three decades of life; (ii) determine the risk for first onset of depression among individuals with a previous history of hypomanic/manic episodes and vice versa; and (iii) determine the clinical and treatment characteristics of these subjects.
Methods: Using the Munich-Composite International Diagnostic Interview, clinically trained interviewers assessed mood episodes and mental disorders in 3,021 community subjects (aged 14–24 at baseline and 21–34 at third follow-up).
Results: The estimated cumulative incidence at age 33 was 2.9% for manic, 4.0% for hypomanic, 29.4% for major depressive, and 19.0% for minor depressive episodes; overall, 26.0% had unipolar major depression, 4.0% bipolar depression, 1.5% unipolar mania, and 3.6% unipolar hypomania (no major depression). Overall, 0.6% and 1.8% had unipolar mania or hypomania, respectively, without indication for even minor depression. A total of 3.6% of the initial unipolar major depression cases subsequently developed (hypo)mania, with particularly high rates in adolescent onset depression (< 17 years: 9%). A total of 49.6% of the initial unipolar mania cases subsequently developed major depression and 75.6% major or minor depression. While bipolar cases had more adverse clinical and course depression characteristics and higher treatment rates than unipolar depressed cases, bipolar cases did not significantly differ in mania characteristics from unipolar mania cases.
Conclusions: Unipolar and bipolar mood disorders are more frequent than previously thought in adolescence and young adulthood, a time period when both the recognition and the intervention rates by the healthcare system are rather low. ‘Conversion’ to bipolar disorder is limited in initial unipolar depression, but common in initial unipolar mania. The remaining unipolar mania cases appear to be significant in terms of clinical and course characteristics and thus require more research attention to replicate these findings.