SEASONAL-VARIATION IN BIPOLAR DISORDER

Background. In patients with bipolar disorder, admissions for manic an d depressive episodes frequently display a seasonal pattern. We examin ed this variation and compared the patterns with the seasonal admissio n rates for schizophrenia. Method. Patients with bipolar disorder or s chizophrenia were identified from the Finnish Hospital Discharge Regis ter of in-patient admissions to all psychiatric hospitals during the y ears 1969-91. They were included in the analysis if the first admissio n had occurred before 30 years of age. A total of 295 bipolar patients were found, and a sample of 295 schizophrenic patients was randomly s elected for comparison. Results. There was no seasonal variation among all hospital admissions for bipolar disorder or schizophrenia. Howeve r. the first admission for a depressive compared with a manic episode of bipolar disorder occurred significantly more often in the autumn (3 3% v. 21% respectively). The peak difference occurred during the week after the autumnal equinox in September. Conclusion. Our findings sugg est that there is no seasonal variation in bipolar disorder, although in some patients the clinical course might be influenced by the autumn , as far as the likelihood of a first admission for depression is conc erned.