Rapid cycling bipolar affective disorder. I. Association with grade I hypothyroidism.

Thirty patients with rapid cycling bipolar affective disorder were studied prospectively to assess presence and severity of thyroid hypofunction. Seven (23%) were classified as having grade I hypothyroidism, while 8 (27%) had grade II and 3 (10%) had grade III abnormalities. This prevalence of grade I hypothyroidism is significantly greater than that reported in studies of unselected bipolar patients during long-term treatment with lithium carbonate, although only 63% of this sample of rapid cycling patients was taking lithium carbonate or carbamazepine. The association of rapid cycling with grade I hypothyroidism cannot be accounted for by lithium carbonate use or by the preponderance of women among rapid cycling patients. These findings (1) indicate that hypothyroidism during bipolar illness is a risk factor for the development of rapid cycling, and (2) leads to the hypothesis that a relative central thyroid hormone deficit occurring in bipolar patients predisposes to a rapid cycling course.