Does subclinical hypothyroidism predispose to tricyclic-induced rapid mood cycles?

A 24-year-old woman with a unipolar depression had an augmented thyroid-stimulating hormone response to thyrotropin-releasing hormone (TRH), suggesting subclinical hypothyroidism. Desipramine produced rapid cycling between depression and hypomania. After discontinuation of the desipramine she was successfully treated with lithium and thyroid hormone replacement. We discuss the possible role of hypothyroidism in the etiology of tricyclic-induced rapid mood cycling, and suggest that the TRH test may help identify depressed patients predisposed to rapid mood cycling on tricyclics. The possibility that such patients respond to lithium and/or thyroid hormone replacement needs to be further investigated.