Clinical evidence for thyroid dysfunction in patients with seasonal affective disorder.

Of 49 consecutive patients over a 21-mo period satisfying conservative criteria for seasonal affective disorder (SAD), a well-characterized syndrome involving seasonal neurovegetative dysregulation, 17 (35%) were found to have elevated serum TSH compatible with mild primary hypothyroidism (TSH > 4.6 microIU/ml). An additional eight patients (16%) met criteria for "conjectural" hypothyroidism (TSH > 3.5 microIU/ml or exaggerated TSH response to TRH). The frequency of cases with supranormal TSH within the SAD group, both with and without inclusion of the "conjectural" cases, proved statistically significant when compared to that within psychiatric patients not satisfying criteria for SAD (N = 381) or to that within the population at large. The author suggests that SAD may in part represent a reformulation in modern neuropsychiatric terms of a previously noted fall-winter decrement, both biochemical and clinical, among hypothyroid patients.