Choriogonadotropin-mediated thyrotoxicosis in a man.

A 38-year-old man with a metastatic gonadotropin-secreting tumor of unknown primary origin presented with both clinical and biochemical findings of hyperthyroidism in association with markedly increased concentrations of human choriogonadotropin (hCG) in plasma. After chemotherapy, the concentrations of both hCG and free thyroxin decreased and the patient became euthyroid. We discuss the rare occurrence of this presumably hCG-driven hyperthyroidism in men and compare it with the relatively more common eumetabolic hyperthyroidism associated with choriocarcinoma in women.