Choriocarcinoma presenting with thyrotoxicosis.

We describe a 26-year-old man with metastatic choriocarcinoma who presented with hyperthyroidism associated with elevated β-human chorionic gonadotropin (B-HCG) and respiratory failure secondary to diffuse lung metastasis. After the first cycle of chemotherapy, the concentration of B-HCG dramatically decreased and the patient became euthyroid, allowing us to discontinue antithyroid medications. The patient's hyperthyroidism was caused by stimulation of the thyroid gland by high B-HCG levels, as shown by the marked improvement of the patient's thyroid function panel after chemotherapy.