Choriocarcinoma induced thyrotoxicosis

Paraneoplastic hyperthyroidism, although uncommon, is a known phenomenon in Germ cell tumors. Trophoblastic thyroidian hyperfunction is a complication of Choriocarcinoma. Choriocarcinoma is associated with high levels of Human Chorionic Gonadotropin (HCG). HCG is a glycoprotein produced by the placenta. It is structurally almost identical to Thyroid Stimulating Hormone (TSH). At high levels HCG can stimulate the TSH receptor causing Hyperthyroidism. This is a case of a 25 year old female diagnosed with metastatic Choriocarcinoma and concomitant Hyperthyroidism. After the first cycle of chemotherapy, the concentration of HCG decreased significantly. Simultaneously patient’s thyroid function test values normalized dramatically and the patient became euthyroid. The two known causative mechanisms are, enhanced thyrotropic activity by HCG and the molecular mimicry between HCG and TSH which causes release of Thyroxine from the thyroid gland.