A Million Reasons for Hyperthyroidism. Reporting a Case of Thyrotoxicosis in a Setting of Metastatic Choriocarcinoma

Background: Human chorionic gonadotropin (hCG) induced transient hyperthyroidism is often seen during pregnancy. Other rare causes of beta hCG induced hyperthyroidism include trophoblastic tumors (hydatidiform mole and choriocarcinoma) and in men, germ cell tumors. The mechanism for hCG induced thyrotoxicosis lies in the structural similarity between TSH and hCG molecules leading to the direct stimulation of the TSH receptors. In regard to treatment, while gestational thyrotoxicosis is usually mild, self-limited and does not need medications, the hyperthyroidism of trophoblastic tumors may require antithyroid medications in addition to treating the underlying tumor. Thionamide use is reserved for moderate to severe cases of hyperthyroidism and for presurgical optimization. In our case report, we present a 22-year-old African American female with choriocarcinoma induced thyrotoxicosis requiring thionamide therapy. Clinical Case: A 22-year-old African American female presented to our emergency room after a witnessed generalized tonic-clonic seizure. Her brain CT scan showed a 4 CM mass concerning for AVM malformation with a subsequent brain MRI confirming parenchymal hematoma with surrounding vasogenic edema. Past medical history was significant for molar pregnancy managed with dilation and curettage followed by laparotomy to remove the pelvic mass. Given her history of molar pregnancy, pelvic ultrasound was performed which showed complex heterologous structure of uterine origin concerning for malignancy. Additional imaging studies of the lung, brain, abdomen and pelvis were performed, which showed possible metastasis to the lung, adnexa, and to the brain. Her clinical exam showed heart rate of 130 beats/min with a normal rhythm, fine tremors, aphasia, and a decrease grip strength in her right upper extremity. Her thyroid gland was slightly enlarged with no tenderness. Laboratory tests showed hCG of >1,000,000 mIU/mL, TSH of < 0.01mcU/mL, free T4 of 5.1ng/dL. Her TPO and TSI were negative. With a diagnosis of hyperthyroidism due to trophoblastic disease, she was treated with methimazole and propranolol resulting in rapid clinical and biochemical improvement. Later, left frontal craniotomy and hematoma evacuation was performed with histology confirming the diagnosis of metastatic choriocarcinoma. She was later transferred to a specialized center where she received chemotherapy. Her hCG subsequently dropped down to 699 mIU/mL. Conclusion: We report a rare case of metastatic choriocarcinoma causing symptomatic hyperthyroidism. The diagnosis is made by excluding other common causes of hyperthyroidism and it should be considered in females of childbearing age. Methimazole is an effective agent to control the hyperthyroidism while waiting for treatment of the underlying cancer.