Thyroid storm as an early presentation of hCG-producing metastatic choriocarcinoma: a case report and review of the literature.

Human chorionic gonadotropin (hCG)-induced hyperthyroidism has been previously reported as a rare paraneoplastic syndrome in non-seminomatous germ cell tumours and usually presents with mild symptoms or subclinical thyrotoxicosis. We present a case of a young adult man who consulted with abdominal pain, nausea and emesis. On admission, he was found to be tachycardic, febrile, anxious and with icteric sclera and tenderness to palpation in the right upper abdomen. A right scrotal mass was also noted. Initial studies revealed transaminitis, hyperbilirubinaemia, suppressed thyroid-stimulating hormone and elevated free T4. Scrotal biopsy confirmed diagnosis of testicular choriocarcinoma with an elevated hCG level of 6074 mIU/mL, which was corrected to 6 760 713 mIU/mL when reassessed with dilution. The clinical scenario reflected hCG-induced thyrotoxicosis concerning for thyroid storm. Euthyroid state was restored after initiation of chemotherapy and a short course of methimazole. Unfortunately, the patient passed away due to progression of his malignant disease. This case suggests that when choriocarcinoma is suspected, the use of iodinated contrast agents should be limited to avoid precipitation of thyroid storm or worsening of hCG-induced hyperthyroidism. Moreover, if the clinical picture does not support a primary aetiology of hyperthyroidism and hCG is not concordantly elevated, reassessment of hCG by dilution should be considered as hCG assays are subject to prozone effect.