SAT-LB89 Choriocarcinoma Induced Hyperthyroidism: Molecular Mimicry Between HCG and TSH

Introduction: Human chorionic gonadotropin(HCG) induced hyperthyroidism is a rare cause of hyperthyroidism. It is usually seen in conditions with extremely high beta HCG levels like hyperemesis gravidarum, hydatiform moles and germ cell tumors. We present a young male patient who had primary mediastinal choriocarcinoma with widespread lung metastasis and hyperthyroidism. Case: 18-year-old male presented to the emergency department for a fever of 105 F, cough, shortness of breath and night sweats for 9 days. He also reported unintentional weight loss for the past few weeks. Upon presentation, he was tachycardic at 104 beats/min, tachypneic and febrile. Physical examination revealed bibasilar crackles. Thyroid and scrotal examination were unremarkable. Laboratory work was significant for leukocytosis of 18.7 k/cmm, AST: 69 Unit/L, ALT: 60 Unit/L, ALP: 123 unit/L and LDH: 438Unit/L. Chest radiology showed bilateral multiple cannonball lesions with mediastinal and periaortic lymphadenopathy. CT chest, abdomen, and pelvis revealed innumerable diffuse bilateral lung masses, large anterior mediastinal mass, enlarged periaortic and paratracheal lymph nodes. Infectious workup was unremarkable. MRI brain revealed leptomeningeal involvement and vasogenic edema. Ultrasound of testicles revealed bilateral severe microlithiasis. CT guided biopsy of lung mass showed poorly differentiated choriocarcinoma. Treatment was initiated with systemic steroids, bleomycin, and cisplatin. Additional blood work revealed, B-HCG:736,598 mIU/mL, TSH:0.009UIU/ml, free T4:2.95ng/dL and total T3: 292.3ng/Dl. Thyroid radioiodine uptake scan was normal and planar imaging was also normal. Treatment with methimazole was deferred due to the up-trending transaminases and the resolution of tachycardia. Repeat labs after chemotherapy were TSH: 0.005UIU/mL, free T4: 2.04ng/dL, free T3:1.70pg/mL and BHCG: 202,471UIU/mL. Unfortunately, the patient had chemotherapy-resistant choriocarcinoma and succumbed to death after 4 cycles. Discussion: Beta HCG has an intrinsic thyroid-stimulating activity. The HCG -alpha subunit is common to all glycoprotein hormones like follicle-stimulating hormone, luteinizing hormone or thyroid-stimulating hormone. Frankly elevated levels should be treated symptomatically with beta-blockers and/or anti-thyroid drugs. Subclinical hyperthyroidism should be monitored closely. Some patients do not develop hyperthyroidism or a toxic goiter, as it is dependent on the timing of onset of cancer or due to the secondary modifications of HCG that can affect the bioactivity of HCG on the TSH receptor. This case draws our attention to the importance of focusing on the molecular mimicry of the HCG and TSH and management of HCG mediated hyperthyroidism.