SUN-564 A Unique Case of Hyperthyroidism Caused by a Primary Mediastinal Tumor

Background: Choriocarcinoma induced hyperthyroidism is a rare entity and usually results in subclinical presentation. Patients with the greatest risk of developing clinical and symptomatic hyperthyroidism are the ones where beta-hCG levels are greater than 200000 mIU/mL. Clinical case: We describe a case of a 27-year-old Hispanic male who presented with weight loss of 40 lbs, fatigue, palpitations, mild dysphagia, and dry cough. His primary provider checked his thyroid function and he was found to have hyperthyroidism. A thyroid uptake and scan showed diffusely increased uptake, 71.5% at 24 hours. He was started on 30 mg methimazole daily and 40 mg propranolol twice daily. Over the next several weeks he also noticed hoarseness, progressively worsening neck swelling and right-sided chest pain. This prompted a chest X-ray, which showed large mediastinal and right hilar grouping of masses with significant narrowing of the left mainstem bronchus and the upper thoracic trachea. An FDG-PET/CT revealed FDG avid multistation conglomerate adenopathy on the neck, in the mediastinum, abdomen and left common iliac region. He had a core needle biopsy of a left supraclavicular mass and pathology was consistent with metastatic primary mediastinal choriocarcinoma. β-hCG level was 3249170 mIU/mL (n<2 mIU/mL). TSH continued to be suppressed at <0.01 µIU/mL (n=0.27-4.2 µIU/mL) and free T4 was 2.5 ng/dL (n=0.8-1.8 ng/dL). It was felt that his hyperthyroidism is due to β-hCG stimulation of his thyroid gland. He was started on etoposide, ifosfamide and cisplatin chemotherapy and underwent 4 cycles. During this time he also remained on methimazole 30 mg daily. 3 weeks after the first chemotherapy cycle his TSH improved to 0.06 µIU/mL and free T4 to 0.78 ng/dL. After completion of his chemotherapy his TSH was 1.99 µIU/mL, free T4 was 1.2 ng/dL and β-hCG was 16 mIU/mL. Conclusions: Our case represents a rare complication of symptomatic hyperthyroidism due to a primary mediastinal choriocarcinoma secreting extreme amount of β-hCG. This case is also unique because the patient’s primary presentation was hyperthyroidism and the cancer diagnosis was made subsequently. This highlights the importance of considering rare etiologies when certain constellations of symptoms are present beyond the classical.