SUN-523 Thyroid Storm: A Rare Presentation of HCG Producing Metastatic Choriocarcinoma

Background: The beta subunit of human Chorionic Gonadotropin (hCG) and TSH are very similar and hCG is known to weakly bind the TSH receptor. hCG induced hyperthyroidism has been previously reported as a rare paraneoplastic syndrome in non-seminomatous germ-cell tumors and usually presents with subclinical thyrotoxicosis. We present a noteworthy case of thyroid storm in a patient with hCG producing testicular Choriocarcinoma. Clinical case: A 19-year-old Hispanic man presented to an outside emergency department (ED) with one day of abdominal pain, nausea, recurrent emesis and subjective fever. He had presented to the same ED 9 days prior with similar symptoms which prompted contrasted CT Abdomen/Pelvis demonstrating hepatic masses and a large right testicular mass, suspicious for primary testicular malignancy. On return evaluation, he was noted to have tachycardia with HR 165, mild scleral icterus, tenderness to palpation of right upper quadrant, abdominal pain and a right scrotal mass (5x5 cm). CBC revealed; WBC 12.0 k/uL (n: 4-10.8), AST: 428 u/L (n: 3-34); ALT: 176 u/L (n: 15-41); total bilirubin: 6.3 mg/dL (n: 0.2-1.3), TSH <0.005 uIU/mL (n: 0.4-4.0) and FT4 5.02 ng/dL (n: 0.7-1.4). Clinical scenario was consistent with thyrotoxicosis concerning for thyroid storm (Burch-Wartofsky Point Scale: 50) requiring intensive care for which he was transferred to our institution. Thyroid US revealed increased thyroid vascularity without nodularity. Laboratory workup revealed negative TG Ab, Anti-TPO Ab, TRAb, and TSIG. Conversely, TBG was elevated at 31.2 mcg/ml (n: 13-30). Initial hCG level was obtained as 6,074. After re-testing with dilution was specifically requested, initial hCG was corrected to 6,760,713. Oncologic workup confirmed diagnosis of hCG producing testicular choriocarcinoma with liver and lung metastases. On admission, he was started on oral methimazole and propranolol as well as intravenous steroids which led to marked symptomatic improvement and normalization of FT4 to 1.37 allowing for discontinuation of antithyroid medication on 7th day of hospitalization. He completed 1 cycle of cisplatin/etoposide and experienced marked reduction of his hCG level to 951,460 which correlated with improvement of his TFTs and resolution of his hyperthyroid symptoms. Conclusion: A low threshold of suspicion should be maintained for the possibility of hyperthyroidism in patients with suspected testicular choriocarcinoma, particularly in the context of recent iodinated contrast imaging. If the clinical picture does not support a primary etiology of hyperthyroidism and hCG is not concordantly elevated, re-assessment of hCG by dilution should be considered as hCG assay is also subject to prozone (hook) effect. Hyperthyroidism should be actively managed and closely monitored as response to treatment can be rapid.