FRI503 HCG-induced And Autoimmune Hyperthyroidism In A Male Patient With HCG Secreting Germ Cell Tumor

Disclosure: A.H. Mohamed: None. M. Basina: None. Background: While Graves’ disease is the most common cause of hyperthyroidism, other rare causes include HCG secreting germ cell tumors. We describe a hyperthyroidism case with metastatic HCG secreting germ tumor and Graves’ disease. Case: 34 years old smoker male presented in 2016 with weakness and hypokalemia 2.7 mmol/L with concerns of paroxysmal periodic paralysis and was found to have hyperthyroidism consistent with Graves’ disease per work up (suppressed TSH <0.01- uIU/ml (ref 0.27-4.2 uIU/ml), elevated FT4 4.08 ng/dl (ref 0.93-1.7 ng/dl), elevated Free T3 15.0 (ref 2.3 - 4.0 pg/ml), and (thyroid stimulating immunoglobulin (TSI) 354 (ref 0 - 139 %). He was started on methimazole 20 mg that he did not use and lost follow up. In May 2022, he presented with expressive aphasia and seizures along with 4 months of right scrotal swelling, generalized lymphadenopathy, and hemoptysis episodes. He had intermittent palpitations, 30 Ibs weight loss and eye bulging. On exam he was tachycardic 120 bpm, enlarged thyroid, brisk reflexes and mild tremors. His eye exam was significant for stare, lid lag, proptosis and bilateral lid edema. His labs were remarkable for suppressed TSH <0.01 uIU/ml, FT4 >7.7 ng/dl , Total T3 394 ng/dl (80 - 200 ng/dl)Thyrotropin receptor antibodies (TRAb) 29 IU/L (ref 0-1.75 IU/L), TSI 4.8 (ref <1.3 index), Thyroglobulin Ab 5.8 IU/ml (ref <4IU/ml), TPO-Ab >900 (ref <9.0) and HCG >1,000,000 (ref <2mIU/ml). Thyroid US showed diffuse heterogeneous enlargement of the thyroid with increased vascularity and without a discrete well-defined nodule. His lymphadenopathy work revealed high grade stage III C non-seminomatous mixed germ tumors (60% teratoma and 40% choriocarcinoma) with metastasis to brain, lungs, liver, spine, iliac and sacral bones. He was started on methimazole (MMI) 20 mg TID, propranolol 40 mg TID, dexamethasone 2 mg q6hrs and chemotherapy. His thyroid labs improved in 3 days to FT4 2.83 ng/dl and TT3 93 ng/dl while TSH and HCG were unchanged. He was discharged on MMI 25 mg daily. Over 3 months, he subsequently underwent right orchiectomy, cyber knife radiation of the brain metastatic lesions and 4 chemotherapy cycles. His HCG levels fluctuated (1,000,000->3980-> 120,181) as well thyroid function test (TSH <0.01-> 5.1->0.01 uIU/ml, FT4 1.02->0.65->5.7 ng/dl and TSI 6.4 ). He required multiple methimazole adjustments. Discussion: Co-occurrence of HCG secreting germ tumors and Graves’ hyperthyroidism is rare. HCG can bind TSH receptors and in high levels has thyrotropic effects. The interplay between HCG thyrotropic effects and thyroid autoimmunity can be challenging and use of both binding and functional bioassays maybe helpful. Close thyroid function monitoring and frequent adjustment of thioamides are needed as patients undergo treatment of the primary HCG source as well as long term follow up. Presentation: Friday, June 16, 2023