SAT-261 Thyroid Stimulating Hormone-Secreting Pituitary Macroadenoma and Papillary Thyroid Cancer in a 55-Year-Old Male: A Case Report

Background: Thyroid-Stimulating Hormone Secreting Pituitary Adenoma (TSHoma) is a rare Endocrinologic finding occurring in 0.5–3% of all pituitary adenomas, and is even rarer to find it coexisting with differentiated thyroid cancer. Clinical Case: A 55-year-old male consulted last 2012 for palpitations and resting tachycardia. Initial tests revealed an ECG of sinus tachycardia, normal electrolytes and TSH 3.16 uIU/mL (0.27–4.2) and FT4 66 pmol/mL (12–22). He was referred to an Endocrinologist where thyroid ultrasound was done revealing bilaterally enlarged thyroid lobes with diffuse thyroid parenchymal changes, and a thyroid scan consistent with Graves’ Disease. He was started on methimazole and beta-blockers. Persistently elevated FT4 and a non-suppressed TSH prompted work-up for secondary hyperthyroidism. Pituitary MRI revealed a sellar mass measuring 3.4cm x 2.7cm x 2.6cm, noted to be compressing the left side of the optic chiasm and prechiasmatic left optic nerve laterally. The consideration was pituitary macroadenoma. He underwent trans-sphenoidal surgery but operative technique only involved near total excision of the adenoma due to proximity of the mass to the pre-chiasmatic left optic nerve. The tumor was reduced to 2.8cm x 1.6cm x 1.5cm. Histopathologic diagnosis and immuno-histochemical staining revealed pituitary tumor cells reactive to TSH but non-reactive to FSH, LH and GH. He eventually underwent intensity-modulated radiation therapy (IMRT) which reduced the tumor size, but did not obliterate the tumor. His thyroid function tests persistently revealed elevated TSH and FT4 levels. Last January 2019, he manifested with an enlarged anterior neck mass. An ultrasound revealed thyromegaly with multiple nodules, largest at 1.4cm with multiple sub-centimeter nodules, mostly complex and solid in description. He underwent total thyroidectomy. Histopathology results revealed Papillary Thyroid Cancer with no extracapsular or lymphovascular invasion. He was scheduled for radioactive iodine at 100mci a month after. His I-131 whole body scan revealed foci of residual thyroid tissue but without distant mestastases. He is currently on levothyroxine at 225mcg daily therapy and advised annual cranial MRI readings which mostly showed a stable pituitary tumor. Conclusion: This is a case of TSHoma, S/P trans-sphenoidal surgery and intensity modulated radiation therapy with significant tumor residuals that eventually led to the development of Papillary Thyroid Cancer and subsequent total thyroidectomy and radioactive iodine administration. He is now on frequent tumor monitoring and levothyroxine suppression dose. Reference: P. Beck-Peccoz, A. Lania, A. Beckers, K. Chatterjee d, J.-L. Wemeau. 2013 European Thyroid Association Guidelines for the Diagnosis and Treatment of Thyrotropin-Secreting Pituitary Tumors. Eur Thyroid J 2013;2:76–82.