SAT-268 Thyrotropin Secreting Pituitary Adenoma Initially Misdiagnosed as Primary Hyperthyroidism in a Taiwanese Man

Background:TSH (Thyrotropin) secreting pituitary adenoma (TSHoma) account for less than 1% of all causes of hyperthyroidism and 1% of all functioning pituitary tumors. Definite diagnosis and treatment of TSHoma are clinical challenges in practice. Here we report laboratory data, imaging findings, endocrine dynamic test, and treatment outcomes in a 50-year-old Taiwanese man with pituitary plurihormonal adenoma secreting TSH and LH. Clinical case:The patient was initially diagnosed as goiter with primary hyperthyroidism and DM while medical check-up by primary care physician in 2014. He had no significant hyperthyroidism symptoms and signs except goiter and mild palpitation. He received propylthiouracil and Metformin. Two years later, he visited to Endocrinologist’s clinic for poor glycemic control. Central hyperthyroidism was diagnosed due to measurable TSH level in the presence of increased serum thyroid hormone level. Moreover sella MRI revealed left sided pituitary lesion. He was referred to Taipei Veteran General Hospital for further management. There was no family history of thyroid disease. Physical examination was not remarkable except diffuse grade 3 goiter and tachycardia (HR 100~115 bpm). Follow up laboratory data showed TSH 4.89; range 0.4~4.0 uIU/ml, free T4: 3.05; range 0.9~1.8 ng/dl, T4: 16.02; range 4.50~12.50 μg/dl, T3: 249; range 58~159 ng/dl, free T3: 8.0; range 2.3~4.3 pg/ml. Two times of TRH stimulation test showed blunted TSH response. Normal limit of thyroid autoantibodies level were found. Thyroid sonography revealed heterogenous echogenicity with increased size and vascularity of both lobes. I-131 uptake was homogenous uptake (94%). Other pituitary hormones level were within normal limit except mild elevation of testosterone 12.69 ng/ml. Sella MRI with contrast showed macroadenoma (size 10x10x7.6 mm) at left pituitary gland. Taken together, he was diagnosed as central hyperthyroidism related to left sided pituitary macroadenoma. Surgery was performed after one year of definite diagnosis due to personal reason. TSH level returned to normal ranges (0.799 uIU/ml) in 1(st) post operative day. Histologically, the pituitary mass was compatible with plurihormonal adenoma and immunohistochemistry showed positivity for TSH (4+) and LH (3+). Post operative condition was well. Antithyroid agent was discontinued after operation. His blood glucose became well controlled after operation. Clinical lessons:A biochemical hallmark of TSHoma is an escape of TSH from the feedback loop that is detectable TSH levels in the presence of increased serum thyroid hormone level. Diagnosis of TSHoma was frequently unrecognized and thus much delayed despite its relatively straightforward. Physician should keep in mind that the importance interpretation of simple laboratory tests to avoid delay diagnosis and unnecessary treatments.