A RARE CASE OF A THYROTROPIN-SECRETING PITUITARY-TUMOR WHICH RESPONDED TO METHIMAZOLE

A 52-year-old Japanese male complained of palpitations and excessive s weating. He showed evidence of hyperthyroidism, but without suppressio n of the serum thyroid-stimulating hormone (TSH). On admission, the se rum level of the alpha-subunit of TSI-I was elevated, but tests for th yroid autoantibodies were negative. The TSH response to thyrotropin-re leasing hormone (TRW) was blunted. Imaging studies revealed a pituitar y tumor 2 cm in diameter. Administration of methimazole lowered the se rum levels of thyroid hormones, and elevated the serum level of TSH. T hese findings led to the diagnosis of a thyrotropin-secreting pituitar y tumor. Immunohistochemical analysis and electron microscopic finding s verified the diagnosis.