Primary hypothyroidism-associated TSH-secreting pituitary adenoma hyperplasia presenting as a bleeding nasal mass and extremely elevated TSH level

A 41-year-old male with primary hypothyroidism and a huge TSH-secreting pit uitary tumor presented with a bleeding nasal mass that was initially misdia gnosed as a paraganglioma. Other unique features of the case include lack o f complaints related to hypothyroidism, an extremely elevated TSH level of 3474 mU/l, and a low prolactin level. The presence of primary hypothyroidis m made differentiating TSH-secreting pituitary adenoma from secondary thyro troph hyperplasia difficult. a low molar ratio of a-subunit to TSH on prese ntation, together with normalization of TSH level and a 50% reduction in th e size of the tumor after 6 weeks of thyroxine replacement therapy, suggest ed the presence of thyrotroph hyperplasia. However, the lack of further dec rease in the size of the tumor that was associated with increased metabolic activity on 18-FDG PET scan, intense uptake on octreotide scan, and an ele vated cr-subunit to TSH molar ratio despite the normalization of free T4 an d TSH levels for 16 months suggested the coexistence of thyrotroph adenoma. Together, the findings support the view that thyrotroph adenoma/irreversib le hyperplasia can result from long standing primary hypothyroidism. (C) 19 99, Editrice Kurtis.