[Hyperthyroidism caused by TSH producing hypophyseal adenoma].

Thyrotropin (TSH-)producing adenomas of the anterior pituitary gland are the least frequently encountered ones and constitute a very rare cause of hyperthyroidism. The case is presented of a 58 year old male patient with a well-known history of hyperthyroidism over a period of at least 9 years growing goiter. Despite different forms of medical treatment he presented a constant clinical pattern consisting of restlessness and paroxysmal tachycardial atrial fibrillation. Laboratory findings revealed elevated levels of circulating thyroid hormones despite inadequately high levels of TSH. MRI scan revealed an adenoma of the pituitary measuring 9 mm in diameter. After microsurgery, consisting of transphenoidal resection of the tumor, the patient recorded no clinical symptoms. Histological examination revealed positive immunohistochemical staining, with antibodies to TSH, but a negative reaction against the GH, PRL, FSH, LH and ACTH hormone antibodies. Moreover, the levels of circulating hormones (GH, PRL, FSH, LH and ACTH) were normal. TSH-alpha subunits were not elevated. Before the correct diagnosis was reached, this patient was treated for nine years with antithyroid drugs. Five months after the operation the patient showed normal values of circulating thyroid hormones and TSH and thus no thyroid-specific medication was necessary.