Hyperthyroidism due to a TSH secreting pituitary adenoma: case report, treatment and evidence for adenoma TSH by morphological and cell culture studies.

A 36-year-old woman with recurrent hyperthyroidism, inappropriately elevated serum TSH, and an 8 mm pituitary microadenoma is described. Transsphenoidal adenomectomy rapidly reduced serum TSH to normal and restored the euthyroid state with retention of other anterior pituitary functions. Tissue removed at operation was examined by light and electron microscopy and cell culture. The tissue was neoplastic, composed of irregular often elongated cells which immunostrained positively only with antisera to beta-TSH. The cells contained small granules (100-170 nm) usually along the cell membrane. In cell culture TSH alone was secreted and the rate of secretion declined with time. We conclude that the patient had a TSH secreting microadenoma as a cause of her hyperthyroidism.