Thyrotropin-secreting pituitary adenomas.

Normal or elevated thyrotropin (TSH) levels in hyperthyroid patients are characteristic of rare TSH-secreting pituitary adenoma (TSH-oma), which is easily detectable by computed tomographic (CT) scan or magnetic resonance imaging (MRI). Other diagnostic aids are an absent/impaired TSH response to thyrotropin-releasing hormone (TRH), discrepant TSH and alpha-subunit responses to TRH, high sex hormone-binding globulin (SHBG) levels, high alpha-subunit levels, and a high alpha-subunit/TSH molar ratio. Familial studies help rule out thyroid hormone resistance (RTH). Surgical removal of TSH-oma leads to clinical and biochemical remission in most patients. In surgical failures, radiotherapy and octreotide treatment have a high success rate. Undetectable TSH 1 week postsurgery suggests a definitive cure, backed up by tests for cosecreted hormones from the adenoma and dynamic tests of TSH suppression.