Thyrotropin-induced hyperthyroidism: evidence for a common progenitor stem cell

A 36-year-old woman with hyperthyroidism, elevated blood thyroid-stimulating hormone (TSH) and alpha-subunit levels, amenorrhea, hyperprolactinemia and no evidence of acromegaly, was found to have a pituitary adenoma containing TSH, alpha-subunit and growth hormone by immunohistochemistry. Preoperative testing revealed elevated TSH and alpha-subunit with no response to thyrotropin-releasing hormone (TRH) but a normal response in prolactin to TRH. Culture of the pituitary cells showed release of TSH, alpha-subunit and prolactin. In vitro, TRH failed to cause TSH discharge; however, it increased prolactin concentrations in the culture medium. Triiodothyronine, added to the pituitary cell culture, resulted in no inhibition of TSH and prolactin discharge. By electron microscopy, the adenoma cells showed features of thyrotrophs. However, some adenoma cells contained fibrous bodies characteristic of some growth hormone cell tumors and acidophil stem cell adenomas, suggesting that the adenoma originated in a common progenitor cell.