Pure alpha subunit-secreting pituitary tumors.

The authors describe six patients with pituitary macroadenomas hypersecreting only the alpha subunit of the glycoprotein hormones. These patients had been previously diagnosed as having "non-functioning chromophobe adenomas." All of the patients had visual field abnormalities and partial hypopituitarism. The elevated serum alpha concentrations showed a variable response to stimulation by thyrotropin-releasing hormone, and could not be suppressed by thyroid hormone administration. Immunological, gel chromatographic, and immunocytochemical studies documented that only the alpha subunit was present. Following pituitary surgery and radiotherapy, serum alpha levels decreased. These patients represent a new subset of functioning pituitary tumors. Determination of alpha subunit concentration is useful in managing some patients with pituitary tumors previously thought to have non-functioning chromophobe adenomas.