Hyperthyroidism due to thyrotropin-secreting pituitary tumors. Diagnostic and therapeutic considerations.

Hyperthyroidism may be caused by the inappropriate secretion of thyroid-stimulating hormone (TSH) from a pituitary tumor. Of 33 reported cases, 17 have occurred in women and 16 have occurred in men. All patients had large tumors, and secretion of a second hormone (growth hormone or prolactin) has been common. Diagnosis requires the detection of TSH in the serum when patients are clinically and biochemically hyperthyroid. Ancillary tests supporting the diagnosis include an alpha-subunit to TSH molar ratio greater than 1.0, an absent TSH response to protirelin, suppression of serum TSH (but not alpha-subunit) by glucocorticoids, and a lack of suppression of serum TSH by dopaminergic agonists. Successful treatment of this disorder requires pituitary surgery and/or pituitary irradiation.