Severe hyperthyroidism due to neoplastic TSH hypersecretion in an old man.

A case is reported of neoplastic TSH hypersecretion in a 62-year-old man with severe hyperthyroidism and cardiovascular disease. He had been known to be hyperthyroid for 14 yr, and had been treated by thyreostatic drugs and subtotal thyroidectomy without satisfactory results. When he was referred to our Center, he was frankly hyperthyroid with both TSH (14 microU/ml) and thyroid hormone serum levels (TT4 24 micrograms/dl, TT3 370 ng/dl, FT41 7.9) above the normal range. alpha-subunit serum level was markedly increased (7.2 ng/ml), while beta-subunit was only 0.3 ng/ml. Skull X-ray showed an enlarged sella turcica with destruction of the dorsum and an intrasellar tumor was visualized on conventional and computer tomography. TSH response was absent after TRH and domperidone, while TSH serum levels decreased by 25% after bromocriptine. Methimazole therapy temporarily decreased serum thyroid hormones to normal levels, while TSH levels rose to 34 microU/ml, thus indicating that pituitary-thyroid feed-back was maintained at a higher set point. Surgical attempt failed because of cardiac problems during anesthesia. Radiotherapy plus methimazole was begun and TSH serum levels first increased markedly, up to 140 microU/ml, and then progressively decreased without reaching normal values. After methimazole withdrawal hyperthyroidism recurred.