Hyperthyroidism caused by a TSH-secreting pituitary adenoma

Elevated levels of free triiodothyronine (fT3) of 8.8 ng/dl (normal range 2.0 to 4.2) and free thyroxin (fT4) of 3.5 pg/ml (0.8 to 1.7) were found in the course of an examination of a 53-year old patient due to a planned hysterectomy. As thyrotropin (TSH) also was elevated with 5.8 mU/l (0.4 to 4.5), these findings corresponded to an inappropriate secretion of TSH (IST). Additional examinations revealed a blunted rise of TSH secretion after i,v. injection of 200 mu g thyrotropin releasing hormone (TRH) as well as lacking suppression of TSH secretion after oral doses of 75 mu g T3 during one week.: alpha-TSH levels with 3.7 mu g/l were elevated in comparison to a matched normal sample just as the molar ratio alpha-TSH/TSH with 6.95 and sex hormone-binding globulin (SHBG) with 175 nmol/l and showed an absence of inhibition in the T3 suppression test. These results were suggestive of neoplastic inappropriate secretion of TSH (nIST) due to a TSH-secreting pituitary adenoma. In concordance, the magnetic resonance imaging (MRI) showed a I cm tumor in the sella. The adenoma could also be visualized by In-111-octreotide and I-123-epidepride scintigraphies of the pituitary gland. After transsphenoidal resection, histological examination of the tumor resulted in the finding of a TSH-secreting adenoma. Postoperative TSH levels were not detectable, indicating the complete removal of the adenoma. Levels of fT3 and fT4 were slightly below normal with 1.9 pg/ml and 0.7 ng/dl, respectively. A control scintigraphy with In-111-octreotide following an equivocal MRI showed no uptake in the pituitary.