Hyperthyroidism in a patient with TSH-producing pituitary adenoma coexisting with thyroid papillary adenocarcinoma

A 27-year-old woman who presented with a left thyroid nodule was found to h ave hyperthyroidism caused by a syndrome of inappropriate secretion of TSH. The levels of free T-3, free T-4 and TSH were 9.50 pg/mL, 4.05 ng/dL and 2 .16 muU/mL, respectively. Magnetic resonance imaging of the head revealed a pituitary macroadenoma. The TSH response to TRH stimulation was normal and responses of other anterior pituitary hormones to stimulation tests were a lso normally preserved. Administration of octreotide with iodine successful ly reversed hyperthyroidism prior to total resection of pituitary adenoma, which was followed by hemithyroidectomy of the left thyroid five months lat er. Histologically, the resected pituitary adenoma was a TSH-producing aden oma (TSH-oma) and the thyroid nodule was a papillary adenocarcinoma. Serum TSH diminished to undetectable levels immediately following pituitary adeno mectomy but gradually normalized over nine months. Coexistence of a TSH-oma with thyroid cancer is very rare and only two similar cases have previousl y been documented. This combination raises the possibility that TSH may be involved in tumorigenesis in the thyroid gland.