Endocrine Abstracts

Hyperthyroidism due to TSH-secreting pituitary adenoma is a rare disease and accounts for 0.4% of all pituitary tumors. About 15% of these tumors show co-secretion of prolactin or growth hormone.

We report the case of a 44-year-old man, presenting with sudden onset of tremor and agitation and central thyrotoxicosis (TSH 1.01 μU/ml, fT3 8.44 pmol/l, fT4 30.2 pmol/l). Ultrasound of the thyroid gland and TSH-receptor antibodies were normal. Imaging of the pituitary demonstrated a 12 mm pituitary macroadenoma. Evaluation of pituitary function revealed no signs of hypopituitarism, but an elevated IGF-1 of 397 ng/ml and growth hormone (GH) of 2.8 ng/ml without any clinical signs of acromegaly. GH was suppressed in an oral glucose tolerance test to a nadir of 0.6 ng/ml. The macroadenoma was completely removed by an endoscopic transsphenoidal approach. Histology showed a pituitary adenoma (WHO grade I) with marked expression of GH (>30%), as well as TSH and α-subunit. Three months after surgery, the patient was completely asymptomatic with normal thyroid function (TSH 0.73 μU/ml, fT3 5.17 pmol/l, fT4 18.7 pmol/l) and normal IGF-1 (132 ng/ml) and GH (0.1 ng/ml). There were no signs of hypopituitarism and imaging of the brain showed no residual tumor. The lack of acromegalic features is probably due to the sudden onset of hyperthyroidism and only mildly elevated GH and IGF-1.

This case highlights the potency of plurihormonal secretion of pituitary adenomas. Transsphenoidal resection is the therapy of choice for TSH-secreting tumors with reported cure rates of 50–80%.