Endocrine Abstracts

TSH-secreting pituitary adenomas are rare and the optimal investigation and management is uncertain.

A 42-year-old lady presented with a three-month history of three stone weight loss, palpitations, heat intolerance and tremor. Her sister was being treated for Graves’ disease. Visual fields were intact.

Thyroid function tests showed free T₄ concentration 29.5 pmol/l (9.0–19.0) and TSH concentration 3.672 mU/l (0.4–4.5). TSH concentration remained elevated after repeat measurement using an alternative assay. Alpha-subunit concentration was 1.1 IU/l (<1.0) and Sex Hormone Binding Globulin concentration 90 nmol/l (20–115). MRI showed a pituitary macroadenoma. There was no clinical or biochemical evidence of co-secretion of growth hormone, prolactin or gonadotropins. A TRH test revealed a flat response and T₃ administration (80 μg daily for 8 days) failed to induce suppression of TSH. TSH suppressed following a test dose of octreotide. Pre-operatively this lady was treated with octreotide, resulting in a reduction in maximal tumour diameter from 22 mm to 11 mm and normalisation of thyroid biochemistry. She proceeded to trans-sphenoidal resection of the pituitary adenoma, with histological examination confirming a TSH-adenoma.

Post-operatively she is clinically euthyroid with TSH in the normal range, but again failed to completely suppress following administration of T₃.

The optimal management of patients with this rare pituitary adenoma is uncertain. We describe a case where pre-operative octreotide therapy normalised thyroid biochemistry and was associated with a significant reduction in tumour size, possibly enhancing surgical outcome.