Endocrine Abstracts

A 51 year old lady presented with a 3 week history of persistent headache, sweating, increase in shoe and ring size and prognathism. Imaging confirmed an 18×19 mm pituitary macroadenoma indenting the optic chiasma. Visual fields were normal.

Bloods: IGF1-181 nmol/l (11.3–30.9 nmol/l), prolactin 76 mU/l (102–496 mU/l), LH 22 U/l (2–13 U/l), FSH 46.6 U/l (4–13 U/l), TSH 0.63 mU/l (0.27–4.2 mU/l), FT4- 25.9 pmol/l (12–22 pmol/l). OGTT confirmed excess growth hormone secretion. A diagnosis of acromegaly was made. She underwent transphenoidal resection and subsequent OGTT and growth hormone day curve showed satisfactory response. Histology showed a densely granulated somatotrophadenoma with FSH immunoreactivity and prolactin immunopositivity. Post-operative imaging showed a very small rim of residual pituitary tissue.

However, IGF1 remained elevated. Post-operatively, her FT4 started to increase with a corresponding slower rise in TSH (normal alpha sub unit). She noticed sweating and hair loss and carbimazole was commenced.

Carbimazole dose titration brought the FT4 levels to normal range but the TSH continued to rise. This suggested the diagnosis of a combined GH/TSHoma. Repeat OGTT showed borderline failure of suppression of growth hormone but MRI was unchanged. Somatostatin analogues, SOM230, pituitary irradiation and thyroidectomy were discussed. A multi-disciplinary decision was made to commence her on octreotide prior to definitive radiotherapy.

There are very few cases in literature of combined GH/TSHoma. This case highlights the challenges in the diagnosis and management of this relatively rare tumour. While growth hormone excess was the prominent clinical and biochemical feature pre-operatively, the thyroid axis abnormality was the predominant feature post-operatively, even before carbimazole was commenced. This case also illustrates the significant increase in TSH in response to a small reduction in FT4 levels – a known characteristic of this tumour.