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 (11.330.9 nmol/l), prolactin 76 mU/l (102496 mU/l), LH 22 U/l (213 U/l), FSH 46.6 U/l (413 U/l), TSH 0.63 mU/l (0.274.2 mU/l), FT4- 25.9 pmol/l (1222 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.
|1.2||33.1||18.3 → Carbimazole 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.