Endocrine Abstracts

Introduction: The prevalence of pituitary adenoma is estimated to be 17% and about half secrete a distinct hormone. Prolactin secretion is the commonest, followed by GH or adrenocorticotropic hormone (ACTH). TSH producing pituitary adenoma is rare and occurs in less than 1% of pituitary adenomas. We report a challenging case of a 30-year-old man who presented with TSH and GH secreting pituitary macroadenoma with mass effect.

Case Report: A 30-year-old man presented with typical symptoms of thyrotoxicosis (palpitation, tremor and weight loss of 20 kg) over four months associated with headache. There were no symptoms suggestive of GH excess or hypogonadism. On examination, he was normotensive. He had a small goitre and fine tremor. He was started on Carbimazole and propranolol by his primary care doctor and referred to the Endocrine Clinic for discordant thyroid function.

His Free Thyroxine (Free T4) was elevated at 69.6 pmol/l (11.5-22.7) with a normal TSH of 4.06 mIU/l (0.55-4.78). This was confirmed with sample sent to a second laboratory. A high alpha subunit of 12 ng/ml (≤0.5) and absent TSH response to Thyrotropin Releasing Hormone (TRH) stimulation test support the diagnosis of TSH secreting tumour. Other anterior hormones were assessed and showed elevated Insulin Growth Factor -1 (IGF-1) of 401.8 ng/ml (74-258) and prolactin, 1167.6 mIU/l (45-375). Oral glucose tolerance test confirmed GH excess. Testosterone level was 2.5 nmol/l (5.72-026.14) with Follicle stimulating (FSH) 7.3 IU/l (1.4-18.1) and Luteinizing Hormone (LH) 3.6 IU/l (1.5-9.3). ACTH level was 1.8 pmol/l (1.8-13.9) and there was appropriate adrenal response to tetracosactrin test. Magnetic Resonance Imaging (MRI) showed a sellar-suprasellar mass measuring 3.8 x 3.3 x 3.5 cm which displaced the optic chiasm and compressed it antero-superiorly. Pituitary stalk was not visualized. Therefore, the elevated prolactin was attributed to stalk effect. Visual field assessment showed bitemporal hemianopia. In preparation for surgery, he was given Carbimazole, Propanolol and Lugol’s iodine. Pre surgery Free T4 was 20.98 pmol/l, TSH 21.04 mIU/l and GH 4.29 ng/ml (<2.47). He underwent Endoscopic Transsphenoidal Surgery with tumour excision successfully. Free T4 post-surgery was 20.66 pmol/l with normalization of TSH at 2.2 mIU/l and GH at 1.26 ng/ml. Preliminary histopathology examination revealed features of pituitary adenoma.

Conclusion: We present here, a rare case of pituitary macroadenoma with TSH and GH co-secretion. This case illustrates the importance of careful evaluation of discordant thyroid function test and the following pre-surgery management of such cases.