Endocrine Abstracts

Background: TSH secreting pituitary adenomas represent small proportion of functional pituitary tumours presenting as hyperthyroidism with elevated thyroid hormone levels and inappropriately normal or increased TSH concentration. They are ≥1 cm in size and quite aggressive with tendency to relapse following transphenoidal adenomectomy (TSA). Surgical resection remains gold standard in their definitive treatment while pharmacotherapy with long-acting somatostatin analogues or dopamine agonists has mainly adjunct role in pre-operative restoration of euthyroidism.

Case report: A 44-year-old premenopausal patient presented with mild thyrotoxicosis as repeated thyroid function tests have consistently shown slightly raised free T₃ and free T₄ in the presence of mid-normal TSH. The SHBG was increased by more than 80% above normal range and the α-SU:TSH ratio was equal to 6.4; equilibrium dialysis has excluded the presence of heterophile TSH antibodies. On further investigations she had flat TSH response to TRH test and has failed to suppress TSH to ≤0.1 mU/l following liothyronine 20 μg QDS 10 days treatment. The thyroid isotope scan has shown diffusely increased uptake of the thyroid gland; findings were inkeeping with autonomous TSH secretion rather than generalised/pituitary resistance to thyroid hormone or familial dysalbuminaemic hyperthyroxinaemia. Subsequent pituitary MRI has shown calcified pituitary macroadenoma with suprasellar extension, away from the optic chiasm. Considering mild thyrotoxicosis and patient’s preference, it was decided to treat her conservatively. She was initially started on cabergoline 1 mg twice weekly; repeated thyroid function tests 4 weeks later were normal. Over the last 10 years she is on cabergoline 500 μg weekly maintenance dose; the TSHoma appearances remains static on serial MRI scans.

Conclusions: Our case illustrates the successful conservative management of TSHoma with relatively low dose of cabergoline. Clinicians are reminded to consider the low cost carbegoline for the conservative management of TSHoma, when treansphenoidal surgery is not a therapeutic option.