Endocrine Abstracts

TSH-secreting pituitary adenomas are rare, comprising under 1% of hyperthyroidism cases and 0.5-3% of functioning pituitary tumors. Ultrasensitive immunometric assays, now routine in thyroid testing, have improved diagnostic accuracy. Gadolinium-enhanced MRI is the main imaging method, as most adenomas (>90%) are macroadenomas. Early diagnosis and treatment help prevent complications. A 47-year-old female presented with dysfunctional uterine bleeding, dysmenorrhoea and irregular periods along with headache, lethargy and palpitations. Thyroid function tests since 2016 revealed persistently raised FT4 with normal TSH. Initial and repeated Pituitary MRI showed no focal mass with incidental possible meningioma in the upper left cavernous sinus. Her pituitary profile was normal. Tests for interference confirmed persistent FT4 elevation with normal TSH, negative thyroid antibodies, SHBG at 183 nmol/l (24.6-122) and a normal alpha subunit. A TRH stimulation test showed TSH remained under 5 mU/l. 11C-Methionine PET-CT showed tracer uptake on the gland’s left-side suggestive of a small microthyrotropinoma but it was difficult to discern a discrete lesion in absence of anatomical correlate from MRI. She was commenced on lanreotide 90 mg as a therapeutic and diagnostic manoeuvre (suppression imaging), resulting in FT4 normalisation and TSH suppression. Following four SSAs injections, repeated 11C-Methioine-PET-CT and MRI showed post SSAs therapy change in T2 signal characteristics in the same area of tracer uptake. This anatomical correlate confirmed a thyrotroph tumour. Lanreotide was stopped due to side effects and a trail of Cabergoline was poorly tolerated. The case is due for re-discussion in the Pit MDT regarding surgical intervention. In conclusion, 11C-Methionine-PET-CT scan with the help of SSAs can be useful tool in localizing microthyrotropinoma when conventional MRI pituitary hasn’t been successful.