Case Report: A 49-year-old man presented with a two-year history of thyrotoxic symptoms for which he had been investigated on several occasions. He had a past medical history of dilated cardiomyopathy, which had been attributed to excess alcohol consumption, and had also suffered episodes of non-sustained ventricular tachycardia. His family history was strongly positive for autoimmune thyroid disease. Eventually, he was found to have an elevated fT4 (53 pmol/L, RR 1222) and fT3 (19.8 pmol/L, RR 3.16.8) with a non-suppressed inappropriately normal TSH (2.9 mU/L, RR 0.254). There was no evidence of assay interference. His SHBG was markedly raised at 197 nmol/l (RR 1555), as was serum alpha-subunit (2.7 IU/L, RR <1.0). TRH testing showed a blunted TSH response: 0min 2.4 mU/L, 20 min 2.7 mU/L, 60 min 2.7 mU/L. Pituitary MRI revealed a calcified macroadenoma (confirmed on CT). Other anterior pituitary function was normal except for significantly elevated total testosterone (48.4 nmol/l, RR 1030). A diagnosis of TSHoma was made and the patient treated with lanreotide autogel® (resulting in rapid resolution of his hyperthyroxinaemia), followed by transsphenoidal surgery. Histology confirmed a thyrotropinoma. Post-operatively, his TFTs normalized and his cardiac function improved.
Key Learning Points: Approximately 30% of patients with thyrotropinomas exhibit normal TSH levels. Measurement of TSH alone can therefore result in undue delay or failure to make the diagnosis with adverse clinical sequelae. Elevated SHBG may result in raised/normal total, but normal/low free testosterone levels (thus masking diagnosis of concomitant hypogonadism), although the possibility of gonadotrophin co-secretion (1.8% of TSHomas) should also be considered. The finding of calcification within a pituitary adenoma is characteristic and should raise suspicion of a thyrotropinoma. Somatostatin analogue therapy rapidly normalises TFTs in TSHoma. Cardiomyopathy may improve/reverse with correction of thyrotoxicosis.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.