Endocrine Abstracts

Discordant thyroid function is common; differential diagnosis includes assay interference, familial dysalbuminaemic hyperthyroxinaemia, thyroid hormone resistance (RTH) and TSHoma. We present four TSHomas, demonstrating the diversity of clinical course. All had assay interference and RTH excluded. Case 1: A 64-year-old lady with thyrotoxic symptoms and no family history. TSH 6.36 mU/l, with fT4 32.6 pmol/l and raised SHBG. Pituitary MRI showed a 7 mM lesion. She was unresponsive to carbimazole and underwent trans-sphenoidal adenomectomy. Histology showed an adenoma with TSH and GH co-expression. Post-surgical thyroid function was normal. She remains disease free 4 years later. Case 2: A 38-year-old man with incidental tachycardia, TSH 9.9 mU/l, fT4 46 pmol/l, fT3 18.9 pmol/l, α-subunit 2.05 mU/l (high). Pituitary function was otherwise normal and MRI showed a 20 mM adenoma extending to the brainstem. Two trans-sphenoidal operations, radiotherapy, carbimazole and Sandostatin-LAR only reduced fT4 to 30 pmol/L, with loss of anterior pituitary function. He died suddenly, attributed to tachycardia with cortisol deficiency. Case 3: A 64-year-old man with AF but otherwise euthyroid, TSH 4.3 mU/L, FT4 35.3 mU/L, FT3 11.9 mU/L, SHBG 103 nmol/l (high), α-subunit normal. TSH response to TRH was not blunted, but TSH was incompletely suppressed after T3 administration, suggesting TSHoma. Pituitary MRI showed a 9×8 mM lesion. Sandostatin-LAR normalised thyroid function, but tumour size was unaffected. After pituitary surgery thyroid and pituitary function were normal. Case 4: A 75-year-old man with renal impairment, AF and stroke was referred with weight loss and TSH 6.23 mU/L, fT4 32.5 pmol/L (remaining pituitary function normal). There was no relevant FH. MRI demonstrated a 9 mM focal pituitary lesion, but co-morbidities precluded dynamic testing or surgery. Empirical treatment with Sandostatin-LAR has normalised thyroid function. These cases illustrate the diversity in treatment and outcome of TSHoma. Management is complex: pituitary surgery may cure; some need radiotherapy, carbimazole and somatostatin-analogue therapy. TSHoma is a heterogeneous condition that requires a multidisciplinary approach.

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.