Endocrine Abstracts

Introduction: Thyrotoxicosis is a common condition referred to endocrine clinics. However, not all of them needed treatment with antithyroid medications. We report a case of thyroid hormone resistance due to a novel TSHRβ mutation who has been treated with subtotal thyroidectomy and antithyroid medications due to raised T₄ levels.

Case report: A 38-year-old south Asian woman was seen in orthopaedic clinic for elective right foot scarf osteotomy for hallux valgus deformity. She has a past medical history of asthma and subtotal thyroidectomy at the age of 11. Incidental blood tests have shown raised FT₄ levels of 38 pmol/l, FT₃ 9.8 pmol/l and TSH 6.62 mU/l. She was referred to endocrine clinic and carbimazole 20 mg OD was started in view of symptoms of palpitations, hot flushes and headache. At the same time, bloods were send to check for heterophile antibodies for TSH, anterior pituitary profile including alpha sub unit and MRI pituitary was requested. Anterior pituitary profile came back as normal with alpha sub unit <0.3 and MRI pituitary was normal as well. Despite being on carbimazole and some improvement in symptoms, Her FT₄ was still high at 35 pmol/l with TSH raised at 5.34 mU/l. Her bloods were send to check mutations regarding thyroid hormone resistance and she was found to have a novel heterozygous thyroid receptor β mutation at 1009 A>C (p. Thr337Pro). Carbimazole was stopped and she underwent a successful surgery for right hallux valgus deformity.

Discussion: Thyroid hormone resistance syndrome is rare and often treated inappropriately with antithyroid medications or thyroidectomy. Raised TSH with raised FT₄ should alert the clinician about possibility of either TSHoma or thyroid hormone resistance syndrome and should be thoroughly investigated before a decision is made to treat the abnormal thyroid function tests.