Endocrine Abstracts

JOINT830

A 23 year-old Chinese lady was referred to the Endocrinology clinic by her primary care physician for hyperthyroidism in July 2024. She had reported 1 year history of worsening anterior swelling and palpitations. Her free thyroxine (fT4) was noted to be persistently elevated on different assay platform since 2017, with an inappropriately high-normal Thyroid Stimulating Hormone (TSH) level (see Table 1). Her primary care physician started her on carbimazole 2.5 mg OM in June 2024 prior to the Endocrinology review. On examination, her weight was 41.8kg (stable for the past few years) with a blood pressure of 89/75 mmHg, heart rate 75/min (regular). She had a moderate diffuse goiter, but no tremors and no proptosis. Her carbimazole was stopped and she underwent additional investigations. Of note, a fT4 by equilibirum dialysis was raised at 3.2 ng/dl (RR 0.8 - 2.0) and an alpha subunit/TSH molar ratio was 1.587. An MRI Pituitary showed no pituitary adenoma. A Thyrotropin Releasing Hormone stimulation test demonstrated a large rise in TSH from 2.92 (0 min) to 24.54 (60 min). Her parents (patient is an only child) had their thyroid function tested and were normal. Genetic testing later revealed a heterozygous mutation in the THRB gene (p. Pro453Thr alteration pointing to the diagnosis of Resistance to Thyroid Hormone Beta. The patient was subsequently managed with propranolol 10 mg TDS PRN for control of her palpitations and remains on follow-up with our clinic.