Endocrine Abstracts

Thyroid hormone resistance is a rare condition, caused by mutations of the thyroid hormone receptor beta (THRB) gene, inherited in an autosomal dominant manner, resulting in decreased tissue sensitivity to thyroid hormone action, leading to high FT4 levels with normal TSH levels. We present a case of thyroid hormone resistance, initially misdiagnosed and treated as hyperthyroidism. An 8 year old girl was referred due to poor appetite, FT4 level was elevated (38.5 pmol/l) with normal TSH (3.47 mIU/l). Due to unusual thyroid function results, she was referred to the paediatric endocrine team. She was thought to be hyperthyroid and commenced on Carbimazole and Thyroxine ‘block and replace’ regimen. Anti TPO and anti TSH receptor antibodies were negative. Thyroid ultrasound was normal. Follow up thyroid function testing revealed elevated TSH levels and compliance was queried. She subsequently developed a large goitre over the next 2 years. On review in clinic at the age of 12 years, further questioning revealed a strong family history of thyroid abnormalities. The patient’s mother had ‘abnormal thyroid tests’ which were not treated. Review of her initial results led to a diagnosis of thyroid hormone resistance, which was confirmed on genetic testing (THR beta gene). Medication was discontinued and goitre resolved. The condition was explained to the patient & her guardian. The impact on future pregnancy was discussed. The patient became pregnant at 17 years of age, but had a miscarriage. She became pregnant at 18 years of age and was reviewed at the specialist endocrine antenatal clinic. She was treated with a low dose Propylthiouracil, pending amniocentesis. Fetal genetic testing was negative. Dose of Propythiouracil was adjusted according to TFTs and she had a healthy baby. This case highlights the importance of detailed family history, clinical assessment and consideration of differentials of abnormal thyroid results. Patient education is vital in cases of rare endocrine conditions which can be misinterpreted. The antenatal management of thyroid hormone resistance is discussed.