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. This results in decreased tissue sensitivity to thyroid hormone action, the hall mark is high FT4 levels with normal TSH levels. The clinical presentation is variable. We discuss 2 cases of thyroid hormone resistance who received Carbimazole treatment. Case 1 is an 8 year old girl, who was initially misdiagnosed as hyperthyroidism. She was 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. Over the following years she developed a large goitre. 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. Medication was discontinued and goitre resolved. Case 2, a 12 year old girl was correctly identified as having thyroid hormone resistance. Due to behavioural symptoms she was treated with Carbimazole. Despite dose adjustment, she became clinically hypothyroid with increasing goitre. These cases highlight the importance of correctly diagnosing this rare condition. When considering treating thyroid hormone resistance, it is essential to concentrate on the patient’s symptoms and clinical picture instead of aiming to normalize thyroid hormone levels. Most patients overcome the resistance by increased thyroid hormone secretion and do not require treatment. Patients who present with symptoms of hyperthyroidism can be treated symptomatically with beta-blockers or antianxiety medications depending on their predominant symptoms