Endocrine Abstracts

A 20 years old primigravida 11weeks pregnant presented with increasing neck size, having noticed some neck swelling 4 years previously. There was no history of dysphagia or stridor. Apart of mild asthma she was well with no significant past medical or family history. TSH was normal at the time she was referred by the GP to the endocrine clinic. On examination she had a smooth thyroid swelling but no cervical lymphadenopathy. Further thyroid function tests confirmed a normal TSH 1.08(NR 0.4-4.0), fT4 of 31.5 (NR 10.0 -25.0) and free T3 of 8.6 (NR 2.8-6.5) and a negative test for thyroid peroxidase antibodies. She later miscarried at 13 weeks though her free hormone levels remained elevated. The working diagnosis was thyroid hormone resistance (THR). Further investigations excluded assay interference due to antibodies to thyroid hormones and familial dysalbuminaemic hyperthyroxinaemia. Pituitary MRI scan showed no evidence of tumour. On further follow up the patient remained asymptomatic with no change of the degree of thyroid enlargement. Pulse rate was elevated at 88 per minute and regular even in the non pregnant state.
THR is usually an incidental finding. In our case the patient presented in pregnancy, where thyroid hormone interpretation may be difficult. The increase in thyroid size can be attributed to physiological increase in thyroid growth in pregnancy on a background of THR. Depending on whether THR is generalised or partial, patients may present with growth retardation, attention deficit hyperactivity disorder, learning difficulties and tachykardia and mimic hyper or hypothyroidism. There are no data from systematic population screening and prevalence of thyroid hormone resistance remains unknown. Genetic analysis should reveal a mutation of the thyroid receptor. It was not performed in our case as it would not have altered management and other diagnoses were confidently excluded. Her siblings are currently being screened for THR.