Endocrine Abstracts

Introduction: Resistance to thyroid hormone beta (RTHβ) is a rare genetic disorder characterized by impaired responsiveness to thyroid hormone in tissues expressing TRβ. This case report explores the clinical manifestation of RTHβ in a 15-year-old male presenting with acute and intensive chest pain and subsequent diagnostic challenges.

Case Report: At midnight, a 15-year-old male reported acute, sharp chest pain, prompting medical attention. Elevated troponin I levels initially raised concerns about myocardial infarction, but electrocardiogram and echocardiography excluded it. The patient is the third child in the family, denied chronic illnesses, and reported regular physical activity in the swimming pool. Family history revealed an older brother’s sudden cardiac death at 29 during cycling. Physical examination revealed an asthenic constitution (BMI: 16.2 kg/m^², -2.18 SD), palpable goiter I grade, and a heart rate of 113 bpm. Holter monitoring detected 365 ventricular extrasystoles and normal arteries were determined in coronography on 1st day of investigation. A cardiac MRI excluded myocarditis on 4th investigation day. Troponin I peaked at 102.95 µg/l, decreasing to 0.09 µg/l (N <0.04). Creatine kinase MB and Lactate dehydrogenase were elevated but eventually stabilized. Coagulation parameters, including D-dimer levels, remained within normal limits. Hormonal investigation revealed elevated concentrations of circulating free thyroxine (fT4 33.99 pmol/l (N 10–19)) and free triiodothyronine (fT3 8.65 pmol/l (N 4.7–7.2)) in the presence of no suppressed thyroid stimulating hormone (TSH 2.05 mU/l (N 0.48–4.7)). Autoantibodies (TgAb, TRAb, TPOAb) were negative; catecholamines were normal. The coronary spasm and myocardial infarction with non-obstructive coronary arteries (MINOCA) related to thyrotoxicosis were considered. Methimazole 10 mg daily was initiated, which led to an increase in TSH with persistently elevated FT4 and FT3 levels A diagnosis of TSHoma was considered but brain MRI showed a normal pituitary gland. Next, RTHβ was suspected, and genetic testing (Rotterdam Thyroid Centre), revealed a known R320C mutation in the thyroid hormone receptor ß gene. The treatment with thyrostatics was stopped after confirmed RTHβ. The beta-blocker is used due to tachycardia up to now.

Conclusion: This case underscores the challenges in diagnosing thyroid hormone receptor resistance, emphasizing the importance of accessibility of genetic testing and a multidisciplinary approach for comprehensive patient care.