A Prolonged QTc Interval Leads to the Diagnosis of Hyperthyroidism in an Adolescent Boy

Background: Syncope is a common cause of pediatric emergency department visits and carries a broad differential diagnosis, which includes a few rare but critical cardiac conditions. Case Report: We review the case of an adolescent boy who presented to the emergency department after a syncopal event. He was found to have a prolonged QTc interval on electrocardiogram (ECG), without personal or family history or known risk factors. He was screened for thyroid dysfunction on a second ED visit for presyncope and was subsequently diagnosed with hyperthyroidism. The patient was treated with methimazole for 2 weeks and a repeat ECG showed normalization of the QTc interval with a QTc reduction of more than 100 ms; routine thyroid studies showed correction of thyroid stimulating hormone and free thyroxine levels shortly thereafter. Why Should an Emergency Physician Be Aware of This?: This case and review of the medical literature should raise awareness for the emergency physician to consider evaluation of thyroid function in pediatric patients with QT interval prolongation and vice versa, potentially averting dangerous dysrhythmias.