A pediatric case of reversible dilated cardiomyopathy caused by autoimmune hypothyroidism

Dilated cardiomyopathy is the most common form of cardiomyopathy in children and often leads to irreversible myocardial dysfunction. To improve the prognosis, it is critical to identify rare but reversible causes. We report a 12-year-old girl referred to the emergency department for dyspnea on exertion and generalized edema that lasted for 1 month. She gained 20 kg over the past 3 years, which had gone uninvestigated. Transthoracic echocardiography demonstrated left ventricular dysfunction with pericardial effusion. Thyroid function tests revealed concentrations of free T4 and thyroid-stimulating hormone of 0.12 ng/dL (reference value, 0.93-1.7) and 86.9 µIU/mL (0.3-4.2), respectively, with anti-thyroid peroxidase and anti-thyroglobulin antibodies elevated, confirming the presence of autoimmune hypothyroidism. We initiated heart failure management alongside levothyroxine replacement therapy. After 5 months of treatment, a follow-up echocardiography showed improved left ventricular and thyroid function.