Reversible Pulmonary Arterial Hypertension Due to Fenfluramine in a Young Child: A Case Report

Fenfluramine is approved for Dravet syndrome and Lennox-Gastaut syndrome (LGS) in children under two years of age and is increasingly used off-label for developmental and epileptic encephalopathies (DEEs). Due to the risk of pulmonary arterial hypertension (PAH) and valvular disease, serial echocardiographic monitoring is required. While fenfluramine-associated cardiac toxicity is well described in adults, data in pediatric patients, especially those under two years of age, remain limited. We report a child under two years of age with SCN1B-related DEE who developed asymptomatic fenfluramine-associated PAH after one year of treatment. Fenfluramine resulted in marked seizure reduction but was discontinued after the detection of PAH. Subsequent echocardiography demonstrated resolution of PAH, accompanied by worsening seizure burden. This case emphasizes the rare occurrence of fenfluramine-associated PAH in children under two years of age and underscores the importance of vigilant cardiac surveillance in this population.