Acute myocarditis (AM) is a rare but severe disease affecting patients of all age. Large multicentric data comparing children and adults are lacking.

We aimed to elucidate differences in presentation, management, and outcomes of AM across age groups.

A comprehensive French national cohort study, encompassing 53 pediatric and adult units from March 2020 to November 2021, was analysed. Baseline characteristics and evolution, management and in-hospital complications were collected. Major cardiovascular events (MACE) within 30 days included all-cause death, cardiogenic shock, cardiac arrest, ventricular arrhythmias, or complete AV block.

We included 745 AM patients (328 children and 417 adults), mainly male (73.4%) with a median age of 19.8 years [IQR: 12.5–30.9]. Multisystem inflammatory syndrome (MIS) was more prevalent among pediatric cases (69.8%), whereas infectious aetiology dominated in adults (13.4 vs. 52.4%). Children exhibited a more severe clinical presentation, with increased risk of heart failure (15.9 vs. 7.2%) and cardiogenic shock (14.4 vs. 6.9%), requiring higher use of inotropes (25.0 vs. 9.4%), vasopressors (12.0 vs. 6.2%), and ventilatory support (12.5 vs. 7.7%). Cardiac treatments such as beta-blockers (33.4 vs. 84.4%) or ACE/ARB (37.3 vs. 63.1%) were less often used in children whereas corticosteroids (68.3 vs. 14.3%) and immunomodulators (65.1 vs. 4.5%) were more often used. MACE occurrence was substantial but not significantly different between children and adults (18.1 vs. 13.4%). Extra-cardiac manifestations at admission were significant predictors of MACE (aOR: 2.40 [1.43–4.38]), regardless of multisystem inflammatory syndrome (MIS) status.

AM exhibits variations in presentation, aetiologies, and management, but shares a comparable 30-day prognosis in children and adults.