Acute Myocarditis as an Immune-Mediated Complication of Mpox Infection.

BACKGROUND: Cardiac involvement is an uncommon and incompletely characterized complication of mpox infection. CASE SUMMARY: A 32-year-old man with well-controlled HIV and polymerase chain reaction-confirmed mpox developed acute chest pain days after a vesiculopustular rash. High-sensitivity troponin I peaked at 12,717 ng/L with elevated inflammatory markers. Coronary and embolic causes were excluded. Cardiac magnetic resonance (CMR) demonstrated lateral-wall edema on T2-weighted imaging and nonischemic late gadolinium enhancement with preserved ejection fraction, satisfying the updated Lake Louise Criteria. He recovered fully with supportive care. DISCUSSION: Mpox-associated myocarditis has predominantly been reported in young, largely immunocompetent men, including some with well-controlled HIV. The mechanism remains uncertain; immune-mediated injury and direct viral involvement both remain possible. This case underscores multiparametric CMR as a noninvasive diagnostic tool that may obviate endomyocardial biopsy in hemodynamically stable patients. TAKE-HOME MESSAGES: Mpox can cause acute myocarditis in immunocompetent patients. Multiparametric CMR enables noninvasive confirmation and may spare selected patients from endomyocardial biopsy.