When the heart cannot keep pace: case report of acute myocarditis in a recreational marathon runner

Marathon running is associated with transient elevations in cardiac and skeletal muscle biomarkers, which generally normalize within 72 h. However, persistent or extreme biomarker elevations may indicate underlying pathology, such as myocarditis. Early recognition and guideline-based management are essential to prevent complications and guide safe return to exercise.

A 21-year-old recreational marathon runner collapsed towards the end of a marathon race. On presentation, he exhibited markedly elevated cardiac and muscle biomarkers, including high-sensitivity cardiac troponin T, creatine kinase, creatine kinase-myocardial band, and myoglobin. The initial electrocardiogram (ECG) demonstrated a tachycardic sinus rhythm with T-wave inversion in Lead III, without evidence of significant depolarization or repolarization abnormalities. Cardiac Magnetic Resonance Imaging (MRI) confirmed acute myocarditis. The patient was managed supportively with intravenous fluids and non-steroidal anti-inflammatory drug analgesics, remained haemodynamically stable, and experienced no arrhythmias or chest pain. At 3-month follow-up, he reported good functional capacity, and both echocardiography and cardiac MRI were completely normal, demonstrating full resolution of myocardial inflammation.

This case highlights the diagnostic challenge of interpreting elevated cardiac biomarkers in endurance athletes. Observational studies indicate that biomarker elevations often correlate with exercise duration rather than with demographic or training-related factors. Cardiac MRI remains essential for non-invasive diagnosis, risk stratification, and follow-up. Importantly, adherence to guideline-based management, i.e. temporary abstinence from competitive sports, monitoring of biomarkers, and serial imaging, can lead to excellent outcomes, as exemplified by the complete normalization observed in this patient. Non-steroidal anti-inflammatory drugs should be used with caution in amateur endurance athletes due to their potential to aggravate myocarditis.