Influenza-associated myocarditis: a case series and structured narrative review

BACKGROUND: Influenza infection is a significant cause of global illness and death. Although mainly a respiratory disease, it can be complicated by extra-pulmonary conditions like myocarditis and myopericarditis. The prevalence and range of influenza-associated myocarditis are not well understood, especially in the Middle East, where case reports are limited. METHODS: We conducted a retrospective case series of adult patients admitted to King Abdulaziz Medical City in Riyadh, Saudi Arabia, from September 2024 to July 2025, with clinically diagnosed influenza-associated myocarditis. Diagnosis was based on the 2024 ACC Expert Consensus Decision Pathway criteria and a positive influenza PCR. Clinical data, diagnostic results, management strategies, and outcomes were collected from electronic medical records. Additionally, we performed a structured literature review of case reports and case series on influenza-associated myocarditis to provide context for our findings. RESULTS: Four patients (ages 37-79 years; three women) were identified with clinically diagnosed influenza-associated myocarditis. Presentations ranged from mild myopericarditis with preserved hemodynamics to fulminant myocarditis complicated by cardiogenic shock requiring venoarterial extracorporeal membrane oxygenation and Impella support. All patients received oseltamivir, and selected patients received colchicine, nonsteroidal anti-inflammatory drugs, or immunomodulatory therapy. Three patients recovered with normalization of cardiac function, while one patient with fulminant disease died despite aggressive support. The literature review identified 24 published cases of influenza-associated myocarditis. Most patients were previously healthy young adults (median age 42.5 years), and 79.2% achieved complete recovery. However, 20.8% died, often following rapid progression to cardiogenic shock and multi-organ failure. CONCLUSION: Influenza-associated myocarditis is a rare, potentially fatal complication affecting healthy adults. Our findings highlight the importance of early recognition, prompt antiviral therapy, and access to mechanical circulatory support when needed. This case series, among the first from Saudi Arabia, along with a literature review, offers insights into the clinical spectrum, management, and outcomes of this underrecognized condition.