<![CDATA[Background: Acute myopericarditis in young adults presents with clinical features indistinguishable from ST-elevation myocardial infarction (STEMI), creating diagnostic uncertainty that may lead to inappropriate invasive procedures or delayed anti-inflammatory therapy. Case Presentation: An 18-year-old male presented with acute chest pain, diffuse ST-segment elevation, and massive troponin I elevation (12.81 μg/L, 640-fold above normal), triggering STEMI protocol activation. Clinical risk stratification using the SAlzburg MYocarditis (SAMY) score yielded 5 points (68% myocarditis probability). Coronary computed tomography angiography demonstrated normal coronary arteries with calcium score of zero, excluding obstructive disease. Multiparametric cardiac magnetic resonance imaging definitively established the diagnosis through fulfillment of revised 2018 Lake Louise criteria: T2-based criteria (myocardial edema on STIR imaging and elevated T2 mapping at 58 ms) and T1-based criteria (native T1 elevation at 1,150 ms and patchy subepicardial/mid-wall late gadolinium enhancement with non-ischemic distribution). Guideline-directed therapy with high-dose ibuprofen 600 mg three times daily and colchicine 0.5 mg twice daily for 3 months, combined with strict exercise restriction, resulted in rapid symptom resolution, complete normalization of cardiac biomarkers by day 7, and excellent three-month outcome. Conclusion: This case exemplifies the integrated diagnostic approach recommended by 2024 ACC Expert Consensus and 2025 ESC Guidelines, demonstrating that multiparametric cardiac MRI with revised Lake Louise criteria, when incorporated into a systematic algorithm including clinical risk scoring and coronary computed tomography angiography, enables accurate differentiation of acute myopericarditis from acute coronary syndrome with 87.5% sensitivity and 96.2% specificity, preventing unnecessary invasive procedures while guiding evidence-based anti-inflammatory therapy.]]>
