Presentation and Background    
A 13-year-old boy with a known diagnosis of Duchenne muscular dystrophy (DMD), confirmed by genetic testing six years prior, arrived at the emergency department with severe retrosternal chest pain. He had no recent infections, flu-like symptoms, or family history of cardiac issues. His condition had been stable with a previous echocardiogram showing a preserved left ventricular ejection fraction (LVEF) of 50%. However, he had missed his deflazacort (a corticosteroid used in DMD management) for four days before the onset of symptoms.

Initial Evaluation    
On examination, he was stable and comfortable, with normal vital signs and unremarkable cardiac and respiratory findings. However, the ECG raised concern, showing ST-segment elevation in the lateral leads. Laboratory tests revealed a markedly elevated cardiac troponin I level (50,000 µg/L), along with significantly raised CK-MB, BNP, CPK, CRP, AST, and ALT levels, suggesting muscle and myocardial injury. Despite these alarming values, his white blood cell count and other hematologic parameters were within normal range. Hepatitis and HIV screenings were negative.

Imaging and Diagnosis    
An echocardiogram showed left ventricular dilation and severely reduced systolic function (LVEF 30%). Despite the ST-elevation, coronary CT angiography showed normal coronary arteries, ruling out ischemic causes like coronary artery disease.
Cardiac MRI (CMR) provided definitive insights. The scan revealed widespread myocardial edema, particularly in the lateral wall, with elevated T2 values and diffuse subepicardial and nearly transmural late gadolinium enhancement in multiple LV regions—hallmarks of active myocarditis. The findings were consistent with an inflammatory myocardial process rather than ischemia, aligning with a diagnosis of acute myocarditis.

Management and Outcome    
During hospitalization, the patient was restarted on his usual medications, and oral prednisolone (15 mg daily) was introduced to control the inflammation. The response was swift and significant: chest pain resolved, lab abnormalities improved, and follow-up echocardiography showed LVEF recovery to 45%.