Asian Journal of Medical Research and Case Reports

Introduction: Myocarditis is a challenging diagnosis that can progress to severe cardiomyopathy and sudden cardiac death. In refractory cases, an underlying genetic etiology should be strongly suspected. This report highlights a rare presentation of Danon disease mimicking chronic lymphocytic myocarditis.

Case Presentation: A 26-year-old female presented with progressive fatigue, dyspnea, and non-specific chest discomfort, suggesting heart failure (HF). Initial investigations revealed an irregular pulse, hypotension (80/50 mmHg), elevated high-sensitivity Troponin I, and severe electrical abnormalities (atrial fibrillation, complete heart block). Transthoracic echocardiography (TTE) showed biventricular hypertrophic cardiomyopathy (HCM) with a severely reduced left ventricular ejection fraction (LVEF 15%). An endomyocardial biopsy (EMB) confirmed chronic lymphocytic myocarditis.

Diagnosis and Treatment: The patient’s symptoms worsened following discontinuation of initial empirical immunosuppressive therapy, necessitating a comprehensive work-up. The combination of refractory myocarditis and HCM prompted genetic testing. This revealed defective splicing of the lysosome-associated membrane protein 2 (LAMP2) gene, confirming the diagnosis of Danon disease, an X-linked lysosomal storage disorder. The patient was re-initiated on a tailored regimen of immunosuppressives (corticosteroids) and immunomodulators (Tacrolimus and Mycophenolate).

Outcome and Conclusion: The combined therapeutic approach led to a favourable clinical outcome, with the patient remaining stable and TTE demonstrating an improved LVEF of 25% after six months. This case underscores the importance of considering rare inherited cardiomyopathies, such as Danon disease, in young patients presenting with unexplained, refractory chronic myocarditis, especially those with hypertrophic features, to guide appropriate disease-specific management.