Myocarditis or 'hot phase' of arrhythmogenic cardiomyopathy? A case series.

Background: Arrhythmogenic cardiomyopathy (ACM) is a genetic condition characterized by fibrofatty replacement of myocardial tissue, leading to arrhythmias and structural heart changes. Recent studies have identified an acute inflammatory phase, or 'hot phase', within the progression of ACM that presents with clinical features similar to myocarditis. This phase complicates the differentiation between ACM and myocarditis, posing a diagnostic challenge. Case summary: We present two cases of young male patients, both with mutations in the DSP and LMNA genes, who initially presented with symptoms of myocardial inflammation. Patient 1, a 23-year-old male, presented with pleuritic chest pain, elevated troponin, and imaging findings suggesting myocarditis. Cardiac magnetic resonance (CMR) revealed extensive subepicardial late gadolinium enhancement (LGE) in a non-ischaemic pattern. Genetic testing confirmed a likely pathogenic (LP) LMNA mutation. Patient 2, a 26-year-old male with family history of sudden cardiac death, presented similarly with chest pain and elevated biomarkers. His CMR showed intramural LGE, and genetic testing identified a LP DSP mutation. He underwent implantation of a subcutaneous defibrillator (ICD) due to arrhythmic risk. Discussion: This case series underscores the importance of recognizing the 'hot phase' of ACM, which can clinically mimic myocarditis. Cardiac magnetic resonance is crucial for differentiating these entities, while genetic testing confirms the diagnosis, offering prognostic information. Mutations in the LMNA and DSP genes, particularly associated with inflammation in ACM, require consideration of arrhythmia prevention strategies, such as ICD implantation. Multidisciplinary management and advanced imaging play essential roles in the care of these patients.