Case Report: Suspected biventricular arrhythmogenic cardiomyopathy presenting as a dilated cardiomyopathy-like phenotype with multimodal phenotyping and cautious genetic interpretation

Arrhythmogenic cardiomyopathy (ACM) may overlap clinically with dilated cardiomyopathy (DCM), particularly when left ventricular dilatation and systolic dysfunction dominate the presentation. We report a 47-year-old man initially diagnosed with DCM whose subsequent multimodal assessment suggested a biventricular ACM (BiV-ACM) phenotype. The clinical assessment integrated clinical history, electrocardiography, ambulatory rhythm monitoring, echocardiography, and cardiac magnetic resonance (CMR) imaging. Findings included marked left ventricular dilatation, severe systolic dysfunction, frequent multifocal ventricular ectopy, nonsustained ventricular tachycardia, right ventricular dysfunction, and biventricular nonischemic myocardial abnormalities on CMR. These phenotypic findings, rather than genetic results, formed the basis of the clinical impression. Whole-exome sequencing performed during follow-up identified four heterozygous variants of uncertain significance, including the truncating DSP variant NM_004415.4:c.7423A>T [p.(Lys2475Ter)]. None provided molecular confirmation. Over approximately 2 years of medical treatment and follow-up, left ventricular ejection fraction increased from 28.9% to 35%, and peak oxygen uptake increased from 24.4 to 26.7 mL/kg/min, while ventricular arrhythmias persisted. These observations do not establish an intervention-specific treatment effect. This case highlights the value of phenotype-based multimodal assessment in DCM-like presentations and the importance of distinguishing uncertain genetic findings from diagnostic evidence.