Dilated cardiomyopathy with anti-mitochondrial M2 antibody: A case series.

Patients with dilated cardiomyopathy (DCM) sometimes show anti-mitochondrial M2 antibody (AMA-M2) positivity. We aimed to compare the characteristics of DCM cases with and without AMA-M2, and to describe cases of DCM with AMA-M2 positivity.A total of 84 patients with DCM were analyzed. Six patients (7.1 %) were positive for AMA-M2. Of these six patients, five (83.3 %) had primary biliary cirrhosis (PBC) and four (66.7 %) had myositis. Patients with AMA-M2 positivity had more atrial fibrillation and more premature ventricular contractions than those without. Left and right atrial longitudinal dimensions were larger in patients with AMA positivity (left atrium, 65.9 mm vs. 54.7 mm, p = 0.02; right atrium, 57.0 mm vs. 46.1 mm, p = 0.02). Of the six patients with AMA-M2 positivity, three underwent cardiac resynchronization therapy with defibrillator implantation and three required catheter ablation treatment. Steroids were used in three patients. One patient died of unresolved lethal arrhythmia and another required re-hospitalization for heart failure; the remaining four patients did not have adverse events.Patients with DCM with AMA-M2 positivity had a higher affinity for PBC and myositis than those without, and are characterized by atrial enlargement and arrhythmias. Learning objective: Patients with dilated cardiomyopathy sometimes exhibit anti-mitochondrial M2 antibody positivity. These patients are at higher risk for primary biliary cirrhosis and inflammatory myositis, and their cardiac disorders are characterized by atrial enlargement and various arrhythmias. The course of the disease up to the time of diagnosis and after steroid use varies, and the prognosis is poor in advanced cases.