Anti-mitochondrial antibody-positive inflammatory myopathy with multiple arrhythmias resistant to high-dose glucocorticoids and intravenous cyclophosphamide: a case-based review.

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of autoimmune diseases characterized primarily by muscle inflammation. Anti-mitochondrial antibodies (AMA) are typically associated with primary biliary cholangitis; however, they have also been linked to a rare subgroup of IIMs, namely "AMA-positive myositis," marked by a chronic disease course and muscle weakness, particularly affecting the paravertebral muscles, alongside muscle atrophy and cardiopulmonary complications. We report the case of a 40-year-old woman diagnosed with AMA-positive myositis, predominantly involving axial myopathy complicated by multiple arrhythmias and biopsy-proven focal segmental glomerulosclerosis with mitochondrial abnormalities on electron microscopy. The patient presented with progressive back pain and palpitations over a 3-month period. Although high-dose glucocorticoids and intravenous cyclophosphamide improved the axial myopathy and proteinuria, the cardiac condition remained unstable, necessitating permanent pacemaker implantation for persistent sinus dysfunction and radiofrequency catheter ablation for worsening atrial fibrillation (Af). Our literature review focusing on cardiac involvement in AMA-positive myositis revealed tachyarrhythmia was the most common (87.7%), particularly Af (55.4%), followed by cardiomyopathy (74.2%), myocarditis (43.2%), and bradyarrhythmia (40.0%). Arrhythmias and/or cardiac function deteriorated in 41.7% of patients treated with immunosuppressants and in 66.7% of patients treated without immunosuppressants, respectively. Furthermore, in the treated group, more patients with worsened cardiac lesions required additional electronic devices compared to those without (53.3% vs. 4.8%). Early detection and adequate management of cardiac complications in AMA-positive myositis are critical to prevent irreversible myocardial damage and fatal outcomes. In addition to cardiac complications, concomitant renal involvement associated with AMA-positive myositis may be also considered.