40PClinical features of cardiac complications and restrictive ventilatory impairment in AMA-positive myositis: findings from a nationwide cross-sectional study

Serum anti-mitochondrial antibodies (AMA) are detected in approximately 5–20% of patients with idiopathic inflammatory muscle diseases, representing a distinct subtype designated as AMA-positive myositis. The clinical features of AMA-positive myositis typically include a chronic disease course, muscle atrophy, frequent cardiac involvement, and restrictive ventilatory impairment. We conducted a detailed subanalysis of cardiac complications and restrictive ventilatory impairment using data from a nationwide questionnaire survey. Between February and August in 2021, we sent an initial questionnaire (first survey) to the heads of neurology departments at 811 facilities certified by the Japanese Society of Neurology. A follow-up survey (second survey) was then conducted to collect detailed clinical data from respondents to the first survey. Among the 85 patients for whom detailed information was obtained from the second survey, 75% had cardiac complications and 49% had restrictive ventilatory impairment. Regarding cardiac complications, 65% of patients had arrhythmias, 44% had heart failure, and 24% had conduction blocks. Echocardiographic findings revealed that 16% of patients had an ejection fraction <50% with diffuse hypokinesis. Holter electrocardiography showed ventricular arrhythmias in 61%, supraventricular arrhythmias in 58%, conduction defects in 9%, and sick sinus syndrome in 2% of patients. Cardiac devices were implanted in 32% of patients. Specifically, catheter ablation, pacemaker implantation, Implantable cardioverter defibrillator implantation, and HeartWare ventricular assist device implantation were performed in 21%, 12%, 8%, and 1% of patients, respectively. Electroencephalographic abnormalities were observed in 27% of patients. With regard to restrictive ventilatory impairment, 12% of patients showed a vital capacity <50% on pulmonary function tests, and 22% had pCO₂ >45 mmHg in arterial blood gas analysis. Ventilatory support was provided to 22% of patients. Among them, 50% received invasive positive pressure ventilation, while the remaining 50% received noninvasive positive pressure ventilation. Previous case reviews have highlighted the presence of both cardiac and respiratory involvement in patients with AMA-positive myositis; however, considerable variability in the reported frequencies across institutions has been noted. In contrast, the present cross-sectional study clarified the prevalence of both cardiac and restrictive ventilatory involvement in Japan and further demonstrated their clinical severity by revealing the frequencies of cardiac device implantation and the use of ventilatory support. These findings emphasize the need for comprehensive monitoring and multidisciplinary management of both cardiac and respiratory involvement in patients with AMA-positive myositis.