Prevalence and risk surveillance of anti-mitochondrial antibody-positive myositis: Outcomes of a nationwide survey

Background: Anti-mitochondrial antibody (AMA)-positive myositis is a chronic disease characterized by skeletal muscle atrophy and is associated with cardiac complications and restrictive ventilatory impairment. This study aimed to determine the prevalence, rate of organ complications, and prognostic risk factors of AMA-positive myositis.

Methods: We conducted a cross-sectional study using a nationwide questionnaire from 2011 to 2021, enrolling participants from neurology departments at 811 facilities certified by the Japanese Society of Neurology.

Results: A total of 380 patients were identified, with a prevalence rate of 0.3 per 100,000 persons. The frequencies of cardiac complications and restrictive ventilatory impairment were 53 and 33 %, respectively; whereas, those of cardiac device and respirator introduction were 32 and 22 %, respectively. The frequencies of recurrence, subacute exacerbation, no muscle strength improvement, cardiac device introduction, respirator introduction, and death were 29, 25, 54, 32, 22, and 12 %, respectively. According to univariate analysis, abnormal echocardiograms (odds ratio [OR], 5.43), restrictive ventilatory impairment (OR, 3.70), and inflammatory changes revealed by muscle biopsy (OR, 0.34) were associated with subacute exacerbations, whereas abnormal echocardiograms (OR, 8.00) and durations from onset to admission and diagnosis (OR, 2.99) were associated with cardiac device introduction. Multivariable analysis showed that restrictive ventilatory impairment was associated with recurrence (adjusted OR, 3.01), adjusted for the duration from onset to admission and diagnosis, and with subacute exacerbations (adjusted OR, 3.86), adjusted for abnormal echocardiograms and inflammatory changes.

Conclusions: AMA-positive myositis is characterized by severe and urgent organ complications, and anticipatory management is critical for management of this disease.