Anti‐mitochondrial antibodies in Indian patients with idiopathic inflammatory myopathies

Aims Anti‐mitochondrial antibodies (AMAs) are associated with distinct clinical phenotypes including cardiac and hepatic manifestations in idiopathic inflammatory myopathies (IIMs). This article studies the prevalence, clinical characteristics and outcomes of AMA in Indian patients with IIM. Methods Patients (97: 81 adult, 16 juvenile) clinically diagnosed with polymyositis or antibody‐negative IIM were retrieved from the MyoCite bio‐archive. They were tested for myositis‐specific autoantibodies / myositis autoantibodies (MSAs/MAAs) using line immunoassay and antinuclear antibodies and AMAs using immunofluorescence assay (IFA). Patients were also screened for cardiac biomarkers (cardiac troponin I [c‐TnI] and N terminal‐pro brain natriuretic peptide [NT‐pro‐BNP] using immunometric immunoassay technique and enhanced chemiluminescence assay testing respectively) and hepatic manifestations using AMA testing. Results were formulated after carrying out analytical tests. Results Of the cohort, 5 adults (6.2%) (M:F 0:1) with a median age and disease duration of 37 years and 2 months respectively, tested AMA+ while the children tested negative. Dermatomyositis was the commonest phenotype, with amyopathic forms being common, often with MSA positivity. Cancer‐associated myositis and polymyositis were also seen. AMA positivity is associated with Gottron's sign and calcinosis. Comparable levels of C‐TnI and NT‐pro‐BNP and AMA testing in patients help to rule out subclinical cardiac and hepatic involvement respectively. Conclusion Anti‐mitochondrial antibodies are rare (6.2%) in different subtypes of IIM in the Indian population, and often coexist with MSAs. Their negative association with cardiac and hepatic involvement and probable association with Gottron's sign and calcinosis merit further investigation and long‐term follow‐up to understand the entire spectrum of the disease.