Myositis-specific and myositis-associated autoantibodies in a large Indian cohort of inflammatory myositis.

The Idiopathic Inflammatory Myositis (IIM) are heterogenous with distinct clinical phenotypes associated with specific myositis specific antibodies (MSA) and myositis associated antibodies (MAA). To evaluate the frequency, pattern and associations of MSA/MAA in a large Indian cohort of IIM. Adult and juvenile IIM (2017 ACR/EULAR criteria), were recruited in the MyoCite cohort between 2017and 2020 at a tertiary center in Northern India. Standardized clinical and laboratory variables were extracted from the database archive. Serum samples were evaluated for the presence of MSAs/MAAs by Line immunoassay and anti-nuclear antibodies (ANA) by Immunofluorescence assay (IFA). The prevalence and clinical associations of different MSA/MAAs were assessed. MSA and MAAs were tested in 250 IIM patients (214 adults, 36 children) of age [40 (30^–49), 13 (7.5–16) years] and disease duration [ 7 (3–17), 6 (2–17) months] comprising predominantly of Dermatomyositis (DM) followed by Overlap myositis (OM). MSAs/MAAs were found in 148 (59.2%, 60.7% adults and 50% JIIM), of which two-thirds were MSA (95, 64% overall). Two cases (0.8%) had more than one MSA. In adult IIM, the most common MSA was anti-Jo-1 (10%), whereas it was anti-MDA5 and anti-NXP2 4 (11%) each in Juvenile IIM (JIIM). 76.0% (172/226) were ANA positive, with speckled pattern being the most common (37%,). Nearly two-thirds (54, 61%) of those with negative ANA had MSA/ MAA. Nearly half (18/54, 54.6%) had MSA associated with cytoplasmic patterns. ARS (anti-aminoacyl-tRNA synthetase) were associated with mechanic's hands (OR-7.06), ILD (OR-4.4), and arthritis (OR-2.23). Clinical associations of anti-Jo-1 and non-Jo-1 Anti synthetase syndrome (ASS) did not differ. Anti-MDA-5 associated with oral ulcers (OR-8.3), fever (OR-8.6) and weight loss (OR-7.35) in adults, and arthritis (OR-11.5), and periungual rash (OR-9.6) in children. Anti-TIF-1γ associated with photosensitivity (OR-10.44) and malignancy (OR-34) in adults, and cuticular overgrowth (OR-11.2) in children. Myositis autoantibodies are seen in two-thirds IIMs and are associated with distinct clinical subsets. Jo-1 and non-Jo-1 ASS exhibit similar characteristics. The association of anti-TIF1 γ with malignancy was confirmed in adults. MSA/MAA were present in two-thirds of those with negative ANA and MSA were nearly always mutually exclusive. [ABSTRACT FROM AUTHOR]