Spectrum of clinical phenotypes associated with myositis-specific and myositis-associated antibodies in juvenile idiopathic inflammatory myositis: Our experience from North India.

BACKGROUND

Myositis-specific autoantibodies (MSAs) and myositis-associated autoantibodies (MAAs) are increasingly being identified in juvenile inflammatory myositis (JIIM). The current study's objective was to characterize the incidence and clinical-phenotypic profile of MSA/MAA in a cohort of JIIM from North India.

METHODS

We reviewed the medical records of the Pediatric Rheumatology Clinic of a tertiary care referral centre in Chandigarh, North India (1992 to 2024) and analysed the clinical details of children with JIIM. MSA/MAAs were assayed using a 16-antigen kit immunoblot assay (Euroline Autoimmune Inflammatory Myopathies 16 Ag, Euroimmune, Lübeck, Germany).

RESULTS

Of the 173 patients of JIIM in our cohort, assay for MSA/MAA was performed in 113 patients which included juvenile dermatomyositis (n=89), clinically amyopathic dermatomyositis (n=8), overlap myositis (n=13), and juvenile polymyositis (n=3). Autoantibody positivity was seen in 72.5% (82/113; MSA =70, MAA=12) of the children, with anti-NXP2 (n=24) being the most common followed by anti-MDA5 (n=14), anti-TIF-1γ (n=12), anti-Mi 2 (n=9) in that order. Patients with NXP2 positivity were younger at onset [3.15 years; (1.2-11.88 years) p=0.015], had severe muscle weakness at onset (p=0.04) and persistent calcinosis (p=0.004) in follow-up. Patients with anti-TIF1γ antibody were observed to have persistent skin lesions (p <0.001) during follow-up. Incidence of arthritis (p=0.001), inverse Gottron papules (p=0.003), skin ulceration (p=0.065), oral ulcers (p=0.012), and ILD (p<0.001) were high in anti-MDA5-JDM.

CONCLUSION

Anti-NXP2 antibody is the most common MSA noted in our North Indian cohort of JIIM. The findings emphasize the importance of region-specific data in understanding disease variability and guiding management.