Background Juvenile dermatomyositis (JDM) is a rare childhood autoimmune inflammatory muscle disorder that can result in severe disability or death. Children with JDM can have autoantibodies in their sera like other autoimmune diseases [1]. Over the last few years, few novel Myositis Specific Antibodies (MSA) have been identified. Some phenotypical associations have been described with these autoantibodies like anti p-140 (anti NXP2) has been shown to have correlation with calcinosis in children with JDM [1–2].

Objectives To study autoantibody profile and to look for phenotypical associations of autoantibodies in JDMS.

Methods Cross-sectional retrospective study. All children diagnosed to have JDM, registered from 1995 to 2015 in Pediatric Rheumatology Clinic at Post Graduate Institute of Medical Education and Research Chandigarh, India and who were tested for autoantibodies were included in the study. Clinical findings, antinuclear antibodies (ANA), autoantibody for MSA and myositis associated autoantibodies (MAA) were noted from the careful scrutiny of case records. Immunoglobulin G (IgG) antibodies against Jo1, threonyl-tRNA synthetase (PL7), alanyl-tRNA synthetase (PL12), glycyl-tRNA synthetase (EJ), Signal Recognition Particle (SRP), Mi-2, MDA-5, Transcriptional intermediary factor 1-γ (TIF-1γ), Ku, PMScl 100, Scl 70 and SSA/Ro 52 have been done by Immunodot. Evaluation for anti p-140 or Nuclear Matrix Protein (NXP2) and anti 200/100 or 3-Hydroxy-3-Methyglutaryl-Coenzyme (HMG CoA reductase) was done using ELISA.

Results Antinuclear antibody (ANA) testing was done in 97 patients. Forty six (47.4%) tested positive. In addition, MSA and MAA were assessed. Anti-SRP antibodies were present in 4 (11.4%) children, anti-MDA5 in 3 (8.6%), anti-Mi2 in 1 (2.9%) and 1 patient tested positive for anti-SSA/Ro52 antibodies. All 4 children with anti-SRP were girls, had polycyclic course and 2 of them developed calcinosis. Patients with anti-MDA5 had predominant skin involvement, less severe muscle disease and followed a monocyclic course. Two of them had arthritis/arthralgia at the time of presentation. The only patient with anti-Mi2 had normal muscle strength/endurance at the time of follow up. None of the patients had anti synthetase antibodies (anti-Jo1, anti-PL-7, anti-PL-12, anti-EJ), anti-ku or anti-Scl-70. None of the subjects tested positive for anti-NXP2 or anti- HMG CoA.

Conclusions Prevalence of autoantibodies in children with JDM in our study is similar to what has been described previously. Type of autoantibodies, though, is not similar. This may be due to ethnic differences of the population. Autoantibodies were tested in children while they were on treatment. This may have resulted in lower positivity. Evaluation of autoantibody profile at the time of diagnosis may assist in predicting the course of disease and response to treatment.

References

1. Targoff IN, Mamyrova G, Trieu EP, Perurena O, Koneru B, O'Hanlon TP, et al. A novel autoantibody to a 155-kd protein is associated with dermatomyositis. Arthritis Rheum 2006; 54: 3682–9.

2. Gunawardena H, Wedderburn LR, Chinoy H, Betteridge ZE, North J, Ollier WER, et al. Autoantibodies to a 140-kd protein in juvenile dermatomyositis are associated with calcinosis. Arthritis Rheum 2009;60: 1807–14.

References

Disclosure of Interest None declared