Juvenile dermatomyositis associated with autoantibodies to small ubiquitin-like modifier activating enzyme: a report of 4 cases from North India and a review of literature

Background Juvenile dermatomyositis (JDM) is the commonest inflammatory myositis in children. The clinical phenotype is often characterized by the presence of myositis-specific antibodies (MSA). Antibodies to small ubiquitin-like modifier activating enzyme (SAE) are amongst the rarest MSA reported in children. Materials and methods A review of medical records of all patients diagnosed to have JDM during the period January 1992–April 2022 in our institute was done. Case records of children with JDM who had significant positivity for anti-SAE antibody by myositis immunoblot were analysed in detail. Results Of the 140 children with JDM, MSA immunoblot was carried out in 53 patients—4 (7.5%) amongst these had significant positivity for anti-SAE antibodies. Median age of onset of symptoms was 5.5 years (range: 5–11 years). Clinical features at presentation included fever, photosensitivity, heliotrope rash, and Gottron papules. Clinically significant proximal muscle weakness was noted in 3/4 patients; 1 had no discernible weakness but had radiological evidence of myositis. None of the 4 patients had evidence of interstitial lung disease or calcinosis. All patients were treated with intravenous pulse methylprednisolone: subcutaneous weekly methotrexate and hydroxychloroquine. One patient received mycophenolate mofetil because of a relapse of muscle disease, while none received cyclophosphamide or biologics. Median follow-up duration was 21.5 months (range: 6–39 months). Conclusion Anti-SAE antibodies were found in 4/53 (7.5%) of North Indian children with JDM. All 4 patients had predominant cutaneous manifestations followed by muscle disease. Response to treatment was brisk and sustained. None had developed calcinosis in the follow-up. Key messages 1. We report high prevalence of anti-SAE antibody positivity (7.5%) in North Indian cohort of JDM. 2. Cutaneous disease precedes muscle weakness in children with anti-SAE positive JDM. 3. No evidence of interstitial lung disease/calcinosis was seen in these children.