Anti-Melanoma Differentiation-Associated Gene 5 Antibody-Positive Juvenile Dermatomyositis Presenting With...

Anti-melanoma differentiation-associated gene 5 (MDA5) positive juvenile dermatomyositis (JDM) (anti-MDA5+ JDM) is a distinct subtype of JDM characterized by marked clinical heterogeneity. Although cutaneous manifestations and interstitial lung disease (ILD) are well recognized, atypical musculoskeletal presentations may lead to diagnostic delay.

We report a 16-year-old male with anti-MDA5+ JDM who presented with progressive joint contractures as the predominant manifestation over a 2-year period. The patient also exhibited restricted mouth opening, with a classical dermatomyositis (DM) cutaneous rash absent or only mild, and proximal muscle weakness, mild to moderate. Laboratory evaluation revealed high-titer anti-MDA5 antibodies and a markedly elevated serum immunoglobulin E (IgE) level. Magnetic resonance imaging (MRI) demonstrated periarticular and soft-tissue involvement, and muscle biopsy confirmed pathological features consistent with DM. Treatment with systemic glucocorticoids in combination with methotrexate resulted in substantial improvement in joint mobility, with good tolerability during follow-up.

Progressive contractures can occasionally become the predominant presenting manifestation in anti-MDA5+ JDM and contribute to diagnostic delay. This case underscores the importance of early evaluation for idiopathic inflammatory myopathies (IIM), including myositis-specific antibody (MSA) testing and muscle biopsy, in adolescents with unexplained progressive joint contractures.