Anti-MDA5 Positive Juvenile Dermatomyositis With Macrophage Activation Syndrome: A Case Report

There are several types of inflammatory myopathies, including juvenile dermatomyositis (JDM), which is characterized by muscle inflammation that can eventually lead to weakness. A devastating complication of JDM is macrophage activation syndrome (MAS), although reports of MAS in JDM patients are limited. Additionally, cases of JDM associated with positive anti-MDA5 are rare and represent a fatal subtype of inflammatory myopathies, with a significant risk of lung impairment. This case report discusses a six-year-old girl presenting with proximal muscle weakness and cutaneous changes, including heliotrope rash and Gottron's papules, who was diagnosed with JDM. Muscle involvement was confirmed through MRI of the thigh muscles. Laboratory findings revealed elevated aldolase, hepatitis, high lactate dehydrogenase, and hyperferritinemia, leading to a diagnosis of JDM complicated by MAS. Pulse steroid therapy combined with cyclosporine was initiated, and she showed significant improvement initially. However, she later tested positive for anti-MDA5 antibodies, a marker associated with a poor prognosis. Highlighting MAS as a potential complication in JDM cases with positive anti-MDA5 antibodies can help physicians recognize this outcome and consider it in the differential diagnosis.