What question did this study set out to answer?

The aim is to highlight the diagnostic challenges and therapeutic approaches for macrophage activation syndrome in the context of MDA5-positive dermatomyositis.

May 5, 2026Open Access

Macrophage Activation Syndrome in MDA5-Positive Dermatomyositis: A Diagnostic and Therapeutic Odyssey in a Young Adult

Key Points

The aim is to highlight the diagnostic challenges and therapeutic approaches for macrophage activation syndrome in the context of MDA5-positive dermatomyositis.
Case study of a 21-year-old male with MDA5-positive dermatomyositis presenting with symptoms consistent with MAS.
Diagnostic workup included laboratory tests, imaging, and biopsies to identify the cause of symptoms.
Treatment involved high-dose corticosteroids, IV immunoglobulin, and subsequent maintenance therapy.
The patient achieved stabilization after high-dose corticosteroids and IVIG, with sustained remission and resolution of symptoms at long-term follow-up.
Rituximab was discontinued due to infusion reactions; however, alternative therapies led to normalized lab values.
No evidence of active myositis or MAS flares was noted in follow-up evaluations.

Abstract

IntroductionMacrophage activation syndrome (MAS) is a rare, potentially fatal hyperinflammatory complication of autoimmune disease, characterized by fever, cytopenias, hyperferritinemia, and multiorgan involvement (1). In patients with inflammatory myopathies, MAS may mimic infection, pancreatitis, or medication reactions, posing diagnostic and management challenges (2).Case DescriptionA 21-year-old male with atopic dermatitis and MDA5-positive dermatomyositis presented initially in October 2023 with fever, fatigue, lymphadenopathy, and rash; EBV serology suggested infectious mononucleosis. Over subsequent months, he developed daily fevers, unintentional weight loss, proximal muscle weakness, inflammatory arthritis, and evolving rash. Laboratory evaluation revealed elevated creatine kinase (CK) (∼300s), ferritin 4,000–5,000 ng/mL, pancytopenia, elevated liver function tests (LFTs), and inflammatory markers. Imaging ruled out pancreatitis despite abdominal symptoms. Extensive workup included skin, liver, and bone marrow biopsies; autoimmune and infectious panels were otherwise unrevealing. MAS was suspected in February 2024 after worsening cytopenias and rising ferritin. The patient was admitted and treated with pulse IV methylprednisolone and intravenous immunoglobulin (IVIG), resulting in stabilization. Rituximab was attempted in April 2024 but discontinued due to an infusion reaction. Maintenance therapy included mycophenolic acid, hydroxychloroquine, and IVIG, with a gradual steroid taper. Long-term follow-up (through 2025) showed sustained remission, resolution of rash and systemic symptoms, and no evidence of active myositis or MAS flares.DiscussionMAS complicating MDA5-positive dermatomyositis is rare, life-threatening, and diagnostically challenging (2, 3). High clinical suspicion is warranted in patients with fever, hyperferritinemia, cytopenias, and multisystem involvement. Prompt high-dose corticosteroids and IVIG can induce remission, while biologics may be required in refractory cases. Multidisciplinary care and longitudinal monitoring (labs, IVIG cycles, and pulmonary evaluation) optimize outcomes.ConclusionsMAS should be considered in young adults with inflammatory myopathies presenting with persistent fever, cytopenias, and hyperferritinemia. Early recognition, aggressive immunosuppression, and coordinated care are essential to achieve remission and prevent long-term complications.

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