Anti-MDA5 Antibody-Positive Dermatomyositis (MDA5-DM): A Case Report

Summary: Background: MDA5-DM is a rare systemic autoimmune disease with clinically amyopathic dermatomyositis (CADM) and rapidly progressive interstitial lung disease (ILD). It is characterized by a typical DM rash, polyarthralgia, and ILD, in the absence of the typical clinical signs of myositis. This case highlights the presentation of a rare and often misdiagnosed disease. Case Presentation: Patient is a 25-year-old male who presented to the rheumatology clinic for persistent fevers along with bilateral upper extremity paresthesia, diffuse rash, arthritis, dyspnea on exertion, dry cough, loose stools, muscle weakness, periorbital edema, and unintentional 40-pound weight loss. He did not improve on antibiotics. Prednisone improved some symptoms. CT showed multiple nodular ground glass opacities in the lung bases. Further workup showed elevated ACE, ESR, LDH, AST/ALT, and positive EBV IgG/Ig. Positive for MDA-5 and SSA. PFTs showed low DLCO at 52%. Given positive MDA-5 and worsening dyspnea on exertion, there was concern for rapidly progressive ILD. He was started on mycophenolate mofetil, IVIG, hydroxychloroquine, and eventually rituximab. Medications were stopped due to nausea and suicidal ideation. Overall, he has seen improvement in his skin ulcers and rash. He still has mild periorbital edema. He continues to have joint swelling. Medications need to be resumed and changed to alleviate GI symptom. d. Discussion MDA5-DM is often misdiagnosed and has high morbidity and mortality, making early diagnosis crucial for better outcomes. This case highlights the importance of clinicians to be able to recognize the combination of distinctive DM rash, ILD, and the absence of muscle involvement as concerning for MDA5-DM. Diagnostic categorization of idiopathic inflammatory myopathies (IIMs) can be challenging. Myositis specific antibodies can help facilitate diagnostic reasoning and help with prognostication and guide management. Treatment of MDA5-DM involves high doses of steroids in addition to aggressive immunosuppression, which might include a combination of MMF, cyclophosphamide, tacrolimus. Additional therapies, such as rituximab, tofacitinib, basiliximab can be used depending on organ manifestations. IVIG may be added for resistant skin disease for quick results. Conclusion: MDA5-DM is a rare but rapidly progressive disease whose diagnosis and treatment poses a huge challenge to clinicians. This case highlights the importance of recognizing the combination of dermatomyositis rash and rapidly progressive ILD as concerning for MDA5-DM. Awareness of the complexity of this autoimmune condition and early recognition of presenting symptoms and associated conditions could help in tackling this challenge.