Rituximab Combined With Azathioprine for Relapsed Anti-MDA5 Antibody-Positive Dermatomyositis With Interstitial Lung Disease: A Case Report.

Background: Antimelanoma differentiation-associated gene 5 (MDA5) antibody-positive dermatomyositis (MDA5(+) DM) is frequently complicated by interstitial lung disease (ILD) and is associated with a high risk of relapse. Optimal management after relapse remains unclear. Case Presentation: A 63-year-old woman presented with characteristic cutaneous manifestations of dermatomyositis and ILD without muscle involvement. She was diagnosed with MDA5(+) DM complicated by ILD and initially treated with high-dose glucocorticoids, tacrolimus, and intravenous cyclophosphamide, resulting in clinical improvement. However, after discontinuation of calcineurin inhibitor therapy due to adverse events, disease relapse occurred, characterized by worsening cutaneous lesions, progression of pulmonary infiltrates, and an increase in anti-MDA5 antibody titers. Subsequently, azathioprine was initiated, and rituximab was administered thereafter. Both clinical and radiological findings improved, and anti-MDA5 antibody titers progressively decreased. Repeated rituximab infusions were followed by stable clinical findings, allowing glucocorticoid tapering without further relapse. Conclusion: This case suggests that rituximab combined with azathioprine may be a therapeutic option for disease control after relapse with MDA5(+) DM-ILD.