Early recognition of a macrophage activation-associated hyperinflammatory state in anti-melanoma differentiation-associated gene 5 antibody-positive dermatomyositis with rapidly progressive interstitial lung disease: a case report

Anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive dermatomyositis is frequently complicated by rapidly progressive interstitial lung disease (RP-ILD) and is associated with poor prognosis. In some cases, excessive systemic inflammation related to macrophage activation may occur and contribute to disease severity. We report the case of a 59-year-old Japanese woman with anti-MDA5 antibody-positive dermatomyositis complicated by RP-ILD. She initially presented with skin rash and dyspnea, followed by declining vital capacity and progressive proximal muscle weakness. Laboratory evaluation revealed cytopenia and hyperferritinemia. Bone marrow examination performed because of leukopenia demonstrated hemophagocytosis by activated macrophages. Although the diagnostic criteria for macrophage activation syndrome were not fully met, these findings suggested a macrophage activation-associated hyperinflammatory state. In view of the progressive interstitial lung disease and suspected hyperinflammation, therapeutic intensification was undertaken by adding plasma exchange and intravenous cyclophosphamide to corticosteroids and tacrolimus. Following treatment escalation, cytopenia, pulmonary function, and muscle strength gradually improved. This case highlights the importance of recognizing macrophage activation-associated hyperinflammation in anti-MDA5 antibody-positive dermatomyositis. Early recognition and prompt therapeutic intensification may contribute to improved clinical outcomes.