Skin vasculitis and cardiac eosinophil extracellular trap formation in eosinophilic granulomatosis with polyangiitis: A case report.

The pathophysiology of organ involvement in eosinophilic granulomatosis with polyangiitis is characterised by vasculitis and eosinophilic inflammation, which can be accompanied by eosinophil extracellular trap cell death (EETosis). Clinically, eosinophilic inflammation is often observed in the lungs, gastrointestinal tract, and heart, whereas vasculitis more frequently affects the peripheral nerves, skin, and kidneys. However, histopathological confirmation of vasculitis and EETosis in different organs within the same patient has rarely been reported. We report a patient with EGPA presenting with both cutaneous and cardiac involvement. Skin biopsy findings were consistent with cutaneous fibrinoid vasculitis with prominent eosinophilic infiltration. Prednisolone therapy led to improvement of the skin lesion and inflammatory markers within 1 month. In contrast, endomyocardial biopsy demonstrated marked eosinophilic infiltration with cytolytic degranulation and extracellular deposition of eosinophil granule proteins, without evidence of fibrinoid vasculitis. Immunofluorescence findings supported the presence of EETosis. Despite prompt methylprednisolone pulse therapy, the cardiac lesion showed limited response and was complicated by refractory arrhythmias. This case suggests that distinct pathogenic mechanisms, namely vasculitis and EETosis, may predominate in different organs even within the same patient, potentially leading to discrepant treatment responses. When EETosis-driven pathology is dominant, conventional immunosuppressive therapy may have limited efficacy, highlighting the need for therapeutic strategies targeting EETosis.