Local neutrophil and eosinophil extracellular traps formation in pyodermatitis pyostomatitis vegetans

Abstract Pyodermatitis pyostomatitis vegetans is a rare inflammatory condition, affecting the skin and/or mucous membrane. Some cases include both skin and mucous involvement, whereas others develop either skin or mucous lesions only. The typically affected areas are the scalp, face, trunk and extremities, including the flexural areas and umbilicus. Clinical features show erosive granulomatous plaques, keratotic plaques with overlying crusts and pustular lesions. Among mucous lesions, oral mucosa is most frequently involved, and gingival erythema, shallow erosions, cobblestone‐like papules on the buccal mucosa or upper hard palate of the oral cavity are also observed. Some of the lesions assume a ‘snail track’ appearance. Although there are several similarities between pyodermatitis pyostomatitis vegetans and other diseases, that is pyoderma gangrenosum, pemphigus vegetans and pemphigoid vegetans, the histopathological features of pyodermatitis pyostomatitis vegetans are unique in that epidermal hyperplasia, focal acantholysis and dense inflammatory infiltrates with intraepidermal and subepidermal eosinophilic microabscesses are observed. Direct immunofluorescence findings are principally negative. Activated neutrophils are supposed to play an important role in the pathogenesis of pyodermatitis pyostomatitis vegetans. The expression of IL‐36 and neutrophil extracellular traps (NETs) was observed in the lesional skin, and additionally, eosinophil extracellular traps (EETs) was detected in pyodermatitis pyostomatitis vegetans. A possible pathogenic role of NETs and EETs in the innate immunity and autoinflammatory aspects of pyodermatitis pyostomatitis vegetans was discussed.