Characterizing the presence of neutrophil extracellular traps in neutrophilic dermatoses

Neutrophil extracellular traps (NETs) are implicated in the pathogenesis of multiple inflammatory dermatoses. However, characterization of NETs in neutrophilic dermatoses was performed on very limited number of patients; this limitation precluded definitive conclusions. In this case series of 57 patients, we compared the amounts of neutrophils producing NETs in cutaneous lesions of different entities of neutrophilic dermatoses (17 with pyoderma gangrenosum, 37 with Sweet's syndrome and three with subcorneal pustular dermatosis). NETs were identified by double immunofluorescence on formalin-fixed paraffin-embedded skin biopsies using antibodies against elastase and citrullinated histone 3. Percentages of neutrophils showing NETs were high across all three entities (62.9% in PG, 48.5% in SS and 37.8% in subcorneal pustular dermatosis). The differences in mean percentages were significant between entities, with PG showing significantly superior percentage of NETs compared with SS. In our series, 15.8% of neutrophilic dermatoses were associated with malignancies, 10.5% with autoimmune diseases and 73.7% were idiopathic. Percentages of NETs were not statistically different between aetiologies. These findings suggest that NETs are abundantly produced in the various entities and different aetiologies of neutrophilic dermatoses. In comparison with SS, the superior percentage of NETs in PG is clinically mirrored in its greater ulceronecrotic nature.