Pyoderma gangrenosum: A systematic review of the molecular characteristics of disease.

Pyoderma gangrenosum is a painful recurrent ulcerative neutrophilic dermatosis in which the pathogenesis is incompletely defined. Current evidence suggests that PG is associated with dysregulation of components of both the innate and adaptive immune system with dysregulation of neutrophil function and contribution of the Th17 immune axis. PG can be present in numerous heterogeneous clinical presentations and be associated with multiple inflammatory conditions including rheumatoid arthritis, inflammatory bowel disease and hidradenitis suppurativa. However, no critical evaluation of the observed molecular characteristics in PG studies in association with their clinical findings has been assessed. Additionally, emerging evidence suggests a potential role for other cell types and immune pathways including B cells, macrophages, autoantibodies and the complement system in PG, although these have not yet been integrated into the pathogenesis of disease. This systematic review aims to critically evaluate the current molecular observations regarding the pathogenesis of PG and discuss associations with clinical characteristics as well as the evidence supporting novel cell types and immune pathways in PG.