Pyoderma gangrenosum and Sweet syndrome: the prototypic neutrophilic dermatoses

Summary Pyoderma gangrenosum, a dramatic ulcerative skin disease, and Sweet syndrome, a papular dermatosis, were described independently. It was subsequently shown that they share many characteristics, including clinical overlap and the frequent association with multisystemic disorders. The group of the neutrophilic dermatoses encompasses these two dermatoses, as well as other conditions having in common an aseptic neutrophilic infiltrate predominating in the epidermis and/or the dermis and/or the subcutis. Some patients also experience neutrophilic infiltrates in other organs, defining the neutrophilic disease. Recent research suggests that the neutrophilic dermatoses could be considered as the cutaneous expression of the autoinflammation, an aberrant hyperproduction of interleukin‐1. Autoinflammation is responsible for monogenic diseases, and is also involved in the mechanism of many polygenic conditions, including the neutrophilic dermatoses. What's already known about this topic? Pyoderma gangrenosum and Sweet syndrome are the prototypic conditions of the vast group of the neutrophilic dermatoses, characterized by an aseptic infiltration of the skin by polymorphonuclear leucocytes. A similar infiltration may also occur in internal organs, defining the neutrophilic disease. The principles of the management of patients with a neutrophilic disease have been properly described. What does this study add? The genetic and molecular mechanisms of neutrophilic inflammation are currently poorly understood. They may be similar to the mechanisms of the monogenic autoinflammatory diseases, which are among the rare causes of neutrophilic dermatoses.