Neutrophilic and Pustular Eruptions

This chapter reviews noninfectious inflammatory dermatoses with mainly neutrophilic infiltrates and the formation of pustules. The infiltrate containing neutrophils may be either mild as in urticaria or very dense, even with leukocytoclasia as in Sweet syndrome or pyoderma gangrenosum. Neutrophilic infiltrates and pustular eruptions are caused by different noninfectious immunomechanisms. For some of them, mutations have been found (e.g., NLRC4 mutation in cryopyrin-associated periodic syndromes (CAPS) leading to activation of the inflammasome; IL36RN mutation in pustular psoriasis resulting in uncontrolled IL36-signaling). Neutrophilic dermatoses are of high interest, as they may present dermatological reaction patterns of underlying benign or malignant conditions.