Neutrophilic dermatoses with unusual and atypical presentations.

Neutrophilic dermatoses (NDs) are a group of reactive, noninfectious autoinflammatory diseases characterized by (1) infiltration of the epidermis, dermis, and or/hypodermis by neutrophils; (2) their association with distinct diseases (eg, hematologic malignancy and chronic inflammatory diseases); (3) potential extracutaneous involvement; and (4) response to anti-inflammatory drugs, such as corticosteroids, dapsone, colchicine, and novel biologic therapies, such as the anti-interleukin-1 blockade. Although distinct NDs have been described, transitional forms with overlapping features are often identified. These justify a simplified classification of NDs with three major forms: superficial (epidermal or pustular) NDs, dermal (en plaques) NDs, and deep NDs. We review selected or novel variants of NDs, including subcorneal pustular dermatosis, the group of immunoglobulin A neutrophilic dermatoses, amicrobial pustular dermatosis of the folds, and neutrophilic urticarial dermatosis, as well as atypical forms of Sweet syndrome and pyoderma gangrenosum closely mimicking severe infectious diseases. Knowledge of these variants is essential for proper diagnosis, adequate management, and avoidance of a dangerous escalation of therapy, such as unnecessary immunosuppression or extensive surgery.