Acute febrile neutrophilic dermatosis, is a reactive process characterized by the sudden onset of tender, red-to-purple papules, and nodules that coalesce to form plaques over the skin. These plaques usually occur in the upper extremities, face or neck, often accompanied by fever and peripheral neutrophilia (increase in white blood cells count).
It was first described in 1964 by Robert Sweet; it can range from Classic Sweet disease which commonly occurs in young women after a mild respiratory illness to a more aggressive neutrophilic process, which may be associated with other inflammatory disease or malignant tumors. In fact, the lesions can be the first evidence of an underlying condition and should prompt further investigation. It can also occur due to some medications.
The diagnosis of Sweet's syndrome is based on clinical and histopathological studies. The characteristics that distinguish the Sweet syndrome lesions from other neutrophilic dermatoses are wound healing without scarring and the absence of vasculitis.