Criteria for diagnosis clinically: Numerous, smooth, erythematous papules with a dusky hue at the periphery distributed on the extremities can be a presentation of Sweet’s syndrome.
Differential diagnosis clinically: Leukocytoclastic vasculitis, urticaria and an urticarial drug eruption have to be excluded by skin biopsy.
Criteria for diagnosis histopathologically: A nodular superficial inflammatory infiltrate that consists of neutrophils, in company with nuclear “dust” of neutrophils, but also of lymphocytes and plasma cells, are changes consistent with an early lesion of acute febrile neutrophilic dermatosis.
Differential diagnosis histopathologically: Identical histopathologic changes can be seen in one presentation of pyoderma gangrenosum. This is not a leukocytoclastic vasculitis since there is no fibrin deposition in the walls of venules.
Clinico-pathologic correlation: The papules seen clinically correspond to the nodular inflammatory infiltrate situated in the upper part of the dermis. The surface is smooth because the epidermis is not affected. The red color is in part due to widened papillary blood vessels that are stuffed with erythrocytes and in part caused by extravasated erythrocytes.
Options for therapy predicated on knowledge of histopathologic findings: Oral corticosteroids, cyclosporine, and anti-TNF-α therapy with infliximab or etanercept have been shown to be successful. Since Sweet’s syndrome may be associated with lymphoproliferative diseases, especially acute myelogenous leukemia, appropriate diagnostic tests have to be performed prior to initiation of any therapy.