Acute febrile neutrophilic dermatosis: a histopathologic study of 31 cases with review of literature.

Sweet syndrome is a neutrophilic dermatosis defined by diagnostic criteria that include the lack of evidence for leukocytoclastic vasculitis. Because of the clinicopathological similarities on the one hand and the strict exclusion on the other hand, we were interested in a systematic evaluation of the relationship between these two diseases. We investigated the clinical and histopathological characteristics of 31 patients with Sweet syndrome, comparing our cases with 32 cases of leukocytoclastic vasculitis (including seven cases of urticarial vasculitis) and tried to place them in the background of published cases. There is a close relationship between Sweet syndrome and leukocytoclastic vasculitis in terms of clinical appearance, histopathological pattern, triggers, disease course, and response to treatment. The majority of the cases (23/31; 74%) showed histologic evidence of vasculitis, including nuclear dust, extravasation of erythrocytes, fibrin in and around vessel walls, and degeneration of collagen. Although one original criterion for Sweet syndrome is the absence of vasculitis, we propose that vasculitic changes should not exclude the diagnosis of Sweet syndrome. In contrast, Sweet syndrome can demonstrate vasculitis and may, similarly to urticarial vasculitis, be regarded a variant of leukocytoclastic vasculitis. Clinicopathologic characteristics with acute onset of juicy papules, plaques mostly on the face, shoulder, and trunk, and prominent edema probably reflect modifications of the pathogenetic process based on location and disease acuity.