S8C34aP20a-1: The pattern is that of a diffuse, neutrophilic collagenosis of the reticular dermis with papillary dermal edema. There are scattered sub-epidermal pustules. The pallor and acidophilia of the epidermis is a degenerative change, possibly related to ischemia. Although the infiltrates of neutrophils are prominent, necrosis is not a feature in this field. The differential diagnosis would include pyoderma gangrenosum and Sweet’s syndrome. Clinically, the process was classified as pyodermal gangrenosum; histologically, it most closely resembles Sweet’s syndrome, but is complicated by an associated vasculitic component.

S8C34aP20a-2: The interstitial infiltrates are composed of neutrophils with an admixture of histiocytes. There are fragments of nuclear debris. The patterns are those of a neutrophilic collagenosis.

S8C34aP20a-3: In this field, there are perivascular deposits of fibrin. The vessel wall is intact but this is a pattern that may be seen in the setting of the so-called leukocytoclastic angiitides. A vasculitic component, as seen in this field, is usually a feature of the patterns in a lesion of pyoderma gangrenosum. It is acceptable in the clinical setting of Sweet’s syndrome (i.e., a presentation in which the clinical setting is more in keeping with Sweet’s syndrome than pyoderma gangrenosum; the distinctions occasionally are that arbitrary).