Sweet syndrome

Sweet syndrome – low magnification 1
Sweet syndrome – high magnification 1

Sweet syndrome – low magnification 2
Sweet syndrome – high magnification 2
Histiocytoid variant

Sweet syndrome – low magnification

LEGEND

There is no true leukocytoclastic vasculitis (no fibrinoid necrosis), but neutrophilic debris and possible endothelial swelling may be observed.

Significant papillary dermal edema may be present, and if severe, can lead to a subepidermal blister. Red blood cell extravasation is noted.

The epidermis is variable. In this case, there is mild spongiosis in response to a few migrating cells in the epidermis

Interstitial dermal infiltrate of neutrophils with some lymphocytes, histiocytes, and eosinophils

Sweet syndrome – high magnification

LEGEND

Diffuse and interstitial dermal infiltrate of neutrophils with neutrophilic debris
Red blood cell extravasation

Sweet syndrome – low magnification

LEGEND

There are several variants of Sweet syndrome. This one is the histiocytoid variant.

Histiocytoid Sweet is not a form of Sweet syndrome that includes histiocytes in the infiltrate, but rather immature myeloid cells (neutrophils) that are large and have non-lobulated nuclei, making them resemble histiocytes

Due to these immature myeloid cells, histiocytoid Sweet must be differentiated from leukemia cutis

The presence of histiocytoid Sweet increases the likelihood that the Sweet syndrome is secondary to a myeloproliferative disorder.

Classic finding: edema in the papillary dermis
Diffuse and interstitial dermal infiltrate of neutrophils with some lymphocytes, histiocytes, and eosinophils