[510] Nine Cases of Histiocytoid Sweet's Syndrome

Xuan Wang, Cynthia M Magro. Weill Medical College of Cornell University, New York, NY

Background: Histiocytoid Sweet's syndrome was first described by Requena et al in 2005 to describe a distinct variant of Sweet's syndrome with specific morphologic features. Its hallmark is an infiltrate of histiocytoid mononuclear cells with an eccentrically disposed C-shaped nucleus. Based on positivity of these cells for myeloperoxidase (MPO), it was hypothesized that the cells were immature neutrophils. Although the original series reported underlying myeloproliferative disease in 1 of 41 cases, subsequent papers described its occurrence in the setting of clonal myeloproliferative disorders. The importance in recognizing this syndrome was to expand the histomorphologic spectrum of Sweet's syndrome and avoid confusion with leukemia cutis.
Design: Nine cases of histiocytoid Sweet's syndrome were encountered. Clinical features, and light microscopic and phenotypic profile were reviewed.
Results: The patients' ages range from 35 to 79 with 6 males and 3 females. There was involvement of arms in 4 and legs in 4 while a truncal distribution was seen in 1. There was accompanying arthralgias and fevers in 1. Among potential triggers and disease associations were myelodysplastic syndrome in 3, acute myelogenous leukemia in 1, advanced endometrial carcinoma in 1 and marginal zone lymphoma in 1. In the patient with marginal zone lymphoma, the eruption was preceded by herpes zoster. One case was related to high doses of Cox 2 inhibitor. The cases showed an interstitial and perivascular mononuclear infiltrate with a minor component of neutrophils. The mononuclear cells demonstrated a distinctive morphology characterized by eccentrically disposed C-shaped nuclei with eosinophilic cytoplasm. In 2 cases the process was confined to subcutis. Phenotypically, the cells were not only positive for MPO but also for CD163 and variably positive for MXA, CD16, CD14, CD123, CD4, and CD68. Chloroacetate esterase was negative.
Conclusions: We found a significant association with underlying myeloproliferative disease and other malignancies. The extent of histiocytoid infiltration varied however; in certain cases the infiltrate was misinterpreted as leukemia cutis. Immunohistochemical studies showed that the MPO+ cells were CD163+ and CD14+ confirming their origin as a monocyte rather than an immature neutrophil. In this regard the designation of histiocytoid seems appropriate. This exact same cell type has been implicated in Kikuchi's disease. The MPO+ histiocyte is a specific subset of macrophages that may be attracted to sites devoid of granulocytes to provide MPO for oxidative processes.
Category: Dermatopathology

Wednesday, March 6, 2013 9:30 AM

Poster Session V # 77, Wednesday Morning


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