Clinicopathologic, immunohistochemical, and molecular features of histiocytoid sweet syndrome

Abstract

IMPORTANCE Histiocytoid Sweet syndrome is a rare histopathologic variant of Sweet syndrome. The nature of the histiocytoid infiltrate has generated considerable controversy in the literature. OBJECTIVE The main goal of this study was to conduct a comprehensive overview of the immunohistochemical phenotype of the infiltrate in histiocytoid Sweet syndrome.We also analyze whether this variant of Sweet syndrome is more frequently associated with hematologic malignancies than classic Sweet syndrome. DESIGN This is a retrospective case series study of the clinicopathologic, immunohistochemical, and molecular features of 33 patients with a clinicopathologic diagnosis of histiocytoid Sweet syndromewas conducted in the dermatology departments of 5 university hospitals and a private laboratory of dermatopathology. MAIN OUTCOME AND MEASURES The clinical, histopathological, immunohistochemical, and follow-up features of 33 patients with histiocytoid Sweet syndrome were analyzed. In some cases, cytogenetic studies of the dermal infiltrate were also performed.We compare our findings with those of the literature. RESULTS The dermal infiltrate from the 33 study patients (20 female; median age, 49 years; age range, 5-93 years; and 13 male; median age, 42 years; age range, 4-76 years) was mainly composed ofmyeloperoxidase-positive immaturemyelomonocytic cells with histiocytoid morphology. No cytogenetic anomalies were found in the infiltrate except in 1 case in which neoplastic cells of chronicmyelogenous leukemia were intermingled with the cells of histiocytoid Sweet syndrome. Authentic histiocytes were also found in most cases, with a mature immunoprofile, but they appeared to be a minor component of the infiltrate. Histiocytoid Sweet syndrome was not more frequently related with hematologic malignancies than classic neutrophilic Sweet syndrome. CONCLUSIONS AND RELEVANCE The dermal infiltrate of cutaneous lesions of histiocytoid Sweet syndrome is composed mostly of immature cells ofmyeloid lineage. This infiltrate should not be interpreted as leukemia cutis.