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Original Investigation
July 2017

Clinicopathologic, Immunohistochemical, and Molecular Features of Histiocytoid Sweet Syndrome

Author Affiliations
  • 1Departments of Dermatology and Pathology, Fundación Jiménez Díaz, Universidad Autónoma, Madrid, Spain
  • 2Department of Dermatology, Hospital Clínico Universitario, Salamanca, Spain
  • 3Department of Pathology, Hospital Universitario 12 de Octubre, Madrid, Spain
  • 4Department of Dermatology, Hospital General, Valencia, Spain
  • 5Department of Dermatology, Medical University of Graz, Graz, Austria
  • 6Dermatopathologie Laboratory, Friedrichshafen, Germany
JAMA Dermatol. 2017;153(7):651-659. doi:10.1001/jamadermatol.2016.6092
Key Points

Question  What is the nature of the infiltrating cells in histiocytoid Sweet syndrome?

Findings  In this case series study, double immunostaining in 33 cases of histiocytoid Sweet syndrome demonstrated that the infiltrate is mostly composed of immature myeloid cells.

Meaning  The dermal infiltrate of cutaneous lesions of histiocytoid Sweet syndrome is composed mostly of immature cells of myeloid lineage, but not of histiocytes, and it should not be interpreted as leukemia cutis; this histopathologic variant of Sweet syndrome is associated with hematologic malignancy with the same frequency as classic neutrophilic Sweet syndrome.


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 syndrome was 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 of myeloperoxidase-positive immature myelomonocytic cells with histiocytoid morphology. No cytogenetic anomalies were found in the infiltrate except in 1 case in which neoplastic cells of chronic myelogenous 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 of myeloid lineage. This infiltrate should not be interpreted as leukemia cutis.