title: Histiocytoid Sweet syndrome is infiltrated predominantly by M2-like macrophages.
abstract: BACKGROUND
  Histiocytoid Sweet syndrome (HSS) is a rare variant of Sweet syndrome (SS). The nature of histiocytoid cells is still uncertain.
  
  
  OBJECTIVE
  We sought to offer a comprehensive overview on clinical features of HSS and further information on immunohistochemical phenotype of the infiltrate.
  
  
  METHODS
  The clinical, histologic, and immunohistochemical features of 12 of our patients with HSS and all cases retrieved through a PubMed search were analyzed.
  
  
  RESULTS
  Lesions consisted of erythematous-violaceous papules and plaques, randomly distributed mostly on the trunk and the limbs. Three patients had myelodysplastic syndrome and 1 had a monoclonal gammopathy. The infiltrate was mainly composed of CD68(+)CD163(+)myeloperoxidase(+)myeloid cell nuclear differentiation antigen(+)CD117(-)CD15(-)CD34(-), a phenotype suggestive of M2-like macrophages. A few mature neutrophils and lymphocytes were also present. Review of all HSS cases showed no sex predominance and no extracutaneous infiltrates; inconstant presence of fever and blood neutrophilia; association with hematologic or solid neoplasms (26%), autoimmune conditions (12%), and infectious diseases (10%); and good response to steroid treatment, with rare relapses or recurrences.
  
  
  CONCLUSIONS
  The study includes a limited case series. The pathogenesis of the disease remains to be clarified.
  
  
  CONCLUSIONS
  HSS lesions are infiltrated mostly by M2-like macrophages. The clinical features present more similarities than differences with SS.
authors.affiliation: Department of Medicine, Section of Dermatology and Venereology, University of Verona, Verona, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Peroni
authors.affiliation: Department of Pathology and Diagnostics, Section of Pathology, University of Verona, Verona, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Colato
authors.affiliation: Department of Medicine, Section of Dermatology and Venereology, University of Verona, Verona, Italy.
authors.forename: Donatella
authors.initials: D
authors.lastname: Schena
authors.affiliation: Department of Health Sciences, Section of Dermatology, University of Genoa, Genoa, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Rongioletti
authors.affiliation: Department of Medicine, Section of Dermatology and Venereology, University of Verona, Verona, Italy. Electronic address: giampiero.girolomoni@univr.it.
authors.forename: Giampiero
authors.initials: G
authors.lastname: Girolomoni
mesh_terms: D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D008264:Macrophages; D008297:Male; D008875:Middle Aged; D016463:Sweet Syndrome / Q000276:immunology* / Q000473:pathology*
keywords: M-2 like macrophages; Sweet syndrome; histiocytoid Sweet syndrome; myelodysplastic syndrome