Histiocytoid Sweet Syndrome in a Patient with CRDM-Type Myelodysplastic Syndrome

Abstract

Histiocytoid Sweet syndrome was first described in 2005 as a histological variant of acute febrile neutrophilic dermatosis. Unlike classic Sweet syndrome, the dermal inflammatory cell infiltrate in histiocytoid Sweet syndrome consists of histiocytoid cells, which are thought to be immature myeloid cells. A 69-year-old male patient with a medical history of CRDM type myelodysplastic syndrome was consulted for a tender and slightly pruritic erythematous papular rash, some lesions showing central vesiculation, disseminated to the trunk and limbs, with an onset of about 1 month. His general condition was relatively good without fever. In the context of the pre-existing haematological condition, a leukemic transformation with concomitant leukaemia cutis was suspected and a skin biopsy was performed. The histopathological examination revealed an infiltrate in the superficial dermis consisting predominantly of mononuclear cells with cytomorphological characteristics of monocyte/histiocyte, with frequent interstitially dispersed neutrophils, and perivascular immature granulocytes and lymphocytes. Immunohistochemical staining was positive for myeloperoxidase and CD68 in numerous cells in the infiltrate, establishing the diagnosis of histiocytoid Sweet syndrome. The histiocytoid variant of Sweet syndrome should be recognized as a distinct entity by clinicians, so Sweet syndrome should not be excluded in the absence of classic clinical and histopathological manifestations.