Histiocytoid Variant of Sweet Syndrome Associated with Azacitidine and Recurrence upon Rechallenge

Insights Into the Pathogenesis of Sweet's Syndrome

Sweet's syndrome, also known as Acute Febrile Neutrophilic Dermatosis, is a rare inflammatory condition. It is considered to be the prototype disease of neutrophilic dermatoses, and presents with acute onset dermal neutrophilic lesions, leukocytosis, and pyrexia. Several variants have been described both clinically and histopathologically. Classifications include classic Sweet's syndrome, malignancy associated, and drug induced. The cellular and molecular mechanisms involved in Sweet's syndrome have been difficult to elucidate due to the large variety of conditions leading to a common clinical presentation. The exact pathogenesis of Sweet's syndrome is unclear; however, new discoveries have shed light on the role of inflammatory signaling, disease induction, and relationship with malignancy. These findings include an improved understanding of inflammasome activation, malignant transformation into dermal infiltrating neutrophils, and genetic contributions. Continued investigations into effective treatments and targeted therapy will benefit patients and improve our molecular understanding of inflammatory diseases, including Sweet's syndrome.

Clinicopathologic, Immunohistochemical, and Molecular Features of Histiocytoid 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.

Sweet's syndrome associated with clonal hematopoiesis of indeterminate potential responsive to 5-azacitidine

Sweet's syndrome (SS) is a rare condition characterized by the abrupt appearance of painful skin lesions due to neutrophilic dermal infiltration. Hematologic neoplasms, particularly acute myeloid leukemia (AML) and myelodysplastic syndromes (MDSs), have been commonly reported in association with SS. Clonal hematopoiesis of indeterminate potential (CHIP) is an emerging entity that is a precursor state to myeloid neoplasms. CHIP has not been previously associated with SS. We report the case of a 71-year-old man who presented with recurrent, painful edematous and erythematous papules and nodules for 18 months despite treatment with corticosteroids. He had normal blood counts, but a macrocytosis was noted (110 fl). Alternative causes of macrocytosis were ruled out. A skin biopsy confirmed a diagnosis of SS. Bone marrow biopsy specimen yielded a normal karyotype except for loss of the Y chromosome and equivocal morphologic findings. Polymerase chain reaction (PCR) and reverse transcription polymerase chain reaction (RT-PCR) of selected genes from the peripheral blood demonstrated a mixed lineage leukemia (MLL) partial tandem duplication (PTD) and sequence variant in CCAAT/enhancer binding protein alpha (CEBPA). These findings were consistent with a diagnosis of CHIP. The patient was treated with 5-azacitidine and achieved a complete remission of his skin lesions and was able to discontinue corticosteroids. To our knowledge, this is the first report of a patient with recurrent SS associated with CHIP. In addition to other myeloid neoplasms like AML and MDS, CHIP should be considered as a potential etiology in cases of recurrent SS. Treatment with a hypomethylating agents such as azacitidine could also serve as an alternative to systemic corticosteroid therapy.