Histiocytoid Sweet syndrome may indicate leukemia cutis: A novel application of fluorescence in situ hybridization

Background: In patients with malignancy-associated Sweet syndrome, a thorough evaluation for leukemia cutis should be considered. Objective: We sought to describe the clinicopathologic characteristics of histiocytoid Sweet syndrome. Methods: We retrospectively identified patients with histiocytoid Sweet syndrome at our institution from January 1992 through December 2010. We evaluated the underlying cutaneous infiltrate using immuno-histochemistry and fluorescence in situ hybridization. Results: We re-evaluated all 22 patients with hematologic malignancy-associated Sweet syndrome. Six patients had a monocytoid infiltrate that was consistent with histiocytoid Sweet syndrome; subsequent evaluation of these patients demonstrated cytogenetic abnormalities on prior bone-marrow biopsy specimens. Fluorescence in situ hybridization analysis was feasible in cutaneous specimens from 5 of the 6 patients and demonstrated the same cytogenetic abnormalities that were identified on prior bone-marrow biopsy specimens in 4 patients. Therefore, these 4 patients may have had a form of leukemia cutis. Limitations: This was a retrospective study. Conclusion: For patients with histiocytoid Sweet syndrome, an underlying hematologic malignancy, and a monocytoid infiltrate on biopsy specimen, fluorescence in situ hybridization of the cutaneous infiltrate may be beneficial to identify cytogenetic abnormalities that may indicate leukemia cutis.