Immature Myeloid Precursors in Chronic Neutrophilic Dermatosis Associated With Myelodysplastic Syndrome Carlo Tomasini, M.D., Filippo Aloi, M.D., Simona Osella-Abate, S.D., Paolo Dapavo, M.D., and Mario Pippione, M.D. Sweet syndrome (SS) associated with myeloproliferative dis- orders has been considered an inflammatory process mediated by neutrophils in which immunologic mechanisms are opera- tive. The authors report the case of a 68-year-old man suffering from a myelodysplastic syndrome, who presented with a re- lapsing skin eruption resembling SS. Histopathologically, the skin infiltrates showed prominent neutrophilic features mask- ing the underlying malignant process. Extensive immunophe- notypic studies of skin revealed the presence of a few immature myeloid cells intermingled with an overwhelming infiltrate of neutrophils. The atypical cells in the skin had a phenotype identical to that of leukemic cells in the peripheral blood and bone marrow. Whether or not immature myeloid cell precursors constitute a specific infiltrate of leukemia cutis or are a result of recruitment of circulating leukemic cells to this area of inflam- mation is discussed. Key Words: Flow cytometry—Histopathology—Immuno- histochemistry—Myelogenous leukemia cutis—Neutrophilic dermatoses—Sweet syndrome. Sweet syndrome (SS), originally described in 1964 as acute febrile neutrophilic dermatosis by Robert Douglas Sweet (1), is an enigmatic disease characterized by an acute onset of erythematous plaques asymmetrically dis- tributed over the face, neck, and limbs, and it is protypi- cally accompanied by fever and neutrophilic leukocyto- sis. Histopathologic findings in SS consist of dense, nodular, or diffuse dermal infiltrates of neutrophils and plentiful neutrophilic nuclear “dust,” edema of the pap- illary dermis, and vessel walls devoid of fibrin. In some cases, papillary dermal edema may progress to subepi- dermal vesiculation. Involvement of the subcutaneous fat may also occur (2). After the initial recognition of SS, its clinical variability has been increasingly appreciated, leading to its inclusion in the spectrum of neutrophilic dermatoses (3–5). Although the pathogenesis of SS remains unknown, it has been viewed by some researchers as an inflammatory condition because of its frequent association with other diseases, especially inflammatory bowel disease, con- nective tissue diseases, and solid and hematologic neo- plasia (6–8). Acute myelogenous leukemias and myelo- dysplastic syndromes (MDSs) are the most frequent ma- lignancies that occur in patients with SS, with the dermatosis usually occurring before or concurrently with the malignancy (9–16). We report on a patient with MDS, in whom the infil- trate of SS contained immature myeloid cell precursor cells blurring the distinction between the inflammatory and neoplastic nature of the condition. CASE REPORT A 68-year-old man came to the authors’ clinic with a 3-month history of fever, malaise, and tender widespread dermatosis. The eruption had begun on the upper arms and face and spread slowly to the trunk and lower ex- From the Department of Medical and Surgical Specialties, Second Dermatologic Clinic (C.T., F.A., P.D., M.P.), and First Dermatologic Clinic (S.O.-A.), University of Turin, Turin, Italy. Address correspondence and reprint requests to C. Tomasini, M.D., Department of Medical and Surgical Specialties, Second Dermatologic Clinic, Via Cherasco 23, 10126, Turin, Italy. The American Journal of Dermatopathology 22(5): 429–433, 2000 © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia 429