J Cutan Pathol 2008: 35: 220–224 doi: 10.1111/j.1600-0560.2007.00780.x Blackwell Munksgaard. Printed in Singapore Copyright # Blackwell Munksgaard 2007 Journal of Cutaneous Pathology Drug-associated histiocytoid Sweet’s syndrome: a true neutrophilic maturation arrest variant Histiocytoid Sweet’s syndrome is a recently described entity which has clinical features identical to typical Sweet’s syndrome but is distinguished by a dermal cellular infiltrate composed not of mature neutrophils but of immature granulocytes. Herein, we report a case of bone marrow granulocytic maturation arrest and a histological histiocytoid Sweet’s-like reaction pattern following trimethoprim- sulfamethoxazole therapy. Wu AJ, Rodgers T, Fullen DR. Drug-associated histiocytoid Sweet’s syndrome: a true neutrophilic maturation arrest variant. J Cutan Pathol 2008; 35: 220–224. # Blackwell Munksgaard 2007. Angela J. Wu 1 , Timothy Rodgers 2 and Douglas R. Fullen 1,2 1 Department of Pathology and 2 Department of Dermatology, University of Michigan Medical Center, Ann Arbor, MI, USA Dr Douglas R. Fullen, University of Michigan Medical Center, M3261 MSI 0602, 1301 Catherine Road, Ann Arbor, MI 48109-0602, USA Tel: 11 734 764 4460 Fax: 11 734 764 4690 e-mail: dfullen@med.umich.edu Accepted for publication March 12, 2007 Acute febrile neutrophilic dermatosis or Sweet’s syndrome, is a reactive condition of unknown etiology characterized by an abrupt onset of tender, erythematous or violaceous sharply marginated plaques and nodules, occasionally associated with pseudovesiculation or pustules. Lesions are asym- metrically distributed over the face, neck and limbs. Associated secondary features include clinical symptoms such as fever and characteristic labora- tory values including neutrophilic leukocytosis, elevated erythrocyte sedimentation rate and posi- tive C-reactive protein. The classic histomorphol- ogy of Sweet’s syndrome is one of a dichotomous reaction pattern comprising striking interstitial neutrophilia accompanied by a mononuclear cell vascular reaction typically without mural and or luminal fibrin deposition. The mononuclear cells may be of monocytic or lymphoid derivation. An underlying systemic disorder, most often a viral or streptococcal infection or inflammatory condition such as inflammatory bowel disease, is found in approximately 50% of cases. Approximately 10– 20% of cases are associated with hematologic or solid malignancies. 1,2 Recently, Requena et al. described a series of 41 patients who presented with typical cutaneous lesions of Sweet’s syndrome. Histologically, these lesions had the architectural features of Sweet’s syndrome, but the cellular infiltrate was composed predominantly of immature myeloid precursors without the morphologic features of either blasts or segmented neutrophils. Requena et al. held that the granulocytic nature of the cells was supported by the phenotypic profile, namely, one comprising CD68, lysozyme and myeloperoxidase (MPO) posi- tivity. However, it should be emphasized that while MPO activity is most pronounced in immature granulocytes, it is discernible in monocytes as well. A truly confirmatory marker of granulocytic deriva- tion, namely that of chloroacetate esterase, along with negativity for a monocyte-specific marker, such as a non-specific esterase stain using alpha naphthyl acetate and alpha naphthyl butyrate was not per- formed. Because of the morphologic resemblance of these immature myeloid precursors to histiocytes, this dermatosis was coined histiocytoid Sweet’s syndrome. 2 In this case report, we present an unusual case of histiocytoid Sweet’s-like reaction and granulocytic maturation arrest in a 44-year-old woman following a course of trimethoprim-sulfamethoxazole (TMP- SFX) therapy for treatment of sinusitis. 220