Abstract

CD30-positive large cells are typically part of lymphoproliferative disorders but can also be seen in inflammatory dermatoses, requiring inclusion of broader differentials and clinicopathologic correlation. We present a case of 47-year-old man with history of B-lymphoblastic leukemia (B-ALL) who presented with fever, leukocytosis, and ulcerating papulonodular skin lesions, involving the left upper extremity and trunk. A punch biopsy demonstrated prominent papillary dermal edema with neutrophilic and histiocytic infiltrate extending into the subcutis. Background leukocytoclasia and necrosis showed no sign of primary vasculitis. However, the infiltrate harbored focal areas of large cells with irregular nuclear envelope, prominent nucleoli, and moderate cytoplasm, comprising 5-8% of the total inflammatory infiltrate. The histiocytic component, including the large, atypical cells were highlighted by CD68, CD43 and lysozyme. The large cells were also highlighted by CD30. CD3 highlighted the background collection of small T-cells. TdT, CD34, CD20 and PAX5 stains showed no evidence of the patient's known B-ALL. CD56 and EBERish stains were negative. A diagnosis of histiocytoid Sweet’s syndrome with CD30+ cells was made. The presence of large CD30+ cells is usually worrisome for a lymphoproliferative process. However, negative expression of T and B cells markers on these cells argued against a (neutrophil-rich) lymphomatous process. B-cell processes including B-ALL are known to transform into histiocytic sarcomas. However, such transformation still carry some B-cell markers that was not seen in this case. Lastly, a secondary leukemia cutis with CD30 expression on monocytes was ruled out as our patient improved with prednisone taper and the lesions completely resolved in two months. The case was also unique in presenting a combined version of different variants and aspects of Sweet’s syndrome with subcutis involvement, histiocytoid morphology and large CD30+ cells.

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