CPC10 A rare post-stem-cell transplant dermatological puzzle

Abstract

Sweet syndrome (SS) is a rare reactive neutrophilic dermatosis characterized by the sudden onset of nonpruritic, often tender, erythematous to violaceous papules, plaques or nodules. It is frequently accompanied by fever, peripheral neutrophilic leucocytosis and other systemic symptoms. Although its pathogenesis remains incompletely understood, SS is known to be associated with infections, medications, autoimmune diseases and malignancies – particularly haematological disorders such as myelodysplastic syndrome (MDS) and acute myeloid leukaemia. Among its histological variants, the histiocytoid form is uncommon and may mimic other inflammatory or neoplastic conditions, including MDS and leukaemia cutis, making diagnosis challenging. We report a case of histiocytoid SS in a 63-year-old man with MDS, who was in cytogenetic remission following recent allogeneic haematopoietic stem cell transplantation. On day +19 post-transplant, he developed widespread, nontender, nonpruritic violaceous papules in the absence of systemic symptoms. The histopathological and immunohistochemical examination revealed a dense dermal infiltrate composed predominantly of immature myeloid cells with histiocytoid morphology, showing diffuse CD68 expression and focal positivity for myeloperoxidase and CD5. No neutrophilic infiltration was seen. These findings are consistent with the histiocytoid variant of SS. MDS cutis was strongly considered as a differential diagnosis; however, subsequent genetic analysis of the skin biopsy did not support this diagnosis. The rash demonstrated a favourable response to a short course of topical corticosteroids, and the patient remained asymptomatic on follow-up. This case highlights the occurrence of histiocytoid SS as a paraneoplastic phenomenon in patients with MDS. In addition, it raises the importance of genetic studies for further differentiation between MDS cutis and histiocytoid SS in such patients, particularly in cases where the MDS is apparently in remission when the rash appears.