Myeloid dermatosis with features of sweet syndrome and leukemia cutis: a case report.

Occult hematologic malignancies can initially present with cutaneous manifestations. We describe a 53-year-old woman with chronic hepatitis C and intravenous drug use presenting with a painful, progressive leg rash and worsening bicytopenias. A skin punch biopsy revealed neutrophilic dermatosis morphologically compatible with Sweet syndrome (SS), along with rare CD117+/CD34 − blastoid cells. Subsequent bone marrow studies revealed acute myeloid leukemia with mutated NPM1. This case highlights the diagnostic challenge of distinguishing SS from leukemia cutis (LC) when skin biopsies demonstrate mixed neutrophilic with rare blastoid cells. LC represents cutaneous infiltration of leukemic blasts, whereas SS represents a non-neoplastic, cytokine-driven process. Prompt immunophenotypic evaluation and genomic testing of myeloid dermatoses, particularly those with blastoid cells, can be critical in distinguishing SS from LC to provide significant insight on prognosis and therapeutic options. This case highlights the clinical and histopathologic spectrum of myeloid dermatoses and further emphasizes the relevance of skin biopsies in the diagnosis of cutaneous involvement by hematologic malignancies, such as myeloid neoplasms.