Concomitant cutaneous langerhans cell hystiocytosis and leukemia cutis

Leukemia cutis develops in <4% of all acute leukemias. Concurrent acute myeloid leukemia (AML) and Langerhans cell histiocytosis (LCH) is rare, with most cases involving lymph nodes or spleen, and no cutaneous involvement. We report the case of a 59-year-old man who presented with fever, malaise, and fatigue. The CBC showed leukocytosis (30.4 × 10 9 /L, 9% blasts), anemia, and thrombocytopenia. Bone marrow biopsy was diagnosed with AML, not otherwise specified, with mutations of FLT3 and IDH2 (R140Q). The patient developed skin rash on the right flank with the clinical differential diagnosis of herpes simplex virus or varicella-zoster virus infection/reactivation versus leukemia cutis. A skin biopsy showed leukemia cutis in mid and deep dermis. Immunohistochemistry positive for CD4, CD33, CD117, and myeloperoxidase (MPO) supported myeloid and monocytic differentiation. Clusters of Langerhans cells positive for S100, CD1a, CD4, langerin and aberrant CD33 and MPO were found admixed with the AML cells. Langerhans cells were negative for BRAF V600E by immunohistochemistry. The diagnosis of leukemia cutis and concomitant LCH was established. The aberrant expression of CD33 and MPO shared by AML and LCH suggests a possible relationship among these 2 lesions. No LCH or Langerhans cell differentiation was found in the bone marrow. The patient achieved complete remission 4 months after chemotherapy and the skin lesions resolved. To our knowledge, we present for the first time a case of concomitant cutaneous LCH and leukemia cutis.