Abstract

Myeloid sarcoma is an extramedullary manifestation of a myeloid neoplasm. It is characterized by a tumor mass composed of myeloblasts with varying degrees of maturation. Commonly affected sites include the skin, soft tissues, lymph nodes, gastrointestinal tract, and head and neck region. Myeloid neoplasms may present as skin lesions in patients with or, less frequently, without a prior history of acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), myeloproliferative neoplasm (MPN), or MDS/MPN.  We discuss a case of a 37 year old woman with a history of sickle cell disease, systemic lupus erythematosus, and immune thrombocytopenic purpura, presenting with body aches, skin rash, and painful oral ulcers. Histologic examination of a left arm lesion revealed a superficial to deep dermal perivascular infiltrate of reactive lymphocytes and eosinophils. Closer inspection disclosed admixed enlarged mononuclear cells with fine chromatin and poorly formed intracytoplasmic eosinophilic granules. Immunohistochemistry showed these atypical cells to be positive for myeloperoxidase and lysozyme, with a subset expressing CD34 and CD117. The overall findings were consistent with myeloid sarcoma. A subsequent bone marrow biopsy showed increased numbers of myelomonocytic blasts, confirming a concurrent bone marrow myeloid neoplasm. The detection of myeloid sarcoma may herald AML, a relapse, or the blast phase of a chronic myeloid neoplasm, underscoring the importance of thorough examination and timely intervention. Our case highlights the diagnostic difficulty of myeloid sarcoma, particularly when the patient lacks prior history of a myeloid neoplasm, and cursory review of the histology suggests a mixed inflammatory infiltrate.