Myeloid Sarcoma Mimicking Intramuscular Abscesses in a Patient With Myelodysplastic Syndrome: A Diagnostic Challenge.

Myeloid sarcoma (MS) is a rare extramedullary tumor composed of immature myeloid cells. It typically occurs in the context of acute myeloid leukemia (AML) but may also present alongside myelodysplastic syndromes (MDS) and other myeloid neoplasms. We present the case of a 63-year-old male with no prior hematologic disease who was admitted with right lower limb swelling, initially diagnosed as cellulitis. During hospitalization, he developed multiple soft tissue lesions and progressive normocytic anemia. CT imaging showed multiloculated intramuscular collections. Despite negative blood cultures, methicillin-sensitive Staphylococcus aureus (MSSA) was isolated from drained material. The patient's anemia and emerging neutropenia prompted bone marrow evaluation, revealing trilinear dyshematopoiesis consistent with MDS. Magnetic resonance imaging (MRI) and positron emission tomography-computed tomography (PET-CT) identified persistent abscess-like lesions without clear evidence of neoplasia. A muscle biopsy from the thigh confirmed MS. The disease later progressed to acute myelomonocytic leukemia with pancytopenia. This case underscores the importance of maintaining a high index of suspicion for MS in patients with atypical soft tissue lesions and unexplained cytopenias, particularly in the absence of overt leukemia. Prompt biopsy and immunophenotyping are essential for accurate diagnosis.