Visual diagnosis: 11-year-old boy with leukemia, fever, elbow, and leg pain.

The diagnosis of pyomyositis requires a high index of suspicion in patients with hematologic malignant neoplasms. Correct diagnosis might be delayed initially because of vague clinical presentation, overlapping symptoms, and nonspecific clinical signs. Pyomyositis should be included in the differential diagnosis when a patient develops swollen or tender muscles after chemotherapy with or without bacteremia. Prompt treatment with broad-spectrum antibiotics that cover S aureus and resistant emerging gram-negative organisms, specifically E coli, should be initiated immediately in patients with hematologic illnesses along with close monitoring and follow-up.