Pediatric acute leukemia mimicking osteomyelitis: clinical and MRI features.

Background: Pediatric acute leukemia (AL) typically presents with symptoms of cytopenias, organomegaly, and fever. In some instances, however, musculoskeletal pain may be the predominant-occasionally the sole-initial symptom, leading to misdiagnoses such as osteomyelitis. Methods: We conducted a retrospective, multicenter, observational, cohort study including children and adolescents (<18 years) diagnosed with acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML) between 2017 and 2024 who initially presented with osteomyelitis-like clinical and/or radiological features. Clinical presentation, laboratory findings, MRI characteristics, and time to leukemia diagnosis were systematically analyzed and compared with the available literature. Results: Six patients were included (four ALL, one ALL relapse, and one AML). All patients presented with musculoskeletal pain; at first evaluation, fever was present in 50% of the individuals. Initial peripheral blood counts were normal in four and only mildly abnormal in two cases. Inflammatory markers and lactate dehydrogenase were elevated in five and four patients, respectively. MRI demonstrated multifocal or diffuse bone marrow signal alterations in all but one case. The median interval from first presentation to leukemia diagnosis was 17 days (range, 1-53). Features observed in patients with delayed diagnosis included transient clinical response to antibiotic therapy, lack of hematologic abnormalities, and multifocal MRI involvement. Conclusion: Pediatric AL can mimic osteomyelitis clinically, hematologically, and radiologically. Awareness of clinical red flags and suspicious MRI patterns may prompt earlier consideration of an underlying hematologic malignancy and reduce diagnostic delay.