Fever and Leg Pain: Consider ALL the Diagnoses

Background: Acute lymphoblastic leukemia (ALL) is the most common childhood cancer diagnosed in the United States. The disease causes a decrease in hematopoiesis, so children often present with symptoms related to anemia, thrombocytopenia, and leukopenia. Symptoms for this malignancy may have significant overlap with other conditions such as osteomyelitis. Case Report: A 2-year-old male with no significant medical history presented with lower extremity pain and fever. Initial investigations, including imaging and complete blood count, led physicians to diagnose bilateral osteomyelitis. The patient was prescribed a course of antibiotics; however, his symptoms returned. Eventually, a bone marrow aspiration showed CD99 membrane-positive small round blue cell tumors. The patient was diagnosed with ALL. He was successfully treated with chemotherapy and is now in remission. Conclusion: This case demonstrates the importance of a broad differential diagnosis for a child presenting with leg pain and fever.