Ian Kilgour, a 4-year-old boy, was brought to his family physician with a two-week history of progressive pallor and easy bruising. Ian has been very irritable, feeding poorly and has been complaining of pain in the left leg for two or three days prior to this visit. Physical examination revealed a pale child who was febrile with an oral temperature of 39.2 degrees C. There were petechiae and bruises over his trunk and extremities. Liver was palpable 4 cm below the right costal margin and spleen tip was felt below the left costal margin. Lymph nodes in the neck and groins bilaterally were enlarged. Musculoskeletal examination revealed tenderness over the sternum and anterior margin of the left tibia.