A PREVIOUSLY healthy 8-year-old boy with no history of trauma was seen during influenza season with a temperature of 100° to 104°F and lower back pain of 4 days' duration, which woke him at night. On examination, he had tense paraspinal muscles with absence of normal lumbar lordosis and normal findings from neurological examination. Possible diagnoses included myositis or possible discitis. Findings from laboratory tests included white blood cell count, 9.9 × 109/L; neutrophils, 0.83; lymphocytes, 0.09; monocytes, 0.06; basophils, 0.02; erythrocyte sedimentation rate, 50 mm/h; aldolase, 5.8 U/L (reference range, 1.2-8.8 U/L); and creatine phosphokinase, 56 U/L. Because of the elevated erythrocyte sedimentation rate and lack of muscle enzyme elevation, a lumbar spine magnetic resonance imaging (MRI) scan was obtained (Figure 1) and showed enhancement and an increased T2-weighted signal in the paraspinal muscles, with normal findings in the vertebral bodies and discs.