Acute Pediatric Monoarticular Arthritis: Distinguishing Lyme Arthritis From Other Etiologies

OBJECTIVE. Identify clinical predictors of Lyme arthritis among patients with acute monoarticular arthritis. METHODS. A medical chart review was conducted of children <= 18 years of age with monoarticular arthritis who underwent arthrocentesis in a pediatric emergency department located in the northeast United States. Patients were classified into 3 categories of arthritis: septic, Lyme, or nonseptic non-Lyme arthritis. Historical, clinical, and laboratory data were compared to identify distinguishing features of Lyme arthritis. RESULTS. One hundred seventy-nine patients were studied: 46 (26%) patients with septic arthritis, 55 (31%) patients with Lyme arthritis, and 78 (43%) patients with nonseptic non-Lyme arthritis. Compared with those with septic arthritis, patients with Lyme disease were more likely to have a tick-bite history, knee involvement, and less likely to have a history of fever or elevated temperature at triage. Erythrocyte sedimentation rate, C-reactive protein, joint white blood cell count, and joint neutrophil percentage were also statistically lower. In comparison to nonseptic non-Lyme arthritis, knee involvement and tick-bite history were predictors of Lyme. Erythrocyte sedimentation rate, joint white blood cell count, and joint neutrophil percentage were also statistically different. Multivariate analysis comparing Lyme to septic arthritis demonstrated fever history and elevated C-reactive protein level to be negative predictors of Lyme arthritis and knee involvement to be a positive predictor (model sensitivity: 88%; specificity: 82%). CONCLUSIONS. Lyme arthritis shares features with both septic and nonseptic non-Lyme arthritis. This overlap prevents the creation of a clinically useful predictive model for Lyme arthritis. In endemic areas, Lyme testing should be performed on all patients presenting with acute monoarticular arthritis. Pediatrics 2009;123:959-965