• Raakhi M Mistry, Diana Lennon, Matthew J Boyle, Karel Chivers, Chris Frampton, Ross Nicholson, and Haemish Crawford.
• *Department of Pediatric Orthopedics, Starship Hospital, Park Road †Starship Hospital ¶Kidz First Hospital, Auckland ‡Gisborne Hospital, Gisborne §Department of Biostatistics, University of Otago, Dunedin, New Zealand.
• J Pediatr Orthop. 2015 Apr 1; 35 (3): 318-22.

IntroductionJoint pain and raised inflammatory markers are features of both acute rheumatic fever (ARF) and septic arthritis, often posing a diagnostic challenge to clinicians. Important differences in the presenting serological inflammatory marker profile may assist patient diagnosis, however, as clinical experience suggests that ARF is associated with a higher erythrocyte sedimentation rate (ESR), whereas other serological markers may be similarly elevated in these 2 conditions.ObjectiveThe goal of this study was to determine the diagnostic value of serological inflammatory markers and white cell count (WCC) in children presenting with acute joint pain secondary to ARF or septic arthritis.MethodsData were obtained from the Auckland regional rheumatic fever database and hospital computer records between 2005 and 2012. Records of all patients under the age of 16 years who were admitted with a new diagnosis of ARF or septic arthritis were analyzed. The diagnosis of ARF was defined on the basis of the New Zealand modification of the Jones Criteria, and the diagnosis of septic arthritis was defined on the basis of joint fluid cytology and culture. Baseline characteristics, serological inflammatory markers, and serum WCC were compared between the ARF and septic arthritis patient groups.ResultsChildren with ARF displayed significantly higher ESR, higher serum C-reactive protein, and lower serum WCC than children with septic arthritis on presentation to hospital. In children presenting with monoarthritis, an ESR>64.5, serum WCC<12.1×109/L, and age above 8.5 years were found to be significant independent predictors of ARF. Children with all 3 predictors had a 71% risk for ARF and a 29% risk for septic arthritis. A significant proportion (30%) of children with the final diagnosis of ARF initially presented with monoarthritis; 14% of these children (5/34) had received nonsteroidal anti-inflammatory medication before hospital presentation, and 74% of these children (25/34) had abnormal echocardiograms on admission.ConclusionsARF and septic arthritis are important diagnoses to consider in children presenting with acute joint pain in New Zealand. A significant proportion of patients with ARF initially present with acute monoarthritis. Serological inflammatory markers and WCC on presentation differ significantly between children with ARF and septic arthritis.

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