Differentiating Lyme Arthritis From Septic Arthritis: Clues Uncovered

Milewski MD, Cruz AI, Miller CP et al. Lyme Arthritis in Children Presenting With Joint Effusions. Journal of Bone and Joint Surgery (2011) 93:252-260. doi: 10.2106/JBJS.I.01776

The prevalence of Lyme arthritis is high in pediatric patients who present with joint effusions in an area of the Northeastern United States in which the disease is endemic, and the disease is more common than septic arthritis. Several clues can help differentiate Lyme arthritis from septic arthritis in this at-risk group, which is useful to clinicians because the initial treatment is inherently different.

Milewski and colleagues retrospectively reviewed records from 391 children who presented with a warm, swollen knee to determine how often symptoms were related to Lyme disease versus sepsis. They also investigated what criteria might reliably differentiate the two conditions.

Of the patients analyzed, 31% had Lyme arthritis, 13% had septic arthritis, and the remainder had periarticular or no infection. The knee was the joint most frequently involved (86% and 45% of patients with Lyme arthritis or septic arthritis, respectively). A patient with septic arthritis was 4.43 times more likely than one with Lyme arthritis to have a fever and 3.63 times more likely to have a high synovial fluid cell count. The biggest differentiator was refusal to bear weight on the affected limb.

The authors noted that greater awareness of Lyme arthritis may lead to increased testing and more timely diagnosis and treatment.