Validation of Septic Knee Monoarthritis Prediction Rule in a Lyme Disease Endemic Area

Abstract

In Lyme disease endemic areas, Lyme and septic arthritis often present similarly. A published septic knee arthritis clinical prediction rule includes 2 high-risk predictors: absolute neutrophil count of 10,000 cells/mm 3 or greater and erythrocyte sedimentation rate of 40 mm/h or greater. The objective of the study was to externally validate this prediction rule in a multicenter prospective cohort. Methods:We enrolled a prospective cohort of children with knee monoarthritis undergoing evaluation for Lyme disease at 1 of 8 Pedi Lyme Net emergency departments located in endemic areas. We defined a case of septic arthritis with a positive synovial fluid culture or a synovial fluid white blood cell count of 50,000 or greater per high powered field with a positive blood culture and Lyme arthritis with a positive or equivocal C6 EIA, followed by a positive supplemental immunoblot. Other children were classified as having inflammatory arthritis. We report the performance of the septic arthritis clinical prediction rule in our study population.Results: Of the 543 eligible children, 13 had septic arthritis (2.4%), 234Lyme arthritis (43.1%), and 296 inflammatory arthritis (54.5%). Of the 457 children (84.2%) with available laboratory predictors, all children with septic arthritis were classified as high risk (sensitivity, 100%; 95% confidence interval [CI], 77.2%-100%; specificity, 68.1%; 95% CI, negative predictive value, 278/278 [100%]; 95% CI, 98.6%-100%). Of the 303 low-risk children, 52 (17.2%) underwent diagnostic arthrocentesis. Conclusions:The septic knee arthritis clinical prediction rule accurately distinguished between septic and Lyme arthritis in an endemic area. Clinical application may reduce unnecessary invasive diagnostic procedures.

Surgical (over) treatment of pediatric Lyme arthritis: a need for faster Borrelia testing

“…This is comparable to data obtained from the CDC, where the overall average age of patients with Lyme arthritis is reportedly between 10 and 14 years old. However, previous studies focusing on more rural endemic regions found the presenting age to be lower, with reported averages of 6.7 and 7 years [4,12,15].…”

“…Small case series have reported 37.5% and 70% of patients with Lyme arthritis had surgical treatment [16,22]. A larger study comparing patients with Lyme to septic arthritis noted 12.4% of Lyme arthritis patients underwent an irrigation and debridement [12]. In a retrospective review of 149 patients comparing patients who underwent operative versus non-operative intervention for Lyme arthritis, Tout et al reported 32% of patients underwent operative intervention.…”

“…Various factors may help differentiate between septic and Lyme arthritis but overall remain controversial. A higher synovial WBC count, absolute serum neutrophil percent, synovial neutrophil percent, ESR, and CRP as well as a negative anti-streptolysin-O, fever, refusal to weight bear, and knee involvement have all been proposed in various combinations as variables more associated with septic arthritis than Lyme arthritis [11,12,[24][25][26]. Even so, some studies showed no significant differences with most of these variables [13,17].…”

“…The significant amount of time it takes for Lyme tests to result makes it difficult to rely on them for distinguishing between Lyme and septic arthritis, as the window for operative treatment is short for true septic arthritis. Since culture results from aspiration samples also take too long to result and gram stains are often negative in pediatric patients with septic arthritis [12], providers must rely on the entire clinical picture and other laboratory results to quickly distinguish between Lyme and septic arthritis.…”

“…Lyme disease is caused by the bacteria Borrelia burgdorferi and is especially common in areas with extensive woodlands where there are many mammalian hosts for the bacteria and vectors for transmission, mainly ticks [10]. Multiple studies have characterized Lyme arthritis in the pediatric population in endemic regions [11][12][13]. Although Lyme disease is more common in these settings, urban areas in close proximity to endemic rural regions, such as New York City, still observe high rates of Lyme arthritis: in 2019, 756 of the 34 945 total Lyme disease cases reported to the Centers for Disease Control and Prevention (CDC) were from New York City [14].…”