Diagnostic Performance of C6 Enzyme Immunoassay for Lyme Arthritis

Utility of Synovial Fluid Biomarkers for Culture-Positive Septic Arthritis in a Lyme Disease-Endemic Region

OBJECTIVE

To evaluate the performance of synovial fluid biomarkers to identify children with culture-positive septic arthritis.

METHODS

We identified children 6 months to 18 years old presenting to a single emergency department between 2007 and 2022 undergoing evaluation for septic arthritis defined by having a synovial fluid culture obtained. Our primary outcome was septic arthritis defined by a positive synovial fluid culture. We evaluated the ability of synovial fluid biomarkers to identify children with septic arthritis using area under the receiver operating characteristic curve (AUC) analyses. We measured the sensitivity and specificity of commonly used synovial fluid biomarkers.

RESULTS

We included 796 children, of whom 79 (10%) had septic arthritis. Compared with synovial white blood cell count (AUC, 0.72; 95% confidence interval [CI], 0.65-0.78), absolute neutrophil count (AUC, 0.72; 95% CI, 0.66-0.79; P = 0.09), percent neutrophils (AUC, 0.66; 95% CI, 0.60-0.71; P = 0.12), and glucose (AUC, 0.78; 95% CI, 0.67-0.90; P = 0.33) performed similarly, whereas protein (AUC, 0.52; 95% CI, 0.40-0.63, P = 0.04) had lower diagnostic accuracy. Synovial fluid white blood cell count ≥50,000 cells/μL had a sensitivity of 62.0% (95% CI, 50.4%-72.7%) and a specificity of 67.0% (95% CI, 63.4%-70.4%), whereas a positive synovial fluid Gram stain had a sensitivity of 48.1% (95% CI, 36.5%-59.7%) and specificity of 99.1% (95% CI, 98.1%-99.7%) for septic arthritis.

CONCLUSIONS

None of the routinely available synovial fluid biomarkers had sufficient accuracy to be used in isolation in the identification of children with septic arthritis. New approaches including multivariate clinical prediction rules and novel biomarkers are needed.

Pediatric musculoskeletal infections

PURPOSE OF REVIEW

The aim of this article is to review the recent guidelines and literature regarding the diagnosis and the treatment of common pediatric musculoskeletal infections: septic arthritis, osteomyelitis, pyomyositis, and Lyme disease.

RECENT FINDINGS

In the last decade, a better understanding of the causative organisms of common bacterial infections, including Kingella , leads to prompt targeted antimicrobial coverage in all musculoskeletal infections. Prompt diagnosis and treatment continues to be the mainstay in the treatment of children with osteoarticular infections. Efforts to improve early detection have lead to improving rapid lab diagnostic testing; however, more advanced diagnostics such as arthrocentesis for septic arthritis and MRI for osteomyelitis and pyomyositis, remain the gold standard. Shorter and narrowed antibiotic courses, with appropriate transition to outpatient oral treatment provide effective infection clearance and reduction in complications of disease.

SUMMARY

Advances in diagnostics, including pathogen identification as well as imaging continues to improve our ability to diagnose and treat these infections, although still lack ability to provide definitive diagnosis without more invasive nor advanced techniques.

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

OBJECTIVE

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/mm3 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%), 234 Lyme 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, 63.6-73.3; 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.

Diagnostic Criteria for the Painful Swollen Pediatric Knee: Distinguishing Septic Arthritis From Aseptic Effusion in a Non-Lyme Endemic Area

Purpose: The child with a painful swollen knee must be worked-up for possible septic arthritis; the classic clinical prediction algorithms for septic arthritis of the hip may not be the best models to apply to the knee. Materials and methods: This was a retrospective case-control study of 17 years of children presenting to one hospital with a chief complaint of a painful swollen knee, to evaluate the appropriateness of applying a previously described clinical practice algorithm for the hip in differentiating between the septic and aseptic causes of the painful knee effusions. The diagnoses of true septic arthritis, presumed septic arthritis, and aseptic effusion were established, based upon the cultures of synovial fluid, blood cultures, synovial cell counts, and clinical course. Using a logistic regression model, the disease status was regressed on both the demographic and clinical variables. Results: In the study, 122 patients were included: 51 with true septic arthritis, 37 with presumed septic arthritis, and 34 with aseptic knee effusion. After applying a backward elimination, age <5 years and C-reactive protein (CRP) >2.0 mg/dl remained in the model, and predicted probabilities of having septic knee arthritis ranged from 15% for the lowest risk to 95% for the highest risk. Adding a knee aspiration including percent polymorphonucleocytes (%PMN) substantially improved the overall model performance, lowering the lowest risk to 11% while raising the highest risk to 96%. Conclusions: This predictive model suggests that the likelihood of pediatric septic arthritis of the knee is >90% when both "age <5 years" and "CRP > 2.0 mg/dl" are present in a child with a painful swollen knee, though, in the absence of these factors, the risk of septic arthritis remains over 15%. Aspiration of the knee for those patients would be the best next step.

The Impact of Operative Intervention in Pediatric Lyme Arthritis

BACKGROUND

Lyme arthritis often presents as acute monoarticular arthritis challenging to distinguish from septic arthritis. Typical management for Lyme arthritis entails antibiotic therapy, while septic arthritis usually warrants operative debridement. During the period when Western Pennsylvania transitioned to a Lyme-endemic region, many children underwent operative intervention who were ultimately diagnosed with Lyme arthritis due to diagnostic ambiguity. We examined the impact of the operative intervention on pediatric Lyme arthritis outcomes.

METHODS

We conducted a retrospective cohort study of patients admitted to a tertiary care children's hospital who were diagnosed with Lyme arthritis from 2008 to 2018 using chart review. Inclusion criteria were positive Lyme serology by Centers for Disease Control and Prevention (CDC) definition, clinical arthritis, and negative bacterial cultures. We recorded clinical presentation, laboratory data, details of hospitalization, costs, and outcomes after therapy to compare the impact of antibiotics alone (nonoperative group) versus antibiotics plus operative debridement (operative group).

RESULTS

A total of 149 patients met the inclusion criteria. Overall, 47 (32%) patients underwent orthopaedic intervention. Operative management was associated with increased length (3.17 vs. 1.40 d) and cost ($27,850 vs. $10,716) of admission. The clinical resolution was documented in 57/58 patients (98%) in the nonoperative group and 41/42 patients (98%) in the operative group. The median duration to resolution was 21 days for both groups.

CONCLUSIONS

Operative management of pediatric patients with Lyme arthritis is associated with increased resource utilization and costs while being similarly efficacious to nonoperative management. As the US Lyme epidemic expands, improved diagnosis and management of acute undifferentiated arthritis may prevent unneeded operative intervention.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.

The potential impact of Helicobacter pylori seropositivity on recombinant, antigen-based Lyme serology

We assessed the impact of Helicobacter pylori seropositivity on recombinant antigen-based Lyme serology. We compared the IgG ELISA+LIA (line immunoassay) reactivity of anti-Helicobacter IgG positive and negative samples. The ELISA S/Co values and LIA band numbers were identical. Our results suggest that Helicobacter seropositivity lacks an apparent effect on Lyme disease test reactivity.