Pediatric Lyme Arthritis of the Hip: The Great Imitator?

BACKGROUND: Lyme arthritis (LA) of the hip can present similarly to septic arthritis (SA) and transient synovitis (TS). The primary purpose of this study was to determine clinical and laboratory parameters differentiating LA of the hip from SA or TS among children who had undergone hip aspiration during the evaluation of hip pain.

METHODS: This was a retrospective review of all patients who underwent hip aspiration for the evaluation of hip pain at a tertiary care children's hospital in a Lyme endemic area. Clinical and laboratory data were reviewed and comparative analyses were performed between those diagnosed with LA, SA, and TS. Independent samples t test, ANOVA, and χ test were used to compare clinical and laboratory variables as appropriate. Multivariable logistic regression was used to elucidate independent predictors of LA. Statistical significance was set at P<0.05.

RESULTS: Ninety-three hip aspirations (93 patients) were included in the final analysis. Seventeen patients were diagnosed with LA, 40 with SA, and 36 with TS. Multivariable logistic regression revealed febrile history (OR=16.3; 95% CI, 2.35-113.0) and increased peripheral white blood cell (WBC) count (OR=1.26; 95% CI, 1.01-1.58) to be significantly associated with increased odds of being diagnosed with SA versus LA. Increased erythrocyte sedimentation rate (ESR) was significantly associated with increased odds of being diagnosed with LA versus TS (OR=1.06; 95% CI, 1.02-1.10), whereas febrile history (OR=0.06; 95% CI, 0.01-0.49) and increased peripheral WBC count (OR=0.8; 95% CI, 0.65-0.98) were associated with decreased odds of LA.

CONCLUSIONS: Children presenting in a Lyme endemic area with an isolated hip effusion are more likely to have LA versus SA if they have no history of fever and a decreased peripheral WBC count. Compared with TS, patients with LA are more likely to have an elevated ESR. This study adds to existing knowledge because there are few investigations examining isolated LA of the hip.

LEVEL OF EVIDENCE: Level III-retrospective case-control study.