title: Pediatric Lyme Arthritis of the Hip: The Great Imitator?
abstract: 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.
  
  
  METHODS
  Level III-retrospective case-control study.
authors.affiliation: *Hasbro Children's Hospital, The Warren Alpert Medical School at Brown University, Providence, RI †The Children's Hospital of Philadelphia, Philadelphia ‡Geisinger Health System, Danville, PA.
authors.forename: Aristides I
authors.initials: AI
authors.lastname: Cruz
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Aversano
authors.forename: Mark A
authors.initials: MA
authors.lastname: Seeley
authors.forename: Wudbhav N
authors.initials: WN
authors.lastname: Sankar
authors.forename: Keith D
authors.initials: KD
authors.lastname: Baldwin
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001170:Arthritis, Infectious / Q000175:diagnosis*; D001799:Blood Sedimentation; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D005260:Female; D005334:Fever / Q000175:diagnosis; D006621:Hip Joint; D006801:Humans; D007223:Infant; D007958:Leukocyte Count; D016015:Logistic Models; D008193:Lyme Disease / Q000175:diagnosis*; D008297:Male; D010146:Pain; D012189:Retrospective Studies; D013585:Synovitis / Q000175:diagnosis*