Primary lyme arthritis of the pediatric hip.

BACKGROUND: Lyme arthritis most commonly affects the knee. It is not commonly considered in the differential diagnosis of monoarticular hip pain. There are only a few case reports describing Lyme disease presenting with isolated hip involvement. The purpose of this study is to review our experience with primary Lyme arthritis of the hip.

METHODS: Clinical records at a tertiary children's referral center in a Lyme endemic region were scanned for key words "Lyme" and "hip." Patients with isolated Lyme disease of the hip were included. Diagnosis was made based on Centers for Disease Control guidelines. Clinical presentation, laboratory evaluation, and treatment information were recorded for eligible patients.

RESULTS: Eight patients met eligibility criteria with an average age of 9.5 years (3 to 20y). All patients presented with hip pain (8), limp (3), or refusal to bear weight (5). One of 8 patients had a fever >38.5°C. Two of 8 patients had a peripheral white blood cell count >12,500/mm and 3 of 8 patients had an erythrocyte sedimentation rate>40 mm/h. Aspiration was performed on 5 patients, with a median synovial fluid white blood cell of 41,500/mm (21,500 to 73,500/mm). Three of 8 patients were treated surgically; all patients were treated with antibiotics and were asymptomatic at last follow-up. With the exception of 1 case, there was a delay before appropriate antibiotics were started.

CONCLUSIONS: Primary monoarticular Lyme arthritis of the hip is uncommon. Clinical presentation and laboratory findings are variable, and differentiating it from septic arthritis or toxic synovitis of the hip may be difficult. In areas where Lyme disease is endemic, it should be considered in the differential diagnosis of monoarticular hip pain associated with an effusion.

LEVEL OF EVIDENCE: Level IV, Case Series.