Lyme arthritis presenting as transient synovitis of the hip.

Transient synovitis of the hip is a common cause of hip pain in children. The etiology of transient synovitis of the hip is unknown. Lyme arthritis is characterized by brief, often recurrent episodes of oligoarthritis. Lyme arthritis most often affects a single knee, but hip involvement is uncommon. This report describes 2 children with Lyme arthritis who presented with features of transient synovitis of the hip. Lyme arthritis should be considered in the differential diagnosis of transient synovitis of the hip in children.