Eur J Pediatr. 2006 Jun;165,6:420-1. Epub 2006 Mar 4. Persistent synovitis in two children with Lyme arthritis linked with HLA-DRB1*1104. Hendrickx G, Demanet C, Vandenplas Y. Department of Paediatrics, Paediatric Orthopaedic and Rheumatology Unit, Academisch Ziekenhuis -Vrije Universiteit Brussel, Laarbeeklaan 101, 1090 Brussels, Belgium. email@example.com We report on two patients with a persistent Lyme arthritis. In addition both had a peculiar disease history. The first patient had oligoarticular juvenile idiopathic arthritis in remission. Five months after an infected tick bite, she developed a relapse of arthritis in the same knee. We considered Lyme borreliosis as the possible trigger for this reactivation. The disease history of the second patient was that of a classical non-responder. After extensive antibiotic treatment osteolytic lesions became visible. MRI images suggested an erosive arthropathy and arthroscopy was used to investigate possible erosive arthritis. Studies on collected material made us consider the following hypothesis. Despite demonstration of a spirochete fragment in a synovial biopsy, the patient recovered without additional antibiotic treatment. Conclusion: delay of antibiotic treatment after appearance of erythema migrans may cause systemic spread of the antigen and predispose to Lyme arthritis. If intra-articular steroids are considered when spontaneous resolution of Lyme arthritis does not occur, magnetic resonance imaging of the affected joint, prior to administration, may provide additional information. The success of synovectomy may be related to removal of undegraded antigenic material which may prolong the inflammation.