[The role of PCR for the diagnosis of Lyme arthritis].
We studied retrospectively four patients with Lyme arthritis of the knee, the role of PCR for the detection of B. burgdorferi DNA and its influence on further therapeutic decisions. All four patients with Lyme arthritis suffered from knee pain and effusions. None of them remembered having had a tick bite or an erythema migrans. The diagnosis was confirmed by positive serology and in three cases by detection of B. burgdorferi DNA by PCR analysis of the joint fluid. In one patient, PCR was also positive in the synovial tissue. Because of persistent symptoms after adequate antibiotic therapy, PCR was repeated in the joint fluid of two patients. In one patient a positive PCR suggested an ongoing infection. Thus, the antibiotic treatment was changed. A further PCR was negative. Symptoms resolved slowly in all patients over a time of two to seven months after the end of the antibiotic treatment. PCR to detect B. burgdorferi DNA in synovial fluid or tissue respectively is a helpful tool for the diagnosis of Lyme arthritis. Moreover, in patients with refractory Lyme arthritis PCR may be helpful in monitoring the course of the disease.