Characteristics and clinical outcomes after treatment of a national cohort of PCR-positive Lyme arthritis.

Objectives: To describe the clinical and microbiological characteristics and outcomes after antibiotic treatment of a national cohort of patients with Lyme arthritis confirmed by PCR testing on synovial fluid and by serology, when available.
Methods: Using the French National Reference Center for Borrelia database, patients with a positive PCR on synovial fluid for Borrelia were identified. Patient clinical and biological characteristics were reviewed from patient records. Long-term outcomes after treatment were studied through a questionnaire and with follow-up data.
Results: Among 357 synovial fluid testing by PCR between 2010 and 2016, 37 (10.4%) were positive for Borrelia. Patients' median age was 36 years (range 6-78) with 61% of men and 28% patients under 18. The presentation was monoarticular in 92% and the knee was involved in 97%. Contrary to the Borrelia species repartition in European ticks, B. burgdorferi sensu stricto was the most prevalent species found in synovial fluid (54%) followed by B. azfelii (29%) and B. garinii (17%). Antibiotic treatments were mainly composed of doxycycline (n = 24), ceftriaxone (n = 10) and amoxicillin (n = 6), for a median duration of 4 weeks (range 3-12). Despite a properly conducted treatment, 34% of patients (n = 12) developed persistent synovitis for at least 2 months (median duration 3 months, range 2-16). Among those, 3 developed systemic inflammatory oligo- or polyarthritis in previously unaffected joints with no signs of persistent infection (repeated PCR testing negative), which mandated Disease-Modifying Antirheumatic Drugs (DMARD) introduction, leading to remission.
Conclusion: In France and contrary to ticks ecology, Lyme arthritis is mainly caused by B. burgdorferi sensu stricto. Despite proper antibiotic therapy, roughly one third of patients may present persistent inflammatory synovitis and a small proportion may develop systemic arthritis. In such cases, complete remission can be reached using DMARD.
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