Persistent Knee Monoarthritis as a Lyme Disease Presentation: A Diagnostic Challenge - Case Report

There are several differential diagnoses for knee monoarthritis. We report a patient with recurrent episodes of knee effusion, in which the non-specific clinical condition implied several diagnostic hypotheses, therapeutic inaccuracies, and a delay in implementing adequate treatment. For more than 2 years, the patient underwent different Orthopedics and Rheumatology visits. She received multiple therapies, including a knee arthroscopy with partial meniscectomy with transient improvement of the complaints but not a definitive diagnosis. After collecting synovial fluid samples and successively negative microbiological tests, we established the diagnosis of overlap of septic arthritis by atypical microorganisms isolated from synovial tissue ( Pantoea spp. and Staphylococcus saprophyticus ) and Lyme arthritis. Washing and surgical debridement followed by targeted antibiotic therapy resulted in a transient response due to persistent infection (stage 3). This case demonstrates the need for a multidisciplinary approach to knee monoarthritis.