[A rare cause of recurrent monarthritis of the knee].

Isolated monarthritis caused by Tropheryma whipplei without involvement of the gastrointestinal tract is rare but is nowadays often described as an early manifestation of the disease. In a male patient with recurrent knee joint arthritis for several years, we could ultimately diagnose Whipple's disease based on PCR positive biopsies of synovial tissue and fluid. Furthermore, the patient was found to be an asymptomatic T. whipplei carrier. With adequate antibiotic therapy the patient has meanwhile fully recovered.