Monoarthritis with heterophil-negative infectious mononucleosis. Case of an older patient.

A patient aged 57 years with infectious mononucleosis and monoarthritis of the knee joint is described. To our knowledge, this association in elderly patients has not been reported heretofore, nor has the pathogenesis of arthritis in infectious mononucleosis been established. Because of the clinical picture and the synovial fluid findings, we suggest that the main mechanism of this arthritis is viral replication in the synovia.