[Lyme arthritis in childhood: monarthritis of the knee joint, clinically indistinguishable from monarthritis of unknown origin].

Four children with monarthritis of the knee had no further manifestations of Lyme borreliosis, but a positive antibody titer against Borrelia burgdorferi as measured by Elisa. About 3 years after antibiotic therapy none of the children had arthritis, but one suffered from fibromyalgia and another child had still a vigorous reactivity against Borrelia burgdorferi antigens by Elisa and immunoblot. In this study 4 out of 20 children with recently recognized arthritis had Lyme arthritis which makes it a rather frequent disease. The clinical presentation could not distinguish these 4 children from 4 other children with monarthritis of the knee of unknown origin. In the absence of better diagnostic criteria, the association of monarthritis, not otherwise explained, with a positive Lyme serology seems to be sufficient evidence to establish a diagnosis of Lyme arthritis. After confirmation of the diagnosis children should be treated without delay.