[Lyme arthritis in children: a diagnostic trap].

Lyme disease incidence is diverse in France. It is rare in many regions but very frequent in Central and Eastern France. Arthritis is a late manifestation of Lyme disease. In children, the clinical and biological picture often resembles that of septic arthritis and juvenile rheumatoid arthritis, which are more frequent. This explains why diagnosis may be delayed, especially when patient lives in a region of low incidence. We report the case of an 8-year old girl with knee arthritis treated as septic arthritis in a region where Lyme disease is rare. Six days later, clinical and biological worsening suggested that the diagnosis had to be reconsidered. Lyme arthritis was confirmed by serology. Treatment was adapted and the progression was positive. This case reminds us that, in children, Lyme arthritis may look alike septic arthritis or juvenile rheumatoid arthritis and must be considered as a possible diagnosis, even in low-incidence areas.