Reactive arthritis.

Concepts about reactive arthritis are changing and must embrace consideration of the fact that bacteria or their products are present in the joint, not just at the portal of entry in the gastrointestinal (GI) or genitourinary (GU) tracts. With chlamydia-associated disease, atypical elementary bodies can be seen in synovium by electron microscopy, and nucleic acids, including RNA, can be found. It is not yet clear if bacterial nucleic acids are present in postenteric reactive arthritis and whether disease courses are predictably different after GI or GU infection. How bacteria are disseminated to joints and local factors, including cytokines that influence their persistence, are under study. Treatment with antibiotics may help some chlamydia-associated reactive arthritis but is not invariably effective.