[Reactive arthritis in children].

Reactive arthritis is arthritis in which, although the nature of the responsible infection is known or suspected upon serological grounds, attempts at recovering the pathogen from the synovial fluid have failed. One of the main pathogenetic problems is the multiplicity of etiologic agents. Some are exogenous and may be related to the articular tropism of certain microorganisms, to immunologic depression due to an antecedent or coincident infection, and to successive reinfections by the same pathogen or by others which may promote an exacerbation of the disease. Others are endogenous and attention should be given to the local or systemic presence of an antigen as well as, in some instances, to the persistence of residual forms of infecting agents, which are more readily demonstrated with current bacteriological and serological methods. Although reactive arthritis is to be distinguished from septic arthritis, it can no longer be clearly differentiated from the classical post-infectious rheumatism. Once it has been produced, the antigenic stimulation is responsible for an immunologic response which tends to check systemic extension but may also produce tissue damage in the host. Some patients have circulating immune complexes which may bind to the joint, thereby damaging it. In other patients, particularly those who are HLA B27 positive, host-pathogen cross-reactions are demonstrated. Actually, the most frequent pathogenetic sequence seems to be a combination of two or more of these mechanisms, as there are reasons to believe that presence of the pathogen in situ is not required for the persistence of the inflammatory process. Reactive arthritis was first reported in adults following either sexually transmitted urethritis due to chlamydiae, mycoplasma or gonococci, or hepatitis B or an intestinal infection due to Yersinia, Campylobacter, Shigella, Klebsiella or Salmonella. Later, it was described in pediatric patients, particularly in Scandinavia where, for genetic reasons, the HLA B27 group is prevailing. Reactive arthritis seems less frequent in caucasian ethnic groups and above all in Latin Americans among whom HLA B27 carriers are more uncommon; however, it must be pointed out that they have not been as extensively studied and that other etiologic factors may still remain to be discovered. The course and etiology of the different forms of arthritis share certain characteristics which have been determined through a better knowledge of these conditions: onset occurs one or several weeks after a respiratory, urinary or, most often in children, digestive infection. This episode is unremarkable or latent and often overlooked.(ABSTRACT TRUNCATED AT 400 WORDS)