[Differential diagnosis of acute arthritis. Quickly assessing infectious etiology].

Acute arthritis of abrupt onset producing symptoms showing peak intensity within a matter of hours, have a largely uniform clinical presentation. Urogenital or gastrointestinal infections (= reactive arthritis) or infectious conditions (= septic genesis) in the patient's history may provide further information of relevance for the differential diagnosis, which includes--in particular in the case of the reactive, infectious/allergic forms--direct and serological demonstration of pathogens. In contrast, imaging procedures in the early stages are of little help in clarifying causes.