When is arthritis reactive?

Reactive arthritis is an important cause of lower limb oligoarthritis, mainly in young adults. It is one of the spondyloarthropathy family; it is distinguishable from other forms of inflammatory arthritis by virtue of the distribution of affected sites and the high prevalence of characteristic extra-articular lesions. Many terms have been used to refer to this and related forms of arthritis leading to some confusion. Reactive arthritis is precipitated by an infection at a distant site and genetic susceptibility is marked by possession of the HLA-B27 gene, although the mechanism remains uncertain. Diagnosis is a two stage process and requires demonstration of a temporal link with a recognised "trigger'' infection. The identification and management of "sexually acquired'' and "enteric'' forms of reactive arthritis are considered. Putative links with HIV infection are also discussed. The clinical features, approach to investigation, diagnosis, and management of reactive arthritis are reviewed.