The spondyloarthropathies.

The spondyloarthropathies occur with variable frequency in the tropics. Ankylosing spondylitis, in particular, is thought to be rare in tropical Africa, reflecting a low frequency of the HLA B27 gene. However, in the Melanesian populations of Papua New Guinea where there is a relatively high frequency of HLA B27, ankylosing spondylosis is infrequent. These diverse observations may be related to variations in B27 sub-types. Reactive arthritis is a common and important form of acute arthritis in the tropics and in Papua New Guinea at least has a strong association with HLA B27. In Africa an increasing prevalence of reactive arthritis may be related to the spread of HIV infection. Extra-articular features such as balanitis and enthositis are helpful pointers to the diagnosis. Disseminated gonococcal infection and tuberculosis must always be considered and treatment offered if doubt exists. The mainstay of treatment of reactive arthritis is, as always, an anti-inflammatory drug, supplemented by hydrocortisone injections; docycline is available for chlamydia-triggered arthritis and chloroquine or dapsone for more chronic, unresponsive cases.