Clinical, epidemiologic, and therapeutic aspects of ankylosing spondylitis.

Ankylosing spondylitis (AS) almost invariably starts before the age of 50, and clinical features suggestive of AS in older age should lead to consideration of other rheumatic disorders. Clinical manifestations of extraskeletal tissue such as renal amyloidosis and lung disease may occur. However, the detection of amyloidosis may not invariably infer poor prognosis, and associated lung disease may include apical fibrosis and also interstitial lung disease. Although the clinical significance and pathogenesis of osteoporosis in AS remain unclear, reduced bone mass may be found in a significant number of patients. Population surveys on AS have shown a correlation between the population frequency of HLA B27 and prevalence of AS. However, neither B27 subgroup distribution nor low frequency of B27 can explain the rarity of AS among certain African regions. Also representing an area of future research is the detection of both disease-related variables and sociomedical factors influencing the final outcome of this disease.