Epidemiological and clinical aspects relating to the variability of rheumatoid arthritis

Objective: To review epidemiological studies dealing with the temporal and geographic variability in the occurrence of rheumatoid arthritis (RA) and clinical studies that address the variability of severity and manifestations among populations. Methods: An extensive search of the literature, including a Medline search, was completed. Studies addressing the origin, history, and trends in the occurrence of RA were reviewed first. Next, studies of the prevalence and incidence of RA in different populations were reviewed, and occurrence rates compared, Standardization was attempted by tabulating adult prevalence rates of studies using equivalent sets of criteria, Studies comparing RA patients from two populations were sought next. Finally, studies dealing with explanations of the presumed variability were reviewed. Results: Temporal variability is indicated by paleopathological evidence that RA has existed in the New World since 4000 sc, whereas there is no evidence that it occurred in Europe before the 17th century, or in Africa before the 20th century. Epidemiological studies show a possible trend of decreasing incidence of RA in the United States and Western Europe, whereas reports from Africa note a rising incidence. In white populations of Europe and America, prevalence is approximately 1%, and incidence is 0.03%. Significantly higher rates are found in some North American Indians, and significantly lower rates in some Asian and African populations, even when the different population structures are taken into account. In the latter populations, different patterns of occurrence from those observed in whites emerge, such as greater female preponderance and a much younger peak age at onset. Direct standardized comparisons of two diverse populations of RA patients showed some differences in expression, severity, or manifestations of RA between populations. Conclusion: The occurrence and manifestations of RA are temporally and geographically variable.