Epidemiological studies in incidence, prevalence, mortality, and comorbidity of the rheumatic diseases

Abstract

Epidemiology is the study of the distribution and determinants of disease in human populations. Over the past decade there has been considerable progress in our understanding of the fundamental descriptive epidemiology (levels of disease frequency: incidence and prevalence, comorbidity, mortality, trends over time, geographic distributions, and clinical characteristics) of the rheumatic diseases. This progress is reviewed for the following major rheumatic diseases: rheumatoid arthritis (RA), juvenile rheumatoid arthritis, psoriatic arthritis, osteoarthritis, systemic lupus erythematosus, giant cell arteritis, polymyalgia rheumatica, gout, Sjögren's syndrome, and ankylosing spondylitis. These findings demonstrate the dynamic nature of the incidence and prevalence of these conditions -a reflection of the impact of genetic and environmental factors. The past decade has also brought new insights regarding the comorbidity associated with rheumatic diseases. Strong evidence now shows that persons with RA are at a high risk for developing several comorbid disorders, that these conditions may have atypical features and thus may be difficult to diagnose, and that persons with RA experience poorer outcomes after comorbidity compared with the general population. Taken together, these findings underscore the complexity of the rheumatic diseases and highlight the key role of epidemiological research in understanding these intriguing conditions. IntroductionEpidemiology has taken an important role in improving our understanding of the outcomes of rheumatoid arthritis (RA) and other rheumatic diseases. Epidemiology is the study of the distribution and determinants of disease in human populations. This definition is based on two fundamental assumptions. First, human disease does not occur at random; and second, human disease has causal and preventive factors that can be identified through systematic investigation of different populations or subgroups of individuals within a population in different places or at different times. Thus, epidemiologic studies include simple descriptions of the manner in which disease appears in a population (levels of disease frequency: incidence and prevalence, comorbidity, mortality, trends over time, geographic distributions, and clinical characteristics) and studies that attempt to quantify the roles played by putative risk factors for disease occurrence. Over the past decade considerable progress has been made in both types of epidemiologic studies. The latter studies are the topic of Professor Silman's review in this special issue of Arthritis Research & Therapy [1]. In this review we examine a decade of progress on the descriptive epidemiology (incidence, prevalence, and survival) associated with the major rheumatic diseases. We then discuss the influence of comorbidity on the epidemiology of rheumatic diseases, using RA as an example. The epidemiology of rheumatoid arthritisThe most reliable estimates of incidence, prevalence, and mortality in RA are those derived from population-bas...

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