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.

Figure 1

Annual incidence of rheumatoid arthritis in Rochester, Minnesota. Shown is the annual incidence rate per 100,000 population by sex: 1955 to 1995. Each rate was calculated as a 3-year centered moving average. Reproduced from [9] with permission.

Figure 2

Mortality in rheumatoid arthritis by sex. Observed mortality in (a) female and (b) male patients with rheumatoid arthritis and expected mortality (based on the Minnesota white population). Observed is solid line, expected is dashed line, and the gray region represents the 95% confidence limits for observed. Reproduced from [25] with permission.

Figure 3

Age-specific mortality in rheumatoid arthritis. Age-specific mortality rates (per 100,000) for women with rheumatoid arthritis (death certificates with any mention of rheumatoid arthritis). Reproduced from [27] with permission.

Figure 4

Annual incidence of psoriatic arthritis by age and sex. Shown is the annual incidence (per 100,000) of psoriatic arthritis by age and sex (1 January 1970 to 31 December 1999; Olmsted County, Minnesota). Broken lines represent smoothed incidence curves obtained using smoothing splines. Reproduced from [55] with permission.

Figure 5

Incidence of osteoarthritis by joint. Shown is the incidence of osteoarthritis of the hand, hip, and knee in members of the Fallon Community Health Plan, 1991 to 1992, by age and sex. Reproduced from [56] with permission.

Figure 6

Incidence of silent myocardial infarction: RA versus non-RA. Shown is the cumulative incidence of silent myocardial infarction in a population-based incidence cohort of 603 RA patients and a matched non-RA comparison group of 603 non-RA individuals from the same underlying population. Reproduced from [108] with permission.

Figure 7

Incidence of sudden cardiac death: RA versus non-RA. Shown is the cumulative incidence of sudden cardiac death in a population-based incidence cohort of 603 rheumatoid arthritis (RA) patients and a matched non-RA comparison group from the same underlying population. Reproduced from [108] with permission.

Figure 8

Incidence of congestive heart failure: RA versus non-RA. Shown is a comparison of the cumulative incidence of congestive heart failure in the rheumatoid arthritis (RA) and non-RA cohort, according to years since index date, adjusting for the competing risk for death. Reproduced from [117] with permission.

Figure 9

Relative risks for overall malignancies in RA patients versus general population. *Excluding nonmelanoma skin. ^†All solid tumors. ^‡Excluding lymphatic and hematopoietic. CI, confidence interval; DMARD, disease-modifying antirheumatic drug; MTX, methotrexate; n, number of malignancies; N, population size; SIR, standardized incidence ratio; TNF, tumor necrosis factor. For original references see Smitten and coworkers [122].

Figure 10

Twelve-month mortality after heart failure. Reproduced from [118] with permission.