Trends in the incidence of polymyalgia rheumatica over a 30 year period in Olmsted County, Minnesota, USA

Objective. To determine time trends in the incidence and survival of polymyalgia rheumatica (PMR) over a 30 year period in Olmsted County, Minnesota, USA. Methods. Using the unified medical record linkage system of the Rochester Epidemiology Project, we identified all incident cases of PMR among residents of Olmsted County, MN, between January 1, 1970, and December 31, 1999. Incidence rates were estimated and age- and sex-adjusted to the 1990 US white population. The annual incidence rates were graphically illustrated using a 3 year centered moving average. A Poisson regression model was used to evaluate predictors of PMR incidence. Survival rates were computed and compared with the expected rates in the population. Results. There were 378 incident cases of PMR during the 30 year study period. Of these 66.6% were female and the mean age at incidence was 72.8 years. The overall age and sex adjusted annual incidence of PMR per 100,000 population aged ≥ 50 years was 58.7 (95% CI 52.8, 64.7). Incidence rates increased with age in both sexes, but in women, unlike in men, incidence fell after age 80. The incidence rates varied over the period of observation, but no significant trends over time were found. In the multivariable analysis, sex (p = 0.023), age (p < 0.001), and age² (p < 0.001), but not calendar year (p = 0.24) were significant predictors of incidence. Survival among individuals with PMR was not significantly different from that expected in the population (p = 0.06). Conclusion. The incidence of PMR has remained relatively stable over the past 30 years.