Juvenile rheumatoid arthritis in Rochester, Minnesota 1960-1993. Is the epidemiology changing?

To examine trends in the incidence and prevalence of juvenile rheumatoid arthritis (JRA) in Rochester, Minnesota, over 33 years.

The diagnostic retrieval system of the Rochester Epidemiology Project was utilized to screen medical records of all Rochester residents with any potential diagnoses of JRA from 1978 to 1993 (based on the American College of Rheumatology 1977 revised criteria). In addition, all cases of JRA from our previously identified cohort from 1960-1979 were verified, and the 2 data sets were combined, resulting in an incidence cohort spanning 33 years (1960-1993).

Of the 1,240 medical records screened, we identified 65 cases of JRA diagnosed between 1960 and 1993 (48 females, 17 males). The average followup for cases was 12.7 years (range 0-34 years) for a total of 833 person-years of observation. A bimodal distribution of age at diagnosis was observed, with peaks between 0 and 4 years and 9 and 15 years. Seventy-two percent of patients had pauciarticular-onset, 17% had polyarticular-onset, and 11% had systemic-onset disease. Progression of pauciarticular to polyarticular disease occurred in 11% of the cases. The overall age- and sex-adjusted incidence rate was 11.7 per 100,000 population (95% confidence intervals 8.7, 14.8). The incidence rate per 100,000 population was 15.0, 14.1, and 7.8 for the time periods 1960-1969, 1970-1979, and 1980-1993, respectively (P = 0.024). A 3-year, centered, moving average, which was used to display time trends in incidence, suggested a cyclical pattern, with incidence peaks in 1967, 1975, and 1987.

An overall decrease in the incidence rate over the last decade was observed, most marked in the pauciarticular- and systemic-onset subtypes. This decrease, along with the observed cyclical pattern, suggest that environmental factors may influence disease frequency.