DECREASING INCIDENCE AND PREVALENCE OF RHEUMATOID-ARTHRITIS IN PIMA-INDIANS OVER A 25-YEAR PERIOD

Objective. To evaluate temporal trends in the incidence of rheumatoid arthritis (RA). Methods. Incident cases of RA were identified among a population-based cohort of Pima Indians in Arizona over the period 196 5-1990. Results. Among 2,894 subjects, 78 incident cases of RA were id entified. The age-adjusted incidence declined by 55% in men (P-trend = 0.225), and by 57% in women (P-trend = 0.017) after controlling for o ral contraceptive or estrogen use and for pregnancy experience. During the same period, age-adjusted prevalence rates of active RA decreased by 29% in men (P-trend = 0.63) and by 40% in women (P-trend = 0.02). Fewer than 17% of subjects with known RA were taking slow-acting antir heumatic drugs (SAARDs) in 1990. Conclusion. The decrease in incidence and prevalence of RA in this population over such a short period impl icates the involvement of an environmental factor(s), other than exoge nous estrogens, in the pathogenesis of the disease. However, the possi bility that the observed decrease might be explained by an increased u se of SAARDs in subjects with RA cannot be excluded.