To investigate the trends in incidence of extra-articular rheumatoid arthritis (ExRA) in a well defined community based cohort of patients with rheumatoid arthritis (RA), and to examine possible predictors of ExRA occurrence.
Using the resources of the Rochester Epidemiology Project, a retrospective medical record review was conducted of a cohort of 609 cases of RA in Olmsted County, MN, diagnosed during 1955-94. These cases had been previously classified using the ACR 1987 criteria for RA. Patients were followed up from 1955 to 2000 (median follow up 11.8 years; range 0.1-42.8), and incident ExRA manifestations were recorded according to predefined criteria. Time to first presentation of ExRA was compared in patients with RA by decade of diagnosis. Possible ExRA risk factors were identified in case record reviews.
ExRA occurred in 247 patients (40.6%). A subgroup of 78 patients (12.8%) had ExRA manifestations considered to be severe in a previous study from Malmö, Sweden. The incidence of severe ExRA did not change significantly over the decades (p=0.165). In a multivariate analysis the main predictors of severe ExRA were smoking at RA diagnosis (risk ratio (RR)=2.94; 95% confidence interval (95% CI) 1.68 to 5.13) and early disability (Steinbrocker class III-IV at diagnosis) (RR=2.45; 95% CI 1.51 to 4.00). The effect of smoking overwhelmed the weaker effect of rheumatoid factor seropositivity.
There was no decrease in the incidence of extra-articular manifestations in patients with RA diagnosed up to 1995. Smoking and early disability are independent risk factors for extra-articular RA.