Background Over the recent decades several studies have observed a shift towards higher age at disease onset in the incidence of rheumatoid arthritis (RA). The cause of this phenomenon is unknown.
Objectives To find out whether the peak-incidence age has still been increasing during this millennium.
Methods From the nationwide drug reimbursement register maintained by the Finnish Social Insurance Institution we collected data on all patients with incident inflammatory rheumatic diseases from January 1st 2000 to December 31st 2014. Patients with incident RA were identified by the ICD-10 codes of M05 and M06. The peak-incidence age of this cohort was modelled using the Poisson regression with restricted cubic splines (5 knots).
Results During the observation time altogether 27 764 patients (mean age 61.3 at disease onset, 67.5% female) with a new diagnosis of RA were identified. Table shows the peak-incidence ages as well as mean ages at disease onset during the whole observation time and by 3-year periods. The peak-incidence age remained stable over the 15 years since the turn of millennium. The mean age at disease onset increased slightly in male.
Conclusions These results suggest that the unknown factors in the population and environment behind the earlier observed shift towards higher age in the incidence of RA have no longer been gaining power during the 21th century.
Disclosure of Interest None declared
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