POS0029 INCIDENCE AND TREATMENT PENETRATION OF RHEUMATOID ARTHRITIS IN NORWAY – A NATIONWIDE REGISTER LINKAGE STUDY

Abstract

Background:Incidence of rheumatoid arthritis (RA) in Norway has not been evaluated in a nationwide setting.Objectives:To estimate the incidence of RA and real-life penetration of disease-modifying antirheumatic drug (DMARD) use in Norway.Methods:The Norwegian Cardio-Rheuma register comprises pseudonymized data from nationwide registries including the total Norwegian population ≥18 years during 2008-2017. Demographic and socioeconomic data were retrieved from the National Population Register and Statistics Norway. Data on public or private somatic specialized care episodes were collected from the Norwegian Patient register (NPR) (ICD-10 codes for diagnoses and medical procedure codes for biologic DMARD infusions). Dispensed DMARD prescriptions were captured from the Norwegian Prescription Database. RA cases were defined as persons with NPR records of all of the following: 1) 1st episode with ICD-10 code M05/M06 as main or contributory diagnosis (index date), 2) 2nd episode with code M05/M06 within 2-year period following index date, 3) M05/M06 recorded in an internal medicine or rheumatology department during the 2-year period. Years 2008-2010 served as a look-back period to identify prevalent RA cases. To estimate person-years (pyrs) at risk, we calculated number of persons aged ≥ 18 living in Norway on the 1st of January of each year 2011-2015 and multiplied it by one year (prevalent RA cases excluded). Standardized estimates were calculated with 5-year age groups using Norwegian adult population 1st of January 2015 as the standard.Results:Between 2011 and 2015, 9,493 persons fulfilled the RA definition (62.4% seropositive based on ICD-10 codes). Incidence rate was 49/100,000 pyrs (32 in men and 65 in women). A sensitivity analysis excluding cases who had dispensed DMARDs >12 months before index date yielded 8,125 RA cases (incidence 42/100,000 pyrs). Whereas absolute number of incident cases was highest among those aged 60-69 in both sexes, incidence was highest among those aged 70-79 (Figure 1). Both crude and age- and sex-standardized incidences were lower among persons with higher education level (crude/standardized incidence per 100,000 pyrs for those below upper secondary education 60/57; upper secondary or post-secondary non-tertiary education 53/52; higher education 36/39). Of incident cases, 94% received any DMARD treatment or glucocorticoids, 78% methotrexate, and 17% biologic DMARDs within 2 years after index date (Table 1).Conclusion:Contemporary register-based estimate of RA incidence in Norway is comparable to other Nordic countries.1,2 In line with treatment recommendations, methotrexate is the most commonly used DMARD in the initial treatment strategy in Norway. One in six patients used a biologic DMARD within 2 years from 1st recorded RA diagnosis.