Major Finding: The incidence rate of newly diagnosed rheumatoid arthritis rises with age, peaking among people in their 70s with an incidence of 73 new cases per 100,000 population annually.
Data Source: Review of Swedish national patient registers for 2006-2008, which identified about 10,000 newly diagnosed cases of RA.
Disclosures: Mr. Eriksson said he had no disclosures.
LONDON – The incidence of rheumatoid arthritis rises with age in both men and women and shows the biggest jump during the sixth decade of life, when the incidence among adults in their 50s nearly doubles compared with those in their 40s, based on findings from an analysis of about 10,000 Swedish patients diagnosed for the first time during 2006-2008.
The nationwide data also showed that peak RA incidence occurs among men and women in their 70s, with a new-onset rate of at least 73 cases per 100,000 population annually, Jonas Eriksson said. h
The nationwide Swedish data that allowed analysis of about 10,000 cases far exceeded the scope of previous incidence estimates, enabling Mr. Eriksson and his associates in the clinical epidemiology unit at the Karolinska Institute, Stockholm, to estimate incidence rates by age and sex. They said they used data collected by the Swedish Rheumatology Quality Register, the National Patient Register, and the Prescribed Drug Register.
To assess incident RA cases, the investigators used three different definitions of new-onset disease. The most restrictive definition involved patients who met all of five separate defining criteria:
▸ A first-ever inpatient visit, a specialist outpatient visit, or inclusion in the Swedish Rheumatology Quality Register with a RA diagnosis during 2006-2008;
▸ At least one visit to a rheumatology or internal medicine department;
▸ At least two visits with a diagnosis of RA during 2006-2008;
▸ A second visit with a RA diagnosis within 1 year after a first visit; and
▸ Exclusion of patients treated with a disease-modifying antirheumatic drug more than 6 months before the first visit with a RA diagnosis, pain in joints, or an unspecified diagnosis.
Applying these criteria to the databases for 2006-2008 identified 7,953 patients with a presumed first-time diagnosis of RA, which resulted in a calculated incidence rate of 35 cases/100,000 population per year. Broken down by gender, the rates were 22 cases/100,000 in men and 48 cases/100,000 in women. Mr. Eriksson also reported incidence rates among men and women broken down by age. (See table.) The peak new-onset rates occurred in people aged 70-79 years, with rates of 60 cases/100,000 per year among men and 86 cases/100,000 per year in women.
To further broaden the analysis, the researchers calculated incidence rates using two less stringent definitions. They applied a “medium” definition that eliminated the exclusion portion of their initial, strict definition. This identified 9,133 new-onset cases during the 3 years studied, with an overall incidence rate of 41 cases/100,000 per year and rates of 25 cases/100,000 per year in men and 55 cases/100,000 per year in women.
A third, “liberal” definition of RA limited the identifying criteria to the first two elements from the original list of five: a first-ever inpatient visit, a specialist outpatient visit, or inclusion in the Swedish Rheumatology Quality Register during 2006-2008; and at least one visit to a rheumatology or internal medicine department. This identified 11,715 new-onset cases in 2006-2008, an overall rate of 52/100,000 per year, with rates of 33/100,000 per year in men and 71/100,000 per year in women, he said.
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Source Elsevier Global Medical News