medwireNews: The overall incidence of rheumatoid arthritis (RA) during 2005–2014 was similar that of earlier decades, but the rates of rheumatoid factor (RF)-negative disease have increased substantially with time, US study data show.
There was a corresponding decrease in the incidence of RF-positive disease, and Elena Myasoedova and colleagues from the Mayo Clinic in Rochester, Minnesota, say that the “changing prevalence of environmental factors, such as smoking, obesity and others, may have contributed to these trends.”
Myasoedova and team used data from the population-based Rochester Epidemiology Project to investigate trends in RA incidence, defined according to the 1987 ACR criteria, for the periods 1985–1994, 1995–2004, and 2005–2014.
Between 2005 and 2014, the overall age- and sex-adjusted RA incidence was 41 cases per 100,000 population per year, which was similar to the rates observed between 1995 and 2004 (43 per 100,000) and between 1985 and 1994 (40 per 100,000).
In women, the age-adjusted rates were 53, 55, and 48 cases per 100,000 population per year for the periods 2005–2014, 1995–2004, and 1985–1994, respectively, while for men, the corresponding rates were 29, 30, and 32 cases per 100,000 population per year.
Although there were no significant differences in the rates of RA overall, the researchers observed a significant increase in the age- and sex-adjusted incidence of RF-negative RA in 2005–2014 compared with 1995–2004 and 1985–1994, at 20 versus 13 and 12 cases, respectively, per 100,000 population per year.
This was accompanied by a significant decrease in the incidence of RF-positive disease, with rates of 21, 30, and 28 cases per 100,000 population per year during 2005–2014, 1995–2004, and 1985–1994, respectively.
The investigators also observed a substantial increase in the proportion of patients who were clinically obese at RA diagnosis, from 24% in 1985–1994 to 41% in 2005–2014, and a decrease in the proportion of smokers, from 21% to 15%.
Radiographic data showed that a higher proportion of patients in the 2005–2014 cohort had erosive disease within the first year of diagnosis than in the 1995–2004 and 1985–1994 cohorts, at 25% versus 21% and 17%, respectively.
However, further analysis revealed that the differences were only significant among the patients with RF-negative disease. For those with RF-positive RA, the prevalence of erosive disease had not changed with time.
“Taken together with our findings of a rising incidence of RF-negative RA, these data suggest a need for increased awareness and timely vigilant management of RF-negative RA,” Myasoedova and co-authors write in The Annals of the Rheumatic Diseases.
They conclude: “Whether these trends represent a changing serological profile of RA requires further investigation.”
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Ann Rheum Dis 2020; doi:10.1136/annrheumdis-2019-216694