The changing incidence of rheumatoid arthritis over time in north-west Greece: data from a referral centre

Objective Rheumatoid arthritis (RA) is a chronic inflammatory disease of unknown aetiology that affects approximately 1% of the population. The disease presents a temporal variability in different geographic areas. We investigated RA incidence over a 40-year-period in a defined area of north-west Greece, with a total population of about 400 000 inhabitants. Method This incidence study was based on retrospective review of clinical records among adults with RA newly diagnosed from 1980 to 2019 at the referral university hospital of Ioannina. An incident case was defined as any patient diagnosed with RA based on the 1987 American College of Rheumatology criteria, over 16-years-old, and resident in the study area for at least 1 year before diagnosis. Results Out of 1411 cases diagnosed, women constituted a 2.65-fold higher number than men, with a lower mean age at diagnosis. The overall age-adjusted annual incidence rate (95% confidence interval) was 9.5 (8.5-10.5) for the total observation period, 11.7 (10.7-13.0) in 1980-1989, 10.4 (9.4-10.8) in 1990-1999, 9.8 (8.9-10.8) in 2000-2009, and 6.1 (5.3-6.9) in 2010-2019, presenting a statistically significant decline over time, along with a constant decrease in rheumatoid factor (RF)-positive incidence for both sexes. Conclusion Our findings suggest a decrease in the incidence of RA over 40 years in a geographically defined Greek population. Also, the progressive decrease in the incidence of RF-positive disease may relate to less severe expression of RA in Greek patients. These trends could be explained by different clinical, serological, and genetic factors reported in Greece compared to northern European countries.