Response to: 'Increasing incidence of autoantibody-negative RA is replicated and is partly explained by an aging population' by Matthijssen et al

We thank Matthijssen and colleagues for their interest in our study on the epidemiology of rheumatoid arthritis (RA), where we have reported a significant increase in incidence of rheumatoid factor (RF)-negative RA and a decrease in RF-positive RA in 2005–2014 compared with previous decades.1 Matthijssen et al have independently assessed the incidence of anticitrullinated peptide antibody (ACPA)-negative and ACPA-positive RA in the Leiden Early Arthritis Cohort. In concordance with our findings, they found increasing incidence of ACPA-negative RA but not ACPA-positive RA.2 Further, Matthijssen et al …