The introduction of tests recognizing ‘anti-citrullinated protein antibodies’ (ACPA) has caused a revolution in rheumatology. Immunization against citrullinated proteins is a feature almost unique for rheumatoid arthritis, although ACPA may occur long before the onset of symptoms. Even if the presence of ACPA does not seem to reveal a distinct arthritis phenotype at symptom onset, it predicts an aggressive disease course with unfavourable outcome. Despite the very high diagnostic specificity for rheumatoid arthritis, ACPA-positivity does not always accord with a traditional diagnosis of rheumatoid arthritis at clinical presentation. However, even when these patients are judged to suffer from mild undifferentiated arthritis, they call for follow-up and special attention by rheumatologists.
A new era began when analyses identifying ‘anti-citrullinated protein antibodies’ (ACPA) were introduced for the diagnosis of arthritis. The question of whether ACPA-positive patients constitute a distinct clinical entity presently attracts great interest. In a previous issue of Arthritis Research and Therapy Annette van der Helm-van Mil and colleagues give a detailed description of clinical characteristics in very early rheumatoid arthritis (RA) at presentation and during 4 years, comparing patients with and without antibodies to cyclic citrullinated peptide (CCP)