What is rheumatoid arthritis? Considering consequences of changed classification criteria.

CHANGES IN CLASSIFICATION CRITERIA Rheumatoid arthritis (RA) was recognised as a separate disease entity in the middle of the 20th century. Since then several sets of classification criteria were developed for use in clinical studies. The 1987 American College of Rheumatology (ACR) criteria have been criticised as they are fulfilled rather late in the disease. Consequently, trials that included patients with RA based on the 1987 criteria studied patients with relatively longstanding arthritis. The aim of the American College of Rheumatology/ European League Against Rheumatism (ACR/EULAR) expert panel was therefore to develop novel criteria without the features of long-standing disease such as erosions or nodules. Indeed the hitherto developed 2010 ACR/EULAR classification criteria for RA are fulfilled earlier in the disease course than the 1987 criteria. 4 Thus, the major objective of the new criteria was achieved. The study of Nordberg et al makes us think about the consequences of the novel criteria for the phenotype of RA. According to the 1987 criteria, the characteristic phenotype of RA consists of symmetric polyarthritis of small joints with morning stiffness (ignoring the features of long-standing disease nodules and erosions). Symmetry and morning stiffness are no longer included in the 2010 criteria. There is less emphasis on clinical elements in the 2010 criteria, and this is paralleled by an emphasis on the results of additional investigations: anti-citrullinated peptide antibodies (ACPA) and acute phase responses were introduced (table 1). The majority of the six points required to fulfil the 2010 criteria can be achieved either by the presence of autoantibodies or on the number of swollen joints. Nordberg et al showed that patients with ACPA-positive RA fulfilling the 2010 criteria have less inflamed joints (measured with either physical examination or with ultrasound) than patients with ACPA-negative RA. This finding is not surprising if we consider the composition of the 2010 criteria. For instance, a patient who presents with clinically apparent arthritis of nine joints, symmetrically distributed in both hands, with morning stiffness and in whom the symptoms persist for more than 6 weeks, has the classic presentation of RA as recognised by fulfilling the 1987 criteria for RA. According to 2010 criteria, this patient is not classified as having RA if there are no RA-related autoantibodies, even not if the acute phase response is elevated. In contrast, a patient who presents with one swollen joint, a high positive rheumatoid factor (RF) and a symptom duration of >6 weeks without an increased acute phase response is classified as RA according to the 2010 criteria. Although the issue that if certain characteristics are absent, others should be available to fulfil classification criteria is generic and not unique for RA, the descriptions of these two patients illustrate the imbalance between the extents of inflamed joints needed to classify RA according to both sets of criteria.