Asymmetry of small joint involvement in rheumatoid arthritis: prevalence and tendency towards symmetry over time.

OBJECTIVES

To quantify asymmetry of radiological joint damage in rheumatoid arthritis (RA), to determine whether asymmetrical damage to joints in RA becomes symmetrical over time, and to identify factors predictive of symmetrization.

METHODS

In phase 1, initial, mid-term (mean follow-up: 3 years) and late (mean follow-up: 8 years) radiographs of 48 patients with definite RA (English population) were graded by the Modified Larsen (ML) system. In phase 2, 27 subjects (Canadian population) with at least one asymmetrical pair of joints in the hands or feet were identified. Two successive radiographs of 77 asymmetrical joints, separated by at least 2 years, were compared. Clinical and biological factors were assessed for their ability to predict symmetrization, defined as a reduction in side-to-side difference over time of two or more ML grades.

RESULTS

In phase 1, the overall rate of asymmetry was 12.9% (95% CI: 11.2-14.5%), increasing from 9.7% (first visit) to 13.8% (mid-term) and 14.4% (last visit). Metacarpophalangeal (MCP) joints were more frequently asymmetrical than thumb (MCP and interphalangeal) joints (P = 0.0064) and proximal interphalangeal (PIP) joints (P < 0.0001); wrist quadrants were more frequently asymmetrical than PIP joints (P < 0.0001). In phase 2, two groups were identified and compared: symmetrizers (22 joints) and non-symmetrizers (55 joints). The overall probability of small joints in the hand and foot symmetrizing was 28.5%. Rheumatoid factor (RF) was predictive of symmetrization. The risk of symmetrization was significantly increased in RF-positive patients with asymmetric joints (P = 0.01). The prevalence of asymmetry did not decrease with disease duration, despite symmetrization.

CONCLUSIONS

Prevalence of asymmetry in joint damage in RA was 13-16%. Symmetry was more evident in PIP joints than in MCP and wrist joints. Seropositive patients are more than twice as likely to symmetrize than seronegative patients. Data regarding the tendency for symmetrization may have value in the clinical management of RA patients with asymmetrical joint damage.