Differing X-ray patterns in seronegative and seropositive rheumatoid arthritis

Anti-citrullinated protein antibody (ACPA) and rheumatoid factor (RF) status are important predictors for rheumatoid arthritis (RA) erosivity. Qualitative differences on hand/feet radiographs have been described, indicating more carpal fusion in seronegative RA. This study explores these differences further using the total Sharp/van der Heijde score (TSS), digital X-ray radiogrammetry (DXR), and qualitative description.

Matched seronegative (ACPA negative, RF negative, snRA) and seropositive (ACPA, RF > 3xULN, spRA) were examined. TSS scores both for erosions and joint space narrowing (JSN) were registered separately and compared for both groups. Joint compartments and single joints were compared, using a heat map. The degree of carpal fusion was quantified 0-5. DXR measurements (bone mineral density, cortical thickness, bone width, metacarpal index) were determined for each hand separately. Finally, selected radiographs were examined unblinded to search for non-quantifiable differences.

A total of 56 snRA and 57 spRA patients were examined. spRA patients had more erosions and joint space narrowing. Erosion load differed significantly between spRA and snRA in the foot and metacarpophalangeal joint, but not in the wrist or proximal interphalangeal joint compartments. Intracompartmental differences were greater in spRA. JSN scores were greater in spRA, in all compartments except wrist. Carpal fusion and DXR scores did not differ between the groups. The qualitative comparison showed that snRA patients displayed periarticular ossifications, carpal shortening, and sparing of the CMC joints, whereas spRA patients had more CMC damage and less shortening.

X-ray manifestations in snRA and spRA are qualitatively and quantitatively different. This suggests pathophysiological differences between the two forms. Key Points • Seronegative and seropositive RA display qualitatively and quantitatively different X-ray patterns, suggesting differences in the underlying pathophysiological process. This is the first time that this has been shown in a systematic, quantitative fashion.