The purpose of this study was to determine useful radiographic findings for differentiating psoriatic arthritis (PsA) from rheumatoid factor (RF)-positive or -negative rheumatoid arthritis (RA) in Japanese patients.
We accrued 85 patients with PsA. Controls included 135 patients with RA (85 RF-positive, 50 RF-negative) matched for gender and disease duration with PsA patients. Radiographs of hands and feet were obtained, and distal interphalangeal (DIP) erosive disease, joint osteolysis, tuft osteolysis, juxta-articular bony proliferation (JBP), periosteal new bone formation and bony ankylosis, which were identified using the definitions developed by an earlier study, were compared between the PsA and RA groups.
For radiographic features of hands, the frequencies of JBP, periosteal new bone, and diffuse soft tissue swelling of the fingers were significantly higher in PsA patients than in RF-positive RA patients. However, only the frequency of JBP significantly differed between PsA and RF-negative RA patients. In feet, the frequencies of DIP erosive disease, tuft osteolysis, JBP, and diffuse soft tissue swelling of the toes were significantly higher in PsA patients than in RF-positive RA patients. However, only the frequency of JBP significantly differed between PsA and RF-negative RA patients.
JBP was the most important radiographic feature for discriminating PsA from both RF-positive and -negative RA, confirming the study by the CASPAR group that showed that JBP is the only radiologic feature that can discriminate PsA from other inflammatory arthritides. This study showed the utility of plain radiographs for diagnosis of PsA.