Objective. To use a modified Sharp score (MSS) to measure radiologic progression and to assess its relationship to other radiologic features, peripheral joint disease, and physical function in psoriatic arthritis (PsA).
Methods. Two sets of hand radiographs (median interval 5.75 years) in 139 patients with established PsA were scored using an MSS. Seventy-four patients had standardized clinical joint and Health Assessment Questionnaire (HAQ) scores and other radiologic features of PsA documented at baseline and followup (median interval 5 years).
Results. Radiologic damage was present in 58% of patients at baseline and 74% at followup. The median MSS and its components, erosion score and joint space abnormality score, were significantly greater at followup (P < 0.001). The median MSS progression was +1.08 units/year. There was strong correlation between MSS and clinical joint scores at baseline and followup (r = 0.72 and r = 0.81, respectively). There was weak correlation between MSS and HAQ at baseline (r = 0.29), but stronger correlation at followup (r = 0.48). There was a strong association between MSS and other characteristic radiologic features of PsA (bony proliferation, periostitis, bony ankylosis) at baseline and followup (P < 0.001). However, the presence of soft-tissue swelling on radiographs at baseline was the only radiologic parameter associated with an increased rate of change of MSS (corrected P < 0.006).
Conclusion. The MSS shows good construct validity with measures of peripheral joint involvement such as clinical joint scores and other radiologic features of PsA, and is able to demonstrate that radiologic damage is progressive beyond early disease.