Background Psoriatic arthritis (PsA) and rheumatoid arthritis (RA) are both destructive arthritides but may differ substantially in their periarticular bone changes.

Objectives To investigate the differences in the structural changes of periarticular bone in patients with PsA and RA by a high-resolution imaging technique designed to visualise the bone architecture.

Methods 30 patients with PsA and 58 patients with RA received a µCT scan to compare structural bone changes in the metacarpophalangeal joints of the dominantly affected hand. Number, extent, form and distribution of bone erosions, osteophytes and cortical thinning were recorded. In addition, the size and depth of bone erosions and the size of osteophytes were determined.

Results Patients with PsA and RA had the same number of bone erosions, but they were less severe and overall smaller in size and depth in PsA. Erosions in PsA were mostly Ω-shaped and tubule-shaped, whereas U-shaped lesions were most typical for RA. Erosions in PsA were more evenly distributed, lacking the strong preponderance for the radial sites found in RA. Osteophytes were increased in number, extent and size in PsA as compared with RA, often affecting the entire circumference of bone (‘bony corona’).

Conclusions High-resolution µCT imaging shows profound differences in periarticular bone changes between PsA and RA. Smaller Ω-shaped and tubule-shaped bone erosions as well as large sometimes corona-shaped osteophytes are typical for PsA. These data suggest that mechanisms of bone repair may be more active in PsA than in RA.