Background Previous studies have shown that around 25% of patients with psoriatic arthritis (PsA) have radiographic erosions at presentation but the level of erosive disease is usually very low. Previous data in established PsA has suggested a higher sensitivity for bone erosions with US compared to plain radiography.

Objectives The aim of this analysis was to investigate how many early PsA patients had erosions only visible using US at presentation.

Methods Within the Tight Control of Psoriatic Arthritis (TICOPA study), all patients had radiographs of the hands and feet at baseline and week 48. Patients seen in Leeds also underwent an US assessment of their most symptomatic or dominant hand assessing MCPs and PIPs at the same timepoints. The presence of erosions seen on radiographs and US were compared at an individual joint level and at a patient level. Joints with erosive changes seen only on US at baseline were checked at 48 weeks for presence of radiographic and/or ultrasound erosions.

Results There were 89 patients who had US scans of the MCP and PIP joints with corresponding radiographs at baseline, the majority of whom had repeat scans at 48 weeks (n=74) contributing a total of 163 scans for analysis. In the majority of cases (81/89 91.0% of patients) there was no evidence of erosive disease on radiographs at baseline, however an additional 19 patients had erosions visible on US alone. 25 (3.5%) joints at baseline and 32 (5.6%) at 48 weeks showed erosive disease spread across the MCPs and PIPs (see table). At follow up, none of these erosions were visible on radiographs, with 13 of 23 joints re-scanned still showing erosions on US.

Conclusions There was a low frequency of erosive disease seen in the TICOPA study with little progression over the 48 week study period. Of those with normal radiographs, 23% of patients had additional erosions in the fingers visualised on US, with less erosions identified in the middle MCP joints where US access can be limited.

Disclosure of Interest L. Coates Grant/research support from: Pfizer, Consultant for: Pfizer, J. Freeston Grant/research support from: Pfizer, J. Nam Grant/research support from: Pfizer, P. Conaghan Grant/research support from: Pfizer, Consultant for: Pfizer, P. Helliwell Grant/research support from: Pfizer, Consultant for: Pfizer