Background Axial involvement in early psoriatic arthritis (ePsA) patients (pts) is often asymptomatic, poorly diagnosed and has not been studied properly. Magnetic resonance imaging (MRI) of sacroiliac joints (SIJs) helps to better define spinal involvement in ePsA.

Objectives to study the prevalence of axial involvement in peripheral ePsA pts.

Methods 89 pts (M/F–42 /47) with peripheral ePsA according to CASPAR criteria were included; mean age 36.5±10.9 yrs, disease duration 12.1±10.1 mo., disease activity index (DAS) 5.2±2.8, C-RP 16.1 [6.6; 31.0] mg/l, ESR 22.5±19.2 mm/h. All patients were evaluated for the presence of inflammatory back pain (IBP) by ASAS criteria. In pts having IBP disease activity was also measured according to BASDAI. The examination included X-ray of sacroiliac joints (SIJs) (pelvic radiograph), HLA B27 antigen, MRI of SIJs was performed in 79 pts, both with and without IBP, on Signa Ovation 0,35T. Bone marrow edema on MRI (STIR), considered as active MRI sacroiliitis (MRI-SI), was evaluated by an independent reader. Radiographic sacroiliitis (R-SI) was defined when 2 grade changes in at least one SIJ appear, and included definite radiographic SI (dR-SI) and “non-definite” radiographic SI (ndR-SI). dR-SI was determined according to New York criteria (unilateral grade≥3 or bilateral grade≥2). 2 grade changes in only one SIJ were qualified as ndR-SI.

Results IBP was found in 58 out of 89 (65.1%) pts, 35 (60.3%) of them had short-term (episodic) IBP, and 23 (39.7%) pts had long-term IBP. MRI-SI was observed in 28 out of 79 (35.4%) pts. R-SI was determined in 42 out of 89 (47.2%) pts, while dR-SI was found in 27 out of 89 (30.3%) pts, the remaining 15 (16.9%) pts had ndR-SI. 34 (38. 2%) pts were HLA B27 positive. In pts having IBP disease activity according to BASDAI was 4.5±1.6. Correlation has been detected between MRI-SI and IBP: among the group of pts having MRI-SI IBP was observed in 92.9% cases while out of the group of patients without MRI-SI in 54.9% cases (p=0.0002). An association was found between MRI-SI and long-term IBP (p=0.003) as well as between MRI-SI and short-term IBP (p=0.006). Moderate correlation has been detected between the presence of dR-SI and IBP (p=0.038). It's worth noting that among the 26 pts having dR-SI, 5 (19.2%) pts never had IBP before. And among the 15 pts having ndR-SI, 6 (40.0%) pts never had IBP before. No association was found between the presence of MRI-SI/R-SI/dR-SI and HLA B27 status.

Conclusions in the Russian cohort of early peripheral psoriatic arthritis pts, careful examination quite often revealed high prevalence of axial involvement: 65% of pts had IBP (moreover, more than half of them (60%) had short-term IBP), 35% of pts had MRI-SI, half of the pts had R-SI, one third of the pts had definite R-SI. A significant number of patients (40%) developed 2 grade changes in one SIJ without previous IBP. An association was found between IBP and SI revealed by any of the visualization methods used. No association has been detected between the presence of MRI-SI or R-SI and HLA B27 status. These data indicate that in peripheral ePsA pts axial involvement is often asymptomatic and is poorly diagnosed. Careful identification of IBP together with MRI of SIJs will help to better define spinal involvement.

Disclosure of Interest None declared