Background Psoriasis is an important clinical feature in spondyloarthritis. However, the influence of psoriasis on the clinical, functional and imaging features of patients with inflammatory back pain (IBP) related to spondyloarthritis is not known.

Objectives To determine the prevalence of psoriasis and its impact in patients with recent IBP suggestive of spondyloarthritis.

Methods The prevalence of psoriasis was determined in 692 patients (mean age 33.3±8.5 years, 53.8% female, 58.3% human leucocyte antigen B27 positive) included in the DESIR cohort. Demographic characteristics, imaging features and blood tests of patients with and without psoriasis were compared.

Results The prevalence of psoriasis was 16.6%. Patients with rather than without psoriasis more often presented with enthesitis (59.1% vs 47.5%; p=0.02) and had more active disease (BASDAI 4.8±1.8 vs 4.4±2.0; p=0.05) and poorer functional status (BASFI 3.6±2.2 vs 3.0±2.3; p=0.006; SF-36 (physical function) 61.9±24.4 vs 66.9±24.9; p=0.04). Patients with psoriasis showed higher levels of C-reactive protein (p=0.02), total cholesterol (p=0.01) and triglycerides (p=0.02). The two groups did not differ in structural changes as assessed by standard x-rays or MRI at the spinal and sacroiliac levels. However, ultrasonography of the Achilles tendon revealed psoriasis associated with bone erosions (p=0.0003) and abnormal vascularisation (p=0.04). Multivariate regression analysis revealed BASFI score (p=0.03), cholesterol level (p=0.02), dactylitis (p=0.0006) and family history of psoriasis (p<0.0001) as independent predictors of psoriasis.

Conclusions In patients with recent IBP suggestive of spondyloarthritis, psoriasis is associated with active axial disease and frequent concomitant enthesopathy and dactylitis.