Comparative Characteristics of Axial Spondyloarthritis and Psoriatic Arthritis with Axial Involvement

The aim of the study was to compare clinical characteristics of patients with axial spondyloarthritis (axSpA)/ankylosing spondylitis (AS) and with axial psoriatic arthritis (axPsA). MATERIALS AND METHODS: . A total of 100 patients were examined: 45 with axSpA/AS (group 1) and 55 with axPsA (group 2). Patients of group 1 were included according to axSpA/AS criteria; patients of group 2, according to CASPAR (ClASsification criteria for Psoriatic ARthritis) criteria, and having axial involvement (axPsA). Axial involvement was detected in case of radiologically significant sacroiliitis (SI, bilateral grade ≥2 or unilateral grade ≥3), or active MRI significant sacroiliitis, or ≥1 syndesmophyte(s) of the cervical and/or lumbar spine. Patients were evaluated for the presence of inflammatory back pain (IBP) by ASAS (Assessment of Spondyloarthritis International Society) criteria. RESULTS AND DISCUSSION. : Patients of group 1 were younger (p < 0.001), more often were HLA-B27 positive (p < 0.001), and more often had IBP (p = 0.001). Patients of group 2 had older age (> 40 years) at back pain onset (p < 0.001) and more often had peripheral arthritis (p < 0.001), dactylitis (p = 0.004), and skin psoriasis (p < 0.001). Nail psoriasis was found only in group 2 patients (p < 0.001). Group 1 patients more often had heel enthesitis (p = 0.005). Group 2 patients had worse axial disease activity scores: BASDAI (Bath Ankylosing Spondylitis Disease Activity Index; p = 0.006) and ASDAS-СRP (Ankylosing Spondylitis Disease Activity Score with C-reactive protein level determination; р < 0.001); and worse patient-reported outcomes: BASFI (Bath Ankylosing Spondylitis Functional Index; p = 0.004), patients' pain (p = 0.005) and patients' global assessments (p = 0.036). Patients of group 2 had more syndesmophytes of the lumbar (р = 0.009) and cervical (р = 0.007) spine. Only in group 2 patients, chunky "non-marginal" syndesmophytes (in 32.1%), as well as spinal lesions without sacroiliitis (in 20.0%) were found. Patients of group 2 had more joint erosions (р = 0.001), osteolysis (р = 0.015), juxta-articular bone formation (р < 0.001) and joint ankyloses (р = 0.02). All patients of group 1 and only 80% of group 2 (р = 0.003) met ASAS criteria for axSpA. AxSpA/AS and axPsA seem to be two different diseases. In our cohort of patients, axPsA patients had worse disease status compared to axSp and AS.