Comparative characteristics of axial spondyloarthritis and psoriatic arthritis with axial involvement

Objective – to compare clinical characteristics of patients with axial spondyloarthritis (axSpA)/ankylosing spondylitis (AS) and with axial psoriatic arthritis (axPsA). Subjects and methods . 100 patients were examined: 45 – with axSpA/AS (group 1), 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 (bilateral grade ≥2 or unilateral grade ≥3) or active MRI sacroiliitis, or ≥1 syndesmophyte(s) of the cervical and/or lumbar spine. Patients were evaluated for presence of inflammatory back pain (IBP) by ASAS (Assessment of Spondyloarthritis International Society) criteria. Results and discussion. Patients of group 1 were younger (p40 years) at back pain onset (p<0.001), more often 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 had more often 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 were found (in 32.1%), as well as spinal lesions without sacroiliitis (in 20.0%). 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.