Comparative analysis of imaging characteristics of axial spondyloarthritis and axial psoriatic arthritis depending on disease duration

Objective: to perform a comparative analysis of the imaging characteristics of axial psoriatic arthritis (axPsA) and other variants (ov) of axial spondyloarthritis (axSpA) at the early stage (ESt) and the advanced stage (ASt) of the disease.
Material and methods. A total of 222 patients were examined: 108 with ov-axSpA (Group 1) and 114 with axPsA (Group 2). Group 1 included patients meeting the criteria for axSpA or ankylosing spondylitis; Group 2 included patients with psoriatic arthritis meeting the CASPAR criteria and having axial involvement. Axial involvement was confirmed by the presence of radiographically definite sacroiliitis (SI; bilateral grade II or unilateral grade III), or active SI detected by magnetic resonance imaging, or by the presence of 1 syndesmophyte in the cervical spine (C-spine) and/or lumbar spine (L-spine). Syndesmophytes were assessed as symmetric and asymmetric, bridging and non-bridging, thin (disc-like) and bulky (non-disc-like), solitary and multiple. The severity of radiographic changes in the spine was assessed using the modified mSASSS score. Each group of patients was divided into two subgroups: those with inflammatory back pain (IBP)/chronic back pain (CBP) duration 24 months (ESt) and those with IBP/CBP duration >24 months (ASt).
Results and discussion. ESt was observed in 25 and ASt in 83 patients with ov-axSpA. In ASt, syndesmophytes were more common than in Est both in the C-spine (p=0.007) and in the L-spine (p=0.035); in ASt thin disc-like syndesmophytes were also more frequent (p=0.021) and more structural changes in the spine overall were noted (p=0.001), and higher mSASSS scores were observed (p=0.001). No significant differences in sacroiliac joint (SIJ) changes were found depending on disease stage. In axPsA, ESt was identified in 37 and ASt in 77 patients. In patients with axPsA, no differences were found between ESt and ASt in the frequency of spine and SIJ changes (for any parameter).
Conclusion. It can be assumed that the differences between the groups in the progression of structural changes in the spine are associated with different mechanisms of new bone formation in axPsA and ov-axSpA.

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