Background The established scoring system of radiographic sacroiliitis implemented in the mNY criteria for ankylosing spondylitis (AS) does not differentiate between different types of structural damage and does not account for minor structural changes resulting in a large inter-reader variability and poor sensitivity to change.
Objectives The objective of the study was to correlate the progression of radiographic sacroiliitis in the standard score with the dynamics of different structural changes in the sacroiliac joints (SIJ) in patients with axial spondyloarthritis (SpA).
Methods Standard plain radiographs of SIJ of 103 patients (206 joints) with definite axial SpA from the German Spondyloarthritis Inception Cohort (GESPIC) performed at baseline and after 4 years of follow up were scored according to the mNY criteria (grade 0 to IV) and according to the proposed new scoring system. The proposed scoring system implements separate scores for subchondral sclerosis, erosions, joint space in each SIJ. Subchondral sclerosis: 0 - no subchondral sclerosis; 1 - possible subchondral sclerosis; 2 - definite subchondral sclerosis. Erosions: 0 - no erosions; 1 - possible erosions or small single erosions (1-2); 2 - definite single erosions (3-5); 3 - multiply erosions (>5), large joining erosions. Joint space: 0 - no changes of the joint space width; 1 - possible narrowing or widening of the joint space; 2 - definite widening of the joint space; 3 - definite narrowing of the joint space; 4 - partial joint ankylosis; 5 - total joint ankylosis.
Results At baseline radiographic sacroiliitis of grade 0/I/II/III/IV according to the mNY criteria was seen in 14.6%/22.8%/23.3%/37.9%/1.5% of the SIJ. Radiographic progression by at least one grade over 4 years occurred in 28.2% of the SIJ, progression in SIJ with baseline sacroiliitis grade 0/I/II/III occured in 53.3%/29.8%/37.5%/12.8% of the cases. Table demonstrates dynamics of structural changes in the SIJ with the worsening of radiographic sacroiliitis by at least one grade in the conventional score. It can be seen that destructive (erosions) and reparative (sclerosis) processes starts parallel and are both responsible for the progression of sacroiliitis at the early disease stage, while at grade II progression was mostly related to the dynamic of the erosion score and joint space changes, while subchondral sclerosis remained unchanged in the majority of the cases. At the same time, progression from grade III to grade IV was attributable not only to ankylosis formation, but also to improvement of sclerosis and, to a lesser extent, erosion score indicating finalization of the bone repair.
Conclusions Progression of radiographic sacroiliitis is related to different structural processes at different disease stages that should be taken into account while assessing disease progression in axial SpA, especially at the early stage.
Disclosure of Interest None Declared
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