Abstract
BackgroundTo compare the glycosaminoglycan (GAG) content of lumbar intervertebral disks (IVDs) of patients with ankylosing spondylitis (AS) and healthy volunteers and to investigate the association of GAG depletion and disease-related clinical and imaging features.MethodsLumbar spines of 50 AS patients (mean age 50 ± 10.5 years) and 30 age-matched volunteers were studied with 3-T magnetic resonance imaging (MRI) and conventional radiographs (CR). The MRI protocol included high-resolution morphological sequences and the compositional GAG chemical exchange saturation transfer imaging technique (gagCEST). Morphological images were analyzed by three raters for inflammatory activity, fat deposition, disk degeneration, and structural changes on CR. Clinical and serological measures included the Bath AS Disease Activity (BASDAI) and Bath AS Function (BASFI) Indices and C-reactive protein (CRP) levels. GagCEST values of both groups were compared using a linear mixed model. Kendall-Tau correlation analyses were performed.ResultsGagCEST values were significantly lower in AS patients (2.0 ± 1.7%) vs. healthy volunteers (2.4 ± 1.8%), p = 0.001. Small, yet significant correlations were found between gagCEST values and CRP levels (τ = − 0.14, p = 0.007), BASFI (τ = − 0.18, p < 0.001) and presence of syndesmophytes (τ = − 0.17, p = 0.001). No significant correlations were found with BASDAI, inflammation, and fat deposition MRI scores.ConclusionsLumbar spines of r-AS patients undergo significant GAG depletion, independently associated with syndesmophyte formation, functional disability, and increased serological inflammation markers. Beyond establishing a pathophysiological role of the cartilage in AS, these findings suggest that gagCEST imaging may have an adjunct confirmatory role in the assessment of disease-related pathological MRI findings in axial spondyloarthritis.Trial registration3980 (https://studienregister.med.uni-duesseldorf.de)
Highlights
Ankylosing spondylitis (AS), called radiographic spondyloarthritis (r-Axial spondyloarthritis (axSpA)), as the prototype disease of all axSpA, is a chronic inflammatory disease that predominantly affects the sacroiliac joints (SIJ) and the spine [1]
The distribution of intervertebral disks (IVDs) according to the Pfirrmann classification were as follows: total study population— grade 1 [n = 0], grade 2 [n = 285], grade 3 [n = 99], grade 4 [n = 14], and grade 5 [n = 2]; radiographic axial spondylarthritis (r-axSpA) patients—grade 1 [n = 0], grade 2 [n = 180], grade 3 [n = 58], grade 4 [n = 10], and grade 5 [n = 2]; volunteers—grade 1 [n = 0], grade 2 [n = 105], grade 3 [n = 41], grade 4 [n = 4], and grade 5 [n = 0]
The most important findings of this study were that lumbar IVDs of patients with r-axSpA had significantly lower glycosaminoglycan chemical exchange saturation transfer imaging (gagCEST) values, i.e., a lower GAG content, than those of an age-matched control group and that these compositional changes were associated with variable structural changes on the level of the patient and the spine
Summary
Ankylosing spondylitis (AS), called radiographic spondyloarthritis (r-axSpA), as the prototype disease of all axSpA, is a chronic inflammatory disease that predominantly affects the sacroiliac joints (SIJ) and the spine [1]. It leads to back pain, restricted mobility, and, if left untreated, to ankylosis and severe functional disability [2, 3]. Magnetic resonance imaging (MRI) is a cornerstone imaging technique for identification and may be helpful in treatment monitoring of axSpA [4] This is reflected by the inclusion of MRI of the SIJ into the Assessment of SpondyloArthritis Society (ASAS) classification criteria [5]. To compare the glycosaminoglycan (GAG) content of lumbar intervertebral disks (IVDs) of patients with ankylosing spondylitis (AS) and healthy volunteers and to investigate the association of GAG depletion and disease-related clinical and imaging features
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