Exaggerated axial osteoproliferation in patients with spondyloarthritis accompanying chronic kidney disease.

INTRODUCTION: Axial spondyloarthritis (axSpA) is a chronic inflammatory disease characterized by entheseal inflammation, pathological new bone formation and structural lesions on spinal radiography. Chronic kidney disease (CKD) especially in its moderate to advanced stages manifests with abnormalities such as secondary hyperparathyroidism, renal osteodystrophy and vascular or ligamentous calcifications. This study aimed to compare radiographic spinal abnormalities in axSpA patients with CKD, axSpA patients without CKD, and CKD patients without inflammatory arthritis. METHODS: This retrospective study used data from the HURBIO registry, including 3207 bDMARD-treated patients with spondyloarthritis (SpA). Patients with axSpA and CKD (axSpA-CKD group, n = 28, 0.87% of the cohort) were compared with 56 age- and sex-matched axSpA patients without CKD (axSpA-nonCKD group) and 38 CKD patients without SpA (non-SpA CKD group). Cervical/lumbar and pelvic radiographs were evaluated for vertebral erosion, squaring, sclerosis, syndesmophyte (any), bamboo spine, and mSASSS scores. RESULTS: The prevalence of syndesmophytes was significantly higher in axSpA-CKD patients compared with axSpA-nonCKD patients (64.2% vs. 25.0%, p = 0.002). Syndesmophyte-like osteoproliferative changes in the axial spine were observed in eight (21.0%) non-SpA CKD patients. Higher total mSASSS scores were independently associated with the presence of CKD (β = 18.5, 95% CI 9.03-28.06, p < 0.001), independent of age at bDMARD initiation, sex, disease duration, smoking, and HLA-B27 positivity, and this association remained significant after further adjustment for BASDAI scores as well as for the presence of amyloidosis and uveitis (all models, p ≤ 0.017). CONCLUSION: The results suggest that enthesial changes in the axial spine are more frequent and severe in axSpA patients with CKD compared to matched axSpA patients without CKD. In patients with axSpA-CKD, the contribution of CKD to new bone formation should be considered in the evaluation of radiographic damage.