To compare the sensitivity to change of different imaging scoring methods in patients with early axial spondyloarthritis (axSpA).
Patients from the DESIR cohort fulfilling the ASAS axSpA criteria were included. Radiographs and MRI of the sacroiliac joints (SIJ) and spine were obtained at baseline, 1, 2 and 5 years. Each image was scored by 2 or 3 readers in 3 separate 'reading-waves'. The rate of change of outcomes measuring spinal and SIJ inflammation (e.g. SPARCC score) and structural damage on MRI (e.g. ≥3 fatty lesions) and radiographs (e.g. mNY grading) was assessed using multilevel generalized estimating equations (GEE) models (taking all readers and waves into account). To allow comparisons across outcomes, rates were standardized (difference between the individual's value and the population mean divided by the standard deviation).
In total, 345 patients were included. Inflammation on MRI-SIJ (standardized rate range: -0.278; -0.441) was more sensitive to change compared to spinal inflammation (range: -0.030; -0.055). Structural damage in the SIJ showed a higher standardized rate of change on MRI-SIJ (range: 0.015-0.274) compared to X-SIJ (range: 0.043-0.126). MRI-SIJ damage defined by ≥3 fatty lesions showed the highest sensitivity to change (0.274). Spinal structural damage slowly progressed over time with no meaningful difference between radiographic (range: 0.037-0.043) and MRI structural outcomes (range: 0.008-0.027).
Structural damage assessed in pelvic radiographs has low sensitivity to change, while fatty lesions detected on MRI-SIJ are a promising alternative. In contrast, MRI-spine is not better than X-spine in detecting structural changes in early axSpA patients.