Apparent Diffusion Coefficient as an Imaging Biomarker for Spinal Disease Activity in Axial Spondyloarthritis

Magnetic resonance imaging (MRI) is increasingly used for the diagnosis of axial spondylarthritis (SpA), but it is unknown whether characteristic lesions are actually specific for SpA. This study was undertaken to compare MRI patterns of disease in active SpA, degenerative arthritis (DA), and malignancy. Fat-suppressed MRI of the axial skeleton was performed on 174 patients with back pain and 11 control subjects. Lesions detected by MRI, including Romanus lesions (RLs) and end-plate, diffuse vertebral body, posterior element, and spinous process bone marrow edema (BME) lesions, were scored in a blinded manner. An imaging diagnosis was given based on MRI findings alone, and this was compared with the gold-standard treating physician's diagnosis. The physician diagnosis was SpA in 64 subjects, DA in 45 subjects, malignancy in 45 subjects, other diagnoses in 20 subjects, and normal in 11 subjects. There was 72% agreement between the imaging diagnosis and physician diagnosis. End-plate edema, degenerative discs, and RLs were frequently observed in patients with any of the 3 major diagnoses. Single RLs were of low diagnostic utility for SpA, but >or=3 RLs (likelihood ratio [LR] 12.4) and severe RLs (LR infinite) in younger subjects were highly diagnostic of SpA. Posterior element BME lesions of mild or moderate grade were also highly diagnostic of SpA (LR 14.5). The most common diagnostic confusion was between SpA and DA, since both had RLs present and the presence/absence of degenerative discs did not change the diagnostic assessment. This study confirms the high diagnostic utility of MRI in axial SpA, with severe or multiple RLs evident on MRI being characteristic in younger patients and mild/moderate posterior element lesions being specific for SpA. However, MRI lesions previously considered to be characteristic of SpA could also be found frequently in patients with DA and patients with malignancy, and therefore such lesions should be interpreted with caution, particularly in older patients.

We tested the discriminatory capacity of diffusion-weighted magnetic resonance imaging (DWI) and its potential as an objective measure of treatment response to tumor necrosis factor inhibition in ankylosing spondylitis (AS).