Background Axial spondyloarthritis (axSpA) comprises ankylosing spondylitis (AS), showing evidence of sacroiliitis on x-rays, and non-radiographic (nr) axSpA, which is regarded as an early form. To date it is not completely understood whether nr-axSpA shows more inflammation at the beginning that later diminishes or vice versa. Secondly, it is of interest to what extent structural damage is already detectable in the earliest stages of nr-axSpA. Whole-body MRI (wbMRI) is a technique to image the entire axial skeleton in a reasonable amount of time.

Objectives To utilise wb-MRI for the evaluation of both active and structural lesions in nr-axSpA in comparison to AS.

Methods 75 patients (mean age 33±8 yrs.) with axSpA were recruited as part of the ESTHER trial (1). Baseline data were analysed for the purpose of this evaluation. Symptom duration was less than 5 years and included patients had to be positive for inflammation at spine or sacroiliac joints (SIJ). Patients were scanned with a comprehensive wbMRI protocol and scored for active inflammatory lesions as well as structural changes in the spine and SIJs (Berlin wb-MRI score) (1). Separation into nr-axSpA and AS patients was made on the basis of x-rays (fullfillment of mod. NY X-ray criteria).

Results The study cohort consisted of 39 patients with AS and 36 nr-axSpA patients. Clinical characteristics were similar for both groups. In the AS group 92% of the patients showed active inflammatory lesions in the SIJ (score 7.6±6.3), 53% in the spine (score 2.6±4.1), but only 5% showed spinal inflammation without sacroiliitis. MRI-inflammation was found slightly less in he nr-axSpA-group, although this difference was not significant: 94% (score 5.7±5.2), 39% (score 1.1±1.9) and 2%, respectively. The posterior segments of the spine were affected in significantly (p=0.04) more patients in the AS (n=10) than in the nr-axSpA group (n=3). SIJ fatty bone marrow deposition was more frequent (p=0.001) in AS (score of 4.8±3.2) compared to nr-axSpA (score 2.4±2.7) patients. SIJ erosions were non-significantly more common in AS (score 4.2±2.3) than in nr-axSpA (score 3.8±1.8) patients. Bone proliferation on the spine and SIJ were more frequent in the AS vs. nr-axSpA group (p=0.02 and p=0.005, respectively).

Conclusions Whole body MRI is feasible method to depict SpA-associated changes of the entire axial skeleton comprehensively. As expected, AS patients show more structural damage on MRI than nr-axSpA patients including fatty bone marrow deposition, erosions, and bone proliferation. However, the amount of active inflammation on MRI is similar for both groups, with only a trend for higher activity scores in the AS group.

1. Song IH, Hermann KG, Haibel H, Althoff CE, et al. Ann Rheum Dis. 2011 Apr;70(4):590-6.

Disclosure of Interest None Declared