FRI0176 Performance of spinal and sacroiliac joint mri findings in patients with axspa
Authors: S. Lee, I. Sari, E.S. Tunc, R.D. Inman, N. Haroon
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Early diagnosis of axial spondyloarthritis (AxSpA) is challenging, particularly in patients with normal sacroiliac joints (SIJs) on radiographs. Currently, magnetic resonance imaging (MRI) is considered as the most sensitive imaging modality for detecting early SpA even before radiographic structural lesions develop. However, there are controversial reports, particularly for the spine, regarding the diagnostic utility of MRI. <h3>Objectives</h3> To determine the diagnostic utility of spine and sacroiliac joint lesions assessed by MRI in patients with ankylosing spondylitis (AS) or non-radiographic AxSpA (nr-AxSpA) compared to chronic mechanical back pain (MBP). <h3>Methods</h3> We included 151 AS, 110 nr-AxSpA, and 37 MBP patients. Spine and SIJ MRIs were performed in all patients. Two independent readers blinded to clinical details of the patients, scored the MRI images. A third reader participated in disputed cases. On T1 weighted sequences, the following structural changes in SIJs were scored: sclerosis (≥5 mm) and extensive sclerosis (≥10 mm), erosions,<sup>1–2</sup> extensive erosions (≥3), partial or complete fusion, and fat deposition. Presence in at least two consecutive slices was required for erosions and fusion. On STIR sequences, the following inflammatory changes in the SIJs were determined: ASAS-defined bone marrow oedema (BME) and SPARCC SIJ scores. For the spine, the following were defined: fat infiltration at the vertebral corner on T1 and the number of corner inflammatory lesions (CILs) on STIR. We calculated sensitivity, specificity, and likelihood ratios (LR) of the above-mentioned structural and inflammatory lesions for both AS and nr-AxSpA groups. <h3>Results</h3> There were 298 patients in the study: 151 AS (mean age: 39 (16–77) years; 62.3% male), 110 nr-AxSpA (mean age 36 (17–64) years; 45.5% male), and 37 MBP (mean age 38 (19–59) years; 40.5% male). Presence of erosion was the most sensitive SIJ-MRI finding for structural lesions in AxSpA (AS 97%, nr-AxSpA 89%). However specificity of this variable was low (19%). Evidence of fusion and extensive sclerosis were the most specific SIJ-MRI findings for structural abnormalities with poor sensitivity levels in both groups. On the other hand, presence of extensive erosions showed acceptable sensitivity (78% and 58%) and specificity (62%) values in both AS and nr-AxSpA. For inflammatory lesions of SIJ, both ASAS BME and SPARCC≥2 had similar sensitivity and specificity values in AxSpA. The presence of SIJ fat and evident erosions was associated with a slight increase in Likelihood of AxSpA. Among spinal lesions, spinal fat was the most sensitive finding in AxSpA (67% and 58%) with limited specificity (40%). CILs had moderate to high specificity but low sensitivity. All spinal parameters had low positive LRs. <h3>Conclusions</h3> Extensive erosions of SIJ showed the most balanced performance in whole spinal MRI assessment. Spinal lesions performed poorly when compared with SIJ findings in discriminating AxSpA from MBP. <h3>Disclosure of Interest</h3> None declared