Fatty Acids Composition of the Sacroiliac Joint in Axial Spondyloarthritis: Analysis Using 3.0 T Chemical Shift‐Encoded MRI

Background Axial spondyloarthritis (axSpA) is a group of inflammatory diseases that may lead to ankylosis of the sacroiliac joint and spine. Fat lesion in the sacroiliac joint is an important feature in diagnosis and disease progression of axSpA. However, whether there is alteration of fatty acids (FAs) composition has not been investigated using MRI. Purpose To investigate bone marrow FA composition of the sacroiliac joint in patients with axSpA compared to controls. Study Type Prospective. Subjects Eighty five participants (mean age, 32.3 ± 6.1 years): 48 axSpA (25 male, 23 female) and 37 non‐SpA controls (18 male, 19 female). Field Strength/Sequence 3.0 T/Two multiple gradient‐echo chemical shift‐encoded (CSE) MRI which differed only in echo times (TEs) were scanned consecutively. Assessment Axial multi‐echo CSE MRI was performed in the sacroiliac joints in vivo. Regions of interest (ROIs) were manually placed on subchondral bone with and without fat lesion in axSpA patients, and on subchondral bone without fat lesion in controls. FA composition was computed within the ROIs using a nonlinear least square method from literature. Statistical Tests Intergroup comparisons were performed using t tests. Results In axSpA, male patients had significantly higher monounsaturated FA compared to controls in areas with fat lesion in the sacrum (+12%) and in the ilium (+9%), and in areas without fat lesion in the sacrum (+10%). Significantly lower polyunsaturated FAs were found in areas with fat lesion in the sacrum (−10%) and ilium (−11%), and lower saturated FAs were found in areas without fat lesion in the sacrum (−6%). In female, patients with axSpA had significantly higher saturated FAs in areas with fat lesion in the ilium (+7%) in comparison to controls. Data Conclusion FA composition of the sacroiliac joint alters in patients with axSpA, and it can be detected using CSE MRI based analysis.