Quantification of Fat Metaplasia in the Sacroiliac Joints of Patients With Axial Spondyloarthritis by Chemical Shift-Encoded MRI: A Diagnostic Trial.

Dong Liu,Jun Qi,Liudan Tu,Ya Xie,Qiujing Wei,Churong Lin,Qingcong Kong,Jieruo Gu,Budian Liu,Huiquan Wen

doi:10.3389/fimmu.2021.811672

Abstract

ObjectiveTo study the diagnostic performance of chemical shift-encoded MRI (CSE-MRI) in the diagnosis of axial spondyloarthritis (axSpA).MethodsCSE-MRI images were acquired for consecutive patients complaining of back pain as well as healthy volunteers. Proton density fat fraction (PDFF) values were measured independently by two readers. Diagnostic performance of CSE-MRI was analyzed by sensitivity analysis and ROC curve analysis. Logistic regression analysis was employed to investigate the risk factors of extensive fat deposition in the SIJs.ResultsA total of 52 r-axSpA patients, 37 nr-axSpA patients, 24 non-SpA patients and 34 healthy volunteers were included. Mean PDFF values in the SIJs of patients with r-axSpA and nr-axSpA (72.7% and 64.5%) were significantly higher than non-SpA patients and healthy volunteers (56.0% and 57.6%) (p<0.001). By defining extensive fat deposition in the SIJs as ≥8 ROIs with PDFF values over 70%, its sensitivity and specificity in diagnosing axSpA reached 72.47% and 86.21%%. By joining bone marrow edema (BME) with ≥8 ROIs (PDFF>70%), 22 (24.71%) and 23 (25.84%) more axSpA patients were classified as SIJ MRI (+) by reader 1 and 2, but specificities decreased by 15.52% and 10.34%. Multivariate logistic regression analysis confirmed longer disease duration as the independent risk factor of extensive fat deposition in SIJs (OR=1.15, 95%CI[1.03, 1.32]), while bDMARDs medication was a protective factor (OR=0.15, 95%CI[0.04, 0.51]).ConclusionCSE-MRI is a reliable tool to quantitively assess the fat metaplasia in the SIJs of axSpA patients. Extensive fat deposition in the SIJs could add incremental diagnostic value to BME, but at the cost of decreased specificities.

Highlights

Quantitative imaging emerges as one of the major breakthroughs in medical imaging over the last two decades
Despite the fact that a variety of MRI lesions could be observed in the sacroiliac joints (SIJs) of patients with axial spondyloarthritis (axSpA), the current definition of a positive SIJ MRI still remains indispensably the bone marrow edema (BME) or osteitis [6, 7]
Sensitivities, specificities, positive predictive values (PPV) and negative predictive values (NPV) were calculated for each cut-off point of mean proton density fat fraction (PDFF) values and counts of regions of interest (ROI) with PDFF values over 70%

Summary

Introduction

Quantitative imaging emerges as one of the major breakthroughs in medical imaging over the last two decades. Despite the fact that a variety of MRI lesions could be observed in the sacroiliac joints (SIJs) of patients with axSpA, the current definition of a positive SIJ MRI still remains indispensably the bone marrow edema (BME) or osteitis [6, 7]. Fat metaplasia has been gaining interests in recent years regarding its capability of assisting in the imaging diagnosis of axSpA as well as predicting radiographic progression. Bakker et al suggested that fat depositions and erosions combined could be used reliably as a substitute for radiographs in the imaging arm of ASAS classification criteria for axial spondyloarthritis [9]. In a most recent study, fat lesions showed the highest specificity in the diagnosis of axSpA, compared with other lesions such as bone marrow edema and erosions, despite relatively low sensitivity [10]. A couple of studies revealed that fat metaplasia developed ensuing the resolution of inflammation, and such fatty lesions were independently associated with the development of ankylosis [13, 14]

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