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. 2022 Jun 27:13:887470.
doi: 10.3389/fimmu.2022.887470. eCollection 2022.

Baseline Severity of Sacroiliitis and Extensive Fat Metaplasia Predicts the Progression of Backfill at the Sacroiliac Joint in Patients With Axial Spondyloarthritis

Yimeng Zhang  1   2 , Zikang Guo  1   2 , Lisong Wang  3 , Ying Zhan  2 , Jin Qu  2 , Xinwei Lei  2
Affiliations

Baseline Severity of Sacroiliitis and Extensive Fat Metaplasia Predicts the Progression of Backfill at the Sacroiliac Joint in Patients With Axial Spondyloarthritis

Yimeng Zhang et al. Front Immunol. .

Abstract

Objectives: Fat metaplasia in an erosion cavity, also known as backfill, is an essential intermediary in new bone formation in axial spondyloarthritis (axSpA) patients; however, the predictors of backfill progression are unknown. This longitudinal study aimed to assess the predictors of backfill progression in axSpA patients on magnetic resonance imaging (MRI).

Methods: Clinical and MRI data were collected at baseline and follow-up in 52 axSpA patients. Backfill progression was defined as the new or increased T1 hyperintensity within the SI joint space. Logistic regression analyses were performed to identify the predictors of the backfill progression.

Results: A total of 19 patients had "backfill" at baseline and 30 patients exhibited the backfill progression after follow-up. The mean disease duration and SPARCC scores at baseline were significantly different between patients with and without backfill progression (P<0.001, P=0.003, respectively). Patients with backfill progression had a higher frequency of backfill at baseline, a higher SSS score of fat metaplasia, and a higher SSS score of backfill than those without (P=0.001, P<0.001, and P=0.002, respectively). A higher fat fraction value in the fat metaplasia area at the baseline was more frequent in patients with, than without, backfill progression (P=0.019). In the univariate logistic regression analyses, a higher SPARCC score for inflammation and a higher SSS score for fat metaplasia at baseline were associated with backfill progression.

Conclusions: Severity of sacroiliitis and extensive fat metaplasia at baseline are predictors of the backfill progression in axSpA patients.

Keywords: axial spondyloarthritis; backfill; fat metaplasia; magnetic resonance imaging; sacroiliac joint; sacroiliitis; spondyloarthritis research consortium of canada (SPARCC).

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Flowchart of the study. axSpA, axial spondyloarthritis; MRI, magnetic resonance imaging; TNFα, tumor necrosis factor alpha.
Figure 2
Figure 2
MRI findings of an 18-year-old male with HLA-B27 positive ankylosing spondylitis at baseline (A) and 6-month follow-up (B). Coronal oblique T1 images show new ‘backfill’ at the right sacroiliac joints (white arrows) after 6-month follow-up.
Figure 3
Figure 3
MRI findings of a 38-year-old female with HLA-B27 negative axial spondyloarthritis at baseline (A) and 12-month follow-up (B). Coronal oblique T1 images show fat metaplasia at both sacroiliac joint surfaces, however, no backfill occurs after 12-month follow-up.
Figure 4
Figure 4
Mean scores in (A) BME, (B) erosion, (C) fat metaplasia and (D) backfill according to backfill progression or not. Mean values in (E) ADC and (F) FF values according to backfill progression or not. BME ranges in score from 0 to 72. Erosion and fat metaplasia range in score from 0 to 40. Backfill ranges in score from 0 to 20. *P < 0.05; **P < 0.01; ***P < 0.001.
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