Abstract

IntroductionErosions of the sacroiliac joints (SIJ) on pelvic radiographs of patients with ankylosing spondylitis (AS) are an important feature of the modified New York classification criteria. However, radiographic SIJ erosions are often difficult to identify. Recent studies have shown that erosions can be detected also on magnetic resonance imaging (MRI) of the SIJ early in the disease course before they can be seen on radiography. The goals of this study were to assess the reproducibility of erosion and related features, namely, extended erosion (EE) and backfill (BF) of excavated erosion, in the SIJ using a standardized MRI methodology.MethodsFour readers independently assessed T1-weighted and short tau inversion recovery sequence (STIR) images of the SIJ from 30 AS patients and 30 controls (15 patients with non-specific back pain and 15 healthy volunteers) ≤45 years old. Erosions, EE, and BF were recorded according to standardized definitions. Reproducibility was assessed by percentage concordance among six possible reader pairs, kappa statistics (erosion as binary variable) and intraclass correlation coefficient (ICC) (erosion as sum score) for all readers jointly.ResultsSIJ erosions were detected in all AS patients and six controls by ≥2 readers. The median number of SIJ quadrants affected by erosion recorded by four readers in 30 AS patients was 8.6 in the iliac and 2.1 in the sacral joint portion (P < 0.0001). For all 60 subjects and for all four readers, the kappa value for erosion was 0.72, 0.73 for EE, and 0.63 for BF. ICC for erosion was 0.79, 0.72 for EE, and 0.55 for BF, respectively. For comparison, the kappa and ICC values for bone marrow edema were 0.61 and 0.93, respectively.ConclusionsErosions can be detected on MRI to a comparable degree of reliability as bone marrow edema despite the significant heterogeneity of their appearance on MRI.

Highlights

  • Erosions of the sacroiliac joints (SIJ) on pelvic radiographs of patients with ankylosing spondylitis (AS) are an important feature of the modified New York classification criteria

  • Erosions can be detected on magnetic resonance imaging (MRI) to a comparable degree of reliability as bone marrow edema despite the significant heterogeneity of their appearance on MRI

  • Recent studies have shown that erosions can be detected on magnetic resonance imaging (MRI) of the SIJ early in the disease course before they can be seen on radiography [6] and that erosions may occur in the absence of bone marrow edema (BME) [7]

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Summary

Introduction

Erosions of the sacroiliac joints (SIJ) on pelvic radiographs of patients with ankylosing spondylitis (AS) are an important feature of the modified New York classification criteria. Recent studies have shown that erosions can be detected on magnetic resonance imaging (MRI) of the SIJ early in the disease course before they can be seen on radiography. SIJ erosions are often difficult to identify on pelvic radiographs and training to recognize radiographic structural changes of the SIJ did not improve the performance of radiologists and rheumatologists in detecting radiographic sacroiliitis [2]. Recent studies have shown that erosions can be detected on magnetic resonance imaging (MRI) of the SIJ early in the disease course before they can be seen on radiography [6] and that erosions may occur in the absence of bone marrow edema (BME) [7]. A recent retrospective analysis confirmed that erosion on SIJ MRI is a highly specific lesion in patients with SpA [8]. Data on the reliability of detection of SIJ erosion by MRI are scarce [9,10]

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