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Arthritis Res Ther. 2012; 14(3): R124.
Published online May 24, 2012. doi:  10.1186/ar3854
PMCID: PMC3446505
Can erosions on MRI of the sacroiliac joints be reliably detected in patients with ankylosing spondylitis? - A cross-sectional study
Ulrich Weber,corresponding author1,2 Susanne J Pedersen,3 Mikkel Østergaard,3 Kaspar Rufibach,4 Robert GW Lambert ,5 and Walter P Maksymowych1
1Department of Medicine, Division of Rheumatology, 562 Heritage Medical Research Building, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
2Department of Rheumatology, Balgrist University Hospital, Forchstrasse 340, CH-8008 Zürich, Switzerland
3Department of Rheumatology, Copenhagen University Hospital at Glostrup, Nordre Ringvej 57, DK-2600 Glostrup, Denmark
4Division of Biostatistics, Institute of Social and Preventive Medicine, University of Zürich, Hirschengraben 84, CH-8001 Zürich, Switzerland
5Department of Radiology and Diagnostic Imaging, University of Alberta, 2A2.41 Walter C. Mackenzie Health Sciences Centre, 8440-122 Street, Edmonton, Alberta, Canada T6G 2B7
corresponding authorCorresponding author.
Ulrich Weber: ulrich.weber/at/balgrist.ch; Susanne J Pedersen: susanne_juhl_ped/at/dadlnet.dk; Mikkel Østergaard: mo/at/dadlnet.dk; Kaspar Rufibach: kaspar.rufibach/at/ifspm.uzh.ch; Robert GW Lambert : robert.lambert/at/ualberta.ca; Walter P Maksymowych: walter.maksymowych/at/ualberta.ca
Received December 17, 2011; Revised March 27, 2012; Accepted May 24, 2012.
Abstract
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. 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.
Methods
Four 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.
Results
SIJ 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.
Conclusions
Erosions can be detected on MRI to a comparable degree of reliability as bone marrow edema despite the significant heterogeneity of their appearance on MRI.
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