ACR Meeting Abstracts

ACR Meeting Abstracts

Abstract Number: 1024

What Constitutes the Characteristic Fat Lesion On MRI of the Sacroiliac Joints in Early Spondyloarthritis?

Ulrich Weber1, Susanne Juhl Pedersen2, Veronika Zubler3, Kaspar Rufibach4, Stanley Chan5, Robert GW Lambert6, Mikkel Ostergaard7 and Walter P. Maksymowych8, 1Rheumatology, Balgrist University Hospital, Zurich, Switzerland, 2Department of Rheumatology, Copenhagen University Hospital Glostrup, Copenhagen, Denmark, 3Radiology, Balgrist University Hospital, Zurich, Switzerland, 4Institute for Social and Preventive Medicine, Division of Biostatistics, University of Zurich, Zurich, Switzerland, 5Division of Ophthalmology, University of Alberta, Edmonton, AB, Canada, 6Radiology, University of Alberta, Edmonton, AB, Canada, 7Dept of Rheumatology RM, Copenhagen University Hospital, Glostrup, Denmark, 8Department of Medicine, University of Alberta, Edmonton, AB, Canada

Meeting: 2012 ACR/ARHP Annual Meeting

Keywords:

Session Information

Title: Imaging of Rheumatic Diseases: Magnetic Resonance Imaging, Computed Tomography and X-ray

Session Type: Abstract Submissions (ACR)

Background/Purpose: It is well known that fat infiltration (FI) of bone marrow may be observed on T1-weighted MRI in the sacroiliac joints (SIJ) of healthy individuals and patients with mechanical back pain and with spondyloarthritis (SpA). But it is unclear whether the MRI features of FI allow characterization of FI as pathological rather than physiological. Moreover, it is unclear if this might have diagnostic utility in early SpA. We aimed to assess which MRI features of fat contribute to diagnostic utility of SIJ MRI in 2 inception cohorts of early SpA.

Methods: Cohort A comprised 69 consecutive patients ≤50 years referred from rheumatology and primary care practices for assessment of clinically suspected SpA, cohort B comprised 88 consecutive patients ≤50 years with acute anterior uveitis and back pain. They were classified according to clinical examination and pelvic X-ray as having non-radiographic axial SpA (nr-axSpA) (n=20 and 31 for cohorts A and B, respectively), ankylosing spondylitis (AS) (n=10 and 24), or mechanical back pain (MBP) (n=39 and 33). Cohort A also comprised 20 healthy volunteers (HV). SIJ MRI were assessed independently in random order by 4 blinded readers for the following morphological features of FI: distinct border around the region of FI, homogeneity of the T1-weighted signal, proximity to subchondral bone, and association with other SIJ lesions (bone marrow edema (BME), erosion (ER)).

Results: In cohort A and B, FI in ≥2 SIJ quadrants was recorded by any 2 readers in AS in 90% and 100%, in nr-axSpA in 45% and 48%, in MBP in 36% and 24%, respectively, and in HV in 10%. Inter-reader agreement for FI expressed as intraclass correlation coefficient over all 4 readers was 0.59 and 0.75 for cohort A and B.
 
Diagnostic utility (mean of 4 readers for cohort A/B) of SIJ FI in nr-axSpA vs MBP patients
Feature Sensitivity Specificity Positive LR Negative LR
FI per se 0.44/0.42 0.73/0.78 1.62/1.91 0.77/0.74
FI with distinct border 0.21/0.21 0.97/0.90 8.29/2.13 0.81/0.88
Homogeneous FI 0.20/0.26 0.97/0.93 6.24/3.78 0.83/0.80
Subchondral FI 0.36/0.35 0.85/0.83 2.36/2.04 0.75/0.78
FI with any 2 features 0.24/0.30 0.97/0.92 9.26/3.58 0.78/0.77
FI+BME 0.19/0.18 0.99/0.92 14.63/2.13 0.82/0.90
FI+ER 0.21/0.24 0.99/0.93 33.15/3.55 0.79/0.81

BME: Bone marrow edema. ER: Erosion. FI: Fat infiltration. LR: Likelihood ratio. FI with any 2 features: ≥2 features out of FI with distinct border/Homogeneous FI/Subchondral FI

Conclusion: SIJ FI characterized by a distinct border or homogeneity on MRI had substantial diagnostic utility in early SpA. FI in combination with BME or ER also showed high diagnostic utility.

Disclosure:

U. Weber,
None;

S. J. Pedersen,
None;

V. Zubler,
None;

K. Rufibach,
None;

S. Chan,
None;

R. G. Lambert,
None;

M. Ostergaard,
None;

W. P. Maksymowych,
None.

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