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)).
|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|
|FI with any 2 features||0.24/0.30||0.97/0.92||9.26/3.58||0.78/0.77|
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.
S. J. Pedersen,
R. G. Lambert,
W. P. Maksymowych,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/what-constitutes-the-characteristic-fat-lesion-on-mri-of-the-sacroiliac-joints-in-early-spondyloarthritis/