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Edited and sorted out by Yimaitong, please do not reprint
without authorization.
Axial
.
Initially, X-ray detection of sacroiliitis is the basis for
diagnosing axSpA.
First, how reliable is the routine X-ray diagnosis axSpA?
The radiographic presentation of the sacroiliac joint is difficult to explain
due to the complex anatomical structure of the pelvis, the oblique position of the sacroiliac articular surface, and the presence of gases in the intestine.
Therefore, cross-sectional imaging techniques (such as MRI) may be more
reliable for positive or negative results than conventional X-rays.
An earlier study published in 2003 showed that 23 radiologists and 100 rheumatologists in the Netherlands were trained in sacroiliitis x-ray readings and that radiologists and rheumatologists had relatively low
diagnostic sensitivity (84.
2.
Compared with conventional X-rays, how about T1-weighted MRI detection of sacroiliitis?
SIMACT was a prospective study involving 110 patients with chronic low
。 Compared with x-rays, MRI had better absolute consistency with CT in erosions (88.
2% vs.
70.
9%), joint space changes (92.
7% vs.
80.
9%), and structural damage (89.
1% vs.
70.
0%), but not in hardening (83.
6% vs.
86.
4%,
respectively).
In a recent study, the German team compared the diagnostic value
of conventional x-ray, CT, MRI (including STIR and T1), conventional x-ray + MRI and CT+MRI sacroiliac joint imaging methods on axSpA using the clinical diagnosis of experts as a reference criterion.
However, these studies also suggest that MRI (T1-weighted and STIR sequences only) is inferior to CT, especially in distinguishing between sclerosis and erosion, a finding that raises questions about whether MRI is suitable for the detection of sacroiliitis
.
Are there other sequences that are more suitable for detecting structural lesions than T1-weighted MRI?
Technology is evolving rapidly today, and new imaging methods
will emerge in the future.
In the context of this review, MRI's three-dimensional disturbance phase gradient echo (3D-GRE) sequences (e.
g.
, volumetric interpolation breath-holding check [VIBE]) are of particular interest
.
Studies have shown that the 3D-GRE sequence MRI is close to CT in detecting sacroiliac joint erosion, outperforming the T1-weighted sequence
.
However, the T1-weighted sequence remains essential
for the detection of steatopathy and adipocytes in the erosive cavity that represents the repair of fibrous tissue.
In addition, the 3D-GRE sequence still does not directly depict the surface
of the bone cortex compared to CT.
What MRI sequences can be used for diagnostic evaluation of sacroiliac joints?
In 2015, radiologists at the annual meeting of the European Society for Musculoskeletal Radiology (ESSR) recommended four MRI sequences for sacroiliac joints: (1) oblique coronal T1 weighting (for steatopathy, erosion, and rigidity); (2) coronary STIR (or another T2-weighted sequence with inhibition of fat signaling, for bone marrow
.
The above sequence is also contained in the international consensus developed by ASAS and SPARTAN and was recently presented
at the EULAR Annual Meeting.
Is the structural change detected by MRI sufficient to define sacroiliitis?
In the current classification criteria, sacroiliac joint imaging changes are those that the X-rays meet the New York modified criteria: bilateral grade 2-4 or unilateral grade 3-4 sacral iliac arthritis, or MRI images of the sacroiliac joint meet the ASAS consensus definition: active inflammatory lesions of the sacroiliac joint with clear bone marrow edema
.
At present, in terms of classification criteria, whether the structural damage detected by MRI can replace the structural damage detected by traditional X-ray is still controversial
.
Based on literature data, scholars believe that sacroiliac joint structural lesions should be assessed using MRI T1-weighted and 3D-GRE sequences, rather than using conventional X-rays only in the absence of MRI
.
Traditional X-rays are neither specific nor sensitive to the diagnosis of axSpA, and the consistency of the reader is low
.
CT (low dose) has good sensitivity and specificity for structural lesions: however, radiation exposure (low-dose CT is comparable to radiation from conventional x-rays) and its description of bone marrow changes (such as edema and fat) are insufficient, so it is not recommended as a first-line imaging test
.
References: Poddubnyy D, Diekhoff T, Baraliakos X,et al.
Diagnostic evaluation of the sacroiliac joints for axial
2022 Aug 25:ard-2022-222986.
doi: 10.
1136/ard-2022-222986.
Epub ahead of print.
PMID: 36008130.