Reliability of MRI-Detected Structural Lesions for AxSpA Classification

The utility of considering MRI-detected structural lesions in sacroiliac joints for the classification of patients being evaluated for axial spondyloarthritis (axSpA) was explored in a recent study led by Pauline Bakker, MD, of Leiden University Medical Center, the Netherlands. Results were published in the Annals of the Rheumatic Diseases.¹

Evidence of sacroiliitis via radiographs or MRI is a major criterion for axSpA in the Assessment in Spondyloarthritis International Society (ASAS) classification criteria. The current definition of a positive MRI in that classification scheme only includes inflammatory lesions, characterized by inflammation in subchondral bone, and not structural lesions, characterized by erosions, fatty lesions, sclerosis and ankyloses.²

The ASAS definition of a positive MRI has not been revised since 2009, although it was recently revisited by a working group of ASAS members with interest and experience in both SpA and MRI. The group reviewed whether the current definition was appropriate and whether structural lesions on MRI should be included. 

Their consensus, published in January 2016, was that “the existing ASAS definition of a positive MRI continues to provide a solid basis for the application of MRI in the ASAS criteria for axSpA.” The working group advised that structural lesions may be taken into consideration when determining whether inflammatory lesions are genuinely due to SpA, but that they are not required to meet the definition. ³

The modified New York (mNY) criteria for the classification of ankylosing spondylitis, which are still in widespread use, require the evidence of sacroiliitis via radiograph.^4,5 However, radiographs are frequently insufficient to detect sacroiliitis.⁴

In the current study, Dr Bakker and colleagues utilized data from DEvenir des Spondyloarthrites Indifférenciées Récentes (DESIR), a prospective longitudinal multicentric French cohort of 708 patients who presented with inflammatory back pain suggestive of SpA in order to evaluate the agreement between the presence of radiograph-detected sacroiliitis and MRI-detected structural lesions. Two readers performed the scoring, blinded to all clinical data and patient characteristics.

The team additionally assessed the impact of the inclusion of structural lesions on the classification of patients according to ASAS axSpA criteria. Patients were placed into groupings based their fulfillment of criteria stipulated in the imaging arm of the ASAS axSpA criteria (either by fulfilling mNY criteria and/or positive MRI); in the clinical arm of the ASAS axSpA criteria; or via both. 

Seven possible combinations emerged: only clinical arm positive; only MRI-active positive; only mNY positive; clinical arm and MRI active positive; clinical arm and mNY positive; clinical arm, MRI active positive, mNY positive; and both MRI active and mNY positive.

Results showed that the addition of positive MRIs for structural lesions to the ASAS axSpA criteria did not alter the classification in 95.5% of patients evaluated by reader 1 and 89.7% of those evaluated by reader 2. In assessing the replacement of radiographic sacroiliitis by structural lesions on MRI, ASAS axSpA  classification was unaltered in 82.1% and 80.6% of patients for readers 1 and 2, respectively.

“When sacroiliitis on radiographs was replaced by structural lesions on MRI, only minor changes in the classification according to the ASAS axSpA criteria were seen,” the authors wrote.  “Most patients change from one subcategory to another subcategory, rather than becoming ASAS axSpA criteria positive or negative.” the authors wrote. They noted that in the absence of pelvic radiographs, MRI may be a reasonable alternative for classification.

Summary and Clinical Applicability

Data from this study suggest that when a T1-sequence MRI is performed in the absence of a pelvic radiographic, it may have sufficient clinical utility for axSpA classification with no further need of obtaining other radiographs.

“Structural lesions on MRI can be used reliably either as an addition to or as a substitute for radiographs in the ASAS axSpA classification of patients,” concluded the research team.

Limitations and Disclosures 

• The cost-effectiveness of MRI needs to be considered for feasibility purposes
• The applicability of MRI use in axSpA classification to patients with longer PsA disease duration was not evaluated in this cohort 

The DESIR cohort is financially supported by unrestricted grants from both the French Society of Rheumatology and Pfizer France. An unrestricted grant from Wyeth Pharmaceuticals was allocated for the first 5 years of the follow-up of the recruited patients. No other competing interests were declared.

References

1. Bakker PAC, van den Berg R, Lenczner G, et al. Can we use structural lesions seen on MRI of the sacroiliac joints reliably for the classification of patients according to the ASAS axial spondyloarthritis criteria? Data from the DESIR cohort. Ann Rheum Dis. August 2016.
2. Rudwaleit M, Jurik AG, Hermann K-GA, et al. Defining active sacroiliitis on magnetic resonance imaging (MRI) for classification of axial spondyloarthritis: a consensual approach by the ASAS/OMERACT MRI group.Ann Rheum Dis. 2009;68(10):1520-1527.
3. Lambert RGW, Bakker PAC, van der Heijde D, et al. Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group. Ann Rheum Dis. January 2016:annrheumdis-2015-208642.
4. van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis. A proposal for modification of the New York criteria. Arthritis Rheum. 1984;27(4):361-368.
5. van Tubergen A, Weber U. Diagnosis and classification in spondyloarthritis: identifying a chameleon. Nat Rev Rheumatol. 2012;8(5):253-261. 

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