ASAS revises MRI spine lesion definitions for axSpa

Definitions of MRI spine lesions in axial spondyloarthritis have been revamped to reflect major advances in knowledge over the past decade.

The first definition of a positive spinal MRI for inflammation and structural changes was issued by the ASAS (Assessment of SpondyloArthritis international Society) MRI working group in 2012.

Since then, “the usage of spinal MRI has increased and the understanding of how to interpret both inflammatory and structural spinal lesions in the context of clinical symptoms in axSpA and differential diagnoses has advanced significantly,” explained Dr Pedro Machado, and ASAS MRI working group member in an interview with the limbic.

“The results from this study may be used in ongoing efforts for the re-evaluation of the definition of a ‘positive’ MRI of the spine in the context of axial spondyloarthritis (axSpA) versus non-spondyloarthritis, [and] will also help ensure a more informed and consistent approach to the use of imaging to support the diagnosis of axSpA”, he added.

The group (12 rheumatologists and two radiologists) reviewed existing literature on possible types of spinal MRI pathologies in axSpA, and then agreed on necessary revisions of lesion definitions compared with those from 2012.

Specific overarching principles for reviewing spinal MRIs in the context of axSpa were agreed upon, with a key difference in the 2022 approach being “the subdivision of lesion definitions according to central and lateral slice anatomical locations in the thoracic and lumbar spinal segments on a sagittal MRI”, according to the paper, published in the Annals of the Rheumatic Diseases.

Revisions were also made for both inflammatory (bone marrow oedema; BMO) and structural (fat, erosion, bone spur and ankylosis) lesions, “including localisation (central vs lateral), extension (vertebral corner [VC} vs vertebral endplate) and extent (minimum number of slices needed)”, and new definitions were suggested for the type of lesion based on lesion maturity (VC monomorphic vs dimorphic).

The research also confirmed that both inflammatory and structural lesions “are frequently observed” in spine MRI of patients with axSpA, and that these lesions “seem to be most frequently located at the VC area, consisting either of fat or bone marrow oedema”.

The authors emphasised that the VC inflammatory lesion type that was both more frequently and more reliably observed was the “monomorphic BMO lesion, where the inflammatory signal extends to the VC, in contrast to the dimorphic BMO lesions, where the signal does not cover the whole corner but extends to both the endplate and anterior or posterior border of the vertebra”.

“This is an important finding, since these lesions especially have been reported to be associated with the highest risk for radiographic progression in follow-up examinations of patients with radiographic axSpA,” they said.

Read the updated lesion definitions in full here

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