MRI in axial spondyloarthritis: understanding an ‘ASAS-positive MRI’ and the ASAS classification criteria

Abstract

In 2009, the Assessment of SpondyloArthritis international Society (ASAS) published a definition of ‘active sacroiliitis on magnetic resonance imaging (MRI) for classification of axial spondyloarthritis’. This new definition of an ‘ASAS-positive MRI’ was integral to new classification criteria for axial spondyloarthritis that were published in the same year. The ASAS MRI definition had the considerable advantage of simplicity and the definition gained popularity as guidance for interpreting MRI of the sacroiliac joints in clinical practice. However, classification criteria are not designed for use in clinical practice with the consequence that overreliance on the presence of bone marrow edema, which is the principal determinant of an ‘ASAS-positive MRI’, may result in a tendency to overcall inflammatory sacroiliitis in the clinical setting. This article aims to inform the reader about the rationale behind the ASAS definition of a positive MRI and ASAS classification criteria, their proper use in research and why they should not be used in clinical practice. The article also contains guidance for an updated imaging protocol and interpretation of images including typical imaging findings, differential diagnosis, and common pitfalls.

Imaging modalities for the diagnosis of axial spondyloarthritis

“…With an active inflammatory phase, high signals in fat‐suppressed T2‐weighted or T1‐weighted post‐contrast sequences could be found frequently in the bone marrow adjacent to the cartilaginous joint surface. As erosion and sclerosis expand, three manifestations should be highlighted as the main observations of the next phase—repair processes: 12 first, the fat lesions show bright T1w‐signals that replace the previously inflamed non‐eroded bone marrow; second, a new bone formation that appears as a fat signal within areas of erosion, also known as backfill; and third, a progressive new bone formation that crosses the original joint space, developing from bone budding to ankylosis. However, due to the multifactorial etiology and complex definition of the disease and their consequent limitations, the ASAS classification criteria have triggered heated debate.…”

“…Of course, in line with the holy grail of precision medicine, patients suspected of having AS can also undergo further genetic testing when there is a lack of radiological evidence. According to previous studies, 18,19 nearly 90% of people with AS carry a human leukocyte antigen (HLA) that is a specific gene for B27 (HLA‐B27), for which there may be a correlation between different clinical manifestations and HLA‐B27 status in patients with AS 11,12 . Nevertheless, carrying this gene is not directly linked to the development of AS, but can only predict the risk of disease in advance to allow preventive measures.…”

Presentation, Diagnosis, and Treatment of Sacroiliac Joint Dysfunction

“…MRI may provide value in diagnosing SIJ dysfunction from sacroiliitis resulting from seronegative spondyloarthropathies due to the ability to visualize bone marrow and SIJ edema (Figure 1). 6,19 However, MRI provides little diagnostic value in other causes of SIJ dysfunction 6…”

Análise das características das Espondiloartrites Axiais

“…Outras lesões inflamatórias, como entesite ou capsulite, e a presença isolada de lesões estruturais não se enquadram na definição de "sacroileíte ativa na RM" (DIEKHOFF T, et al, 2022; PODDUBNNY D, 2020). Para o diagnóstico alterações inflamatórias na SIJ são necessárias e devem estar adjacentes à superfície cartilaginosa da articulação (não à parte ligamentar) com uma quantidade suficiente de BME que não seja explicada por artefato ou outras causas; a distribuição deve ser indicativa de axSpA, não restrita ou pronunciada na porção mais ventral da articulação; lesões estruturais devem ser consideradas, por exemplo, a presença de erosões ou lesões de gordura dariam suporte à impressão de axSpA (DIEKHOFF T, et al, 2022;HAY CA, et al, 2022).…”