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ASAS MRI Sacroiliitis — SCE Rheumatology MCQ

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HardMusculoskeletal ImagingASAS MRI SacroiliitisSCE Rheumatology

A 40-year-old man with chronic back pain beginning before the age of 45 years undergoes MRI of the sacroiliac joints during assessment for axial spondyloarthritis. Which statement best describes the current ASAS definition of an MRI positive for active sacroiliitis for classification purposes?

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Correct answer: A — Clear bone marrow oedema in subchondral bone, with an overall appearance highly suggestive of axial spondyloarthritis; no fixed lesion-count or slice threshold is required

The current ASAS definition requires clear bone marrow oedema/osteitis in a typical subchondral location, with the overall MRI appearance being highly suggestive of axSpA. There is no longer a fixed minimum lesion-count or slice threshold. The former rule of two lesions on one slice or one lesion on two consecutive slices is an outdated quantitative formulation and cannot override the qualitative assessment. Small, non-specific periarticular signal may reflect mechanical stress, vessels or artefact. Structural lesions such as erosions and fat metaplasia can increase confidence that oedema is SpA-related but do not independently satisfy the definition. Synovitis, capsulitis and enthesitis without subchondral oedema are likewise insufficient. This is a classification definition and should not be used in isolation to make a clinical diagnosis.

Reference: Diekhoff T, Lambert RG, Hermann K-G. MRI in axial spondyloarthritis: understanding an 'ASAS-positive MRI' and the ASAS classification criteria. Skeletal Radiology. 2022;51:1721–1730. https://pubmed.ncbi.nlm.nih.gov/35199195/