EXPERT ANALYSIS FROM A SPARTAN-GRAPPA SYMPOSIUM
DENVER (FRONTLINE MEDICAL NEWS) – MRI of the sacroiliac joint now serves as the primary imaging driver for a diagnosis of spondyloarthritis, especially early spondyloarthritis, and has largely supplanted radiographic assessment, Walter P. Maksymowych, MD, said at an educational symposium organized by the Spondyloarthritis Research and Treatment Network.
“MRI is reliable for early diagnosis; radiographic assessment of early spondyloarthritis is problematic,” said Dr. Maksymowych , a rheumatologist and professor of medicine at the University of Alberta in Edmonton. “The EULAR recommendations now say that early diagnosis of spondyloarthritis needs to focus on MRI.”
While the recommendations from the European League Against Rheumatism (EULAR) that came out last year on using imaging for diagnosing and managing spondyloarthritis (SpA) cite radiography of the patient’s sacroiliac joint as the recommended first imaging method to use to diagnose sacroiliitis as part of a diagnosis of axial SpA, the EULAR recommendations place MRI very close behind.
The recommendations list MRI as an “alternative” first-line approach for diagnostic imaging. For patients who appear negative for axial SpA on radiographic imaging but who remain suspected of having SpA the EULAR panel “recommended” MRI of the sacroiliac joints as a backup method for imaging assessment and to definitively rule out SpA. No other imaging method received EULAR’s endorsement for SpA diagnosis aside from these two approaches.
The recommendations direct the MRI examination to include assessment of inflammation based on bone marrow edema, and also structural abnormalities including bone erosion, new bone formation, sclerosis and fat infiltration. The 2015 EULAR recommendations also cite roles for MRI in diagnosing peripheral SpA, monitoring disease activity in axial and peripheral SpA, monioring structural changes in axial and peripheral SpA, predicting outcome and treatment effect in axial SpA, assessing spinal fracture in patients with axial SpA and to assess osteoporosis in selected axial SpA patients.
The MRI imaging sequences particularly useful for SpA diagnosis are “short tau inversion recovery” ( STIR ), a “water sensitive” sequence that involves suppression of the fat MRI signal, and a T1 weighted sequence that is a “fat sensitive” scan, explained Dr. Maksymowych at the symposium, also organized by the Group for the Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA). He strongly encouraged clinicians to apply a standardized approach to imaging in every patient suspected of having axial SpA.
The definition of an MRI imaging result that is positive for SpA remains a consensus of expert opinion without a firm evidence base. The currently accepted MRI marker of SpA involves identifying several areas of bone marrow edema in a single T1 and STIR MRI image-slice through the sacroiliac joint, or focal bone marrow edema visible in at least two consecutive sacroiliac joint T1 and STIR image slices.
The confluence of a structural lesion at the same site as bone marrow edema provides further confirmatory information, he said. “A structural lesions at the site of bone marrow edema enhances your confidence in the diagnosis,” he said.
“The specificity of MRI for SpA is quite high,” Dr. Maksymowych noted, with specificity rates often in the range of 85%-95%. Sensitivity rates are lower, often 50%-70%. Sensitivity further improves by factoring in the presence of bone erosions. Diagnostic confidence also increases as the number of lesions visualized increases.
MRI has become so integral to the assessment of SpA that “to understand SpA you need to understand the language of MRI,” Dr. Maksymowych concluded.
Dr. Maksymowych has received honoraria from eight drug companies and research grant support from Abbvie and Pfizer.
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