Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group

Abstract

The definition of a positive MRI for classification of axial SpA should continue to primarily depend on the imaging features of 'active sacroiliitis' until more data are available regarding MRI features of structural damage in the sacroiliac joint and MRI features in the spine and their utility when used for classification purposes.

Radiographic Evaluation of Sacroiliac Joints in Axial Spondyloarthritis — Still Worth Performing?

“…These criteria consist of 2 arms -imaging and clinical. The more specific imaging arm is fulfilled if either definite radiographic sacroiliitis (as defined in the modified New York criteria for AS 1 ) or sacroiliitis on MRI (according to the ASAS definition 4 ) is present, together with at least 1 additional SpA feature, in a patient with chronic back pain that started prior to 45 years of age 3 . Importantly, the ASAS definition of sacroiliitis on MRI relies largely on the presence of bone marrow edema, reflecting the presence of active inflammation; chronic structural changes (erosions, sclerosis, ankylosis, and fatty lesions) provide only contextual information.…”

Imaging Findings Suggestive of Axial Spondyloarthritis in Diffuse Idiopathic Skeletal Hyperostosis

“…Since the development of the widely used modified New York criteria for the diagnosis of sacroiliitis on pelvic radiographs (3), recent advances in magnetic resonance imaging (MRI) have greatly helped in the early detection of sacroiliac or spinal inflammatory features of axial SpA. Consequently, ASAS has proposed a consensual definition of an active sacroiliitis on MRI, which has been included in the ASAS classification criteria (4). More recently, ASAS also developed criteria for a spine MRI highly suggestive of axial SpA based on spinal inflammatory lesions (5).…”

Infectious Sacroiliitis: A Radiographic No Touch Lesion

“…Therefore, MRI remains the gold standard for diagnosis of sacroiliitis. A consensus in the literature defines the following MRI findings necessary to diagnose sacroiliitis: active inflammatory lesions of sacroiliac joints, bone marrow edema on STIR or osteitis on T1 postGadolinium, and sole presence of other active inflammatory lesions such as synovitis, enthesitis, or capsulitis without bone marrow edema [7,8]. One study directly compared different imaging modalities in six cases of ISI and found all six cases had positive MRI studies, whereas only three cases had positive computerized tomography (CT) scans studies and only one case had a positive bone scan study [9].…”