Sacroiliitis Associated with Axial Spondyloarthropathy: New Concepts and Latest Trends

Abstract

The sacroiliac joints are involved in most cases of axial spondyloarthropathy, the first manifestation usually being sacroiliitis. A finding of sacroiliitis at radiography is the classic diagnostic hallmark of axial spondyloarthropathy. However, radiographic changes reflect structural damage rather than active inflammation, which may delay the diagnosis by several years. In the past decade, the field of spondyloarthropathy has undergone major changes, largely driven by the development of new drugs for the treatment of ankylosing spondylitis. In recent years, the Assessment of SpondyloArthritis international Society has focused on the reassessment of existing classification criteria and the development and validation of diagnostic tools to facilitate early diagnosis and assessment of treatment response. Magnetic resonance (MR) imaging is the most recent innovation and the important change with respect to the previously established classification criteria. This modality has become an integral part of managing patients with sacroiliitis. MR imaging can serve as a biomarker of disease activity, allows monitoring, and can provide guidance for the treatment of affected patients, and it will likely become even more central to the care of these patients. Familiarity with the anatomy, anatomic variants, and physiologic changes of the sacroiliac joints is important for correctly interpreting findings and avoiding misdiagnosis.

Update on MR imaging of spondyloarthritis. Part one: The sacro-iliac joint

“…-In the setting of suggestive axial pain of more than 3 months duration in a patient with less than 45 years of age at onset of symptoms, the rheumatologist may prescribe MRI of the SI joints to look for signs of active inflammation (7). -More specific structural osseous changes are depicted in more advanced cases, and rarely occur within the two first years after the onset of the disease (8). These osseous changes are better detected with radiography or CT than with MRI.…”

“…MRI acquisition protocols tailored to suspected SpA should at least maximize sensitivity for the detection of edema and include the SI joints (8). MRI of the SI joints should include one T1-weighted as well as one fluid-sensitive fat-saturated sequence (Table II).…”

Contrast Enhanced Magnetic Resonance Imaging in Sacroiliitis

“…Clinical demonstration of sacroiliitis can be difficult due to location of SIJ, its anatomic feature and limited range of motion. Therefore, imaging techniques play an important role in the diagnosis of SpA (1)(2)(3). In practice, conventional imaging tools fail to show active inflammation, which may delay the diagnosis (1).…”

“…There are four MRI findings of active (acute) sacroiliitis associated with axial SpA: osteitis/bone marrow edema, enthesitis, capsulitis and synovitis (2,3).…”

“…Enhancement does occur in osteitis edema and contrast difference may be highlighted using post-contrast T1 WI with fat saturation (3,4). For the assessment of active disease, the use of fat suppression is recommended (2,3,9).…”