MRI of sacroiliac joints can detect inflammation, damage early

Magnetic resonance imaging (MRI) of sacroiliac (SI) joints in patients with recent-onset back pain can reliably detect inflammation and structural changes and is likely to be helpful in diagnosing sacroiliitis, often a sign of ankylosing spondylitis (AS) in such patients Dr Liesbeth Heuft-Dorenbosch (University Hospital Maastricht, the Netherlands) and colleagues report in Arthritis Research & Therapy that about one third of patients with recent-onset inflammatory back pain showed inflammation of the SI joints and that one sixth of patients showed structural changes in at least one SI joint.

Senior author Dr Desire van der Heijde (University Hospital Maastricht) told rheumawire, “MRI of sacroiliac joints is sufficiently reliable to be used in determining inflammatory and structural changes due to sacroiliitis, and looking for [MRI evidence of] bone-marrow edema and/or subchondral inflammation is sufficient, since other sites contribute relatively little additional information.”Researchers hope MRI can reduce time to diagnosis of ankylosing spondylitisThe Dutch researchers tested interreader reliability of SI-joint MRI in 68 patients with inflammatory back pain. Patients had back pain for less than two years and met at least four of these five criteria: onset before age 40, insidious onset, morning stiffness, duration of more than three months, and improvement with exercise. Alternatively, patients could have three of the criteria plus night pain. They investigators write that the study was undertaken in part as an attempt to find ways to improve the diagnosis of ankylosing spondylitis, of which sacroiliitis is a characteristic feature. They note that there is currently a mean lag time of about eight years between the start of symptoms and the diagnosis of AS.Patients were scanned in a supine position with a 1.5-T Philips Gyro scan. The researchers used a coronal oblique scan plan parallel to the length of the sacrum, one transversal slab positioned cranially to the region of interest (to diminish flow artifacts) and one positioned frontally through the bowel and anterior abdominal wall (to diminish motion artifacts of breathing and bowel movement). The scan observers looked for inflammation and structural changes, including erosions, sclerosis, and ankylosis. The regions examined were the subchondral region, bone marrow, joint capsule, joint space, and retroarticular ligaments. Scans were read by two MRI readers, and interreader reliability was determined.The most frequent MRI finding was inflammation of the subchondral region and bone marrow. Interreader agreement was 85% for inflammation in the right SI joint and 78% in the left SI joint. Inflammation was detected in 22 of 68 patients, and 10 of these 22 patients also had structural changes. “One of the important aims of this study was to establish whether inflammation and structural changes on MRI could reliably be assessed … With agreement levels around 85% for the presence of inflammation overall and at different locations, it seems sufficiently high to justify a conclusion of inflammation made by one observer in clinical practice,” the authors write. They also conclude that the search for inflammation can be limited to looking for bone-marrow edema and/or subchondral inflammation without requiring examination of other sites such as the joint capsule, joint space, or retroarticular ligaments, since these added little to the accuracy of the diagnosis.The clinical and research usefulness of sacroiliac-joint MRI in diagnosing inflammatory back pain would be increased by a reliable scoring system for sacroiliitis on MRI. Van der Heijde tells rheumawire that the Assessment in Ankylosing Spondylitis (ASAS) Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT) working group recently reviewed several scoring methods used in research but concluded that data are insufficient for preferring one over the others [2].From the viewpoint of the typical rheumatologist, van der Heijde says that MRI should be considered in the patient with inflammatory back pain and one or two other features linked to spondyloarthropathy, such as inflammatory bowel disease, psoriasis, uveitis, positive family history, heel pain, peripheral arthritis, dactylitis, good response to nonsteroidal anti-inflammatory drugs (NSAIDs), or elevated acute-phase reactants. “If the patient has three or more of these features, information from MRI is not necessary to make the diagnosis,” she adds. She also recommends combining information from MRI with that from conventional radiographs for diagnosis of sacroiliitis in recent-onset inflammatory back pain [3].(Sources:[1] Heuft-Dorenbosch L, Weijers R, Landewe R, et al. Magnetic resonance imaging changes of sacroiliac joints in patients with recent-onset inflammatory back pain: inter-reader reliability and prevalence of abnormalities. Arthritis Res Ther 2006; 8:R11. [2] Landewe R, Hermann KG, van der Heijde D, et al. Scoring sacro-iliac joints by magnetic resonance imaging, a multiple-reader reliability experiment. J Rheumatol 2005; 32:2050-2055. [3] Heuft-Dorenbosch L, Landewe R, Weijers R, et al. Combining information obtained from MRI and conventional radiographs in order to detect sacroiliitis in patients with recent-onset inflammatory back pain. Ann Rheum Dis 2005; DOI:10.1136/ard.2005.044206Rheumawire: Joint and Bone: March 2006.)