AN EARLY DIAGNOSIS OF ANKYLOSING SPONDYLITIS IN PATIENTS WITH INFLAMMATORY BACK PAIN (IBP) OF LESS THAN 2 YEARS DURATION BY THE USE OF MRI INFLAMMATION AS A SUBSTITUTE FOR RADIOGRAPHIC SACROILIITIS

Background: Conventional radiographs are considered to be insensitive to early changes of structural damage of SI joints. MRI can show active inflammatory changes. Little is known on the concordance of these changes on MRI and conventional radiographs and on the usefulness of inflammatory changes on MRI for the fulfilment of the modified New York (NY) criteria.Objectives: To study the percentage of patients with recent onset IBP have active inflammatory changes in the SI joints on MRI and how this relates to radiographic sacroiliitis as part of the modified NY criteria.Methods: Patients with IBP (at least 4 of the 5 following criteria: symptom onset before age of 40, insidious onset, morning stiffness, duration >3 months, improvement with exercise) or 3 out of 5 plus night pain were included if symptom duration was <2 years. An MRI scan of the SI joints (Philips 1.5 T) was made in the coronal plane with the following sequences: T1-SE, STIR, T2-Fast SE, T1-SE with fat saturation post gadolinium. For the present analysis, both SI-joints were scored for inflammation (in subchondral bone and bone marrow, joint space, joint capsule, and ligaments) by two observers independently. If both readers agreed that inflammation was present, the MRI scan was scored positive for inflammation. Radiographs of the pelvis were made and scored independently by three other observers according to the New York grading (0-4). Majority grades are used. The NY radiographic criterion was met if at least grade 2 SI-itis bilaterally, or at least grade 3 SI-itis unilaterally was present.Results: 68 patients (62% male; mean age 34.9 (SD 10.3), 46% HLA-B27+; mean symptom duration 18 months) were included and had MRIs and radiographs of the SI-joints available.14 of the 68 patients fulfilled the radiographic criterion of the modified NY criteria. Twelve of these 14 patients showed inflammation on MRI in 1 (n=6) or 2 (n=6) SI joints. In addition, 10 patients not fulfilling the NY radiographic criterion on the conventional radiographs showed inflammation on MRI (6 patients in 1 SI joint, 4 patients in both SI joints). 9 out of these 10 patients fulfilled SpA criteria sets according to ESSG, Amor as well as Berlin. The remaining patient fulfilled only the Berlin criteria set which is the only criteria set that includes MRI. Structural MRI changes did not further contribute to classifying patients. New York radiographic New York radiographic All criterion present criterion absent patients MRI inflammation present in both SI joints 6 4 10 MRI inflammation present in one SI joint only 6 6 12 MRI inflammation absent 2 34 36 All patients 14 44 68 Conclusion: An early diagnosis of AS in patients with IBP of short duration is possible in 21% of patients by conventional radiographs and clinical signs, and this figure may increase to 35% if the radiographic criterion is substituted by unilateral or bilateral MRI-inflammation in patients that already fulfil established criteria for SpA. Follow up of these patients will show whether the specificity of MRI-inflammation is sufficiently high.Citation: Ann Rheum Dis, volume 64, supplement III, year 2005, page 383Session: Diagnostics and imaging procedures