Radiographic Sacroiliitis vs MRI Structural Lesions for Axial Spondyloarthritis Classification

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Assessment of structural lesions on MRI of the sacroiliac joints instead of or in addition to conventional radiographs does not lead to a different ASAS axSpA classification in most patients.
Assessment of structural lesions on MRI of the sacroiliac joints instead of or in addition to conventional radiographs does not lead to a different ASAS axSpA classification in most patients.

Structural lesions on sacroiliac joints detected by magnetic resonance imaging (MRI) can be used reliably as an addition to or a substitute for radiographs in the Assessment of Spondyloarthritis International Society (ASAS) axial spondyloarthritis (axSpA) classification, according to the results of study published in Rheumatology.

Patients were recruited from 5 participating centers in the Netherlands, Norway, and Italy. Each patient received a full diagnostic workup, including human leukocyte antigen-B27 testing, conventional radiographs and MRI of the sacroiliac joints, and assessment of all other SpA features, in agreement with the ASAS descriptions. Well-calibrated readers independently scored assessments of conventional radiographs and MRI to determine whether the patient could be diagnosed with SpA. Descriptive statistical analysis was used to determine the disease characteristics of each patient and cross-tabulation was used to assess the absence or presence of structural lesions using both imaging modalities.

The analysis included 294 patients with complete imaging data at baseline. The results showed that 35% of participants fulfilled the ASAS axSpA disease criteria using the standard definition, and fatty or erosive lesions were present in 10.5%. If conventional radiographs were replaced by MRI of the sacroiliac joints, using a combination of fatty lesions and erosions, only 3 patients would be additionally classified as having ASAS axSpA and 5 patients would no longer be classified as having ASAS axSpA. Only 2 of these 5 patients had high disease probabilities and could have been missed in error.

These results support those of a similar analysis of the French DESIR cohort, which included patients with inflammatory back pain with a high suspicion for axSpA.

Because of feasibility issues related to the cost of MRI equipment and the existing familiarity with the modified New York criteria among radiologists and rheumatologists, the authors suggest adding structural lesions to the imaging criteria for ASAS axSpA rather than replacing conventional radiographs. The authors did, however, note that replacing conventional radiographs with MRI would eliminate the need to expose patients to ionizing radiation and that the 3-dimensional character of MRI could be superior to that of the 2-dimensional traditional radiographic results.

Reference

Bakker PA, van den Berg R, de Hooge M, et al. Impact of replacing radiographic sacroiliitis by magnetic resonance imaging structural lesions on the classification of patients with axial spondyloarthritis [published online March 23, 2018]. Rheumatology (Oxford). doi:10.1093/rheumatology/kex532

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