Page 147 - Recognizing axial spondyloarthritis - Janneke de Winter

pain. In conclusion, serum anti-CD74 IgG and IgA antibodies are both elevated in patients with AS compared to healthy controls, serum anti-CD74 IgG antibodies are not elevated in patients with early axial SpA compared to patients with chronic back pain (CBP), serum anti-CD74 IgA antibody levels are elevated in patients with early axial SpA compared to patients with CBP, but serum anti-CD74 IgA antibodies lacked diagnostic value in patients with early back pain due to limited numerical differences. And although anti-CD74 antibodies do not seem to have a role in the diagnostic process, they might help to predict radiographic damage or serve as a marker for treatment response. The results of this study are in line with a recent study showing that there is little hope for robust serum biomarkers such as antibodies in the diagnostic process of axSpA (27). However, initiatives as the SPondyloArthritis Caught Early (SPACE) cohort, the GErman SPondyloarthritis Inception Cohort (GESPIC) and the Pre-SpA cohort will hopefully enable us to identify new and promising biomarkers.
SpA-specific sacroiliitis on MRI-SI occurs frequently in healthy individuals
In recent decades, MRI has been increasingly used to visualize inflammation in the sacroiliac (SI) joints since inflammation on MRI facilitates the early identification of patients with axial SpA by preceding structural damage on radiography (28,29). The ASAS criteria reflect this development, since they are the first criteria including sacroiliitis on MRI to aid identification of axial SpA patients in an early stage (30,31). Chapter 5 therefore focused on the specificity of MRI in the detection of SpA-specific sacroiliitis. For this purpose we compared MRI of the sacroiliac joints (MRI-SI) of healthy individuals and those with known mechanical strain acting upon the sacroiliac joints (SI joints). To that purpose, we scored MRI-SI 1) 47 healthy individuals 2) 47 positive controls; axial SpA patients with a previously positive scored MRI-SI 3) 47 negative controls; CBP patients irrespective of MRI-SI outcome, 4) 22 frequent runners and 5) women with postpartum back pain. The results of this study suggest that a substantial proportion of healthy and asymptomatic individuals, runners, and women with postpartum back pain may have positive findings on MRI of the SI joints that are highly suggestive, but not reflective, of axial SpA. Patients with axial SpA have more extensive lesions (reflected by SPARCC scores ≥5 and the presence of deep (extensive) lesions) than healthy, asymptomatic individuals.
The key message of this study is that misclassification of MRIs of the SI joints as positive is a real threat, which may lead to a falsely high number of patients being diagnosed with axial SpA. Evidence of such a mechanism has been reported by previous studies (32,33), showing that nearly 25% of patients with chronic back pain could be classified as having axial SpA when MRI of the SI joints was the leading factor in the diagnostic consideration. Since we and others (34) have demonstrated that MRIs that are highly suggestive of axial SpA may be seen frequently in unaffected individuals, relying too much on a positive MRI finding will result in over-diagnosis, and consequently in over-treatment of these patients
GENERAL DISCUSSION AND SUMMARY
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