Dr. Ogdie suggested testing for fecal calprotectin in patients suspected of inflammatory bowel disease and highlighted a 2015 study that included 895 patients with a mean age of 33 years.3 The population comprised patients diagnosed with inflammatory bowel disease (10.2%), another gastrointestinal condition associated with an abnormal gastrointestinal tract (7.3%) and functional gastrointestinal disease (63.2%).
When the investigators applied a threshold of ≥50 µg/g for inflammatory disease vs. functional disease, they calculated a sensitivity of 0.97. However, it is important to note that the threshold had a specificity of only 0.74, for a positive predictive value of 0.37. The negative predictive value was 0.99.
Non-Radiographic Axial Spondyloarthritis
Dr. Ogdie emphasized that although the Assessment of SpondyloArthritis International Society (ASAS) classification criteria for axial spondyloarthritis (axSpA) are not diagnostic criteria, they can be useful in guiding the thought process for diagnosis.4
The criteria state that to classify a patient as having axSpA for research purposes, the patient must have experienced at least three months of back pain and be younger than 45 years old at disease onset. Patients must also have sacroiliitis visible on imaging and at least one spondyloarthritis feature, or HLA-B27 plus at least two spondyloarthritis features, such as inflammatory back pain, arthritis or enthesitis.
Unfortunately, according to Dr. Ogdie, untrained radiologists have poor inter-rater reliability in reading imaging of sacroiliac joints. She suggested that rheumatologists personally examine each scan, and she recommends that rheumatologists review the 2009 ASAS handbook for guidance on reading scans of sacroiliac joints.4
Dr. Ogdie also emphasized, however, the importance of obtaining dedicated sacroiliac joint films. These specific images are important because images of the lumbar spine are unlikely to provide the necessary information about the sacroiliac joint.
Likewise, she explained that it is difficult to assess the sacroiliac joint with a magnetic resonance imaging (MRI) of the lumbar spine and instead an MRI of the pelvis or sacrum is required.
Dr. Ogdie then highlighted the complications that can occur when reading a post-partum MRI of the pelvis. She explained that one study found that at six months post-partum, 15% of women met the ASAS definition of sacroiliitis.5
Thus, she suggested that when rheumatologists read scans of post-partum women they keep in mind that although bone marrow edema may suggest inflammation, it is not specific for axSpA. In contrast, erosion is more specific for axSpA and is much less common than bone marrow edema in post-partum women. Dr. Ogdie concluded that “if you have erosion, you are probably more likely looking at real disease.”
