Page 66 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER FOUR
months but ≤2 years) with an onset before the age of 45 years. We used baseline data unless specified otherwise. Positive SPACE controls were defined as patients with axial SpA (who were diagnosed by a rheumatologist and fulfilled the ASAS criteria for axial SpA (3)) with an MRI of the SI joints that was previously scored as positive for sacroiliitis according to the ASAS definition by at least 2 of 3 central readers. Negative SPACE controls were defined as patients with chronic back pain (who were neither diagnosed as having axial SpA nor fulfilled the ASAS criteria for axial SpA), irrespective of their MRI findings. Healthy controls were matched with positive and negative SPACE controls for age and sex.
The local medical ethics committees of the participating sites approved the study, and all participants gave their written informed consent.
MRI
MRI was performed on 1.5T systems. At least 12 slices of coronal oblique T1- weighted turbo spin-echo and short tau inversion recovery sequences of the SI joints were acquired. The slice thickness was 4 mm.
Scoring
Three readers (JdW, MdH, and RL) who had received standardized training and were blinded with regard to subject group independently scored all MRIs in random order. The readers were instructed to quantify MRIs as positive or negative by judging for the presence or absence of bone marrow edema (BME) according to the ASAS definition that was recently updated by the ASAS MRI working group (14). As this definition describes, the focus was on scoring only lesions that were considered “highly suggestive of axial SpA” as positive. In addition, the readers quantified the extent of BME according to the Spondyloarthritis Research Consortium of Canada (SPARCC) scoring system (15). For SPARCC scoring, 6 consecutive coronal slices were selected and each SI joint was divided into 4 quadrants: the upper and lower ilium and upper and lower sacrum. Each quadrant was assigned a score of 1 for the presence of BME or 0 for the absence of BME. Each coronal slice per SI joint was also scored for the presence of “intense” lesions (high signal as bright as or brighter than that of veins or intervertebral discs) or “deep” lesions (a homogeneous, unequivocal increase in signal extending ≥1 cm from the articular surface). The maximum SPARCC score for all 6 slices was 48 for BME, 12 for intensity, and 12 for depth, resulting in a maximum total score of 72 (15). To determine the distribution of BME anatomically in the SI joints, we used the SPARCC distribution of the 4 quadrants, divided into anterior and posterior slices. BME was considered to occur in a particular region if it was concordantly recorded at that region by at least 2 of the 3 readers.
In the analysis, an MRI was considered positive if at least 2 of 3 readers agreed it met the ASAS MRI working group criteria for defining sacroiliitis by MRI (14). SPARCC scores are presented as the mean total SPARCC scores from all 3 readers. We chose SPARCC score cutoff values of ≥2 and ≥5 to discriminate between low
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