Structural lesions of the sacroiliac joints (SIJ) may be present on MRI in patients with nonradiographic axial spondyloarthritis (nr-axSpA), even when radiographs are normal or inconclusive for such lesions and there is no evidence of inflammation on MRI, according to findings from a cohort of patients in a randomized trial.

In the study, the patients who exhibited such lesions, especially erosions, were more likely to have more severe disease and greater spinal inflammation than were patients who did not have the structural lesions on MRI.

Walter P. Maksymowych, MD , professor of medicine, the University of Alberta, Edmonton, and his colleagues looked for the presence of structural lesions and bone marrow edema (BME) or osteitis in 183 patients with nr-axSpA, 60% of whom were male. They found evidence for sacroiliac joint erosions on MRI in 11% of patients who did not have BME (defined as Spondyloarthritis Research Consortium of Canada [SPARCC] score less than 2), which was significantly less than its occurrence in 45% of those with BME (SPARCC score of 2 or greater). Fat metaplasia occurred in a relatively small percentage of patients in both groups, although it was significantly more common among patients with BME (11% vs. 2%). Ankylosis occurred at similar rates of 1.8% in patients without BME and 2.3% in those with BME. None of the patients without BME developed backfill structural lesions, compared with 20% of patients with signs of inflammation ( Arthritis Res Ther. 2017;19:126 ).

The presence of MRI structural lesions appeared to reflect more severe disease with greater spinal inflammation, the investigators said, based on higher mean SPARCC spinal scores in 23 discovertebral units. The mean number of discovertebral units involved was significantly greater overall among patients with structural lesions (6.5), compared with those without (3.3). Both Bath Ankylosing Spondylitis Activity Index and Bath Ankylosing Spondylitis Functional Index scores were also significantly higher for patients with BME but no MRI structural lesions (a mean of 6.4 cm and 4.6 cm, respectively), when compared with patients who had both (a mean of 5.7 cm and 3.7 cm, respectively).

Age, sex, and HLA-B27 status also appeared to play a role in the frequency with which MRI structural lesions coexisted with BME. The group of patients with both BME and structural lesions in the sacroiliac joint were significantly more often male (83% vs. 48%), younger (mean age of 30 vs. 34 years), and HLA-B27 positive (87% vs. 63%) than in those with only BME.

“These data support the concept that nr-axSpA is an early stage of axSpA and that structural lesions in the SIJ are associated with a more severe phenotype characterized by more active spinal inflammation,” the investigators wrote.

The presence of structural lesions might also identify patients who would benefit the most from early treatment with biologics, they suggested. “It has been suggested that there is a window of opportunity for disease modification with anti-inflammatory agents by treating acute inflammatory lesions before bone formation pathways are triggered in more complex inflammatory lesions. Consequently, the presence of structural lesions in the SIJ may help select patients for intervention with anti-TNF agents early in the disease course.”

The study was funded by Pfizer. Three of the authors are employees of Pfizer. Two authors have received consulting fees and/or research funding/grants from a variety of companies that make drugs for the treatment of ankylosing spondylitis, including Pfizer.


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