Risk of progressing to AS within 10 years is low, study finds

TNF inhibitors, bone marrow swelling, HLA-B27 among factors predicting risk

Margarida Maia PhD avatar

by Margarida Maia PhD |

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An X-ray hangs on wall as a doctor speaks with a patient.

While some people with recent-onset axial spondyloarthritis whose joint damage isn’t visible on an X-ray will progress within 10 years to ankylosing spondylitis (AS), where joint damage becomes evident on an X-ray, the risk is relatively low, a French study found.

The risk was about halved in patients on TNF inhibitors, but more than tripled in those who had bone marrow swelling on MRI scans, particularly if they tested positive for HLA-B27, a known genetic risk factor for AS.

Understanding these risk factors can help doctors identify patients who may benefit the most from early intervention to prevent joint damage. “Low progression rates are observed in patients who are diagnosed and treated early in their disease,” the researchers wrote.

Their study, “Sacroiliac radiographic progression over 10 years in axSpA: data from the DESIR inception cohort,” was published in the Annals of the Rheumatic Diseases.

Axial spondyloarthritis causes joints in the spine to become inflamed. It mainly affects the sacroiliac joints, which join the spine to the pelvis. Persistent inflammation can damage the joints, leading to back pain and stiffness.

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Determining risk factors

Earlier data from the DESIR study (NCT01648907) showed that about 5% of patients progressed within five years from non-radiographic axial spondyloarthritis to AS, where sacroiliac joint damage became visible on an X-ray.

Despite the use of TNF inhibitors, a type of medication that reduces inflammation, some patients continued to have poor functional status as a result of ongoing damage.

“It seems therefore important to be able to determine which factors are associated with radiographic progression among patients receiving the standard of care,” the researchers wrote.

They looked at how sacroiliac joint damage progresses in patients with symptoms for less than three years who continued to be followed in the DESIR study for as long as 10 years.

In addition to looking at the number of patients who developed AS — based on X-ray evidence of minimal abnormalities on both sides, or clear abnormalities on one side of the sacroiliac joints — the researchers searched for baseline factors linked to progression.

Out of 659 patients, 294 completed the study, meaning there were pelvic X-rays available both at baseline and at 10 years. Both the total group and the subset of those who completed the study had an almost equal proportion of women (54% in the larger group and 52% for the group of study completers) and similar mean age (33.6 for the larger group and 34.3 for the completers).

Seventeen patients, or 5.8%, who completed the study progressed to AS within 10 years, a proportion “almost identical as the one observed at 5 years,” the researchers wrote.

When considering the total group of 659 participants, however, the probability of progressing to AS was estimated to increase 0.87% each year, resulting in a progression rate of 8.7% after 10 years.

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TNF inhibitors’ role ‘needs to be interpreted with caution’

At some point over the 10 years, 244 patients, or 37%, were treated with TNF inhibitors. When considering this factor, the probability of progressing to AS was estimated to increase 0.45% each year, or 4.5% after 10 years.

While the use of TNF inhibitors about halved the risk of progressing to AS, this “needs to be interpreted with caution,” the researchers wrote, “as the causal effect of … exposure cannot be demonstrated in this setting.”

Certain baseline factors were linked to a higher risk of developing AS within 10 years. These included having bone marrow swelling on pelvic MRI scans, which increased the odds by 3.07 times in patients who tested negative for HLA-B27 and by 6.15 times in those who tested positive for HLA-B27.

Other baseline factors were being male, having symptoms for more than 1.5 years, and having high disease activity, based on a score of 2.1 or higher on the Axial Spondyloarthritis Disease Activity Score. Smoking was linked to higher risk in HLA-B27-positive patients.

The results support HLA-B27 as a strong genetic risk factor for AS. Factors other than genetic predisposition may play a role in driving and maintaining the inflammation that results in joint damage, the researchers said.

“Our results on radiographic progression reflecting the long-term structural outcome of these patients at the sacroiliac level are reassuring, and provide valuable data for clinicians to use to inform their patients,” the researchers wrote.