Bimekizumab reduced MRI inflammation and erosions in axial spondyloarthritis, with minimal radiographic progression to two years

Design

MRI and radiographic analyses of two phase 3 trials and open-label extension

Population

Patients with non-radiographic and radiographic axial spondyloarthritis in BE MOBILE 1 and 2

Primary outcome

MRI inflammation and structural scores; radiographic progression

Effect

SPARCC SIJ −7.6 / −5.1 at week 52; mSASSS +0.3 at week 104

BE MOBILE 1 (non-radiographic) and BE MOBILE 2 (radiographic axial spondyloarthritis) were phase 3 trials of bimekizumab, which blocks both IL-17A and IL-17F. After 16 weeks of placebo-controlled treatment, all patients received bimekizumab 160 mg every 4 weeks, with an open-label extension from week 52.

By week 52, patients randomised to bimekizumab showed reduced sacroiliac joint inflammation (SPARCC change −7.6 in non-radiographic and −5.1 in radiographic disease) and spinal inflammation (Berlin score −0.5 and −2.5). Erosion scores fell (−1.8 in both), while backfill and fat lesions increased, consistent with repair. Ankylosis barely changed. At week 104, radiographic progression was minimal: mean change 0.03 in modified New York grade and 0.3 mSASSS units.

This supports bimekizumab controlling inflammation on imaging, not only symptoms. But after week 16 there was no control group and the data are observed cases, so the structural findings cannot be compared with untreated disease or with other biologics.

• Use MRI inflammation, not only symptoms, to judge response where imaging is accessible
• Interpret increasing fat lesions after treatment as a likely repair response
• Do not cite these data as proof that bimekizumab slows progression more than other agents
• Continue to address smoking, which is linked to radiographic progression

Why it matters

Showing that inflammation and erosions resolve on imaging strengthens the case for treating axial disease early.

Don't overread it

No control group beyond week 16 — structural results are uncontrolled observed cases.

The statistics, in plain English

Observed case data include only patients who stayed on treatment and had imaging, who tend to be responders, so improvements are likely overstated. An mSASSS change of 0.3 over two years is small, but without a comparator its meaning is limited.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.