Bimekizumab kept spinal MRI inflammation down for two years in axial spondyloarthritis

Design

Imaging analysis of a phase 3 randomised trial and open-label extension

Population

102 patients with radiographic axial spondyloarthritis with four spinal MRIs

Primary outcome

Change in CANDEN spinal MRI inflammation and structural scores to week 104

Effect

Inflammation score −7.3 at week 16 and −6.6 at week 104; minimal change in erosions and new bone

This analysis used spinal MRI from the phase 3 BE MOBILE 2 trial of bimekizumab, a dual IL-17A and IL-17F inhibitor, and its open-label extension in radiographic axial spondyloarthritis. Of 332 trial patients, 102 had scans at baseline, weeks 16, 52 and 104 suitable for detailed Canada-Denmark (CANDEN) scoring.

Total inflammation scores fell by a mean of 7.3 points by week 16 and remained 6.6 points below baseline at two years, across all spinal locations including posterolateral elements. Fat lesions increased early (by 1.6 points) in patients who had baseline inflammation, then changed little. Erosions and new bone formation changed minimally.

The pattern fits rapid, sustained suppression of inflammation, with fat lesions appearing where inflammation resolved, a sequence thought to precede new bone in some patients. Whether this reduces structural progression over longer periods is not answered by two years of data. The analysis covers under a third of trial patients, uses observed cases only and has no comparator beyond week 16.

• Expect spinal inflammation on MRI to settle within about 16 weeks of starting an IL-17 inhibitor in responders.
• Use MRI to assess inflammation where clinical response is unclear, not routinely for every patient.
• Recognise that new fat lesions after treatment usually mark resolved inflammation.
• Do not yet counsel patients that bimekizumab prevents new bone formation; two-year data cannot show that.

Why it matters

Durable control of inflammation is the necessary first step if biologics are to change structural outcomes in axial spondyloarthritis.

Don't overread it

An open-label, observed-case analysis of a third of the trial does not show bimekizumab prevents spinal fusion.

The statistics, in plain English

These are mean changes from baseline in patients who had all four scans, which favours those who stayed on treatment and did well. Without a placebo arm after week 16, the two-year results cannot be compared with what would have happened untreated.

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.