Bimekizumab on spinal MRI: inflammation fell and stayed low for two years

Design

Post hoc MRI analysis of a phase 3 trial and its open-label extension

Population

102 of 332 patients with radiographic axial spondyloarthritis with MRI at baseline and weeks 16, 52 and 104

Primary outcome

Change in CANDEN spinal MRI inflammation and structural lesion scores

Effect

Total inflammation score -7.3 at week 16 and -6.6 at week 104; fat lesion score +1.6 and +1.8

A sub-analysis of the BE MOBILE 2 phase 3 trial and its open-label extension used the Canada-Denmark (CANDEN) MRI system to follow spinal lesions in patients with radiographic axial spondyloarthritis treated with bimekizumab, an inhibitor of IL-17A and IL-17F. Of 332 patients, 102 had gradable scans at all four time points: baseline and weeks 16, 52 and 104.

Mean total inflammation score fell by 7.3 at week 16 and by 6.6 at week 104 against baseline, with a similar pattern across anatomical subscores. Fat lesion scores rose by 1.6 at week 16 and 1.8 at week 104, mainly in patients who had inflammation at baseline. Erosions and new bone formation changed little.

The analysis used observed cases in about a third of the trial population, had no placebo comparison beyond week 16 and cannot say whether structural progression on radiographs changes. It supports an anti-inflammatory effect on MRI, not a claim about long-term structural outcome.

• Spinal MRI inflammation fell by week 16 and remained low at two years.
• Fat lesions increased early in patients who started with inflammation; this reflects resolved inflammation, as the authors read it.
• Erosions and new bone formation changed little over two years.
• Only 102 of 332 patients had scans at every time point; read it as descriptive.

Why it matters

It shows the MRI signature of IL-17 blockade, including a fat lesion rise that could be misread as worsening.

Don't overread it

Observed-case data from about a third of trial participants; no structural outcome benefit was shown.

The statistics, in plain English

Mean change from baseline in a lesion score tells you the average direction, not how many individual patients improved. Using only patients with scans at every visit can favour those who stayed on treatment.

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