Bimekizumab in axial spondyloarthritis: less MRI inflammation, little radiographic change at two years

Design

MRI and radiographic analysis of two phase 3 RCTs with open-label extension

Population

Adults with non-radiographic and radiographic axial spondyloarthritis

Primary outcome

MRI inflammation and structural scores; radiographic progression

Effect

SPARCC SIJ -7.6 and -5.1 at week 52; mSASSS change 0.3 at week 104

This analysis drew on the phase 3 BE MOBILE 1 (non-radiographic) and 2 (radiographic) trials of bimekizumab, which blocks interleukin-17A and 17F. After 16 placebo-controlled weeks, all patients received bimekizumab 160 mg every four weeks, with an open-label extension beyond week 52. MRI sub-studies scored sacroiliac and spinal inflammation and structural lesions; radiographs were compared at baseline and week 104.

At week 52, patients randomised to bimekizumab had reduced sacroiliac inflammation (SPARCC change -7.6 in non-radiographic and -5.1 in radiographic disease) and spinal inflammation, lower erosion scores, and modest increases in backfill and fat lesions, a pattern thought to reflect repair. Radiographic progression to week 104 was minimal (mSASSS change 0.3 in radiographic disease).

These are observed-case data without a placebo comparison beyond 16 weeks, and the analysis was conducted with the manufacturer. The imaging response is consistent with other biologics in this disease; it does not show bimekizumab slows progression more than alternatives.

• Expect MRI inflammation to fall within a year on effective IL-17 blockade.
• Do not use these data to rank bimekizumab above other IL-17 or TNF inhibitors.
• Use MRI selectively to assess response when clinical measures are unclear.
• Choose between biologics on comorbidities such as uveitis and inflammatory bowel disease, cost and access.

Why it matters

Imaging evidence of reduced inflammation supports dual IL-17 inhibition as a credible option, not a superior one.

Don't overread it

Observed-case, open-label data after week 16 with no comparator; this cannot show slower progression than other treatments.

The statistics, in plain English

Observed-case analysis includes only patients still on treatment with scans, who tend to be responders, which can make results look better than for everyone who started.

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