Rituximab in MS was linked to more inflammatory bowel disease

Design

Population-based registry cohort with matched general population comparators

Population

9251 adults with relapsing MS starting rituximab, natalizumab, dimethyl fumarate or fingolimod, Sweden

Primary outcome

New-onset inflammatory bowel disease

Effect

110 vs 13 per 100,000 person-years; HR 0.10 (95% CI 0.04-0.22) for other DMTs vs rituximab

This Swedish population-based cohort used the national MS register to follow 9251 adults aged 18 to 55 with relapsing MS who started rituximab, natalizumab, dimethyl fumarate or fingolimod between 2011 and 2023, alongside matched general population comparators. Published in JAMA Neurology on 22 October 2026.

New inflammatory bowel disease (IBD) occurred at 110 per 100,000 person-years with rituximab, 13 with the other therapies and 41 in the general population. After adjustment, the other therapies carried a hazard ratio of 0.10 compared with rituximab. Crohn disease made up 62% of cases on rituximab against 29% in the general population. The number needed to harm was 131 over five years.

Anti-CD20 therapy is widely used for MS, and rituximab is often used off-label where newer agents are costly. This gives a figure for a risk that had mostly been reported in case series.

The absolute risk is low and the study is observational, but persistent diarrhoea, abdominal pain or rectal bleeding on anti-CD20 therapy should prompt investigation rather than reassurance.

• Mention IBD risk when discussing rituximab or other anti-CD20 therapy for MS
• Ask about bowel symptoms at each review of patients on anti-CD20 therapy
• Investigate persistent diarrhoea, abdominal pain or rectal bleeding with stool calprotectin and referral
• Take extra care in patients with a personal or family history of IBD
• Expect about one extra IBD case for every 131 patients treated for five years

Why it matters

Bowel symptoms in a patient on anti-CD20 therapy are a possible drug effect, not just irritable bowel.

Don't overread it

This was observational and studied rituximab only; other anti-CD20 drugs were not assessed directly.

The statistics, in plain English

A number needed to harm of 131 means that treating 131 people with rituximab rather than another therapy for five years would be associated with one extra case of IBD. The confidence interval (93 to 228) shows the size of that estimate is reasonably firm.

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