Rituximab in MS linked to far more new inflammatory bowel disease

Design

Population-based register cohort with matched general-population comparators

Population

13,748 MS therapy starts in 9,251 Swedish adults aged 18–55 with relapsing MS

Primary outcome

New-onset inflammatory bowel disease

Effect

110 vs 13 per 100,000 person-years; comparator DMTs vs rituximab HR 0.10 (95% CI 0.04–0.22); NNH 131 at 5 years

Using the Swedish MS register and national health data, investigators followed 13,748 treatment starts in 9,251 adults aged 18 to 55 with relapsing MS between 2011 and 2023: rituximab, natalizumab, dimethyl fumarate or fingolimod. Each was matched to general-population comparators.

New inflammatory bowel disease occurred at 110 per 100,000 person-years with rituximab, 13 with the other therapies and 41 in the general population. After adjustment for demographics and MS characteristics, the other therapies carried about a tenth of the rituximab risk (HR 0.10). Over five years, one extra case occurred for about every 131 people treated with rituximab rather than an alternative. Six in ten rituximab-associated cases were Crohn disease, against three in ten in the general population.

Rituximab is used off-label for MS in Sweden and widely in India because of cost. B-cell depletion has been linked to colitis in case series; this is the first population-scale estimate.

The study covers rituximab only, so the risk with ocrelizumab or ofatumumab is not established here, though a class effect is plausible. It is observational, and absolute risk remains low. It does not argue against anti-CD20 therapy, but for asking about the bowel before and during it.

• Ask about personal and family history of inflammatory bowel disease before starting anti-CD20 therapy for MS.
• Take new diarrhoea, abdominal pain or rectal bleeding seriously in patients on rituximab, and investigate promptly.
• Include the risk in treatment discussions, especially for patients with a family history of Crohn disease or colitis.
• Consider a gastroenterology referral early rather than treating persistent symptoms as infection or side effects.
• Do not stop effective anti-CD20 therapy on this finding alone without a specialist review.

Why it matters

Gastrointestinal symptoms on rituximab may be a new disease, not a side effect to wait out.

Don't overread it

This was observational and studied rituximab only; it does not establish the same risk for other anti-CD20 drugs.

The statistics, in plain English

A hazard ratio of 0.10 for the comparator drugs means about a tenth of the rituximab rate, or rituximab carrying roughly ten times the risk. The number needed to harm of 131 over five years shows the absolute risk is still small. With only four events in the comparator group, the estimate is imprecise, though the interval (0.04 to 0.22) stays far from 1.

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.