Skeletal muscle effects of Janus kinase inhibition in rheumatoid arthritis (Rheumatoid Arthritis and Muscle (RAMUS)): a single-arm, experimental medicine study
An erratum to this article was published (Lancet Rheumatol, May 2026 ↗)
Authors' conclusion
Tofacitinib treatment in patients with rheumatoid arthritis was associated with increased muscle volume after 6 months.
Study context
- Population
- Patients aged >18 years with RA (2010 ACR-EULAR criteria) initiating tofacitinib, with ≥1 sarcopenia risk factor, no previous JAKi, no systemic GC for ≥4 weeks; Freeman Hospital, Newcastle upon Tyne, UK22 screened
- Participants
- 15 patients
- Outcome
- Change in lower limb muscle volume by quantitative MRI
- Follow-up
- 1 and 6 months
Methodological detailssingle-centre, proof of concept, People with lived experience with RA were involved in the design and set-up phases
- Single-centre
- Proof of concept
- People with lived experience with RA were involved in the design and set-up phases
Main finding
As reported in the abstract
Lower limb muscle volume, mean increase · 6 months
Mean increase in lower limb muscle volume, particularly in the thigh
242 cm³
95% CI 44–441p=0.017
Observational data: associations, not effects.
Secondary outcomes
Serum creatinine · 6 months
- Significant increase in serum creatinine
- P = 0.0011
Disease activity (DAS28-CRP) · 1 month
- Significantly reduced after 1 month, no further changes at 6 months
- P = 0.0064
Appendicular lean mass index, muscle strength, muscle function
- No significant changes observed
Safety
| Outcome | Values |
|---|---|
| Adverse events | Tofacitinib 87% |
- Adverse events — Total adverse events recorded
- 28
- Adverse events — Severe and serious event (hospitalisation with COVID-19 pneumonitis before commencing tofacitinib)
- 1
Original publication
Skeletal muscle effects of Janus kinase inhibition in rheumatoid arthritis (RAMUS): a single-arm, experimental medicine study. Lancet Rheumatol. Published 15 October 2025. doi:10.
Composed by AI from the published abstract and checked against it. How Briefs are made →