TOPLINE:

Patients with rheumatoid arthritis who took tofacitinib for 6 months had increased lower limb and thigh muscle volume, a small prospective study found.

METHODOLOGY:

• Researchers evaluated 15 adult patients with rheumatoid arthritis (mean age, 59.6 years; 87% women) at a hospital in the UK who initiated tofacitinib 5 mg twice daily as the standard of care.
• Patients had to have at least one sarcopenia risk factor, no previous treatment with JAK inhibitors, no systemic glucocorticoids for at least 4 weeks prior, and elevated serum creatinine levels.
• Blood samples were collected at baseline, 1 month, and 6 months; participants underwent vastus lateralis muscle biopsies at baseline and again at 6 months.
• The primary outcome measure was a change in lower limb muscle volume, assessed by quantitative MRI at baseline, 1 month, and 6 months; secondary outcomes included changes in serum creatinine levels.

TAKEAWAY:

• Mean muscle volume increased significantly at 6 months by 242 cm³ (4%; P = .017) in lower limbs and by 200 cm³ (5% increase; P = .019) in thighs vs a nonsignificant 52 cm³ (2%) increase in lower legs.
• Disease Activity Score in 28 joints based on C-reactive protein decreased significantly at 1 month (P = .0064) with no further changes at 6 months; mean serum creatinine levels increased significantly by 5.6 μmol/L (P = .0011).
• Appendicular lean mass index, muscle strength, or muscle function did not change significantly, but mean grip strength showed a nonsignificant increase from 12.6 kg at baseline to 15.8 kg at 6 months.
• Adverse events were recorded in 87% of participants, but a notable proportion of these were mild or moderate.

IN PRACTICE:

“Tofacitinib is associated with an increase in leg muscle volume, possibly through suppression of inflammation-induced muscle loss. This study suggests a novel role for tofacitinib in the treatment of sarcopenia,” experts wrote in an accompanying editorial.

SOURCE:

This study was led by Joshua L. Bennett, PhD, Translational and Clinical Research Institute, Newcastle University in Newcastle upon Tyne, England. It was published online on October 15, 2025, in The Lancet Rheumatology.

LIMITATIONS:

The increase in muscle volume cannot be definitively attributed to tofacitinib therapy because of the single-arm nature of the study. The small sample size, absence of a control group, and high tender joint count limited the power to detect changes in muscle strength and function. Nutritional assessments were not included in this study.

DISCLOSURES:

This study was funded by an Investigator Initiated Research Grant from Pfizer. Some authors disclosed receiving funding, reimbursement for travel and conference registration, speaker honoraria, research grants or support, consultancy fees, and support for conference attendance; participating in advisory‑board roles; and having other ties with various pharmaceutical companies.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.