Impact of muscle mass on mortality in patients with rheumatoid arthritis: insights from NHANES 1999-2018.

BACKGROUND

Muscle loss is linked to multiple adverse outcomes, but its impact on rheumatoid arthritis (RA) prognosis is unclear. This study aimed to examine the association between muscle mass and mortality in RA patients.

METHODS

RA patients from the NHANES database were followed for survival until December 31, 2021. Muscle mass was measured using dual X-ray absorptiometry, low muscle mass was defined as appendicular skeletal muscle mass index (ASMI) < 7.0 kg/m² in men or < 5.5 kg/m² in women. The relationship between ASMI and mortality was analyzed using weighted Cox regression.

RESULTS

The study included 892 participants (weighted mean [SE] age 52.22 [0.59] years, 57.36% female). During a median (SE) follow-up of 11.44 (0.33) years, 291 deaths (32.62%) were recorded, of which 197 (28.23%) were attributed to cardiovascular disease. In fully adjusted models, a 1 kg/m²increase in ASMI was associated with decreased all-cause and cardiovascular mortality risk by 34% (HR = 0.66, 95% CI 0.50-0.86) and 40% (HR = 0.60, 95% CI 0.38-0.93), respectively. When ASMI stratified, RA with low muscle mass had a 1.42-fold higher risk of all-cause mortality (HR = 1.42, 95% CI 1.01-2.00) and a 2.58-fold higher risk of cardiovascular mortality (HR = 2.58, 95% CI 1.18-5.62) than those with normal muscle mass. Restricted cubic spline analysis showed a nonlinear association between ASMI and cardiovascular (Pnonlinear = 0.04) but not for all-cause mortality (Pnonlinear = 0.25).

CONCLUSIONS

Muscle loss in RA patients is linked to higher mortality risk, underscoring the need to recognize its harmful effects.