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

Abstract

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 (P_nonlinear = 0.04) but not for all-cause mortality (P_nonlinear = 0.25).

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

Keywords: Appendicular skeletal muscle mass index; Cardiovascular; Mortality; NHANES; Rheumatoid arthritis.

Fig. 1

The flow chart of identifying eligible subjects. Abbreviations: NHANES, National Health and Nutrition Examination Survey; RA, rheumatoid arthritis; DEXA, dual energy X-ray absorptiometry

Fig. 2

Kaplan-Meier curves of all-cause (A) and cardiovascular (B) mortality in patients with RA stratified by muscle mass. Abbreviations: RA, rheumatoid arthritis

Fig. 3

Nonlinear dose-response analysis on the association of ASMI with the risk of both all-cause and cardiovascular mortality. Abbreviations: NHANES, National Health and Nutrition Examination Survey; RA, rheumatoid arthritis; ASMI, appendicular skeletal mass index; PIR, poverty income ratio; CRP, C-reactive protein; BMI, body mass index; eGFR, estimated glomerular filtration rate; CVD, cardiovascular disease; HR, hazard ratio; CI, confidence interval.^*Adjusted for age, gender, race/ethnicity, marital status, education level, family PIR, smoking status, drinking status, CRP, BMI, eGFR, history of hypertension, diabetes, hyperlipidemia, CVD and malignancy

Fig. 4

Associations of muscle mass with mortality in various subgroups in patients with RA in NHANES cohort. Abbreviations: NHANES, National Health and Nutrition Examination Survey; RA, rheumatoid arthritis; ASMI, appendicular skeletal mass index; PIR, poverty income ratio; CRP, C-reactive protein; BMI, body mass index; eGFR, estimated glomerular filtration rate; CVD, cardiovascular disease; HR, hazard ratio; CI, confidence interval.^*Adjusted for age, gender, race/ethnicity, marital status, education level, family PIR, smoking status, drinking status, CRP, BMI, eGFR, history of hypertension, diabetes, hyperlipidemia, CVD and malignancy