Low Muscle Density in Rheumatoid Arthritis Predicts Deterioration in Strength, Physical Functioning

Female sex, higher disease activity, smoking, and lower insulin-like growth factor-1 (IGF-1) levels may predict worsening skeletal muscle density in patients with rheumatoid arthritis (RA). This lower muscle density is in turn associated with poorer muscle strength and physical functioning, according to results published in Arthritis Care & Research.

Investigators conducted a cohort study of patients aged 18-70 years who met the 2010 American College of Rheumatology criteria for active RA. Participants were recruited from the University of Pennsylvania and the Philadelphia Veterans Affairs Medical Center. Individuals with juvenile idiopathic arthritis, active cancer, or a history of chronic disease known to affect bone health were excluded from the study. At baseline, participants underwent whole-body dual-energy x-ray absorptiometry and peripheral quantitative computed tomography to calculate lean and fat mass indices and muscle density. Dynamometry was used to assess hand, knee, and lower leg strength. Disability and physical function were measured with use of the Health Assessment Questionnaire (HAQ) and the Short Physical Performance Battery (SPPB). Disease activity was captured by using the Modified Disease Activity Score of 28 joints including C-Reactive Protein (M-DAS28). Assessments were repeated at a follow-up visit typically conducted 2-3 years after baseline. Regression analyses were performed to assess changes in muscle density and strength over time.

A total of 107 patients with RA completed the baseline assessment, of whom 79 (74%) returned for a follow-up visit at a median follow-up time of 2.71 years (interquartile range, 2.35-3.57). Mean (standard deviation) age at baseline was 55.5 (12.7) years; 55 (51%) were women and 32 (30%) were black. In analyses adjusted for age, sex, race, and baseline muscle density Z-score, baseline factors that predicted decline in muscle density included female sex (P =.02), current smoking (P =.01), higher M-DAS28 score, and current use of methotrexate (P =.08). Higher IGF-1 levels were associated with significantly less decline per year in muscle density Z-score (P =.01). Inflammatory cytokines and adipokines were not associated with changes in muscle density. Low muscle density was associated with worsening of physical function over time, including HAQ score, SPPB score, walking speed, and hand grip strength. In adjusted models, lower muscle density at baseline was associated with increased odds for significant worsening in HAQ score (odds ratio [OR], 1.90; 95% CI, 1.06-3.42; P =.03) and walking speed (OR, 2.87; 95% CI, 1.05-7.89; P =.04).

These data identify several factors that may predict long-term changes in muscle density and physical function in patients with RA. Investigators noted that the small cohort size limited the statistical power of some analyses. “Reductions in skeletal muscle quality may have important implications for long-term outcomes that are among the most important to patients with arthritis,” the investigators wrote.

Reference

Baker JF, Mostoufi-Moab S, Long J, Taratuta E, Leonard MB, Zemel B. Low muscle density is associated with deteriorations in muscle strength and physical functioning in rheumatoid arthritis [published online December 16, 2019]. Arthritis Care Res (Hoboken). doi: 10.1002/acr.24126.