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Low Muscle Density is Associated with Deteriorations in Muscle Strength and Physical Functioning in Rheumatoid Arthritis

Author

Baker JF1,2,3, Mostoufi-Moab S4, Long J5, Taratuta E6, Leonard MB5, Zemel B4. Arthritis Care Res (Hoboken). 2019 Dec 16. doi: 10.1002/acr.24126. [Epub ahead of print]

Author Information

1 Philadelphia VA Medical Center, Philadelphia, PA, USA.

2 Division of Rheumatology, University of Pennsylvania, Philadelphia, PA.

3 Department of Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, PA, USA.

4 Children's Hospital of Philadelphia, Philadelphia, PA, USA.

5 Stanford University, Palo Alto, CA, USA.

6 Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.

Abstract

PURPOSE: 

Rheumatoid arthritis (RA) is associated with low muscle density due to accumulation of intramuscular fat. This study identified predictors of changes in muscle density and determined whether low muscle density predicted changes in strength and physical function.

METHODS: 

Patients with RA, ages 18-70, completed whole-body DXA and peripheral quantitative CT (pQCT) to quantify lean and fat mass indices and muscle density. Dynamometry was used to measure strength at the hand, knee, and lower leg. Disability and physical function were measured with the Health Assessment Questionnaire (HAQ) and the Short Physical Performance Battery (SPPB). Assessments were performed at baseline and at follow-up. Regression analyses assessed associations between patient characteristics, muscle density, and deteriorations in strength and function.

RESULTS: 

Muscle density was assessed at baseline in 107 patients with RA. Seventy-nine (74%) returned for a follow-up assessment at a median follow-up time of 2.71 years (IQR: 2.35-3.57). Factors associated with declines in muscle density included female sex, higher disease activity, smoking, and lower IGF-1 levels. Greater muscle density Z-Score at baseline (per 1 SD) was associated with less worsening per year of HAQ, SPPB, and 4-meter walk time and a lower risk of a clinically important worsening in HAQ [OR 1.90 (1.06,3.42) p=0.03] and walking speed [OR 2.87 (1.05,7.89) p=0.04].

CONCLUSION: 

Worsening of skeletal muscle density occurred in patients with higher disease activity, smokers, and those with lower IGF-1. Low muscle density was associated with worsening of physical function. Interventions addressing reductions in muscle quality might prevent functional decline.