Development of new adjusted equations to estimate the skeletal muscle mass stratified by nutritional status for patients with rheumatoid arthritis: a methodological study

Abstract Our objective was to adjust and validate predictive equations for appendicular skeletal muscle mass (ASM) in patients with Rheumatoid Arthritis (RA). Whole-body DXA data in 90 RA patients were used for measurement of ASM (kg). The prediction equation anthropometric for muscle mass proposed by Lee et al was used to generate estimates of ASM. Appendicular skeletal muscle mass index (ASMI, kg/m2) was calculated. Frequency analysis, Paired student's t-test, Linear regression, Pearson correlation, Intraclass correlation coefficients, and Bland-Altman scatter were performed. The statistical significance considered was p<0.05. Lee’s equation was overestimated by 30% when compared with ASMI by DXA. When stratified by nutritional status, Lee’s equation overestimated the ASMI by 30% in overweight patients and by 50% in obese patients when compared with DXA (p<0.05). These adjusted equations estimated values for ASMI were closer to those obtained by DXA than those estimated by the original Lee’s equation (p<0.05). This greater concordance was confirmed by the observed interclass correlation coefficients and by Bland-Altman scatter graphs. In conclusion, the prediction of muscle mass in RA patients may be performed with equations that consider the nutritional status of patients.

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Appendicular skeletal muscle mass: effects of age, gender, and ethnicity

Journal of Applied Physiology ◽

10.1152/jappl.1997.83.1.229 ◽

1997 ◽

Vol 83 (1) ◽

pp. 229-239 ◽

Cited By ~ 530

Author(s):

Dympna Gallagher ◽

Marjolein Visser ◽

Ronald E. De Meersman ◽

Dennis Sepúlveda ◽

Richard N. Baumgartner ◽

...

Keyword(s):

Skeletal Muscle ◽

African Americans ◽

Multiple Regression ◽

Muscle Mass ◽

Skeletal Muscle Mass ◽

Whole Body ◽

Mass Effects ◽

Wide Range ◽

Appendicular Skeletal Muscle ◽

Appendicular Skeletal Muscle Mass

Gallagher, Dympna, Marjolein Visser, Ronald E. De Meersman, Dennis Sepúlveda, Richard N. Baumgartner, Richard N. Pierson, Tamara Harris, and Steven B. Heymsfield. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J. Appl. Physiol. 83(1): 229–239, 1997.—This study tested the hypothesis that skeletal muscle mass is reduced in elderly women and men after adjustment first for stature and body weight. The hypothesis was evaluated by estimating appendicular skeletal muscle mass with dual-energy X-ray absorptiometry in a healthy adult cohort. A second purpose was to test the hypothesis that whole body40K counting-derived total body potassium (TBK) is a reliable indirect measure of skeletal muscle mass. The independent effects on both appendicular skeletal muscle and TBK of gender ( n = 148 women and 136 men) and ethnicity ( n = 152 African-Americans and 132 Caucasians) were also explored. Main findings were 1) for both appendicular skeletal muscle mass (total, leg, and arm) and TBK, age was an independent determinant after adjustment first by stepwise multiple regression for stature and weight (multiple regression model r 2 = ∼0.60); absolute decrease with greater age in men was almost double that in women; significantly larger absolute amounts were observed in men and African-Americans after adjustment first for stature, weight, and age; and >80% of within-gender or -ethnic group between-individual component variation was explained by stature, weight, age, gender, and ethnicity differences; and 2) most of between-individual TBK variation could be explained by total appendicular skeletal muscle ( r 2 = 0.865), whereas age, gender, and ethnicity were small but significant additional covariates (total r 2 = 0.903). Our study supports the hypotheses that skeletal muscle is reduced in the elderly and that TBK provides a reasonable indirect assessment of skeletal muscle mass. These findings provide a foundation for investigating skeletal muscle mass in a wide range of health-related conditions.

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