Background/Purpose:
Significant differences in adiposity between men and women with RA have been observed (1). Another alteration of body composition, rheumatoid cachexia, characterized by low lean mass, is also clinically important because it has been linked to increased risk of disability and mortality (2). Our objective was to identify the extent of lean mass deficits in men and women with RA compared to age- and sex-specific national reference data.

Methods:
Subjects were recruited from a university-based cohort of patients with RA. Exclusion criteria were non–English speaking, age >18 years, current daily oral prednisone dose >50 mg/day, pregnancy, and joint replacement within 1 year. Body composition and regional fat and lean mass distribution were assessed with whole body dual energy X-ray absorptiometry (DXA) using a Lunar Prodigy DXA system. Precision error (1 SD) was 1.0 kg for fat mass, and 0.8 kg for lean mass. Appendicular lean mass and overall lean body mass were adjusted for height to create indices (ALMI and LBMI, respectively). Indices for each subject were compared to previously published NHANES reference ranges to generate age- and sex-specific Z-scores according to the guidelines defined by Kelly et al (3). Sarcopenia was defined as an ALMI Z-score <-1 (corresponding to the16^th percentile) (4).

Results:
DXA was performed for 141 individuals (56 men, 85 women). There were no significant differences in self-reported disease activity, functioning (by Health Assessment Questionnaire), prednisone use, or disease duration. Men had significantly lower ALMI and LBMI Z-scores compared to women (Table). On average among men, ALMI and LBMI were at the 8^th and 7^th percentiles, respectively. In contrast, average ALMI and LBMI among women were at the 37^th and 32^st percentiles, respectively. Sarcopenia was present among 55% of men and 25% of women, with the odds of sarcopenia significantly greater for men ([OR 3.78 [1.84-7.78], p<0.001).

 

Table. Mean lean mass Z-Scores (SD) and percentiles for men and women with RA based on NHANES reference ranges
	Men (n = 56)	Women (n = 85)	p*
Appendicular lean mass index (ALMI) z-score	-1.39 (1.34)	-0.34 (0.92)	<.0001
ALMI percentile	8th	37th
Overal lean body mass index (LBMI) Z-score	-1.44 (1.36)	-0.47 (0.86)	<.0001
LBMI percentile	7th	32nd
* p-value from t-tests comparing men and women

Conclusion:
Among subjects with RA, men had significantly greater lean mass deficits than women. Combined with previous observations of greater obesity among men with RA, it appears that men with RA may experience greater alterations in body composition than women when compared to normal sex-specific ranges. Further study may help confirm these findings and to clarify the factors leading to these differences.

References

1.         Katz PP et al. Sex differences in assessment of obesity in rheumatoid arthritis. Arthritis Care Res 2013;65(1):62-70.
2.         Roubenoff R. Rheumatoid cachexia: a complication of rheumatoid arthritis moves into the 21st century. Arthritis Res Ther 2009;11(2):108.
3.         Kelly TL et al. Dual energy X-Ray absorptiometry body composition reference values from NHANES. PLoS One 2009;4(9):e7038.
4.         Coin A et al. Prevalence of Sarcopenia Based on Different Diagnostic Criteria Using DEXA and Appendicular Skeletal Muscle Mass Reference Values in an Italian Population Aged 20 to 80. J Am Med Dir Assoc 2013.

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