Loss of Lean Mass in Rheumatoid Arthritis Is Associated With Loss of Total and Visceral Fat.

The study combined three independent longitudinal RA cohorts to evaluate changes in body composition over time.

• 451 patients total with mean (SD) age of 58.3 (10.5) years
• Mean (SD) appendicular lean mass index (ALMI) was 6.97 (1.41) kg/m2
• Longitudinal analyses conducted in 361 participants with follow-up data
• Average follow-up was 2.65 (0.71) years
• Whole body DXA was used to quantify ALMI (kg/m2) and fat mass index FMI (kg/m2)

Among participants with follow-up data, the majority experienced loss of lean mass during the follow-up period.

• 195 of 361 participants lost lean mass (experienced a negative change in ALMI during follow-up)
• 166 of 361 participants gained lean mass
• Mixed-effects regression was used to account for clustering by study

Participants who lost lean mass had significantly greater reductions in BMI compared to those who gained lean mass.

• BMI change in lean mass losers: -0.77 (95% CI: -1.21, -0.33)
• BMI change in lean mass gainers: +1.07 (95% CI: 0.56, 1.59)
• Models adjusted for age, sex, race, baseline body composition, and study

Loss of lean mass was associated with greater reductions in total fat mass index and significantly greater odds of having a reduction in FMI.

• FMI change in lean mass losers: -0.17 (95% CI: -0.48, 0.14)
• FMI change in lean mass gainers: +0.46 (95% CI: 0.08, 0.83), p = 0.07
• Odds of having a reduction in FMI among lean mass losers: OR 2.30 (95% CI: 1.31, 4.05), p = 0.004

Loss of lean mass was associated with declining leptin levels and declining visceral fat area.

• Adipokines assessed included adiponectin and leptin
• Visceral fat area was determined from DXA (cm2) in one of the cohorts
• Participants losing lean mass had declining leptin levels over follow-up
• Participants losing lean mass had declining visceral fat area over follow-up

Associations between loss of lean mass and loss of fat mass were strongest among those with high fat mass index at baseline.

• Subgroup analyses by baseline FMI level were performed
• The association between ALMI loss and FMI loss was most pronounced in participants with high FMI at baseline
• This suggests baseline adiposity may modify the relationship between lean and fat mass changes

The findings challenge the traditional description of rheumatoid cachexia as a process of concurrent muscle loss and fat gain.

• Rheumatoid cachexia has traditionally been described as concurrent muscle loss with gain of adipose tissue
• These longitudinal data show that loss of lean mass in RA tends to occur alongside loss of both total and visceral adiposity
• Authors state these observations 'help to inform our understanding of the mechanisms leading to loss of muscle and rheumatoid cachexia in RA as well as to inform potential screening practices'