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

Rheumatoid cachexia has been described as a process of concurrent muscle loss and gain of adipose tissue. We evaluated longitudinal changes in body composition in patients with rheumatoid arthritis (RA) to evaluate the changes in adiposity that accompany loss of lean mass.

We combined and assessed three independent longitudinal RA cohorts that included assessments of body composition. Whole body DXA was performed in all participants to quantify appendicular lean mass index (ALMI, kg/m²) and fat mass index (FMI, kg/m²). Independent associations between loss of ALMI during follow-up and FMI over the same time-period were assessed adjusting for age, sex, race, baseline body composition and study using mixed-effects regression to account for clustering by study. Changes in adipokines (adiponectin and leptin) were also assessed over time in similar models. Visceral fat area was determined from DXA (cm²) in one of the cohorts and was also assessed.

Among 451 patients with a mean (SD) age of 58.3 (10.5), the mean (SD) ALMI was 6.97 (1.41) kg/m². Longitudinal analyses were conducted in 361 participants with follow-up data [average follow-up 2.65 (0.71) years]. Of these, 195 lost lean mass (experienced a negative change in ALMI during follow-up), while 166 gained lean mass. Participants that lost lean mass had greater reductions in BMI [-0.77 (95% CI: -1.21, -0.33) v. +1.07 (95% CI: 0.56, 1.59)], greater reductions in FMI [-0.17 (95% CI: -0.48, 0.14) v. +0.46 (95% CI: 0.08, 0.83) p = 0.07] and a greater odds of having a reduction in FMI [OR: 2.30 (1.31, 4.05) p = 0.004], and had declining leptin levels and visceral fat area. Associations were strongest among those with high FMI at baseline.

In RA, loss of lean mass tends to occur in the context of a loss of weight and a loss of both total and visceral adiposity. 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.