<p><strong>PURPOSE: </strong>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.</p>

<p><strong>METHODS: </strong>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.</p>

<p><strong>RESULTS: </strong>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].</p>

<p><strong>CONCLUSION: </strong>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.</p>

<p><strong>PURPOSE: </strong>Rheumatoid arthritis (RA) is associated with adverse body composition profiles, and low muscle density due to accumulation of intramuscular fat. This study assessed associations between muscle density, body composition, muscle strength, and physical functioning in patients with RA and a reference group.</p>

<p><strong>METHODS: </strong>Patients with RA, ages 18-70 years, and healthy control participants completed whole-body DXA and peripheral quantitative CT (pQCT) to quantify appendicular lean mass (ALMI, kg/m) and fat mass indices (FMI, kg/m), visceral fat area, and muscle density. Dynamometry was used to measure hand-grip strength and muscle strength at the knee and lower leg (ft-lbs). Disability and physical functioning were measured with the Health Assessment Questionnaire (HAQ) and the Short Physical Performance Battery (SPPB). Linear regression analyses assessed differences related to RA and associations between muscle density, strength, and function.</p>

<p><strong>RESULTS: </strong>The study consisted of 103 RA patients (51 men) and 428 healthy participants. Low muscle density was associated with greater disease activity, CRP, and Interleukin-6, greater total and visceral fat, lower ALMI Z-Scores, physical inactivity, and long-term use of glucocorticoids (&gt;1yr). Patients with low ALMI Z-Scores had lower muscle density Z-Score compared to reference participants with similarly low ALMI. Low muscle density was independently associated with lower muscle strength, higher HAQ, and lower SPPB after adjusting for ALMI and FMI Z-Scores.</p>

<p><strong>CONCLUSIONS: </strong>Low muscle density observed among patients with RA is observed in association with low muscle mass, excess adiposity, poor strength, and greater disability. Interventions to address poor muscle quality could potentially affect important functional outcomes. This article is protected by copyright. All rights reserved.</p>

<p><strong>OBJECTIVE: </strong>Rheumatoid arthritis (RA) is associated with low muscle mass and density. The objective of our study was to evaluate associations between 2 serum biomarkers [insulin-like growth factor 1 (IGF-1) and adiponectin] and skeletal muscle in RA.</p>

<p><strong>METHODS: </strong>Whole-body dual energy X-ray absorptiometry measures of the appendicular lean mass index (ALMI; kg/m(2)) and total fat mass index (kg/m(2)), as well as the peripheral quantitative computed tomography measures of the lower leg muscle and fat cross-sectional area (CSA; cm(2)) and muscle density (an index of fat infiltration) were obtained from 50 participants with RA, ages 18-70 years. Multivariable linear regression analyses evaluated associations between body composition and levels of adiponectin and IGF-1, adjusted for age, sex, and adiposity.</p>

<p><strong>RESULTS: </strong>Greater age was associated with higher adiponectin (p = 0.06) and lower IGF-1 (p = 0.004). Eight subjects had IGF-1 levels below the reference range for their age and sex. These subjects had significantly lower ALMI and muscle CSA in multivariable models. Lower IGF-1 levels were associated with greater clinical disease activity and severity, as well as low ALMI, muscle CSA, and muscle density (defined as 1 SD below normative mean). After adjusting for age and sex, greater adiponectin levels were associated with lower BMI (p = 0.02) as well as lower ALMI, and lower muscle CSA, independent of adiposity (p &lt; 0.05). Only greater Health Assessment Questionnaire scores were significantly associated with lower adiponectin levels.</p>

<p><strong>CONCLUSION: </strong>Low IGF-1 and greater adiponectin levels are associated with lower muscle mass in RA. Lower IGF-1 levels were seen in subjects with greater disease activity and severity.</p>

<p><strong>OBJECTIVE: </strong>Rheumatoid arthritis (RA) is associated with muscle loss, osteoporosis, and fracture. We examined associations between skeletal muscle mass, strength, and quality and trabecular and cortical bone deficits in patients with RA and healthy controls.</p>

<p><strong>METHODS: </strong>Participants, ages 18-75 years, completed whole-body dual-energy x-ray absorptiometry and peripheral quantitative computed tomography (pQCT) of the tibia to quantify appendicular lean mass and fat mass indices (ALMI, FMI), muscle density at the lower leg, trabecular bone density, and cortical bone thickness. Age-, sex-, and race-specific Z scores were calculated based on distributions in controls. Associations between body composition and pQCT bone outcomes were assessed in patients with RA and controls. Linear regression analyses assessed differences in bone outcomes after considering differences in body mass index (BMI) and body composition.</p>

<p><strong>RESULTS: </strong>The sample consisted of 112 patients with RA (55 men) and 412 controls (194 men). Compared to controls, patients with RA had greater BMI Z score (p &lt; 0.001), lower ALMI Z score after adjustment for FMI (p = 0.02), lower muscle strength Z score (p = 0.01), and lower muscle density Z score (p &lt; 0.001). Among RA, ALMI Z scores were positively associated with trabecular density [β: 0.29 (0.062-0.52); p = 0.01] and cortical thickness [β: 0.33 (0.13-0.53; p = 0.002]. Associations were similar in controls. Bone outcomes were inferior in patients with RA after adjusting for BMI, but similar to controls when adjusting for body composition. Radiographic damage and higher adiponectin levels were independently associated with inferior bone outcomes.</p>

<p><strong>CONCLUSION: </strong>Patients with RA exhibit deficits in cortical bone structure and trabecular density at the tibia and a preserved functional muscle-bone unit. A loss of mechanical loading may contribute to bone deficits.</p>