Muscle thickness of the rectus femoris is lower in patients with copd than in healthy patients matched for sex, age and stature: an exploratory study

Rationale: Currently use of muscle thickness measured with ultrasound is suggested as an indicator for overall muscle mass in nutritional assessment. However, not much is known about how the muscle thickness measured in patients with chronic obstructive pulmonary disease (COPD) compares to the muscle thickness in healthy persons. This study explores body mass index (BMI) and rectus femoris (RF) muscle thickness in patients with advanced COPD matched with healthy controls. Methods: Patients with advanced COPD at the start of a pulmonary rehabilitation program were matched for age (5 years difference tolerance), sex (exact match), and stature (0.1 m difference tolerance) with healthy controls in a 1:4 case control ratio. BMI (kg/m2) was calculated and muscle thickness (mm) of the RF was measured with a Bodymetrix device. Paired sample t-tests were performed. BMI and RF muscle thickness of the cases were paired with the average BMI and RF of their controls. A p-level of <0.05 was considered significant and 95% CI were presented for the mean difference. Results: In total, 21 cases (median GOLD score 3 [interquartile range 3-4]; age 64.5±6.4y; female 62%; height 1.68±0.07m; BMI 26.9±6.1 kg/m2; RF 12.4±3.4mm) and 84 controls (age 64.5±6.4y; female 62%; height 1.71±0.09 m; BMI 25.8±4.5; RF 14.6±4.5mm) were included in the analyses. In the paired test, BMI was not significantly different between cases and controls (p=0.645, mean difference 0.95 kg/m2 [CI:-2.12 – 4.01]), whereas RF muscle thickness of cases was significantly lower (p=0.003, mean difference -2.33 mm [CI:-3.73 - -0.92]). Conclusion: In this limited sample of patients with COPD, RF muscle thickness in cases was significantly lower than RF muscle thickness in matched controls. Research in bigger samples is needed to confirm whether RF muscle thickness measured with US provides more useful information about body composition for clinicians than BMI in patients with COPD.