Effects of respiratory disease and age in quadriceps muscle mass: a pilot study with ultrasonography

INTRODUCTION: Patients with chronic obstructive pulmonary disease (COPD) have been shown to present more muscle wasting than their healthy peers, which affects their quality of life [1,2]. The mechanisms behind muscle wasting in COPD are still little understood and even less is known in other chronic respiratory diseases (e.g. interstitial lung diseases – ILD) [3]. Ultrasound (US) is a safe and inexpensive imaging modality which can provide reliable measurements of muscle size and quality [2]. Thus, US may be a useful technique to enhance our understanding of muscle waste in chronic respiratory diseases. This study aimed to explore differences in quadriceps muscle mass in patients with COPD, hypersensitivity pneumonitis (ILD-HP) and healthy people (elderly and young). MATERIALS AND METHODS: A cross-sectional pilot study was conducted with 10 patients with ILD-HP (68.4 ± 9.8yrs), 10 patients with COPD (69.4 ± 6.7yrs) and 10 healthy elderly volunteers (67.8 ± 8.7yrs). Groups were gender (5f/5m) and age matched. A group of 10 young university students (21.9 ± 3yrs) was also included. An US equipment (GE LOGIQ P6) with multifrequency linear probe (10–13 MHz) was used to obtain B-mode US images. The following measures were taken: Rectus Femoris Thickness (RF(T)), Quadriceps Thickness (Q(T)) and Rectus Femoris cross sectional area (RF(CSA)). Data were analysed using SPSS version 24. Data normality and homogeneity were assessed. Between-group differences and correlations were performed with non-parametric tests (Kruskal–Wallis, Mann–Whitney U-test and Spearman´s correlation coefficient). Statistical significance was set at .05. RESULTS: RF(CSA) (median and IQR) was 5.44 [3.56–6.57] cm(2); 4.29 [3.58–4.50] cm(2); 6.06 [4.61–9.41] cm(2) and 7.99 [5.92–9.41] cm(2) for ILD-HP, COPD, elderly and young people, respectively. RF(T) results were 1.51 [1.08–1.78] cm; 1.16 [1.07–1.53] cm; 1.64 [1.36–1.76] cm and 2.06 [1.68–2.27] cm, respectively. There were significant differences in RF(CSA) (p = .027), RF(T) (p = .041) and Q(T) (p = .011) between COPD and elderly people. No differences were found between ILD-HP group and elderly. Significant differences between the elderly and young groups were found for the same measurements (RF(CSA) p = .034; RF(T) p = .016; Q(T) p = .034). Moderate and negative correlations were found between age and RF(CSA) (r(s)=–0.416), RF(T) (r(s)=–0.540) and Q(T) (r(s)=–0.450). A strong and positive correlation was found between RF(T) and RF(CSA) (r(s)=0.891). DISCUSSION AND CONCLUSIONS: Our results seem to corroborate previous findings supporting the existence of quadriceps muscular wasting in patients with COPD when compared with age-matched healthy controls [2,4]. In the group of patients with ILD-HP, muscle mass seems to be somewhat preserved. To confirm our results, future studies should include a larger sample with quantitative measures of muscular quality (e.g. echointensity) and relationship between muscle size/quality and muscle strength.