Pectoral muscle area derived from chest computed tomography to identify quadriceps muscle weakness in COPD.

Background: In patients with COPD, reduced quadriceps strength is associated with poor prognosis. Measuring quadriceps strength requires specific equipment and expertise, which limits its dissemination. Chest computed tomography (CT) scans are routinely performed in COPD patients. It was hypothesised that pectoral muscle area (PMA) derived from chest CT scans was related to quadriceps strength, and that low quadriceps strength could be derived from PMA in stable COPD patients. Methods: In a retrospective cross-sectional study, thoracic CT scans and quadriceps strength were obtained simultaneously. The highest quadriceps strength value of the dominant leg was recorded (in kg). The PMA (sum of right and left measurements, in cm2) was obtained from a single axial inspiratory CT slice at the aortic arch. Results: A total of 82 outpatients with stable COPD of varying levels of severity were analysed. The unadjusted r2 between PMA and quadriceps strength was 0.32. A formula for estimating quadriceps strength from PMA was established: estimated quadriceps strength=25.2+0.41×PMA (cm2)-0.29×age (years)+6.35 (if male) (r2=0.43). The area under the receiver operating characteristic curve for identifying low quadriceps strength (lowest tercile of the studied population) using PMA was 0.76 (95% CI 0.65-0.87), with a PMA threshold of 28.5 cm2. Conclusions: PMA is a reliable surrogate for quadriceps strength assessment in routine COPD management. This easily accessible imaging biomarker could be used to identify COPD patients with low quadriceps strength, not only for prognostic purposes but also to enable them to benefit from interventions aimed at improving muscle weakness.