Utility of Rectus Abdominis Ultrasound as a Respiratory Function Test for Amyotrophic Lateral Sclerosis

BACKGROUND: Amyotrophic lateral sclerosis (ALS) causes deterioration of respiratory function. Muscle weakness of the orbicularis oris interferes with the accurate assessment of respiratory function using spirometry. Reduced forced vital capacity (FVC) is an indicator that helps determine the appropriate timing to provide noninvasive ventilation (NIV) for the survival of ALS patients. We employed ultrasonography to evaluate changes in respiratory function by measuring the thickness of the rectus abdominis (RA) muscle as a possible alternative to spirometry.

METHODS: Sixteen subjects with ALS were included in this study. The thickness of RA muscles was measured using ultrasonography, and respiratory fluctuations, such as vital capacity (VC), FVC, FEV₁, percentage of predicted VC (%VC), percentage of predicted FVC (%FVC), percentage of predicted FEV₁ (%FEV₁), and FEV₁/FVC, were evaluated using spirometry.

RESULTS: Sixteen subjects underwent assessment by ultrasonography. A positive correlation was observed between the percent change in RA muscle thickness evaluated from maximal expiration to maximal inspiration and %VC (P = .001), %FVC (P = .001), FEV₁ (P = .009), and %FEV₁ (P = .02).

CONCLUSIONS: RA ultrasonography was useful for predicting a reduction in VC in subjects with ALS and may help determine the best timing for introducing NIV.