Contribution of Diaphragmatic Ultrasound for Monitoring Diaphragmatic Function in Patients With Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neuromuscular disease that occurs in adults. It is characterized by a progressive degeneration of the first and second motor neurons leading to muscle failure. In its spinal form, ALS manifests by a progressive worsening of limb involvement, whereas the bulbar form presents with swallowing disorders, dysarthria and feeding difficulties. Respiratory impairment is the most serious feature of ALS. Phrenic nerve damage causes diaphragmatic weakness, which inevitably leads to chronic restrictive respiratory failure. At the stage of symptomatic nocturnal or diurnal alveolar hypoventilation, non-invasive ventilation (NIV) prolongs survival while improving quality of life by relieving respiratory symptoms. The indication for the initiation of NIV is based on the appearance of respiratory symptoms but also on the demonstration of diaphragmatic insufficiency. A quarterly follow-up of diaphragmatic function has been recommended by the French Health Authority since 2006. It is based on functional respiratory explorations (VC in sitting and lying position, measurement of maximal inspiratory pressure) and screening for diurnal or nocturnal hypoventilation with the measurement of PaCO2 or the nocturnal recording of SpO2. Access to these examinations remains limited and they are sometimes complex to perform (in particular issues with mouth occlusion during respiratory manoeuvres in case of bulbar damage). Thus, only 60% of patients undergo a complete evaluation. Moreover, these explorations are only late markers of diaphragmatic dysfunction, and it has recently been shown that they do not correlate with histological diaphragmatic amyotrophy. The development of new, reliable, and easily available tools for the evaluation of diaphragmatic function, and that are capable of detecting diaphragmatic insufficiency early in the course of the disease, are therefore necessary. Such tools would make it easier to implement NIV at the optimal ti