Respiratory muscle imaging by ultrasound and MRI in neuromuscular disorders

Respiratory muscle weakness is common in neuromuscular disorders (NMDs) and leads to significant respiratory difficulties. Therefore, reliable and easy assessment of respiratory muscle structure and function in NMDs is crucial. In the last decade, ultrasound and magnetic resonance imaging (MRI) have emerged as promising imaging techniques to assess respiratory muscle structure and function. Respiratory muscle imaging directly measures the respiratory muscles and, in contrast to pulmonary function testing, is independent of patient effort. This makes respiratory muscle imaging suitable to use as a tool in clinical respiratory management and as an outcome parameter in upcoming drug trials for NMDs, particularly in children. In this narrative review, we discuss the latest studies and technological developments in imaging of the respiratory muscles by ultrasound and MRI, and its clinical application and limitations. We aim to increase understanding of respiratory muscle imaging and facilitate its use as an outcome measure in daily practice and clinical trials.