WS7.12. The role of quantitative muscle ultrasound in disease

Abstract

Quantitative Muscle Ultrasound (QMUS) is a valid and reliable diagnostic imaging technique for the evaluation of nerves and muscles. Muscle ultrasound is currently used for both diagnostic screening and biomarker follow up purposes. A recent systematic review based on publications from 2000 to 2014 confirmed the utility and acceptability of US for the diagnosis of pediatric skeletal muscle disorders, with high sensitivity and specificity of around 90–95%. In comparison to electromyography (EMG), muscle US is better tolerated. In addition, the distribution of US abnormalities as well as the pattern of muscle involvement can aid in the diagnosis of NMD. In QMUS both echogenicity and muscle diameter are routinely quantified. Echogenicity increase is the most robust and reproducible measure of muscle pathology, while muscle atrophy alone has a low diagnostic accuracy for detecting neuromuscular disease and discrimination between neurogenic disorders and myopathies. However, a combined cut-off based on echogenicity and muscle thickness can detect neurogenic disorders with a sensitivity of 67%, a specificity of 94%, a PPV of 86%, and a NPV of 84% QMUS is routinely supplemented with dynamic screening of muscle movements, and ultrasound is better at detecting fasciculations than using needle EMG screening or clinical examination. The combination of US and EMG increased the diagnostic category of probable or definite ALS from 48% to 79%. In ALS patients who had fasciculations, a score using the US results of 9 muscles can discriminate between ALS and ALS-mimics with 92% sensitivity and 100% specificity. In practice the author advocates the use of muscle US as a first line screening tool when a neuromuscular disorder is suspected. Muscle ultrasound is not a replacement to the electrodiagnostic examination. As EMG is a measurement of function, and ultrasound is concerned with structure, the use of both techniques is complementary, similar to EEG and MRI or CT. Like the electrodiagnostic exam, neuromuscular ultrasound yields the best information when it is informed by the history, examination, and by an examiner with knowledge of the patterns of neuromuscular disease. When used together, ultrasound and EMG provide a more satisfactory and complete evaluation than either alone.