Ultrasound in Neuromuscular Disorders

Electrodiagnosis with nerve conduction studies and needle electromyography has been the standard method of diagnosis of neuromuscular conditions for over 80 years. Although ultrasound technology has been in existence for approximately the same time, application of this technology to assessment of the neuromuscular system only began in the 1980s. In the past 2 decades-mainly because of advances in resolution enabled by high frequency transducers and improved image processing-ultrasound has enabled the real-time, morphologic evaluation of focal and diffuse neuropathies, motor neuron diseases, and myopathies. Although methods of nerve and muscle assessment continue to evolve (i.e., Doppler imaging to evaluate intraneural and intramuscular blood flow), nerves have most commonly been evaluated based on their cross-sectional area, which seems to correlate with nerve swelling and pathology, particularly in focal and also in some diffuse neuropathies. Qualitative and more recently quantitative measures of muscle echogenicity have been used in the assessment of myopathies and motor neuron diseases. Collection of normal values in heterogeneous populations, extremes of age and patients with differing anthropometric profiles, has helped develop tables of normal values, thereby allowed ultrasound measurements to be judged against a reference standard, as has previously been established for nerve conduction studies.