Electrodiagnostic studies are often at the centre of diagnostic strategies in neuromuscular disorders. The basic electrophysiological techniques commonly used are focused on documenting sufficient proof of dysfunction emanating from different parts of the peripheral nervous system: peripheral motor neuron, nerve root, plexus and peripheral nerve, neuromuscular junction, and skeletal muscle. In short, dedicated nerve conduction studies and needle myography or a combination of these may be needed to help accurately identify the site and nature of the neuromuscular disorder (Fig. 4.1A–C). Appropriate and standardized instrumentation, including control of temperature and uniform sampling, is essential for meaningful interpretation. The electrodiagnostic techniques aligned with the main anatomical correlates underlying different neuromuscular disorders are discussed in this chapter.

A 50-year-old man was initially seen by a rheumatologist because he had crooked fingers on the left hand and painful cramps. No rheumatological abnormalities were found. In the next three years, he developed severe atrophy and weakness of the left hand, and could not hold a glass of water. There were no sensory complaints. His GP considered motor neuron disease.

A similar diagrammatic approach shows how demyelination affecting nerves of different diameters will produce various combinations of potentials that are delayed, small or polyphasic. In extreme pathology conduction will be blocked. Clinical examples relating to sensory and motor studies are included. By contrast with the findings in degeneration, the location of demyelination may often be easily achieved by the demonstration of abnormal conduction over the segment between the stimulating and recording electrodes. This is also explained diagrammatically and clinical examples are included. The value of limiting the distance between stimulating and recording electrodes when trying to localise a mild lesion is illustrated by examples of palm to wrist studies in carpal tunnel syndrome.