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How to get the most out of nerve conduction studies and electromyography
  1. G Fuller
  1. Correspondence to:
 Dr Geraint Fuller
 Department of Neurology, Gloucester Royal Hospital, Great Western Road, Gloucester GL1 3NN, UK; geraintfullerg.demon.co.uk

https://doi.org/10.1136/jnnp.2005.067355

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    Why should we think hard when requesting nerve conduction studies (NCS) and electromyography (EMG)? Aside from the reasons that should determine our use of all investigations there are two particular issues that relate to these tests:

    • NCS/EMG is at best uncomfortable, at worst painful, for the patient—despite the neurophysiologist’s best efforts

    • NCS/EMG are expensive, although this cost is borne by the health care system. They take 30–60 minutes of a neurophysiologist’s time, a scarce and expensive resource.

    ELECTRODIAGNOSTIC STUDIES ARE AN EXTENSION OF CLINICAL EXAMINATION

    Very early on in just about every textbook or article on NCS/EMG the following two observations are made:

    • The tests do not replace a careful history and examination of the patient

    • NCS/EMG are an extension of the clinical assessment.

    These observations may seem implausible to those who do not perform these tests and view electrodiagnostic tests as a “black box” from which answers magically appear. However, neurophysiology is very definitely used in the same way as clinical examination to solve clinical problems, and complements the clinical evaluation rather than replacing it. In clinical examination you determine the site of the lesion by assessing the distribution of weakness, reflex changes, and sensory loss. Neurophysiologically you not only examine the distribution but also the type of abnormalities detected in the nerve conduction studies and EMG. Neurophysiology can be thought of as the clinical examination with the ability to “probe” nerves and muscles in a different manner.

    There are a few obvious parallels with clinical examination:

    • It is usually more straightforward to localise a significant weakness clinically than a milder degree of weakness where you tend to be less certain in distinguishing mild weakness from normal strength. Similarly “soft” sensory signs tend to be more difficult to localise. These same problems arise neurophysiologically—a more significant lesion is easier to localise as the neurophysiological abnormalities are more …

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