The scope of NCS

Broadly speaking, NCS are used to investigate diffuse processes such as polyneuropathies and motor neuron disease, multi-focal processes such as mononeuritis multiplex and focal neuropathies such as carpal tunnel syndrome. They are highly sensitive in detecting peripheral nervous system disease, allow the precise anatomical localisation of the lesion and are central to the classification of the underlying pathophysiology.

As with any other functional test, the specificity is relatively poor. Although some specific patterns do exist, in general one ‘dying back’ neuropathy, for example, looks pretty like another, irrespective of the aetiology. So, while NCS can narrow down the underlying pathophysiology (eg, axonal vs demyelinating), and give an idea of the severity of the process, they are an adjunct to other more specific tests to determine the final diagnosis. Similarly, since they give a snapshot of peripheral nerve function, a single study gives little or no information as to whether the process is static or progressive. For this information, repeated studies over time may be needed.

General considerations

NCS use electrical stimulation …