16 - Clinical–Electrophysiologic Correlations: Overview and Common Patterns

Abstract

Recognizing the combined pattern of abnormalities on nerve conduction studies (NCSs) (motor, sensory, late responses, and repetitive nerve stimulation) and needle electromyography (EMG) (spontaneous activity, motor unit potential morphology, recruitment, and activation) is the first step toward achieving an electrophysiologic diagnosis. The pattern of abnormalities usually can mark the underlying pathology as neuropathic, myopathic, or secondary to a neuromuscular junction (NMJ) disorder. In neuropathic lesions, the underlying primary nerve pathophysiology—axonal loss or demyelination—usually can be determined. In addition, it is usually possible to assess the temporal course (hyperacute, acute, subacute, or chronic) and severity of the underlying disorder. Localization of the disorder is then determined from the distribution of abnormalities. In the interpretation of a study, no single piece of information leads to a diagnosis. The following important patterns on NCSs and needle EMG are key to recognize: axonal loss (hyperacute, acute, subacute, chronic); demyelination—generalized or at distal, intermediate, and proximal sites (slowing alone, conduction block alone, or a combination); myopathy (acute, chronic, associated with denervating features, and/or associated with myotonic features); NMJ disorder (presynaptic, postsynaptic); and central nervous system lesion. Once these individual patterns are recognized, the distribution of all findings can be put together to recognize important clinical syndromes. Among these are mononeuropathy (non-localizing and localizing); polyneuropathy (axonal loss, demyelinating [acquired vs. inherited], symmetric vs. asymmetric); plexopathy; radiculopathy (single root or multiple roots); motor neuron disorder; NMJ disorder (pre- and post-synaptic); myopathy (proximal, distal, generalized, with or without denervating or myotonic features); and central nervous system disorder.