Excerpt from Clinical Utility of Evoked Potentials
Synonyms, Key Words, and Related Terms: VEP, VER, BAER, BAEP, SEP, SLSEP, visual evoked responses, short-latency somatosensory evoked responses, short-latency brainstem auditory evoked responses
Evoked responses measure the electrophysiological responses of the nervous system to a variety of stimuli. Almost any sensory modality can be tested in theory; in clinical practice, however, only a few are used on a routine basis. The ones most often encountered are the visual evoked responses (VEP, both flash and checkerboard types), short-latency somatosensory evoked responses (SSEP), and short-latency brainstem auditory evoked responses (BAER, BAEP). Late-evoked responses are used for studying higher cortical functions, such as P300 in Alzheimer disease. The clinical usefulness of the late-evoked responses is limited by the experimental paradigm and they are not used routinely or widely in general clinical neurology. Nevertheless, the late responses show promise and may gain more inroads in clinical use in the near future. Some centers have developed testing paradigms for olfactory and taste-evoked responses as well. The clinical use of evoked potentials (EPs) has changed over time. Progressive advances in imaging technology have limited the frequency of evoked-response studies in clinical practice. Current use of MRI technology is mostly responsible for this. The basic difference that persists is that the MRI largely remains an imaging, structural, or anatomical test, while the EP explains the functionality of certain pathways of the nervous system. The MRI scan gives more accurate information about structural problems, while the EP gives us information about the physiology of a certain anatomical pathway with much less spatial or localizing information. Under given circumstances they may be complementary. However, most clinical questions are answered better by MRI of the pertinent neurological structures. Recently, SSEP has shown promise in predicting outcome in postanoxic coma. Types of EPs in every day clinical use include (1) VEP, usually pattern-shift checkerboard visual evoked responses, (2) SSEP, short latency, somatosensory evoked responses, and (3) BAEP, short latency brain stem evoked responses.
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