Evoked Potentials

Evoked potentials were more frequently used in the diagnosis of MS prior to the advent of MRI. The data are generated by presenting repeated stimuli and recording a wave form or EP from scalp surface electrodes. An alternating checkerboard pattern is used as a visual stimuli for visual EP, repeated auditory clicks are used for brain stem auditory EP, and repeated electrical sensory stimulation is used for tibial and somatosensory EP. As a result of repeated stimulation, the EP has a defined latency and amplitude. Based on standards established in each laboratory, a prolongation of the latency of these responses suggests that demyelination has occurred. A loss of amplitude of those responses is abnormal but not necessarily due to demyelination. These studies are nonspecific and are most helpful in confirming a suspicious clinical finding. For example, a distant history of unusual symptoms suggestive of optic neuritis may be confirmed by a prolonged visual evoked response recorded from stimulation of one eye. Confirmed clinical findings do not need to be further assessed with EPs since additional information is not gathered. Currently, EPs are not used to define prognosis or as surrogate markers of disease activity in clinical trials.



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