Which stimulation techniques are used in somatosensory evoked potential (SEP) testing?

Updated: Oct 25, 2019
  • Author: Andrew B Evans, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

Mixed nerve stimulation need not be supramaximal; a small twitch is sufficient. The duration of the stimulus is typically 200-300 msec, though some prefer longer stimuli. The repetition rate is usually 3 Hz, though some patients tolerate only 1-2 Hz. There is no change in SEP until the 15-Hz stimulation frequency and no need for random stimuli (thought they may be needed to trigger off the electrocardiogram [ECG]).

Cutaneous nerve stimulation is used with the trigeminal and lateral femoral cutaneous nerves; dermatomal studies may be used to study segmental innervation disturbances. Dermatomal SEPs may be technically difficult and therefore are not used routinely. Current MRI technology has largely replaced dermatomal SEP studies in suspected radiculopathies and spinal cord lesions. In expert hands, however, the latter may have value in selected cases.


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