What characteristics of somatosensory evoked potentials (SEPs) are measured?

Updated: Feb 26, 2019
  • Author: Sombat Muengtaweepongsa, MD, MSc; Chief Editor: Selim R Benbadis, MD  more...
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Several characteristics of SEPs can be measured, including peak latencies, component amplitudes, and waveform morphology. Peak latencies are consistent across subjects, whereas amplitudes show large intersubject variability. Therefore, interpretation of extraoperative diagnostic SEP studies is predominantly based on peak latencies and measures derived from them, such as interpeak intervals and right-left differences. Component amplitudes are more consistent during repeated SEP recordings in the same subject and may change sooner than latencies change, or in the absence of any latency changes, if the somatosensory pathways are damaged during surgery. Therefore, both peak latencies and component amplitudes should be measured and followed during intraoperative monitoring. [3]

Absolute SEP latencies vary with limb length. Interpeak intervals are useful because they separate out effects of limb length and of peripheral nerve disease, which may prolong absolute SEP latencies in the absence of central nervous system pathology. Aging is associated with some prolongation of SEP latencies. Latencies are considered abnormal when they are more than either 2.5 or 3 standard deviations above the mean of the normative data (depending on the laboratory's conventions).

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