What is the role of somatosensory evoked potentials (SEPs) in the workup of neurologic conditions?

Updated: Oct 25, 2019
  • Author: Andrew B Evans, MD; Chief Editor: Selim R Benbadis, MD  more...
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Giant SEPs have been reported in cortical reflex myoclonus. Kofler et al described enlarged cortical responses in 14 patients with progressive supranuclear palsy (PSP), attributing this finding to cortical hyperexcitability. [72] Given that frontal lobe dementia is frequently present in patients with PSP, striatofrontal deafferentation and intracortical disinhibition may explain the increase in the size of the SEP.

Ferri et al observed large-amplitude middle latency SEPs in children with benign epilepsy of childhood with centrotemporal spikes. The mechanism of this is not known. An age-related decrease in amplitude and a lack of SEP after age 12 years were noted. The findings may be interpreted as maturational changes.

Rinsho described a 66-year-old woman with corticobasal degeneration, cortical reflex myoclonus with related cortical spike, aphasia, clumsiness, and dystonia with rigidity. The right side was affected, and median nerve stimulation elicited a giant SEP over the left scalp. He also described a 58-year-old woman with reflex myoclonus cortical myoclonic tremor and a giant cortical SEP. In a study of 2 patients with corticobasal degeneration, 1 showed a giant SEP and 1 did not.

Striano et al studied a family with cortical tremor, myoclonus, and epilepsy and found giant SEP potentials and enhanced long latency reflex I; genetic study revealed linkage on chromosome 2p. [73]

Valeriani studied cortical myoclonus and concluded that the initial giant SEP corresponded to physiologic potentials evoked in healthy subjects, whereas the late giant SEP could be explained by the hyperpolarization that follows the postsynaptic excitation of the early components.

Tsuda et al described Lafora body myoclonus with giant SEP; positron-emission tomography revealed no increase in glucose metabolism in the somatosensory cortex. [74]

Ugawa reported that the dipole responsible for the giant SEP is localized in the sensory cortex. Some patients showed the localization for the dipole in the superior frontal gyrus in the paracentral lobule.

In a study by Schmitt et al, increased amplitude of SEP was noted in all cases of ceroid lipofuscinosis.

Myoclonus and giant SEP have been described in herpes simplex encephalitis. Triggs described giant SEP with anterior spinal artery syndrome. The hypothesis has been advanced that this is due to lack of inhibition of the anterolateral inhibitory influences on the dorsal column medial lemniscal system.

Saitoh described giant SEP in the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (ie, MELAS syndrome). Lu reported dyssynergia cerebellaris myoclonica in 3 brothers in whom alcohol decreased both the myoclonus and the giant SEP amplitude.

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