Somatosensory Evoked Potentials in Man: Cerebral, Subcortical, Spinal, and Peripheral Nerve Potentials

Somatosensory and brainstem auditory evoked potentials in the Gunn rat model of acute bilirubin neurotoxicity

Brainstem auditory evoked potentials (BAEPs) are a sensitive indicator of bilirubin neurotoxicity. Somatosensory evoked potentials (SEPs) have been proposed as another measure of toxicity, though the lemniscal pathways that generate the SEP are not involved in kernicterus. In 16 to 17-d-old jaundiced (jj) Gunn rats, serial BAEPs and SEPs were obtained up to 8 h after acute bilirubin toxicity. jjs were injected with 150 mg/kg sulfadimethoxine to displace bilirubin into brain tissue (n = 8); littermate controls were jjs given saline (n = 4) and nonjaundiced given sulfadimethoxine or saline (n = 7). After anesthesia, BAEP and SEP recordings were obtained at baseline and serially after injection. SEPs to median nerve stimulation were recorded from surface electrodes over the brachial plexus (Erb's) and contralateral parietal cortex, and subtracted to obtain central conduction time (CCT). There were no statistically significant different baseline values between groups. Baseline BAEP I, I-II, and I-III were 1.22 +/- 0.13, 1.11 +/- 0.12, and 2.10 +/- 0.15 ms, and SEP Erb's and CCT were 1.48 +/- 0.20 and 5.59 +/- 0.50 ms, respectively (n = 19). At 6.8 +/- 1.5 h after injection BAEP I, I-II, and I-III increased 0.10 +/- 0.08, 0.18 +/- 0.17, and 0.56 +/- 0.33 ms over baseline, respectively (p = 0.005, 0.01, and 0.001, respectively, paired, 1-tailed t-tests), in experimental but not control groups. SEP Erb's decreased slightly, -0.06 +/- 0.04 ms in experimental and -0.08 +/- 0.08 ms in control groups, while CCT did not change significantly. BAEPs were completely abolished in two jjs with no SEP changes. When injection of sulfonamide induced significant peripheral and central BAEP abnormalities in jaundiced rats, no SEP abnormalities occurred. SEPs assess proprioception but not other somatosensory function or sensory integration. The results demonstrate the selectivity of acute bilirubin toxicity for the auditory nervous system.

Clinical effectiveness of dermatomal evoked cerebrally recorded somatosensory responses

Among 129 patients with spine pain and radiculopathy in both the cervical and lumbar region, there were significant differences between the upper and lower extremity DSER groups, noting the higher number of normal studies by our criteria in the upper extremities as compared to the lower extremities. This difference may be due to the intertwining of the "nerve circuitry" of the input pathways. It appears that the dermatomal somatosensory evoked response is a study of low sensitivity and of high specificity.

The clinical role of somatosensory evoked potential studies: a critical appraisal

The clinical utility and limitations of somatosensory evoked potential (SEP) studies are reviewed. Somatosensory evoked potentials may help to identify a lesion in the sensory pathways, but do not indicate its nature. In multiple sclerosis subjects, the SEP findings may help to establish that there is a multiplicity of lesions, but multimodality evoked potential abnormalities may occur in other disorders. Somatosensory evoked potential abnormalities do not reflect either the severity or the prognosis of cervical spondylosis and do not reliably permit early recognition of the totality of traumatic cord lesions, while the role of SEPs in monitoring cord function intraoperatively awaits definition. Somatosensory evoked potentials do not reliably indicate the individual prognosis after severe head injury, and discrepancies in published findings suggest that their use in the evaluation of brain death is premature. In hereditary spinocerebellar degenerations, SEP abnormalities may reflect central or peripheral pathology. Somatosensory evoked potentials can be used to determine conduction velocity in peripheral nerves and to identify inaccessible proximal lesions of these nerves, but the findings may lead to misleading conclusions about brachial plexus lesions, especially if pre- and postganglionic lesions coexist.

Dermatomally stimulated somatosensory cerebral evoked potentials in the clinical diagnosis of lumbar disc disease

Somatosensory evoked response--dermatomal (SER-D) is a new, apparently accurate method of diagnosis of lumbar nerve root compression. It is noninvasive and may be of subsequent value in choosing patients who are to be subjected to myelography in the future.

Lumbar spinal cord and early cortical evoked potentials after tibial nerve stimulation: effects of stature on normative data

Short-latency somatosensory evoked responses to tibial nerve stimulation were recorded simultaneously over the spinous processes of the lumbar vertebrae and scalp in normal young subjects. This non-invasive test revealed values which are highly reproducible and could be closely correlated with subject-related variables such as height and leg length. A nomogram describing the close relationship between absolute latency of various response components and stature was derived and shown to be an important variable in the establishment of normative data nad interpretation of SSEP in relation to disorders affecting the peripheral and central nervous system. In contrast, central conduction times of interpeak intervals (N22-P37 and N22-N45) were unrelated to variations in the subjects, stature providing a reliable clinical measure in the assessment of the central somatosensory pathway.

Somatosensory evoked potentials: variability analysis in unilateral hemispheric disease

A new method to study SEP using signal-to-noise estimate was applied to 35 patients (age 3 days-81 years, mean 12.1 years) with unilateral supratentorial cerebral lesions. The patients were grouped according to severity of deficits: minimal, mild, moderate and severe. Based on the observation that the SEPs were much more variable over the diseased hemisphere, we proposed the following hypothesis: normal neurons when stimulated generate a series of wave forms which are stable and reproducible. These are seen as stable and 'clean' scalp EPs. Diseased neurons on the other hand are malfunctioning and may tend to depolarize erratically. This can be seen as variable, 'noisy' and poorly reproducible EPs. To test this hypothesis, we measured the degree of variability of the SEPs on both the normal and affected sides, using the technique of Wong and Bickford (1980). Overall, 30 of the 36 SEPs (83%) had a greater variability on the diseased side. The prediction accuracy was greatest with the severely affected cases and least in the minimally affected cases. There are minor suggestions that the variability parameter may be useful for long-term follow-up. Clearly, if used with care, the amount of 'noise' in an EP can be a useful parameter.

Somatosensory evoked response: application in neurology

One technique used for short-latency somatosensory evoked response (SER) is described. SER following nerve stimulation is a unique non-invasive, clinical test used to evaluate the somatosensory pathways. It tests the physiological function of the median nerve, the brachial plexus, the C6-7 cervical roots, cervical spinal cord, the cuneate nuclei, the medial lemniscus, the thalamus, and the contralateral sensory cortex. It has been shown to be a reliable and useful clinical test particularly in multiple sclerosis and comatose patients. The promising technique of SER following peroneal nerve stimulation is mentioned.