Somatosensory evoked potentials (cutaneous nerve stimulation) and electromyography in lumbosacral radiculopathy.

In order to evaluate the usefulness of SEP with cutaneous nerve stimulation in lumbosacral radiculopathy, we investigated 19 patients by EMG including H-reflex and SEP. All patients had radiculopathy proven by myelography and/or CT scan and, if indicated, operative treatment. The findings by EMG and SEP were compared with operative and radiological findings. In this preliminary study, SEP was as sensitive as EMG in detecting lumbosacral radiculopathy. Further investigation seems justified.     

Somatosensory evoked potentials following stimulation of the trigeminal nerve in man

Summary Somatosensory evoked potentials following trigeminal nerve stimulation can regularly be recorded from the contralateral scalp on C5/C6 (10–20 system), a region which overlies the primary face region of the somatosensory cortex. From the first three peaks analyzed (N 13, P 19 and N26), the first positive peak (P 19) is most prominent and reliable and therefore is recommended for the routine measurements of neurophysiological examination.

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Zusammenfassung Nach der Stimulation des N. trigeminus am Mund lassen sich regelmäßig sensible evozierte Potentiale über dem kontralateralen somatosensorischen Cortex ableiten. Innerhalb der ersten 50 msec nach Reizbeginn treten typischerweise zwei negative und zwei positive Potentialschwankungen mit sehr variabler Amplitude auf. Aufgrund der an 55 Normalpersonen ermittelten mittleren Latenzzeiten kann der erste negative Gipfel als N 13, der erste positive Gipfel als P 19 und der zweite negative Gipfel als N 26 definiert werden. N 13 und P 19 zeigen eine Altersabhängigkeit mit leichter Latenzzunahme in der höheren Altersgruppe. P 19 ist wegen seiner konstanten Ausprägung für die klinische Diagnostik besonders geeignet.

     

Somatosensory evoked potentials,sensory nerve potentials and sensory nerve conduction in hereditary motor and sensory neuropathy type I

Summary Thirty-nine patients from six families with hereditary motor and sensory neuropathy type I and control subjects were included in this study. A neurological deficit score (NDS) was derived from a neurological examination and compared with neurophysiological test findings. Further, sensory nerve conduction velocities (SNCV) were compared with the motor nerve conduction velocities (MNCV). Five patients whom peaks of N11/N13 complex and N20 of the median nerve sensory evoked potential (SEP) could be recorded showed normal interpeak latency. The interpeak separation P14 N20 measured in six patients was normal. These findings point to the normal function of the central conductive pathways. Erb and cervical potentials of the median nerve SEP could be recorded in 10% and 12% of the patients, respectively. In contrast, about half of the patients showed a scalp N20, while in most of them no SNCV could be measured. In six patients far-field potential P14 of the median nerve SEP was the first detectable potential. Therefore, we argue in view of the anatomical structure of the thalamus, that the first generator for synchronizing and amplification of impulses is probably located in the thalamus. A third of the patients had a cortical sural nerve SEP, while no sural nerve potentials could be recorded. No association was found between the SEP findings and the NDS. There was an inverse correlation between median SNCV and the NDS, but no relationship between the former and sensory deficit alone. In 40% of the patients median SNCV and in 13% sural SNCV could be recorded and considered to be severely decreased. In contrast, the majority of the patients had mild to moderate sensory deficit. Furthermore, patients with measurable SNCVs had higher MNCVs and lower NDS than patients without measurable SNCVs.     

Somatosensory evoked potentials in the evaluation of lumbosacral radiculopathy.

We performed lower extremity somatosensory evoked potential (SEP) studies in 59 patients with signs or symptoms suggestive of lumbosacral radiculopathy and compared them with results of myelography with post-myelogram CT (myelogram/CT), MRI, and other electrodiagnostic studies. Of 38 patients with abnormal myelogram/CTs, 32 had abnormal SEPs, while 11 demonstrated EMG abnormalities. All 21 patients with normal myelogram/CTs had normal SEPs. SEP improved electrodiagnostic sensitivity in patients with weakness or reflex changes as well as in those with sensory deficits only. SEP was less sensitive in patients in whom spinal stenosis was the only radiographic finding. MRI generally corresponded well with the results of myelogram/CT and SEP but overestimated the significance of disk bulges in some patients. SEP is useful in the electrodiagnostic evaluation of lumbosacral radiculopathy, particularly when EMG is nondiagnostic.     

Somatosensory evoked potentials to posterior tibial nerve stimulation in children

The somatosensory evoked potentials (SEPs) to stimulation of the tibial nerve were studied in 88 children ranging in age from 1 day to 16 years. SEPs were not evidenced in 10 out of 44 infants less than 1 year old. In others it was a major positive wave (P) with a variable topographic distribution on the midline. The onset and peak latencies of this P were highly variable in different subjects of the same age or body-size, and in the same subject with the active electrode placed in different locations. The lowest values for latency were in subjects about 3 years old. The ascending time of P was the only parameter strictly correlated with age. The results are compared with SEPs to upper limb stimulation, which are constant and more reliable. These results indicate: that the maturation of the peripheral somatosensory pathway proceeds at a faster rate than that of the central somatosensory pathway; that the maturation of the somatosensory pathway of the upper limb precedes that of the lower limb; and that the ascending time of P is a good index of thalamo-cortical maturation. The clinical utility of these SEPs in pediatrics is discussed.     

Spinal somatosensory evoked potentials following segmental sensory stimulation. A direct measure of dorsal root function

Dorsal root function cannot presently be measured directly. The H-reflex is an indirect measure of dorsal root function but only for the S1 root. Spinal somatosensory evoked potentials (SEPs) following dermatomal stimulation of the legs have the potential of providing direct data reflecting dorsal root function but have not been reliably recorded in normal subjects. We have developed a reliable technique for recording SEPs at the lumbar root entry zone following segmental sensory stimulation of the legs. The saphenous, superficial peroneal, and sural nerves were stimulated representing the L3/L4, L5 and S1 roots respectively. Reproducible responses (N-wave) were recorded over the lumbar spine in all 60 normal limbs examined. The N-wave peak latency was significantly correlated with lower limb length. The conduction velocities from the stimulation sites to the lumbar spine were similar to published values for peripheral conduction velocities in these nerves. The mean inter-limb latency differences for the N-wave peak were: L3/L4 0.61 msec; L5 0.35 msec; and S1 0.57 msec. The mean N-wave amplitudes were: L3/L4 0.11 microV; L5 0.28 microV; and S1 0.23 microV. This technique is a direct measure of dorsal root integrity. Unlike scalp recorded SEPs, the lumbar N-wave is not state-dependent and is unaffected by lesions within the brain and rostral cord.     

Somatosensory evoked potentials after median and tibial nerve stimulation in healthy newborns.

Cortical and spinal somatosensory evoked potentials (SEPs) have been recorded after median and tibial nerve stimulation in healthy newborns. Spinal SEPs were readily obtained and recorded in all but one neonates after stimulation of both nerves. Cortical SEPs were more frequently recorded after median nerve (87%) than after tibial nerve stimulation (73%) but the shape of cortical SEPs obtained after tibial nerve stimulation was less variable. The mean feature of cortical SEPs was a negative wave (N27) for median nerve and a positive wave (P32) for tibial nerve. The present results demonstrate the feasibility of obtaining in the same baby, spinal and cortical SEPs after stimulation of median and tibial nerve, giving information on the functional integrity of central and peripheral somatosensory pathways which supply upper and lower limbs.     

Somatosensory evoked potentials elicited by dorsal penile and posterior tibial nerve stimulation

SEPs were elicited by stimulation of the dorsal penile nerve (DPN) or posterior tibial nerve (PTN) under 3 conditions of stimulation: random and constant interstimulus intervals, and subject-initiated stimulation. Within these conditions, the effects of repeated stimulation were also examined. The latency of the N90 peak decreased with repeated stimulation. N90 amplitude decreased with increased foreknowledge as well as with repeated stimulation. Factors extracted by principal components analysis revealed similar effects. A difference between DPN and PTN stimulation was seen in a factor associated with the N90 peak, wherein the condition involving subject self-initiation of the stimulus reflected a significantly greater decrease in SEP amplitude when the DPN was stimulated. Morphological commonalities were observed in the SEPs elicited by DPN and PTN for a given subject.     

Somatosensory evoked potentials after posterior tibial nerve stimulation in focal spinal cord diseases.

We investigated the somatosensory evoked potentials (SEPs) produced by posterior tibial nerve (PTN) stimulation in 8 infants and children with focal spinal cord disorders. The spinal responses of the PTN-SEPs were considered to assist in the localization of spinal lesions because their abnormalities were consistent with the neurologic and/or radiologic findings in all 6 examinations that revealed abnormal spinal SEPs. The cortical responses correlated significantly with proprioception in the lower limbs because proprioception was only disturbed when the cortical SEPs were absent (3 examinations). When both the spinal and cortical responses were abnormal, the spinal lesion probably involved the dorsal column so extensively that it completely interrupted the afferent impulses. In contrast, when SEP studies demonstrated abnormal spinal and normal cortical SEPs (3 examinations), the dorsal column involvement was probably less severe; therefore, both the spinal and cortical responses provided useful information regarding afferent conduction in the dorsal column. PTN-SEPs appear to have the potential to be of value in the diagnosis of focal spinal disease, especially in infants and young children who cannot cooperate with detailed neurologic examinations.     

Somatosensory evoked potentials in patients with cervical spondylotic myelopathy

Somatosensory evoked potentials (SEPs) to posterior tibial nerve (PTN) and median nerve (MN) stimulations were recorded in 30 patients with cervical spondylotic myelopathy. Measurements performed include N20-P2 interpeak latency (IPL) for PTN-SEPs, EP-N13 IPL and EP-N20 IPL for MN-SEPs. Limits of normal IPL were defined by the mean + 3S.D. of the normal control group. PTN-SEPs was more sensitive (with 73.3% abnormal) than MN-SEPs (with 33.3% abnormal) and strongly correlated with the clinical signs of posterior column, but not with those of anterolateral column indicated by superficial sensory disturbances and spasticity of lower limbs. Severities of cord compression (sagital diameter/transverse diameter ratio) calculated from the picture of metrizamide CT were not correlated with SEPs findings and clinical signs. In patients with cervical myelopathy, SEPs, especially PTN-SEPs, were thought to be very useful examination.     

Somatosensory evoked potentials from cervical and lumbosacral dermatomes

A method for recording the somatosensory evoked potentials after stimulation of the cervical and lumbosacral dermatomes is described. Normative values and their ranges are given for each dermatome including left-right differences. A significant correlation was found between latencies and conduction distance. Dermatomal SEPs may play a role in diagnosing cervical and lumbosacral radiculopathies.     

Somatosensory and spinal evoked potentials in patients with upper cervical neurinoma.

Scalp somatosensory evoked potentials (SEPs) and spinal evoked potentials (SpEP) were simultaneously recorded from the exposed surface of the upper cervical cord after median nerve stimulation in five patients undergoing surgery for upper cervical neurinomas. Two of the neurinomas were localized at C1 nerve root, two at C2, and one at C3. All patients showed good postsurgical recovery, suggesting that the tumors had not progressed to the stage where most of the nerve fibers were irreparably damaged. In patients with unaffected superficial and deep skin sensation, both SEP and SpEP were normal. In patients with more advanced tumor, the superficial sensation was abnormal but the deep skin sensation was intact. In these patients, the action potential propagation slowed down but continued partially through the tumor site on the relatively less affected side contralateral to the tumor; however, it stopped at the site of the tumor on the ipsilateral side. It is possible that full functional recovery becomes more difficult during the next stage of tumor development when the propagation of action potentials ceases bilaterally. The intraoperative monitoring of both SEP and SpEP thus appears useful for inferring details of functional integrity and prognosis of the spinal cord near a space-occupying tumor during the critical first two stages of neoplasm in which the spinal function is normal, or a sufficiently large fraction of ascending and descending nerve fibers are functionally suppressed, but are capable of recovery after a surgical intervention.     

Somatosensory evoked potentials following stimulation of the lower limb in cortical reflex myoclonus.

Generating mechanisms of giant somatosensory evoked potentials (SEPs) following stimulation of the posterior tibial nerve as well as the big toe were investigated in three patients with cortical reflex myoclonus. Scalp distributions of recognisable components were very similar to those in normal subjects, except that their amplitude was much larger. The tibial nerve SEPs were remarkably attenuated by interfering tactile stimulation. Therefore, the giant SEPs observed in the present cases seem to be, at least partially, due to input from cutaneous nerve fibres on the background of extremely enhanced excitability in area 3b of the primary sensory cortex where normal SEPs are generated.     

Somatosensory evoked potentials after multisegmental upper limb stimulation in diagnosis of cervical spondylotic myelopathy.

Radial, median, and ulnar nerve somatosensory evoked potentials (SEPs) were recorded, with non-cephalic reference montage, in 38 patients with clinical signs of cervical myelopathy and MRI evidence of spondylotic compression of the cervical cord. Upper limb SEPs are useful in spondylotic myelopathy because SEPs were abnormal in all patients for at least one of the stimulated nerves and SEP abnormalities were bilateral in all patients but one. Reduction of the amplitude of the N13 potential indicating a segmental dysfunction of the cervical cord was the most frequent abnormality; it occurred in 93.4%, 84.2%, and 64.5% of radial, median, and ulnar nerve SEPs respectively. A second finding was that the P14 far-field potential was more sensitive than the cortical N20 potential to slowing of conduction in the dorsal column fibres. The high percentage of N13 abnormalities in the radial and median rather than in the ulnar nerve SEPs correlated well with the radiological compression level, mainly involving the C5-C6 vertebral segments. Therefore the recording of the N13 response is a reliable diagnostic tool in patients with cervical spondylotic myelopathy and P14 abnormalities, though less frequent, can be useful in assessing subclinical dorsal column dysfunction.     

Somatosensory evoked potentials in pure sensory stroke and related conditions

Somatosensory evoked potentials were reviewed for their correlation with CT scan and clinical features of ischemic "pure sensory stroke" and "pure sensorimotor stroke". Somatosensory evoked potentials were normal in all 11 cases of pure sensory stroke, and CT was normal in ten. The N2-P2 components of the somatosensory evoked potentials were abnormal in all 4 cases of pure sensorimotor stroke, and all had low density CT lesions in the lateral thalamus and/or posterior limb of the internal capsule. It is concluded that somatosensory evoked potentials and CT scans are routinely abnormal in pure sensorimotor stroke, but they are consistently normal in pure sensory stroke, and should not be interpreted as evidence against a clinical diagnosis of pure sensory stroke.