Somatosensory evoked potentials in patients with thalamic lesions

Summary Somatosensory evoked potentials (SEPs) were recorded in 20 patients with thalamic lesions confirmed by CT (10 with infarction, 10 with haemorrhage). The changes in SEP configuration are discussed in their relationship to clinical symptoms. Four types of SEP abnormality produced by thalamic lesion are distinguished: (1) FF type, (2) N20/P23 dissociation type, (3) N18/N20 false shift type, and (4) reduced early component type. It was shown that clinically similar lesions might produce different SEP patterns.     

Somatosensory evoked potentials in patients with hypocalcaemia after parathyroidectomy

Summary The effects of hypocalcaemia on somatosensory evoked potentials (SEPs) were studied in five patients after parathyroidectomy. Despite normal latencies the mean value of amplitudes of the SEPs in hypocalcaemic patients was greater than that in normocalcaemic subjects. Recovery functions of the SEPs showed a significant decrease in hypocalcaemic patients at interstimulus intervals of about 10 ms compared with those in normocalcaemic patients and in normal volunteers. Recovery functions appear to be a valid indicator of synaptic efficacy, especialy for evaluation of the reduction in conduction efficacy of the central nervous system in hypocalcaemia.     

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 in patients with occlusions of cerebral arteries

The material consists of 100 patients suffering from occlusion of a cerebral artery, admitted for the performance of arterial bypass. Before the operation SEPs of the median nerve and CT scans were taken. Three main types of SEP were found (symmetric, asymmetric-attenuated, asymmetric-augmented) and pathological changes of latency, amplitude and wave form of the primary complex N1-P2 were described. The changes were correlated with the localization and extent of the hypodense lesion in the cerebral hemispheres. The cause of the decreased latencies on the side of the lesion is discussed and reported in relation to 'travelling waves' (Cracco 1980) in normals. The cause of the increased amplitude on the side of the lesion is also discussed and reported in relation to a disturbance of the suppressor cortex 8s, 19s and of the head of the caudate nucleus.     

Somatosensory evoked potentials in abetalipoproteinemia

Visual, brain-stem auditory, and somatosensory evoked potentials (SEPs) were obtained on a patient with known abetalipoproteinemia. Only the SEP was abnormal, and it correlated with the reported neuropathology of this disease. Serial SEP studies remained stable, as had the clinical condition of this patient on vitamin E therapy. The SEP may supplement clinical examination in follow-up of patients under treatment.     

Somatosensory evoked potentials in healthy volunteers and in patients with dementia

In 56 healthy volunteers short, middle and long latency somatosensory evoked potentials were recorded bilaterally. The median nerve was electrically stimulated at the wrist. The impact of arm length and age on the peak latencies of the identified SEP components was investigated. Arm length relates to shoulder and neck SEP and to the N20, the primary cortical response. Age relates to all components of the SEP. A pilot study was performed in a small number of patients with senile dementia. A significant delay of the middle and long latency potentials compared to healthy volunteers was shown.     

Somatosensory evoked potentials: correlations with height

Somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation were studied in 160 subjects aged 20-90 years. Height was highly correlated with latencies of spinal and cortical SEPs (N13, N20, N22, and P40). Although tibial central conduction (N22-P40) was also highly correlated with height, median conduction (N13-N22) was not correlated with the latter. Multiple correlation and regression analysis showed that except for the median N13-N20 latency, height provided the best prediction of the remaining SEP latencies. Age alone was not correlated with SEP latencies, but its significance was observed when age and height were considered together as the predictors. Effects of age and height on SEP latencies were independent of gender. The present data indicate that except for the N13-N20 conduction, height is the most important parameter for SEP latencies and can be used for construction of normograms.     

Somatosensory evoked potentials in intraspinal tumors

SEPs have been recorded in 15 patients with spinal cord tumors (mostly ependymomas) and in 5 patients with cord compression due to meningiomas (3 cas), neuromas (1 case) or neurosarcoma (1 cas). All the patients have been operated on so that precise informations were available on the histology and the location of the tumor. SEPs were monitored during surgery in 8 patients. The main conclusions of this study are as follows: There was a good correlation between the somatosensory troubles for touch, vibration sense and joint position sense, and SEPs abnormalities, however, SEPs may be clearly abnormal in the absence of any somatosensory deficit when the dorsal columns are compressed and not infiltrated by the tumor. In the latter situation the reverse dissociation (i.e., normal SEPs with somatosensory troubles) may be observed. The possibility of a dissociation between normal N11 and N13 cervical components and absent P14 far field components (non-cephalic reference) has been confirmed in 6 patients with cervicomedullary tumors. In 3 of them, this dissociation was found to be reversible and early SEPs returned to normal after surgery. Peroperative monitoring of scalp SEPs recorded with a non-cephalic reference electrode allowed the detection of transient SEP abnormalities related with a traction on the dorsal columns of the cord. SEP monitoring is recommended for any surgical removal of tumor that needs a posterior myelotomy.     

Somatosensory evoked potentials in chronic alcoholics with spasticity

Somatosensory evoked potentials to median and bilateral tibial nerve stimulation were investigated in eight chronic alcoholics with spasticity, 12 patients with alcoholic polyneuropathy, and 11 normal subjects. Central conduction velocities from the third lumbar vertebra to the fifth cervical vertebra and from the 12th thoracic vertebra to the fifth cervical vertebra were significantly lower in the chronic alcoholics with spasticity than in the alcoholic polyneuropathy group and in the healthy nonalcoholic group. The result indicates that chronic alcoholics with spasticity have conduction disturbance in the posterior column and/or the medial lemniscus, which is considered to be due to alcoholic myelopathy and/or a brainstem lesion.     

Somatosensory evoked potentials in Arnold-Chiari malformation

Nearly all patients with repaired myelomeningoceles have an Arnold-Chiari (AC) malformation and about 20% of these patients develop clinical signs of brainstem dysfunction. The management of symptomatic AC malformation is still controversial and techniques are needed to provide an objective assessment of brainstem function. We recorded somatosensory evoked potentials (SEPs) in 52 patients aged between 8 months and 20 years (median 7.3 years) with AC malformation, to determine whether the SEPs discriminate patients with symptomatic AC malformation from those without symptoms. The subcortical far-field components P13, P14 and N18, which are generated within the brainstem, were recorded with non-cephalic reference electrodes and the cortical N20 with a frontal reference. Fourteen patients (27%) had signs and symptoms of brainstem dysfunction, which were related to the AC malformation. Abnormal SEPs were mainly recorded in symptomatic patients (sensitivity 0.7, specificity 0.9). The SEPs were particularly useful in patients from 4 years of age (sensitivity 0.9, specificity 0.9), but not in the younger age group. Abnormal somatosensory conduction reflects dysfunction of the brainstem or the upper cervical cord and may be clinically useful to assess patients with late onset symptomatic AC malformation.     

Somatosensory evoked potentials in Huntington's disease

Scalp recorded somatosensory evoked potentials (SEPs) elicited by left and right median nerve stimulation were obtained in 21 patients with Huntington's disease (HD), 14 individuals at risk (AR) for HD, and 21 non-patient controls matched for age and sex. Although SEP abnormalities were not uniform in the HD group, no HD patient had SEPs that conformed fully to the normal configuration with respect to peak latencies, presence of all components and spatial distribution. The most common abnormality was non-specific in nature, consisting of amplitude reduction or virtual abscence of components after 100 msec. More specific deviations were noted in the early SEP events. In half of the HD patients, peak P30 seemed to occur at approximately 45 msec poststimulus; this peak could have been taken as the normal P45 had it not reversed in phase between the central and frontal leads. In these cases peak P45 prepared to be missing. Peak N20 latency values were longer in the HD group than in the non-patient controls, whereas the P15 latencies did not differ significantly. The conduction time between P15 and N20 was significantly longer in HD patients than the non-patient controls. SEPs of the majority of the ARs were similar to those of the non-patients controls in terms of overall configuration, although mean amplitudes were generally lower for ARs than non-patient controls and 4 ARs exhibited prolonged P15-N20 latency differences.     

Somatosensory evoked potentials in Huntington's chorea

Somatosensory evoked potentials were measured in 21 patients with Huntington's chorea and 12 controls. Central brain conduction time was normal. Early cortical component amplitudes were reduced in the patient group, latencies were normal. These abnormalities probably can be attributed to cortical dysfunction in Huntington's chorea. No indication of brain-stem dysfunction was found.     

Somatosensory evoked potentials in Charcot-Marie-Tooth disease

SEPs by median nerve stimulation have been performed in 18 adult patients (12 males and 6 females) affected by CMTD (type I, 13 patients; type II, 5 patients). All patients underwent MCV studies (median, ulnar, peroneal nerve), SCV studies (median and sural nerve), VEP, BAEP. N9 and N13 peaks were not detectable in 7/13 and 5/13 cases (HMSN type I) while cortical N19 were always recorded. Latency values of all responses were moderately or markedly delayed in all cases with HMSN type I, but proved normal or slightly delayed in HMSN type II cases. The prolonged latencies were mainly related to slowing of peripheral conduction. N9-N13 inter-peak was abnormally prolonged in 2 cases and N13-N19 in 2 other cases; both were prolonged in another case. In another 3 cases an abnormal BAEP was recorded. The few patients with abnormal CCT and BAEP probably belong to a borderline form between HMSN and hereditary ataxias.     

Somatosensory evoked potentials in lacunar syndromes

Summary Parietal and prerolandic somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded from 40 patients with lacunar syndromes due to CT-verified lacunar infarcts. The control group consisted of 30 age-matched normal controls. Nineteen patients showed SEP abnormalities, mainly an increase of height-covariated latency of cortical components and/or of the central conduction time. Such changes occurred independently of the clinical features of lacunar syndromes, being related more to the lesion location than to its size. SEP studies may be a useful adjunct to the clinical diagnosis of lacunar infarct, possibly also when the CT scans are normal.     

Somatosensory evoked potentials in syringomyelia.

The two types of upper limb somatosensory evoked potential abnormality observed in nine patients with syringomyelia were reduced amplitude or absent cervical potentials and an abnormal central conduction time. Although this pattern of abnormalities resembles that observed in other intrinsic spinal cord lesions, it differs from peripheral nerve diseases and cervical radiculopathy in which the central conduction time is normal.     

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.