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.     

Intracerebral tuberculoma. Clinical and x-ray computed tomographic characteristics

Intracranial tuberculomas have become uncommon in industrial nations, while they still have a high incidence in underdeveloped countries. Four cases of intracerebral supratentorial tuberculomas are reported in this paper. Clinical findings suggestive of tuberculosis were present in only one case. The other cases were thought to be gliomas or metastases and the diagnosis was made only after surgery. The CT scan provided a good image of the lesions whose characteristics, however, were diagnostically confusing. When a tuberculoma is suspected, medical therapy alone should be administered initially. Surgery should be resorted to in cases of markedly increased intracranial pressure.     

Parallel processing of sensory inputs: an evoked potentials study in Parkinsonian patients implanted with thalamic stimulators.

In two drug-resistant Parkinsonian subjects, who underwent thalamic chronic stimulation for extrapyramidal symptoms relief, median nerve somatosensory evoked potentials (SEPs) were recorded before and at different times following the thalamic lead implant. In both subjects, a transient obliteration of post-rolandic SEPs components was detected; pre-rolandic waves' amplitude was preserved or showed a tendency to increase after the beginning of chronic stimulation. Parietal waves' amplitude totally recovered pre-surgical values after 1 month. Latency of both pre- and post-central components remained stable. The 'dissociate behaviour' of the examined waves following the thalamic implant reinforces the hypothesis that short-latency sensory inputs are processed by separate and independent routes which are functionally segregated at subcortical level.     

Clinicophysiological study of multimodality evoked potentials and computed tomographic findings in persistent vegetative state

The auditory brainstem response (ABR), short latency somatosensory evoked potential (SSEP) and visual evoked potential (VEP) of patients in the persistent vegetative state (PVS) are reported, and the correlations between the electrophysiological findings and the CT scan findings with the three clinical grades of the PVS (transitional, incomplete and complete vegetative syndromes) are discussed. Twenty two patients in a vegetative state caused by subarachnoid hemorrhage (3), hypertensive intracerebral hemorrhage (5), cerebral infarction (6), head injury (3), cerebral anoxia (4) and brain tumor (1). Each evoked response was evaluated for the presence or absence of abnormalities and assigned a grade ranked I to III. Briefly an evoked response was assigned a grade I, II, III if it satisfied the respective criteria of normal, moderately abnormal and severely abnormal or absent electrical activity. On the other hand CT scan findings in the PVS were evaluated for abnormal low density areas, ventricular dilatation and enlargement of the sulci and cisterns indicative of atrophy of the brain parenchyma. SSEP and VEP were better correlated with the clinical grade than ABR, and upper brainstem atrophy and abnormal low density area in CT scan findings were more valuable as an index to expresses the clinical features than ventricular dilatation. On the basis of these results, it is concluded that studies of ABR, SSEP and VEP associated with CT scan findings in the PVS could be a useful diagnostic aid to evaluate the lesions of these patients.     

Cortical somatosensory evoked potentials in patients with thalamic lesions (author's transl)]

The influence of thalamic lesions on the configuration of the somatosensory evoked cortical potential is studied on the basis of two own observations and of the literature. An increased latency of the initial component N1 and a reduced voltage in the beginning of the potential recorded on the side of the thalamic lesion are the most frequent findings in patients with thalamic syndromes. Most dramatic changes of the evoked response occur in cases with lesions of the VPL nucleus and with proprioceptive sensory disturbances. Considering the morphological basis of the normally configurated potential possible developmental mechanisms of the pathological evoked response are discussed.     

脑卒中患者急性期脑电生理变化与CT成像的临床研究

目的 探讨急性缺血性脑卒中患者脑电生理变化和CT成像的临床意义. 方法 对56例发病后即刻入院的缺血性脑卒中患者检测的CT、脑电图(EEG)、脑电地形图(BEAM)、体感诱发电位(SEP)、经颅磁刺激运动诱发电位(MEP)和神经功能缺损评分(MESSS)及日常生活能力评分(BI)情况进行对比研究及相关分析. 结果 EEG局限性异常与CT显示病变位置基本一致,但病灶范围存在一定差异.自身患/健侧SEP和MEP比较差异有统计学意义(P<0.05).入院不同时间MESSS与入院第28天BI值分析显示两者呈正相关(r=0.58,P<0.05).结论 CT成像与脑电生理检查在缺血性脑卒中急性期具有较高的早期诊断价值.     

Early evoked potentials in patients with acoustic neuroma.

Using clicks with varying interstimulus intervals and coherent tone-bursts, early components of the auditory evoked potential (brain stem responses) were studied in four patients with confirmed acoustic neuroma. Abnormalities in responses appeared with shorter interstimulus intervals and with tone-bursts delivered monaurally to the involved ear; bilateral alterations occurred in one patient with brain stem displacement. The results indicate that BSR can provide a stable, independent, noninvasive measure of auditory nerve function useful in the early detection of acoustic neuroma. The results contribute to the understanding of the so-called human FFR.     

Abnormalities in sensory and mixed evoked potentials in ataxia-telangiectasia.

Electromography, motor, sensory and mixed nerve conduction velocity, and H reflex were studied in four patients with ataxia-telangiectasia. The earliest and most striking electrophysiologial finding was the reduced amplitude of evoked nerve potentials. In the oldest patient, findings suggestive of spinal atrophy and mild reduction of the motor and sensory nerve conduction velocities were found. Reduced amplitude in the evoked nerve potentials can be observed without clinical evidence of peripheral neuropathy. Electrophysiological abnormalities are more severe in older than in young patients. Sural nerve biopsy in one patient showed mild changes: loss of the largest myelinated fibres and demyelination of some fibres. The ratio between maximum conduction velocity of the sural nerve and the diameter of the largest fibres was in the lower limits of the normal range. The resemblance between electrophysiological abnormalities in Friedreich's ataxia and ataxia-telangiectasia is discussed.     

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.     

Trigeminal evoked potentials and sensory deficits in atypical facial pain--a comparison with results in trigeminal neuralgia

Trigeminal evoked potentials (TEPs) and sensory deficits in eighty-three patients admitted for first surgical treatment of facial pain were retrospectively analysed. Thirty-seven patients suffered from trigeminal neuralgia (TN), 10 from symptomatic TN (sTN), and 36 from atypical facial pain (AFP). Eighteen percent of the TN patients reported sensory deficits on the pain side, but 35% had delayed ipsilateral N13 waves. Of the sTN patients, 60% had either sensory deficits or a pathological corneal reflex and 62.5% a pathological N13. Of the AFP patients, 61% complained of sensory deficits, but only 31% had a pathological N13. The percentage of pathological P19 waves was slightly lower (20%, 50%, and 11%, respectively), but showed a similar trend. Normal TEPs were found even in the presence of a sensory deficit (reported only in the AFP group). These findings may add weight to the hypothesis of underlying psychiatric disorders in AFP.     

Correlation between somatosensory evoked potentials and sensory disturbance in stroke patients

Somatosensory evoked potentials (SEP) were recorded in 125 (n = 151) stroke patients more than 3 weeks after disease onset and in 55 healthy adults. The correlation between sensory disturbance, N20 amplitude ratio, and the central conduction time (CCT) was then investigated. N20 amplitude ratio was given by the amplitude of the affected side divided by that of the unaffected side and presented as a percentage, while CCT represents the time interval between N20 and N13. For the healthy subjects, normal values of CCT were 6.1 +/- 0.4 msec (20-59 years old) and 6.4 +/- 0.4 msec (over 60 years old). Normal amplitude ratios were left side/right side = 97.5 +/- 16.4% and right side/left side = 105.4 +/- 17.7% with the value at the second standard deviation, 64.7%, representing the normal range of the amplitude ratio. Of 98 stroke patients with an abnormal amplitude ratio and 23 with an abnormal CCT, 91.8% and 95.7%, respectively, had sensory disturbance. Conversely, 82.6% of those with sensory disturbance showed an abnormal amplitude ratio, while only 38.6% with sensory disturbance showed an abnormal CCT. There was a definite correlation between sensory disturbance and either CCT or amplitude ratio, however, there was none between CCT and amplitude ratio. On the basis of these results, we concluded that amplitude ratio would be more effective than CCT as a parameter for monitoring sensory disturbance in stroke patients.     

Motor and sensory evoked potentials in progressive supranuclear palsy.

Motor potentials evoked in the biceps, thenar, and tibialis anterior muscles by electrical stimulation of the scalp and of the spinal regions were recorded in 12 patients with progressive supranuclear palsy (PSP) and in a control group. Abnormalities of central motor conduction for at least one muscle were present in five patients (41.7%), characterized by a long illness duration. The central sensory conduction time of the median nerve was normal, but five patients showed a depressed frontal N30 wave. These findings support the possible occurrence of functional damage to the corticospinal tracts and to the supplementary motor area in PSP.     

Dissociation of thalamic high frequency oscillations and slow component of sensory evoked potentials following damage to ascending pathways.

OBJECTIVE: Somatosensory evoked potentials (SEPs) recorded from the thalamus have a slow component and high frequency (approximately 1000 Hz) oscillations (HFOs). In this study, we examined how lesions in the sensory afferent pathway affect these components. METHODS: Thalamic SEPs to contralateral median nerve stimulation were recorded from deep brain stimulation electrodes in two patients. Patient 1 had spinal cord injury at the C4/5 level. Patient 2 had multiple sclerosis with mid brain lesions. Seven patients with no brain or cervical spinal cord lesions served as controls. RESULTS: In both patients, the low frequency component of the SEP (LF SEP) was delayed and/or prolonged and greatly decreased in amplitude compared with controls. HFOs were recorded in both patients. The latencies of onset and peak of the HFOs were approximately the same as those of the LF SEPs and their amplitudes were similarly reduced. However, their frequency was similar to that of the control group. Cortical SEPs were absent in both patients. CONCLUSIONS: Normal frequencies of thalamic HFOs in association with increased peak latencies, and decreased amplitudes provide further evidence that the HFOs are likely due to intrinsic oscillations in the thalamus rather than high frequency synchronous inputs. SIGNIFICANCE: Thalamic HFOs are closely associated with the LF SEP but are generated by a different mechanism.     

Differential effect of thalamic and subthalamic lesions on early and late components of the somatic evoked potentials in man.

The effect of thalamic (Vo), subthalamic (Raprl) and combined (Vo-Raprl) unilateral lesions on early and late components of the somatic evoked potentials (SEPs) was investigated in a group of 16 cases operated on for the treatment of contralateral dyskinetic movements. In these cases, SEPs were independently produced by stimulation of the left and right median nerves and recorded at the corresponding somatosensory scalp regions. In addition, EEG frequencies and reaction time (RT) were independently and bilaterally determined. These tests were performed before and after operation and changes in SEP, EEG and RT were quantitatively evaluated in relation to both ipsilateral preoperative and contralateral postoperative controls. 1. All cases with either thalamic or combined lesions involving Vo nucleus showed an ipsilateral reduction in amplitude of late SEP components and EEG frequency and a contralateral increase RT. A peculiar form of "inattention" to the contralateral hand was also found. Quantitative evaluation of the total group showed significant amplitude reduction in late SEP components in relation to both ipsilateral preoperative and contralateral postoperative controls. Changes in EEG and RT were only significant in relation to their preoperative ipsilateral controls. 2. Two cases with subthalamic lesions and quick postoperative recovery showed no apparent change in SEP, EEG and RT. Three cases with similar lesions and slow postoperative recovery showed bilateral decrease in amplitude of late SEP components, EEG frequency and increase in RT. Clinical inattention to contralateral hand was also found in all these cases. Quantitative evaluation of the total group showed no significant changes in these parameters in relation to preoperative controls. 3. None of these lesions produced changes in early SEP components or somatosensory deficits at the contralateral hand.     

Rimmed vacuolar distal myopathy: a clinical,electrophysiological, histopathological and computed tomographic study of seven cases

Summary The following report describes the clinical, laboratory, electrophysiological, histopathological and computed tomographic studies of seven cases of distal myopathy with rimmed vacuoles in the muscle fibers. Each displayed several characteristic features. First, the onset was in early adulthood. Second, there was a unique distribution of muscle involvement: tibialis anterior and extensor digitorum and hallucis muscles were initially and most severely affected. The hamstrings and adductors of the thigh were also markedly involved. The gluteus medius and minimus muscles and the neck flexors were mildly affected in the relatively early stages. In contrast, the gastrocnemius, soleus, quadriceps femoris, and gluteus maximus muscles were well preserved until an advanced stage. Third, serum creatine kinase activity was normal or only mildly elevated; fourth, EMG were mainly myopathic, with certain neuropathic features; and fifth, histopathologically rimmed vacuoles in muscle fibers were found associated with certain neuropathic features, such as angular fibers, clustering of atrophic fibers, pyknotic nuclear clumps, and fiber-type predominance. The characteristic distribution of skeletal muscle involvement was particularly noticeable, together with certain neuropathic features of the EMG and muscle biopsy in rimmed vacuolar distal myopathy.     

Early computed tomographic findings for thrombolytic therapy in patients with acute brain embolism.

BACKGROUND AND PURPOSE: The benefits and safety of thrombolytic therapy was studied in patients with acute brain embolism. METHODS: We intravenously administered recombinant tissue plasminogen activator (20-30 MU for 1 hour) to 10 patients with acute (less than 6 hours) brain embolism and examined the neurological outcomes in relation to the findings on computed tomography and angiography. RESULTS: The symptoms ameliorated in four patients within 24 hours after onset, and reopening of the occluded arteries occurred in two of the patients immediately after recombinant tissue plasminogen activator infusion. On the initial computed tomographic scan (less than 3 hours), four patients had already demonstrated early indications of brain ischemia, that is, an obscure margin of the lentiform nuclei, reduced tissue attenuation, or effacement of cortical sulci. These patients failed to demonstrate reopening of the occluded arteries, and one developed a massive brain hemorrhage with clinical deterioration. Of the remaining six patients, two obtained clinical improvement with recanalization soon after the therapy and demonstrated little to slight hemorrhagic complications. The outcomes at 1 month were favorable in five patients and poor in three; death occurred in two. CONCLUSIONS: Thrombolytic therapy with recombinant tissue plasminogen activator may be safe and effective when there are no early computed tomographic findings within 3 hours from the onset of embolic stroke.     

Effects of brain-stem and thalamic lesions on the corneal reflex: an electrophysiological and anatomical study.

In 9 patients with Wallenberg's lateral medullary syndrome, one patient with a midbrain lesion involving the right side of the tegmentum, and 2 patients with a thalamic lesion, corneal reflexes were investigated by a new electromyographic technique. The electrophysical results were compared with the results obtained by clinical observation. In the lateral medullary lesions the electrophysiologically obtained reflex responses showed four types of abnormality. Type A consisted of a bilateral delay and type B a bilateral absence of the corneal reflex response to stimulation on the affected side in combination with a normal reflex response on both sides when the cornea on the normal side was stimulated. Type C, which was present in one case, and type D which was seen in 3 cases, consisted of a bilateral absence of the corneal reflex upon stimulation on the affected side; stimulation on the unaffected side produced a normal reflex response on the intact side in combination with, respectively, a delay or absence of the corneal reflex response on the affected side. Comparison of the clinical observations with the electrophysiological findings revealed minor discrepancies in type A and B abnormalities. However, the electrophysiological type C and D abnormalities were not detected by clinical observation. These findings demonstrate that electrophysiological recording of the corneal reflex may reveal clinically undetectable abnormalities. From the electrophysiological findings it is concluded that the corneal reflex is conducted along medullary pathways running both ipsilaterally and contralaterally from the stimulated side before connecting, respectively, with the ipsilateral and contralateral facial nucleus. From the anatomical findings it is suggested that the ascending pathways from the spinal fifth nerve complex to the facial nuclei are located in the lateral reticular formation of the lower brain-stem. The normal corneal reflex responses in the presence of thalamic and midbrain lesions involving nociceptive fibres in the trigeminothalamic tract do not support a previously postulated long-loop reflex arc passing through this tract. The suprabulbar influence upon the corneal reflex is discussed.