Ultralate cerebral potentials in a patient with hereditary motor and sensory neuropathy type I indicate preserved C-fibre function.

Late and ultralate cerebral potentials in response to cutaneous heat (CO2 laser pulses) and electrical nerve stimuli were studied in a patient with hereditary motor and sensory neuropathy type I who showed severe impairment of myelinated nerve fibre function. Cerebral potentials in response to electrical stimuli were absent (tibial nerve) or small (median nerve). With the laser pulses applied to the foot only ultralate, but no late potentials were observed, indicating intact C-fibres, but disturbed A delta-fibres. Laser stimulation of the hand resulted in both late and ultralate components, indicating at least partly preserved A delta-fibre function. The results document the usefulness of laser stimuli in the assessment of small nerve fibre function.     

The effects of axotomy on the conduction of action potentials in peripheral sensory and motor nerve fibres.

Medial gastrocnemius and sural nerves in one hindlimb of the cat were transected and prevented from regenerating. After periods ranging from 29-273 days, compound action potentials were recorded from axotomised and contralateral control nerves. The amplitude and integrated area of action potentials decreased and conduction velocity slowed following axotomy. The area under compound action potentials generated by stimulating sensory fibres declined significantly faster than that generated by stimulating motor fibres. Analysis of changes in whole nerve conduction velocity distributions showed that the velocities of fast conducting sensory fibres decreased at the most rapid rate. The conduction velocities of motor fibres and slow sensory fibres declined at significantly slower rates. The loss of electrical activity in the largest sensory nerve fibres following axotomy, may play a role in determining the faster rate at which their action potentials deteriorate.     

Mechanically evoked sensory and motor responses to dynamic compression of the ulnar nerve

Mechanical deformation of a peripheral nerve can evoke action potentials in sensory and motor axons. The generation of these impulses with brief stimuli (<0.5 s) and their relationship to the deformation conditions have not been systematically studied in human subjects. Controlled compression stimuli over a range of amplitudes, durations, and loading rates were delivered to the ulnar nerve at the medial epicondyle in awake human subjects. Compound muscle action potentials were recorded from the first dorsal interosseous muscle. Subjects rated the magnitude of evoked paresthesias. Mechanically evoked motor and sensory responses varied linearly with the magnitude (P < 0.001) and rate of deformation (P < 0.01), but not the duration, and occurred only during the compression phase. Cutaneous axons had lower mechanical thresholds than motor axons. We relate these findings to the viscoelastic properties of peripheral nerves and differences in biophysical properties of cutaneous and motor axons.     

Nerve impulse propagation along central and peripheral fast conducting motor and sensory pathways in man

Forty-four limbs from 11 healthy volunteers were examined. Spinal and scalp somatosensory evoked potentials to median and peroneal nerve stimulation were recorded and the peripheral (wrist-Erb, Erb-cervical, knee-thoracic spine) and central (cervical-scalp, thoracic-cervical spine, spine-scalp) conduction times and velocities (CTs, CVs) were calculated. Sensory and mixed trunks of median and peroneal nerves were also stimulated and their motor and sensory CVs in mid-distal districts were measured. Motor responses to scalp (motor areas for hand and leg muscles) and spinal cord stimulation (cervical and lower thoracic levels) were carried out through skin rectangular plate electrodes delivering high voltage (880-1870 V) brief anodal pulses. The intracranial (scalp-cervical) and intraspinal (cervical-thoracic spine) CTs and CVs of motor pathways were measured. The elbow-cervical and knee-thoracic spines CTs of motor fibres were also calculated through the F wave method, which gave values almost superimposable on those obtained through direct spine stimulation. Nerve propagation was faster in sensory than in motor fibres in peripheral nerve mid-distal districts, while this difference was reduced or reversed in more proximal segments, including nerve roots. The scalp-cervical CT was slightly shorter in motor than in sensory fibres after subtraction of synaptic delays (6.12 vs. 6.18 msec). The scalp-lower thoracic spine, as well as the intraspinal, CVs were 7-12% faster in sensory than in motor pathways (45.3 vs. 38.7 m/sec for the former; 62.65 vs. 55.4 m/sec for the latter). The reported method allows the evaluation of fast conducting motor and sensory pathways along 'central' and 'peripheral' nerve structures of the entire body. Preliminary findings on scalp stimulation of brain motor areas with low voltage pulses are also included.     

The effects of temperature on human compound action potentials.

The upper limbs of 10 healthy subjects were cooled and then warmed over physiological temperature ranges. The compound action potentials of median digital nerves, median sensory nerve at the wrist, radial sensory nerve at the wrist, and median thenar muscle, all showed progressive reduction in latency, amplitude, duration and area during rising temperature. Our studies suggest that the sensory compound action potential changes occur predominantly because of the summated effects of reduction in the duration of the action potentials of single myelinated fibres, although disproportionate increase in the conduction velocity of larger myelinated fibres also plays a role.     

Respective importance of different electrophysiological parameters in alcoholic neuropathy.

An electrophysiological study of alcoholic and normal subjects is presented. The aim was to evaluate the respective importance of the various parameters. The subjects were divided into 4 groups: (I) normal subjects; (II) chronic alcoholics without clinical evidence of neuropathy; (III) chronic alcoholics with sensory symptoms; (IV) chronic alcoholics with both motor and sensory symptoms. The electrophysiological parameters tested were: conduction velocity (CV) in Ia sensory fibres, motor fibres, and cutaneous sensory fibres of the popliteal nerve, CV in the sural nerve, amplitude of the cutaneous sensory action potentials (SAP) in the sural and popliteal nerves, H reflex and M response of the soleus muscle, and electromyograms from the extensor digitorum brevis muscle. In the 3 groups of alcoholics, the electrophysiological findings were more abnormal than the clinical symptoms could have predicted. The more sensitive parameters were: (1) CV in the Ia sensory fibres of the popliteal nerve, which is slowed very early (in Group II) and (2) measurement of the amplitude of sural and popliteal SAP's which are also reduced early (in Group II). The nature of the mechanisms involved are discussed.     

Friedreich's ataxia: electrophysiological and histological findings

ABSTRACT- Electromyography was performed, and motor and sensory nerve conduction velocities were measured in 19 patients definitely affected by Friedreich's ataxia. Biopsy of the sural nerve was also performed in 9 patients.
Most patients presented a moderate to severe loss of motor units, a significant increase in mean duration of motor unit potentials, and in the incidence of polyphasic potentials. Short-lasting spontaneous activity was rarely seen. Conduction velocity along the motor and sensory fibres of the median and tibial nerves was moderately slowed, while distal conduction time to muscle was significantly increased and the sensory orthodromicallyevoked response markedly reduced. Intraoperative electrophysiological recordings obtained during biopsy of the sural nerve in 4 patients were consistent with the changes conventionally observed in the median, tibial and sural (6 patients) nerves.
Quantitative histology revealed a reduced number of total myelinated fibres with a severe loss of large fibres, and a moderate loss of fibres of less than 7 μm in diameter. In teased nerve fibre preparations, the most evident abnormality consisted of fibres with uniformly short internodal length, while signs of remyelination were less prominent. Signs of active axonal degeneration were rarely observed in electron microscopy.
Electrophysiological and histological findings were uniformly distributed, and the changes were neither related to the duration nor to the severity of the clinical condition.     

Electrophysiological studies in diabetic neuropathy

In 30 patients with diabetic neuropathy sensory potentials in the median nerve, motor conduction in the lateral popliteal and median nerves, and electromyographic findings in distal and proximal muscles were compared with the severity of symptoms and signs. All patients had abnormalities in at least one of the electrophysiological parameters. The sensory potentials were the most sensitive indicator of subclinical involvement; abnormalities were found in 24 patients, 12 of whom had no sensory symptoms or signs and five of whom had no other clinical or electrophysiological evidence of neuropathy in the upper extremities. This indicates that sensory nerve fibres may be affected before motor. The next most sensitive parameter was the presence of fibrillation potentials, found in more than half the distal muscles examined. Slowing in motor conduction in the lateral popliteal nerve was the only electrophysiological change correlated to the severity of the neuropathy, and no other electrophysiological parameter was correlated to the duration or the severity of the neuropathy or the diabetes. An onset of neuropathy before or simultaneously with the manifestations of the diabetes, as well as the frequent occurrence of asymptomatic changes in sensory conduction, support the evidence at hand that the neuropathy develops concomitantly with and as an integral part of the metabolic disturbance rather than as a consequence of the vascular complications of diabetes. Of three patients with clinical signs or symptoms of a diabetic amyotrophy, two had asymptomatic electrophysiological abnormalities in distal nerves and muscles, consistent with widespread involvement of the peripheral nerves. The third patient had electromyographic changes in the medial vastus muscles suggestive of a myopathy. Motor and sensory conduction in distal and proximal nerves were normal.     

Changing electromyographic findings during the chronic course of polymyositis

Ten patients with polymyositis were studied with repeated EMG investigations over several years. In the chronic phase of the disease the following neuropathic EMG changes were found; large muscle action potentials with increased duration, grouped polyphasic potentials, loss of motor units and increased motor unit territory. The importance of collateral sprouting of terminal nerve fibres and of reinnervation of muscle is emphasized. Possible explanations for these changes have been considered.     

Motor, sensory electroneurographic and electromyographic results as well as somatosensory evoked potentials in comparison to clinical findings following nerve suture

A group of 37 patients (total 41 nerves) with a traumatic transection of median or ulnar nerves at the wrist were reinvestigated clinically and electrophysiologically 4-59 months after primary or secondary suture or grafting. Clinically there was no relation between the time after the operation, and sensory recovery determined according to the schedule of Nicholson and Seddon (1957), two-point discrimination, vibration threshold. There was also no relationship between the time after suture, and the motor latencies as well as amplitudes of evoked muscle action potentials from the abductor pollicis brevis or hypothenar muscles. In sensory nerve fibres there was a statistically significant increase of the maximum amplitude and of the cumulative amplitude during the period after operation, due to an increasing number of regenerated nerve fibres. Sensory nerve conduction velocities showed no relation to the time after suture. Cumulative amplitudes were significantly related to two-point discrimination and to restitution of sensibility. As indicated by the great scatter, however, this parameter is merely a moderate predictor for the degree of clinical recovery. Somatosensory evoked potentials can be helpful in some cases to indicate nerve regeneration when nerve action potentials in peripheral nerves cannot be recorded. However, latencies and amplitudes of the individual peaks did not reveal any relationship to either clinical findings or to period of time after operation. Needle electromyography also yielded highly variable findings. A constant finding was a persistent loss of motor units. Most of these were increased sin size, as indicated by prolonged duration of their action potentials during slight voluntary effort.     

Impact of pulse duration in single pulse TMS

Objective

The intensity of transcranial magnetic stimulation (TMS) is typically adjusted by changing the amplitude of the induced electrical field, while its duration is fixed. Here we examined the influence of two different pulse durations on several physiological parameters of primary motor cortex excitability obtained using single pulse TMS.

Methods

A Magstim Bistim² stimulator was used to produce TMS pulses of two distinct durations. For either pulse duration we measured, in healthy volunteers, resting and active motor thresholds, recruitment curves of motor evoked potentials in relaxed and contracting hand muscles as well as contralateral (cSP) and ipsilateral (iSP) cortical silent periods.

Results

Motor thresholds decreased by 20% using a 1.4 times longer TMS pulse compared to the standard pulse, while there was no significant effect on threshold adjusted measurements of cortical excitability. The longer pulse duration reduced pulse-to-pulse variability in cSP.

Conclusions

The strength of a TMS pulse can be adjusted both by amplitude or pulse duration. TMS pulse duration does not affect threshold-adjusted single pulse measures of motor cortex excitability.

Significance

Using longer TMS pulses might be an alternative in subjects with very high motor threshold. Pulse duration might not be relevant as long as TMS intensity is threshold-adapted. This is important when comparing studies performed with different stimulator types.     

Nervous propagation along 'central' motor pathways in intact man: characteristics of motor responses to 'bifocal' and 'unifocal' spine and scalp non-invasive stimulation

In 23 healthy adult volunteers motor action potentials (MAPs) were elicited in upper and lower limb muscles during stimulation of appropriate sites at spinal and scalp level, through skin electrodes. 'Bifocal' stimulation of scalp and spine motor tracts was performed with 2 plaques (3.5 cm2 each), delivering single pulses of 440-940 mA, less than 50 microseconds in duration, which elicited high voltage (up to 10 mV) MAPs in arm and leg muscles. 'Unifocal' stimulation of scalp was carried out through a cathode consisting in a belt or in a series of rectangular interconnected plaques secured around the head, 1-2 cm rostral to the nasion-inion plane, and in a circular anode placed on the appropriate scalp site. MAPs with similar amplitude-latency characteristics were recorded with both 'bifocal' and 'unifocal' stimulating methods. However, the 'unifocal' stimulation necessitated 5-10 times less current than the 'bifocal' one. The 'unifocal' device using the interconnected plaques (6-12 in number) provided the most tolerable stimuli with the lowest amount of current (60-106 mA, rectangular pulses of 100-150 microseconds). Conduction times and velocities of motor pathways in various 'central' and 'peripheral' districts were calculated. Voluntary contraction of target muscles remarkably enhanced MAP amplitudes during scalp, but not during spine stimulation. A nerve action potential was recorded from ulnar nerve during scalp stimulation. MAPs in hand muscles to scalp stimulation were obliterated by the simultaneous activation of the peripheral fibres innervating the target muscle, because of collision between ortho- and antidromically propagated motor impulses. Anodal stimuli showed liminal values significantly lower than the cathodal ones. Mapping studies have been carried out with 'unifocal' scalp stimulation by using different types of anode and of stimulus parameters.     

Evoked electrospinogram in spinal cord and peripheral nerve disorders

Spinal cord evoked potentials have been studied by means of intrathecal application in 80 patients with various spinal cord and peripheral nerve disorders.
The segmental spinal cord potentials are normal in acute motor polyneuropathy, generalized anterior horn cell disease and in discrete lesions of dorso-lumbar segments. On the other hand, the first component of the segmental response is delayed, reduced and sometimes dispersed or lost in chronic sensory-motor polyneuropathy and in hereditary spinocerebellar degeneration. the reduction in amplitude is also present in multiple sclerosis with clinical signs of dorsal funiculus involvement.
In compressive lesions of the cauda-conus, recordings of lower thoracic intervertebral level show that the segmental responses are delayed with marked amplitude reduction.
The potentials recorded from lumbo-sacral segments show a greater the amplitude of the second component proportionally to the first one as the duration of second component is longer in spastic paraplegia regardless of its etiology.
The cervical tractus response is seen to be markedly slowed with a reduction of amplitude or is often absent in chronic polyneuropathy, spinocerebellar degeneration and in multiple sclerosis.
The primary sensory neurones lying both in periphery and in the dorsal column are assumed to be responsible for the segmental evoked potentials especially for the first component. the late slow component is related to the activation of interneurones situated within the segmental gray matter and segmental collaterals of the dorsal root fibres carrying impulses to those cells. Cervical tractus responses are mostly formed by the dorsal column fibres and their physiological action upon demyelination is similar to that of the peripheral nerves.     

Korrelationen zwischen Veränderungen des sensiblen Nervenaktionspotentials und gestörter Vibrationsempfindung bei urämischer Polyneuropathie

1. The sensory action potentials of the tibial nerve at the medial malleolus were studied by averaging in 51 patients with chronic renal failure treated by hemodialysis. Vibratory sense was also tested quantitatively on the dorsum of the foot with a pallesthesiometer. 2. Good correlation was found between sensory tibial nerve potentials and vibration sense in subclinical as well as in clinical uremic polyneuropathy. A biphasic potential correlated with unaffected vibration sense in 18 out of 23 patients, and impaired vibratory sense with a polyphasic response in 20 of 28 patients. Maximal nerve conduction of sensory fibres was faster (mean 37.4 m/sec) in cases with normal vibratory sense, but slower (mean 31.3 m/sec), when vibratory sense was impaired. Furthermore there was a correlation between the threshold of vibratory perception and sensory nerve conduction. 3. Sensory function, tested with conventional methods, was impaired only 5 times in 28 patients with altered vibratory perception. 4. The earlier impairment, especially of the vibratory sense, may be explained by the following neurophysiological mechanisms: a) Because of the polyphasic prolonged response of the sensory potentials, no rhythmical groups of impulses reach the central nervous system, but only a continual stream of small peaks arrives, so that vibration perception does not develop. b) A multiplication of the frequency of discharges caused by alternating firing of different sensory fibres is impossible due to the reduction of the number of axons. c) The prolongation of the relatively refractory period due to demyelinization of the surviving fibres prevents the transmission of frequent impulses. 5. Alterations of the sensory action potentials of the tibial nerve, as well as of vibratory perception tested quantitatively, are earlier signs of uremic polyneuropathy than the prolonged motor nerve conduction velocity. Since not all patients give accurate information when tests of vibratory sense are performed both methods should be applied. Physiological polyphasia of sensory action potentials and diminishing vibration perception in advanced age must be taken into account.     

A quantitative electrophysiological study of acute idiopathic polyneuritis.

The motor unit content and the dimensions of individual motor unit action potentials were studied in 17 patients with acute idiopathic polyneuritis from one week to 9 1/2 years after the onset of the illness. An initial decrease in motor unit numbers is followed by a progressive increase with the passage of time from the onset of the illness. The latencies, areas, amplitudes, and durations of individual motor unit potentials were increased above normal values. The results suggest the presence of significant axonal damage in the majority of cases of acute idiopathic polyneuritis. The intramuscular nerve fibres are the site of most severe electrophysiological dysfunction in this study.     

Single fibre electromyography in various processes affecting the anterior horn cell

SFEMG recordings were carried out in patients with amyotrophic lateral sclerosis, progressive muscular atrophy, familial spinal muscular atrophy and syringomyelia. The fibre density was increased in all conditions, especially in progressive muscular atrophy indicating marked collateral sprouting. The duration of the action potential was increased indicating a mixture of hypertrophic and atrophic fibres and slowly conducting newly formed nerve sprouts. The action potentials were unstable with varying degree of impulse blocking especially in the more progressive cases (ALS), representing recent re-innervation. The SFEMG method is used to characterize the functional status of the motor unit and helps in diagnosis and in predicting prognosis. In addition, SFEMG recordings reveal abnormalities in clinically and electromyographically normal muscles.     

Nerve, spinal cord and brain somatosensory evoked responses: a comparative study during electrical and magnetic peripheral nerve stimulation.

Somatosensory evoked potentials (SEPs) and compound nerve action potentials (cNAPs) have been recorded in 15 subjects during electrical and magnetic nerve stimulation. Peripheral records were gathered at Erb's point and on nerve trunks at the elbow during median and ulnar nerve stimulation at the wrist. Erb responses to electrical stimulation were larger in amplitude and shorter in duration than the magnetic ones when 'electrical' and 'magnetic' compound muscle action potentials (cMAPs) of comparable amplitudes were elicited. SEPs were recorded respectively at Cv7 and on the somatosensory scalp areas contra- and ipsilateral to the stimulated side. SEPs showed a statistically significant difference in amplitude only for the brachial plexus response and for the 'cortical' N20-P25 complex; differences were not found between the magnetic and electrical central conduction times (CCTs) or for the peripheral nerve response latencies. Magnetic stimulation preferentially excited the motor and proprioceptive fibres when the nerve trunks were stimulated at motor threshold intensities.     

Subacute progressive sensory ataxic neuronopathy after Rickettsia conorii infection

A case is presented in which sensory ataxic neuronopathy developed after serologically proven infection with Rickettsia conorii and continued to be progressive after appropriate antibiotic treatment. Electrophysiological studies showed decreasing sensory nerve conduction velocities ending with the absence of sensory nerve action potentials as well as peripheral and cortical somatosensory evoked potentials. Histological studies revealed a profound loss of myelinated fibres due to primarily axonal degeneration. The clinical course and the electrophysiological and histological findings suggest primary involvement of the dorsal root ganglion. Peripheral neuropathy due to infection with R. conorii is rare and usually of the mixed motor and sensory type. We believe this to be the first report of sensory ataxic neuronopathy associated with R. conorii infection.     

Peripheral neuropathy following a single exposure to arsenic. Clincal course in four patients with electrophysiological and histological studies.

Four patients are described who developed a peripheral neuropathy 10 days to 3 weeks after ingestion of a single dose of arsenic. All improved slowly, but after 6 to 8 years 3 of them still had abnormal neurological symptoms and signs. Electrophysiological studies showed reduction of motor conduction velocity and marked abnormalities of sensory nerve action potentials. The findings suggest that conduction is abnormal in at least some surviving nerve fibres. Sural nerve biopsies from 2 patients showed axonal degeneration, which was at an early stage in some fibres, even 10 weeks after intoxication.     

Decreased sensory cortical excitability after 1 Hz rTMS over the ipsilateral primary motor cortex.

OBJECTIVES: To study changes in the excitability of the sensory cortex by repetitive transcranial magnetic stimulation (rTMS) in humans. METHODS: Somatosensory evoked potentials (SEPs) and antidromic sensory nerve action potentials (SNAPs) were elicited by right median nerve stimulation at the wrist before and after low frequency (1 Hz) rTMS over the left motor cortex, lateral premotor cortex, sensory cortex, and also after sham stimulation. The intensity of rTMS was fixed at 1.1 times the active motor threshold at the hand area of motor cortex. RESULTS: N20 peak (N20p)-P25 and P25-N33 amplitudes were suppressed after rTMS over the motor cortex, whereas the N20 onset (N20o)-N20p and SNAP amplitudes were not affected. They recovered to the baseline about 100 min after the rTMS. rTMS over the premotor cortex or sensory cortex or sham stimulation had no suppressive effect on SEPs. CONCLUSIONS: The reduction of N20p-P25 and P25-N33 components without any changes of N20o-N20p amplitude suggests that the suppression occurs in the sensory cortex. rTMS (1 Hz) of the motor cortex induces a long-lasting suppression of the ipsilateral sensory cortex even at an intensity as low as 1.1 times the active motor threshold, probably via cortico-cortical pathways between motor and sensory cortex.