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R Benecke

Publications and source records attributed to R Benecke.

At least 91 records · Page 5Linked to original sources
PubMed1992

Motor responses evoked by magnetic brain stimulation in Huntington's disease.

In 34 patients with manifest Huntington's disease (HD), and in 21 first-degree offspring without clinical signs or symptoms, the sizes, central motor latencies (CMLs) and variation in latencies of EMG responses (MEPs) following transcranial magnetic brain stimulation were studied in muscles of the upper and lower extremities. In subgroups of patients and their offspring median and tibial nerve somatosensory evoked potentials (SEPs) and electrically elicited long-loop reflexes (LLRs) in hand muscles were also investigated. Increased MEP thresholds were observed in 10% of the HD offspring, while CML, latency variability and MEP amplitudes always lay within normal range. In contrast, SEPs were abnormal in 33%. In HD patients MEPs were found to be abnormal in up to 72% of patients when all available response parameters were taken into consideration. MEP abnormalities correlated with the duration of motor symptoms and the severity of choreic motor activity. When both MEPs and SEPs were evaluated, abnormalities could be detected in 91% of all HD patients. We suggest that abnormal MEPs might reflect an altered excitability of the cortico-spinal system as a consequence of basal ganglia dysfunction, rather than a structural damage of the investigated descending pathways. To localize the pathological mechanism responsible for altered LLRs, a "loop analysis" was performed by recording LLRs, MEPs and SEPs in the same patients. Alterations of LLRs correlated best with abnormal SEPs and might therefore be explained by reduced somatosensory input to the motor cortex.

Adolescent↗
PubMed1992

[Normal values and age-related changes in magneto-electric evoked compound muscle potentials].

A number of 57 normal subjects was investigated using transcranial magnetic stimulation of the motor cortex and transcutaneous magnetic stimulation of the spinal nerve root in order to obtain normative data for central and peripheral motor latencies. Under standardized conditions (site of stimulation, stimulus intensity, degree of voluntary tonic background activation) muscle compound action potentials were recorded from different muscles of the upper and lower extremity: M. biceps brachii, M. extensor carpi radialis, M. interosseus dorsalis I, M. vastus medialis, M. tibialis anterior, and M. extensor digitorum brevis. Onset latency, peak to peak amplitude (% of maximal M-wave), duration and configuration of the muscle compound action potentials were evaluated (Fig. 1 and Tab. 1-6). Central and peripheral motor latencies were determined by stimulation over two different points of the neuraxis (cortex/cervical or lumbar nerve roots). Central motor latencies were calculated by subtracting the peripheral conduction time from the onset latency of the fastest cortically evoked muscle response. Not only the peripheral but also the central motor latencies were found to increase in higher ages (Tab. 6). This has to be taken into account when elderly patients are examined for diagnosis of disorders of the descending motor tracts.

Adult↗
PubMed1991

Abnormal conduction in corticospinal pathways in Wilson's disease: investigation of nine cases with magnetic brain stimulation.

Electromyographic (EMG) responses evoked by transcranial magnetic brain stimulation were studied in nine patients with Wilson's disease (WD). Six of the nine patients had prolonged central motor latencies (CMLs), reduced amplitude, or absent responses in at least one of the examined muscles. In one patient, abnormal EMG responses normalized following treatment with penicillamine. Pathophysiologically abnormal EMG responses might result from a potentially reversible impairment of corticomotoneuronal pathways and/or a reduced excitability of motoneurons due to basal ganglia dysfunction. The possible pathophysiological mechanisms are discussed.

Adult↗
PubMed1991

Reorganisation of descending motor pathways in patients after hemispherectomy and severe hemispheric lesions demonstrated by magnetic brain stimulation.

Numerous clinical studies on patients after hemispherectomy (HS) have provided clear evidence that two distinct groups can be recognized on the basis of the quality of their motor functions after operation. One of these consists of cases where HS was performed after normal brain maturation, the other of patients where the removed hemisphere was damaged early in life. The postoperative motor function has been found to be much better in the latter group. In the present paper it is demonstrated that in contrast to normal subjects ipsilateral compound muscle action potentials (CMAPs) induced by magnetic stimulation of the one intact motor cortex are present in patients after HS. The amplitudes of ipsilateral CMAPs in the muscles roughly correlate with their individual residual motor capacities and show a proximo-distal gradient. In patients with early brain damage prior to HS, CMAPs had short latencies and large amplitudes, whereas in patients with later acquired brain damage prior to HS, CMAPs had long latencies and small amplitudes. It is suggested that reinforcement of the ipsilateral corticospinal pathway may be responsible for residual motor functions in patients with early brain damage, whereas in patients with later acquired brain damage cortico-reticulospinal pathways may play a dominant role in ipsilateral motor control.

Action Potentials↗
PubMed1991

Wilson's disease: normalisation of cortically evoked motor responses with treatment.

A newly diagnosed patient with Wilson's disease is reported in whom the only clearly pathological neurophysiological findings before treatment were abnormal electromyographic (EMG) responses evoked by transcranial magnetic brain stimulation. Serial examinations over 10 months following commencement of treatment with D-penicillamine revealed normalisation of EMG responses. Pathophysiologically, the initially abnormal EMG responses probably resulted from reversible impairment of impulse propagation along cortico-motor-neuronal pathways and/or a reduced excitability of cortical cells due to impaired function of the basal ganglia.

Adolescent↗
PubMed1991

Plasma level monitoring of mitotane (o,p'-DDD) and its metabolite (o,p'-DDE) during long-term treatment of Cushing's disease with low doses.

Mitotane (o,p'-DDD) can be used for the treatment of various adrenocortical diseases such as Cushing's syndrome, but the usual doses of 6-8 g per day are often associated with severe adverse effects. This paper reports the results of much lower doses of o,p'-DDD (0.5-2 g per day) in two patients with Cushing's disease over periods of 8 and 5 years, respectively, under concomitant monitoring of the plasma levels of the parent drug and its major metabolite, o,p'-DDE. It became apparent that o,p'-DDD and o,p'-DDE have a strong tendency to accumulate in the body due to their high lipophilicity. As a consequence, changes in dose regimens had long lag times before they were reflected in plasma levels and once an increase or decrease had started one had to be careful not to cause overshoot. Steady state plasma levels of o,p'-DDD between 5-10 micrograms/ml appeared sufficient to induce and to maintain remission of the disease, which was accompanied with normal cortisol levels in plasma and urine. DDD-levels below 5 micrograms/ml for several weeks may lead to relapses, whereas DDD-levels over 10 micrograms/ml gave rise to side effects. On the other hand, o,p'-DDE seemed inactive at levels up to 4 micrograms/ml in plasma.

Adolescent↗
PubMed1991

Variability of cortically evoked motor responses in multiple sclerosis.

The calculated central motor conduction time (CMCT), onset latency variability (expressed as the mean consecutive difference; MCD) and amplitude (expressed as percentage of maximum peripheral M wave size) of electromyographic (EMG) responses in the first dorsal interosseous (FDI) muscle following magnetic motor cortex stimulation were investigated in 20 normal subjects and 21 patients with multiple sclerosis (MS). EMG responses were present in all patients studied. CMCT was prolonged (greater than 8.1 msec; the mean CMCT for normals plus 3 S.D.) in 19 out of 42 muscles (12 patients). Onset latency variability was increased (greater than 1.1 msec; mean plus 3 S.D. for normals) in 20 out of 42 muscles (14 patients). Maximal response amplitudes varied between 5% and 67% and were not significantly different from the normal group (range 16-64%). In 3 patients, increased onset latency variability was the only neurophysiological abnormality. Prolonged CMCT was the sole abnormal finding in only 1 patient. Abnormally large onset latency variability was associated with the clinical finding of both impaired fine finger movements and increased finger jerks. Abnormal CMCT was associated with increased finger jerks only. This study confirms the findings of prolonged CMCT in multiple sclerosis. The additional finding of abnormal variability in response latencies which correlates with the clinical signs suggests that this variability may also be a useful measure of pyramidal tract function.

Adolescent↗
PubMed1991

Coil placement in magnetic brain stimulation related to skull and brain anatomy.

The influence of coil position on the size of electromyographic responses evoked by transcranial magnetic brain stimulation was systematically evaluated. The position of the stimulation coil (11.6 cm outer diameter, Novametrix) was recorded by constructing individual grids on the skull surface using extracranial bony landmarks and was then related to underlying cerebral sulci by analysis of magnetic resonance images of the brain and skull. The largest responses in the right first dorsal interosseus (FDI) muscle, when using anticlockwise coil currents as viewed from above, were found, on average (5 subjects), to occur with the coil centred 2 cm behind and left of the vertex. For the right tibialis anterior (TA) muscle the largest responses were obtained, on average, with the coil centred around a point 4 cm anterior to and 4 cm left of the vertex. Between individuals, the optimal coil position for responses in a particular muscle varied up to 2 cm. This variability could be explained by the variability in the relationship between the central sulcus and the extracranial bony landmarks of each individual. Responses could be obtained whenever the windings of the coil passed over the appropriate region of the motor cortex, providing evidence that magnetically evoked responses do originate from activation of the precentral gyrus. The size of the cortically evoked responses for a given stimulus intensity depended on the direction of the coil currents passing over the motor area. For FDI muscles, the largest responses were obtained when the coil currents passed over the lateral part of the motor strip from forwards behind and transversely to the central sulcus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Central motor pathways in patients with mirror movements.

Central motor pathways were investigated in three patients with congenital mirror movements using magnetic motor cortex stimulation. Response thresholds, amplitudes and latencies were normal. The projection of the corticomotoneuronal pathways was assessed by placing the coil over the vertex and comparing the size of responses in the first dorsal interosseous (FDI) muscles evoked by anticlockwise and clockwise [corrected] coil currents. In normal subjects, right FDI responses are larger with anticlockwise currents than with clockwise [corrected] currents at the same stimulation strength and vice versa. In two out of three patients with congenital mirror movements, this sensitivity of response amplitude to coil current direction was reversed. The third patient with congenital mirror movements and a fourth patient with acquired mirror movements had responses which were normally sensitive to current direction. These findings support the hypothesis that some cases of congenital mirror movements may be due to abnormal projection of corticomotoneuronal pathways.

Adult↗
PubMed1991

Magnetic stimuli applied over motor and visual cortex: influence of coil position and field polarity on motor responses, phosphenes, and eye movements.

Transcranial magnetic stimulation was performed over the motor and visual cortex with the Novametrix 12-cm diameter stimulation coil. The influence of coil position on the size of electromyographic responses and on the intensity and position of phosphenes in the binocular visual field was studied. Furthermore, it was investigated whether stimulation over the visual cortex or over the frontal eye field evoked or disturbed eye movements. Coil position was recorded by constructing grids on the skull surface using extracranial bony landmarks, and was then related individually to underlying cerebral sulci by analysis of magnetic resonance images of the brain. Motor responses. Excitatory effects were maximal when the coil windings in the middle of the coil ring lay over the particular motor representation field of area 4. The response size depended on the direction of the coil currents passing over the motor cortex. For example, coil currents passing over the lateral part of the precentral gyrus from the front and transversely to the central sulcus elicited maximal responses in hand muscles. With the currents passing over the same area in the opposite direction, response amplitudes were much smaller, suggesting activation of different inputs to cortical motoneurons. Phosphenes. Fields of fixed, white and unstructured phosphens occurred in the lower half of the visual field when the coil center was placed about 7 cm anterior to the inion on the inion-nasion line. Counterclockwise or clockwise coil currents elicited phosphenes within the left or right lower quadrant of the binocular visual field, respectively, which could be attributed to an activation of the right or left primary visual cortex (area 17). The 'cortical' phosphenes moved with voluntary eye movements, but not during caloric and optokinetic nystagmus. Phosphenes resulting from an excitation of the optic nerve rather than the retina could be evoked by stimulation over frontal parts of the skull. Eye movements. The application of single magnetic field pulses over the frontal eye field or over the visual cortex did not elicit eye movements except for small vertical eye movements as part of a magnetically elicited blink.

Adolescent↗
PubMed1991

Magnetic stimulation of corticonuclear systems and of cranial nerves in man: physiological basis and clinical application.

After transcranial magnetic brain stimulation, two types of responses in muscles supplied by cranial nerves (trigeminal, facial, accessory, and hypoglosseal nerves) can be observed. With a placement of the coil center approximately 6 cm lateral of the vertex on the interaural line, purely ipsilateral responses can be evoked in the cranial muscles which are induced by excitation of the nerves at or near their intracisternal course ('short-latency' responses). With the coil center 4 cm lateral of the vertex bilaterally 'long-latency' responses can be evoked which are the result of an excitation of that part of the motor cortex which mediates impulses to the motoneurons of cranial nerves via the corticonuclear tract. Evaluations of latencies and amplitudes of the responses in cranial muscles, and of the excitability of their supplying nerves at a proximal site considerably improve the electrophysiological assessment of the site, severity, and prognosis of cranial motor disturbances, especially in facial nerve palsies.

Cranial Nerves↗
PubMed1991

Electrophysiological characterization of the X-linked recessive bulbospinal neuronopathy (XRBSN).

Detailed electrophysiological analyses including nerve conduction velocity measurements of motor and sensory nerves, EMG recordings of a variety of muscles, evoked potentials, magnetic brain stimulation, electrophysiological testing of autonomic functions, tremor measurements and testing of voluntary movements were applied to three patients with X-linked recessive bulbospinal neuronopathy (XRBSN). All three patients presented with a slowly progressive anterior horn impairment, involvement of sensory nerves and posterior columns, but intact central descending motor pathways and an essential tremor responding to propranolol treatment. The spectrum of electrophysiological findings helps to diagnose XRBSN reliably even in sporadic cases.

Adult↗
PubMed1990

Safety aspects of transcranial brain stimulation in man tested by single photon emission-computed tomography.

Single photon emission-computed tomography (SPECT) using 99mTc-labelled hexamethylpropyleneamine oxime (99mTc-HMPAO), a new method to visualize regional cerebral blood flow (rCBF) and epileptogenic foci, was used to study acute and long-term effects of transcranial brain stimulation. Magnetic and electric brain stimulation increase rCBF not more than voluntary muscle activation mimicking the motor effects of transcranial brain stimulation. Focal rCBF increase, typical for epileptogenic foci, or other pathological findings could not be detected even when the subject had received several thousand stimulations in the past. Transcranial brain stimulation does not produce rCBF patterns indicating acute or chronic adverse effects.

Adult↗
PubMed1990

Clinical use of the magnetic stimulator in the investigation of peripheral conduction time.

The application of rapidly changing magnetic fields (magnetic stimulation) over the neck or lower back elicits EMG responses in the muscles of the arm or leg respectively. Such responses have stable onset latencies but their amplitudes vary depending on the position of the coil over the neck or lower back. Supramaximal responses could not be obtained. Comparison of onset latencies with estimates of peripheral conduction time using a conventional F-wave technique suggest that the site of excitation of the motor axons is about 1.3 msec conduction time distal to the cervical motoneurons and 3 msec distal to the lumbosacral motoneurons. Response configuration after paravertebral magnetic stimulation was similar to that of the standard electrically evoked M-wave in the small hand muscles but not in lower limb muscles. Responses in lower limb muscles after paravertebral magnetic stimulation may consist of additional F-wave and H-reflex components. The possible clinical role of paravertebral magnetic stimulation in the investigation of peripheral and central motor pathways is discussed in the light of these findings.

Adult↗
PubMed1989

Investigation of unilateral facial weakness: magnetic stimulation of the proximal facial nerve and of the face-associated motor cortex.

Twenty-four patients with unilateral facial weakness of various aetiologies were investigated using a magnetic stimulator to stimulate the proximal segment of the facial nerve directly (short latency response) and also to activate the facial motoneurons bilaterally via corticonuclear pathways by placing the stimulating coil over the motor cortex (long latency responses). Electromyographic recordings were taken from both mentalis muscles using concentric needle electrodes. Seventeen patients were investigated at various times after onset of idiopathic facial palsy (Bell's palsy). In the acute stage (less than 5 days after onset) short and long latency responses on the paretic side were abnormal, being absent in all but one patient, in whom the short latency response was delayed. These abnormal responses were the earliest neurographic correlate for nerve conduction block. In 4 out of 9 patients seen up to 30 days after onset of palsy, trans-synaptically evoked long latency responses were absent. In patients examined more than 2 months after onset, long latency responses could always be obtained and, in 5 of 8 patients, short latency responses could also be elicited, indicating a return of the direct excitability of the nerve. Five patients with cerebral hemisphere lesions causing mild unilateral facial weakness had absent long latency responses when stimulating over the affected hemisphere, but normal bilateral long latency responses following stimulation over the unaffected cerebral hemisphere; short latency responses were normal. Magnetic stimulation of the brain and of the facial nerve can differentiate between central and peripheral causes of unilateral facial weakness and may prove useful in the early assessment of the degree of conduction block in Bell's palsy.

Adolescent↗
PubMed1989

Brachial plexus lesions following cardiac surgery with median sternotomy and cannulation of the internal jugular vein.

There are many possible complications after cannulation of the internal jugular vein (IJV) including injury to the brachial plexus. Neurologic injuries can also occur from sternal splitting. The present study looked at the incidence of brachial plexus lesions after cardiac surgery with and without IJV cannulation. Over 12 months, 815 patients were studied after all types of cardiac surgery. In one half of the group, cannulation of the IJV was avoided when possible. Reducing the incidence of IJV catheterization did not lower the overall incidence of brachial plexus lesions (1.8% to 1.4%). However, there was a higher incidence of neurologic lesions in patients with IJV catheters (3.0% to 0.8%) during the entire study period. All 13 plexus lesions were in the C8-T1 distribution, and seven of the patients had a Horner's syndrome on the same side. No posterior first rib fractures could be detected by radiographs. The brachial plexus lesions were transient but the Horner's syndromes were longer-lasting. It is concluded that the injuries are due to compression and traction of the plexus due to stretching and possibly from hematoma formation from the IJV punctures.

Adult↗
PubMed1989

The Bereitschaftspotential is abnormal in Parkinson's disease.

The average Bereitschaftspotential (BP) preceding a rapid, self-paced voluntary extension movement of the index finger was recorded from 6 scalp locations in 14 patients with Parkinson's disease who had been withdrawn from their normal drug therapy for at least 12 h before testing. The amplitude of the potential was measured at the peak negativity (N1) and 650 ms prior to this (NS1), and compared with that recorded in a group of 12 age-matched control subjects. The N1 amplitude was the same as in the normals, but the NS1 component was smaller in the patients, especially in midline leads. As a result, the rise in the BP between the peak NS1 and N1 component (termed NS2) was larger in the patient group. The NS1 component of the BP is thought to reflect preparatory activity in the supplementary motor area (SMA) of cortex. Since the basal ganglia provide a major source of afferent input to SMA, the reduction in NS1 in the patients probably results from inadequate basal ganglia activation of SMA. The larger NS2 component may reflect extra activity in other brain areas to compensate for the reduced SMA activity.

Aged↗