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Biomedical subjects

M R Dimitrijevic

Publications and source records attributed to M R Dimitrijevic.

At least 55 records · Page 3Linked to original sources
PubMed1986

Voluntary supraspinal suppression of spinal reflex activity in paralyzed muscles of spinal cord injury patients.

Having previously demonstrated that residual facilitatory brain influence on segmental structures occurs in paralyzed spinal cord injury patients, we sought evidence of suprasegmental suppression in such patients. By recording EMG activity from leg muscles, we studied changes in segmental excitability of the plantar reflex elicited by cutaneous stimulation of the plantar surface. Using surface EMG recordings, 50 paralyzed spinal cord injury patients were examined for their ability to volitionally suppress the plantar reflex on three repeated trials after three baseline trials. The patients, who had no voluntary EMG activity in the monitored muscles, were able to volitionally suppress the plantar reflex responses by 45% in the tibialis anterior, hamstring, and triceps surae muscles and to suppress the quadriceps response by 72%. In this patient group, 73 of 100 tibialis anterior muscle groups showed suppression of more than 20% compared with the control response. On reexamination, these findings were consistent during a period of 2 years in six patients. We conclude that suprasegmental suppression of segmental activity does occur in paralyzed spinal cord injury patients, and that in clinically complete patients, neurological evaluation should include assessment of the degree of preservation of suprasegmental neurocontrol on segmental activity below the lesion.

Adolescent↗
PubMed1986

Spinal cord stimulation for the control of spasticity in patients with chronic spinal cord injury: I. Clinical observations.

The effectiveness of spinal cord stimulation for control of spasticity was studied in 59 spinal cord injury patients. SCS was markedly or moderately effective in reducing spasticity in 63% of the patients. We found that control of spasticity by SCS was not correlated with the severity of spasticity, the type of spasticity (flexor or extensor), or the ability to ambulate. However, stimulation was more effective in patients with incomplete cervical lesions than in complete cervical lesions. Stimulation below the lesion was more effective than above. We conclude that SCS was effective when electrodes were properly positioned below the lesion over the posterior aspect of the spinal cord in patients with some residual spinal cord function. We hypothesize that SCS controls spasticity by modification of activity of spinal-brainstem-spinal loops and by suppression of segmental excitation through antidromic activation of propriospinal pathways.

Adult↗
PubMed1986

Spinal cord stimulation for the control of spasticity in patients with chronic spinal cord injury: II. Neurophysiologic observations.

We sought neurophysiologic evidence that spinal cord stimulation could modify the behavior of spinal reflexes in 15 chronic SCI patients who showed the beneficial effect of SCS on spasticity. We studied the behavior of passive stretch, clonus, cutaneous touch, plantar reflex irradiation, and the response to the neck flexion reinforcement maneuver during spinal cord stimulation by use of surface PEMG recordings. Fifty-five percent of the responses were changed during spinal cord stimulation, but with widely varying patterns of response in individual patients. Exceptional patients showed changes in most or all responses; most showed changes in two or three. Thirty of seventy-five responses showed a reduction in motor unit activity in the recordings. Eleven of seventy-five responses were increased. Excessive stimulation strength enhanced spasticity in patients in whom another stimulus setting suppressed spasticity. We conclude that spinal cord stimulation could modify segmental reflexes but that the effects were selective, probably dependent on the preserved segmental structures and ascending and descending pathways.

Adolescent↗
PubMed1985

Characteristics of the tonic stretch reflex in spastic spinal cord and head-injured patients.

Spasticity is a known sequelae of spinal cord injury and head injury. We sought to examine whether there were any significant differences in the characteristics or underlying mechanisms of spasticity in these two groups in the chronic period which may be related to the level of injury of the neuraxis. The response to vibration applied to the muscle, or the tonic vibratory reflex, has been shown to be related to the degree of spasticity, and was therefore studied along with phasic reflexes and passive movements. These studies were carried out on cooperative, stabilized patients who were otherwise healthy, 5 with head injuries, and 5 with spinal cord injuries. The patients were examined in a supine position while surface EMG recordings were made of quadriceps and triceps surae muscles bilaterally. Tendon jerk responses, passive and volitional movements, and responses to a powerful vibratory stimulator were measured. In both head injury and spinal cord injury patient groups, a large EMG response was elicited by passive maneuvers, and tendon jerks were exaggerated. The tonic vibratory response, previously shown to be dependent upon brain influence, was present in both groups. These observations suggest that similar suprasegmental mechanisms may be responsible for hypertonia in both head-injured and spinal cord-injured patients.

Adolescent↗
PubMed1984

Suprasegmentally induced motor unit activity in paralyzed muscles of patients with established spinal cord injury.

In an attempt to demonstrate the presence of functional descending fibers in patients with clinically apparent functional spinal cord transection, we examined electromyographically recorded paralyzed leg muscle responses to the Jendrassik and other reinforcement maneuvers. Two patterns were observed: a low-amplitude, short onset time reinforcement maneuver response (RMR) restricted to one to three muscle groups (RMR1), and a larger-amplitude response with a longer onset time that occurred bilaterally in essentially all of the recorded muscles (RMR2). The responses imply preserved descending facilitory influence on isolated populations of motor units (RMR1) or on segmental interneuron pools (RMR2). Such findings indicate the presence of functioning fibers traversing the injured portion of the spinal cord in patients diagnosed as having a complete lesion. In such cases, it is possible for patients to initiate subclinical motor unit activity or suprasegmentally induced gross movement through reinforcement maneuvers, but not to control the amplitude or duration of the response.

Adolescent↗
PubMed1984

Electrophysiological characteristics of lumbosacral evoked potentials in patients with established spinal cord injury.

Surface electrodes positioned over the S1 and T12 vertebrae and referenced to T6 were used to record spinal potentials evoked by unilateral stimulation of the posterior tibial nerve at the knee. Data were collected on 24 patients who received spinal cord injuries 2 months to 31 years previously. The recording sites were below the level of spinal injury. The lumbosacral evoked potentials (LSEPs) were compared with the results of measurements obtained from 19 neurologically healthy subjects. Additional data were collected on each patient to characterize segmental reflex responses and preservation of sensory and motor functions associated with the L5 through S2 segments of the spinal cord. Assuming that the LSEP reflects the activity of spinal cord interneurons, the results demonstrate a degree of spinal cord dysfunction caudal to the area of injury in a substantial number of the patients with spinal cord injury which we studied.

Adolescent↗
PubMed1984

Meningomyelocele: a clinical, urodynamic and neurophysiological evaluation.

A total of 11 children with chronic meningomyeloceles underwent a clinical neurological, urodynamic and neurophysiological evaluation to define further the level and type of lesion present in the lumbosacral spinal area. The neurophysiological evaluation was correlated with detrusor activity. Detrusor hyperreflexia was present in 45 per cent of the patients and functional activity of the somatic sacral reflex arc was demonstrated in 4. Absolute interruption of the somatic sacral reflex arc was found in the remaining patients with detrusor areflexia. All patients had evidence of a lower motor neuron lesion on clinical neurological evaluation, with weak or absent myotatic and musculocutaneous reflexes. Electromyographic evaluation revealed signs of severe partial to complete denervation of the affected muscle groups. However, increased motor unit potentials were observed in 5 patients after coughing and stimulation of the perianal skin. The bulbocavernosus reflex was absent clinically and electrophysiologically in all 6 patients tested. However, this finding did not indicate absolute interruption of the reflex arc, since further temporal and spatial stimuli resulted in an increase in motor unit potentials. Somatosensory cortical evoked potentials were useful in demonstrating an intact afferent input system to the spinal cord and brain area. However, lumbosacral evoked potentials appeared to be the least useful neurophysiological method to demonstrate partial preservation of the input to the spinal cord level. Therefore, detrusor and external urethral sphincter function may be documented on urodynamic and neurophysiological evaluation when the clinical examination has revealed a complete lower motor neuron lesion. The complexity of the lesion caused by the malformation in patients with meningomyelocele is shown.

Adolescent↗
PubMed1983

Somatosensory perception and cortical evoked potentials in established paraplegia.

In 66 patients who suffered severe spinal cord injury 7 months to 28 years previously, somatosensory cortical evoked potentials were recorded to electrical stimulation of the leg nerves and compared to clinical assessment of light touch, pain, position sense and two-point discrimination. The patients were separated into 4 categories according to the degree of disintegration of the somatosensory evoked potential waveform. A clear correlation was found between the impairment of somatosensory perception and the deterioration of the somatosensory evoked potential in each group. However, it was not possible to observe any direct correlation between the sensory score or impairment of a single modality and somatosensory evoked potential changes, or among the impairment of single modalities on a case by case basis. This study indicates that the somatosensory evoked potential can be used to provide electrophysiological information independent of the clinical examination on functions of the dorsal columns in the chronic stage of spinal cord injury.

Adolescent↗
PubMed1983

Neurophysiological assessment of electrode placement in the spinal cord.

The use of neurophysiological techniques in addition to radiographic methods to determine the location of electrodes to be introduced into the epidural space for spinal cord stimulation is beneficial. Information on the distribution of paresthesias and muscle twitches provides an indication of the level and lateral location in relation to the midline of the spinal cord. For electrodes placed posteriorly, the threshold currents necessary for sensation are lower than those for muscle responses. Somatosensory evoked potentials resulting from epidural stimulation demonstrate effective depolarization of ascending structures. Evoked potentials recorded from the electrodes in response to peripheral nerve or spinal cord stimulation at a distant segment illustrate the possibility of activation of underlying generators of the spinal cord.

Brain Injuries↗
PubMed1983

Spinal cord stimulation as a tool for physiological research.

The use of spinal cord stimulation for alleviation of disabilities due to motor neuron lesions has provided the opportunity to explore a new approach to measurement of spinal cord physiology. Externalized leads of epidural electrodes provide the possibility of recording evoked spinal cord activity, while both externalized or implanted leads can be used to study cortical evoked responses and twitches induced by spinal cord stimulation. The use of such electrophysiological techniques can be expected to expand greatly the applicability of the technique for alleviating motor disabilities, through a better definition of the degree, nature and extent of the lesion.

Afferent Pathways↗
PubMed1983

Neurocontrol of upper motor neurone muscle paralysis.

An attempt was made to describe upper motor neurone dysfunctions on the basis of changes in volitional activity, the effects of reinforcement maneuvers on motor units and sustained and unsustained characteristics of segmental reflexes. According to the above criteria, patients with paralysis due to established spinal cord injury can be divided into groups with clinical and subclinical paralysis, clinical paralysis with subclinical evidence of residual suprasegmental motor control, and clinically incomplete paralysis with a subclinical variety of neurocontrol patterns of motor activities. This categorization of paralysis according to neurocontrol criteria is opening new avenues to the use of residual motor activity for the modification of abnormal motor control by peripheral nerve stimulation and spinal cord stimulation procedures for the alteration of upper motor neurone dysfunctions.

Humans↗
PubMed1983

Motor control in man after partial or complete spinal cord injury.

The essential features of motor control in spinal man can be understood in terms of segmental reflexes interacting with, and controlled by, the influence of distant segments and even by the brainstem. Thus, overall motor control in patients with spinal cord lesions can be classified according to structure as: (1) simple segmental stretch and withdrawal reflexes; (2) plurisegmental gross reflex movement of paralyzed muscles; or (3) propriospinal processes with partial brain influence (i.e., severe spasticity and traces of position and postural control). Because of the variable nature of the injuries, there may be exceptions to this rule. However, the basic mechanisms can be understood by studying stretch reflex responses to various stimuli. The segmental reflexes are under a powerful influence of the propriospinal interneuron system which conducts impulses up and down the spinal cord. Finally, the apparently "isolated" spinal cord in which clinical signs indicate complete motor paralysis and lack of sensation below the lesion is not always isolated from supraspinal control of involuntary motor activity. In a significant proportion of the clinically complete spinal injuries we studied, it was possible to demonstrate the presence of preserved bulbospinal influences on spinal reflex responses.

Electromyography↗
PubMed1982

Study of propriospinal interneuron system in man. Cutaneous exteroceptive conditioning of stretch reflexes.

Functional characteristics of the propriospinal interneuron system have been studied in 20 patients with clinically complete chronic transverse spinal cord injury by conditioning repetitively elicited Achilles tendon jerks with noxious electrical stimuli applied to the thoracic, lumbar, and sacral dermatomes. Such conditioning stimuli caused an increase of ipsilateral and contralateral Achilles tendon jerks except when they were applied to the ipsilateral plantar surface when they caused suppression. This effect is due to inhibition of the tested extensor motoneurons by the conditioning stimuli applied to the plantar surface. More generally the observed increase of Achilles tendon jerks can be explained by excitation spread from distant ipsilateral and contralateral thoracic, lumbar and sacral segments. It is likely that this effect is mediated by the fibers of the fasciculi proprii of the spinal cord as this system survives complete transection of the spinal cord.

Adolescent↗
PubMed1982

Neurophysiological approaches to chronic pain following spinal cord injury.

Pain occurring in patients with spinal cord injury can be classified on clinical grounds into five types: peripheral, central, visceral, mechanical and psychic. An attempt has been made to correlate each type of pain with present neurophysiological knowledge. Mechanisms as to how unpleasant sensations reach the conscious level can be deduced when clinical and neurophysiological data are pooled. Eight case histories are presented which typify each class. The authors' evaluation and treatment offered is presented for each type.

Abdomen↗
PubMed1982

A study of posterior column function in familial spastic paraplegia.

A family is described in which affected members have clinical features consistent with the late onset form of Strümpell's Familial Spastic Paraplegia which is of dominant inheritance. Abnormalities in cortical somatosensory to peroneal nerve stimulation were found in all affected members of the family and in several who were clinically unaffected. In some cases responses were better defined at slow rates of stimulation. Peripheral nerve conduction velocity was normal. These changes are consistent with previous findings of degeneration in the posterior columns at necroscopy and with a dying back process in the first sensory neuron. Clinically unaffected members of the family with abnormalities in the somatosensory response may represent asymptomatic heterozygotes.

Adolescent↗
PubMed1981

Remarks on spinal cord stimulation and the placebo effect.

Spinal cord stimulation, which has been shown to be beneficial in multiple sclerosis as well as in sustained spinal cord injury, works through modification of specific motor mechanisms. This modification occurs through regional recruitment of spinal cord activity in posterior aspects of the spinal cord. Substantial involvement of the placebo effect can be ruled out by noting the persistence of beneficial effects observed in spinal cord injury patients and by the fact that the effects are related only to depolarization of posterior structures of the spinal cord, rather than to perception of a 'tingling' sensation caused by spinal cord stimulation. Such a sensation can also occur when electrodes are over anterior or lateral structures of the spinal cord, when the stimulation is not effective in alleviating motor symptoms.

Electric Stimulation Therapy↗