Detrusor areflexia in suprasacral spinal cord injuries.

Patients with high thoracic or cervical spinal cord injuries normally have a detrusor contraction during cystometry. Thirteen patients with detrusor areflexia and a high spinal cord lesion underwent neurophysiological evaluation with electromyography of the pelvic floor muscles, lumbosacral-evoked potential to tibial nerve stimulation, the bulbocavernosus reflex and water cystometry. Two groups of patients were identified. Of those patients with initial detrusor areflexia evidence was found for a subclinical second lesion involving the lumbosacral arc, which accounted for the acontractile bladder. In the remaining patients of this group, who had an intact sacral reflux arc, a detrusor contraction developed after a mean of 16.6 months from the date of injury. The second group of patients exhibited initial detrusor hyperreflexia that subsequently converted to areflexia. A reason was found for the alteration in bladder behavior in each case. The possible reasons for differential recovery of the somatic and autonomic nervous systems are discussed together with a rationale for the second subclinical spinal cord lesion. The most predictive neurophysiological test was electromyography of the pelvic floor.

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.

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.

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.

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.

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.

Activation of paralysed leg flexors and extensors during gait in patients after stroke.

EMG activity of long foot flexor and extensor muscles was studied during gait in 34 ambulatory hemiparetic patients, correlating the EMG to phases of the gait cycle as monitored by switches placed on the plantar surface of the foot. EMG patterns during stance and swing phases were categorized into six groups, ranging from normal alternation of muscle contraction, to tonic activity of the extensors, with no alternation. The deterioration in activity appears to be related to the (unbalanced) release of extensor and flexor mechanisms which arises in varying degrees and combinations after capsular lesions. The extensor thrust postural reaction appears to be essential for gait in pathological conditions which result in upper motor neuron weakness.

Underlying mechanisms of the effects of spinal cord stimulation in motor disorders. A review of the discussion.

Possible underlying neurophysiological mechanisms of spinal cord stimulation in the modification of motor disorders were discussed by scientists working in research on motor control mechanisms. Changes of motor unit properties in upper motoneuron lesions were reviewed, the role of proprioceptive input and long-loop reflexes in motor control was discussed, analysis of ramp and ballistic movements in motor control was presented, and some aspects of neural control of locomotion were reviewed. Some physiological considerations of the influence of electrical stimulation on various neural functions were given and the conclusion was reached that, at present, no definitive models of the action of spinal cord stimulation are available.

Clinical evaluation of the effect of spinal cord stimulation on motor performance in patients with upper motor neuron lesions.

The effect of chronic electrical stimulation of the spinal cord was evaluated in a group of 24 patients with multiple sclerosis, spinal cord injury, and degenerative disorders of the central nervous system. The systems for stimulation had been implanted from 12 to 30 months prior to completion of evaluation. At the time of completion of evaluation, 23 of the 24 patients still had implanted systems, although 6 of them had not used spinal cord stimulation because of no noticeable effect. In 3 patients stimulation had been disconnected because of technical failure of the system. In 1 patient the system had been removed 8 weeks after implantation because of inflammation in the under-skin receiver pocket. The effects on motor performance of the remaining 14 patients who had continuously active systems were improved bladder control, diminished spasticity, improved movement coordination, and increased endurance.

Study of sensation and muscle twitch responses to spinal cord stimulation.

Electrically induced sensation and muscle twitches were studied in a group of 43 patients in whom epidural electrodes were percutaneously placed for the evaluation of the effect of spinal cord stimulation on modification of their impaired motor control. Mean stimulus strength for sensory threshold was 5.25 +/- 2.75 mA and the tolerance level was at the stimulus strength of 10.8 +/- 4.4 mA. Muscle twitches with short latencies were recorded in limb and trunk muscles within the segments at the stimulating cathode. Exceptionally, higher stimuli elicited muscle twitches of distant segments.

Neurophysiological evaluation of chronic spinal cord stimulation in patients with upper motor neuron disorders.

Spinal cord stimulation was found to be an effective method for improving motor performance in patients with upper motor neuron disorders. Electromyographic analysis of segmental and suprasegmental activity was performed in 11 patients who had used spinal cord stimulation for more than 12 months. Neurophysiological analysis of electromyographic findings revealed improvement of volitional motor control and a reduction of spasticity in the examined muscles of the lower limbs in all patients.

Habituation: effects of regular and stochastic stimulation.

The different effects of regular and stochastic stimulation on the flexor reflex of patients with the spinal cord totally divided and of normal subjects and on the blink reflex of normal subjects were studied.When the cutaneous stimulus was above but less than twice threshold, with regular stimulation habituation occurred; with stochastic stimulation, habitutaion either did not occur or it was minimal. Stochastic stimulation was at random stimulus intervals or with random stimulus intensities.When stimulus intensity was around threshold, habituation occurred with both kinds of stimulation, the response to stimulation soon ceasing to occur. When stimulus intensity was greater than twice threshold, habituation did not occur with both kinds of stimulation.When regular stimulation was given after the response had ceased to occur, extinction of the response beyond zero occurred.When a dishabituating stimulus was repeatedly applied in a regular manner, habituation to the dishabituating stimulus occurred.With regular and stochastic stimulation given as conditioning and test series, it was seen that stochastic stimulation caused, in addition to the short-term excitatory effect, the same long-term cumulative depressing effect on excitability as did regular stimulation.