Segmental reflex pathways in spinal shock and spinal spasticity in man

Increased H(max):M(max) ratio in community walkers poststroke without increase in ankle plantarflexion during walking

OBJECTIVE

To investigate whether changes in H-reflex response at midswing and midstance are related to excessive plantarflexion during walking in community walkers poststroke compared with control subjects without stroke.

DESIGN

Survey of functional walking handicap in a random sample of an annual stroke cohort followed by H-reflex and M(max) testing of a smaller sample.

SETTING

Community and laboratory testing.

PARTICIPANTS

Forty individuals with stroke (IWS group) completed the functional walking handicap survey, 10 of whom agreed (with 10 age-matched controls) to enroll in a study of of the H(max):M(max) ratio in soleus during walking.

INTERVENTION

Electromyography during treadmill walking.

MAIN OUTCOME MEASURES

Functional Walking Handicap Scale, soleus H(max):M(max) ratio, and the ankle joint's angle of displacement.

RESULTS

Nine of the 10 stroke patients were community walkers. All had significantly (p <.05) more variable ankle movement during walking than the controls. The H(max):M(max) ratio was significantly (p <.01) increased in the IWS group because of a decrease in M(max) response without significant (p >.05) increase in H(max) response.

CONCLUSIONS

Individuals with community-level walking ability after stroke have significantly (p <.05) less repeatability of ankle joint movement than controls at both midswing and midstance. Simultaneous soleus H(max) and M(max) testing showed a significant (p <.01) reduction in the H(max) and H(max):M(max) ratio at midswing in controls only. This inhibition at midswing was lost by the IWS group without significant increase in H(max), suggesting that central synaptic excitability was within the normal range, and possibly accounting for the absence of excessive ankle plantarflexion during walking in the IWS group with community level walking ability.

Continuously infused intrathecal baclofen over 12 months for spastic hypertonia in adolescents and adults with cerebral palsy

OBJECTIVE

To determine if the continuous intrathecal delivery of baclofen will control spastic hypertonia caused by long-standing cerebral palsy (CP).

DESIGN

Case series.

SETTING

Tertiary care outpatient and inpatient rehabilitation center directly attached to a university hospital.

PATIENTS

Thirteen CP patients (average age, 25yr; range, 13--43yr) with intractable spastic hypertonia and quadriparesis (one of whom had predominate diplegia) who had not responded to oral medications including baclofen.

INTERVENTION

Patients were screened via a bolus injection of baclofen intrathecally. Those who dropped an average of 2 points on their lower extremity (LE) Ashworth scores were offered computer-controlled pump implantation for 12 months of continuous delivery of intrathecal baclofen (ITB).

MAIN OUTCOME MEASURES

Ashworth rigidity scores, spasm scores, and deep tendon reflex scores were collected for both the upper extremities (UEs) and LEs. Differences over time were assessed via descriptive statistics and Wilcoxon's signed-rank test.

RESULTS

After 1 year of continuous ITB treatment, the average LE Ashworth score +/- standard deviation decreased from 3.4 +/- 1.2 to 1.5 +/- 0.7 (p <.0001), spasm score from 1.4 +/- 1.6 to 0.6 +/- 1.2 (p =.1024), and reflex score from 2.5 +/- 1.2 to 0.7 +/- 1.1 (p <.0001). The average UE Ashworth score decreased from 3.0 +/- 1.2 to 1.7 +/- 1.0 (p <.0001), spasm score from 1.2 +/- 1.6 to 0.2 +/- 0.6 (p =.0135), and reflex score from 2.3 +/- 0.7 to 0.5 +/- 0.9 (p <.0001). The average ITB dose required to attain these effects at 1 year was 263 +/- 91microg continuously infused per day.

CONCLUSION

Continuously infused ITB can reduce spastic hypertonia in the UEs and LEs associated with long-standing CP. This reduction in tone will allow more freedom of movement and the potential for improved function.

Continuously infused intrathecal baclofen for spastic/dystonic hemiplegia: a preliminary report

The objective of this study was to determine whether the continuous intrathecal delivery of baclofen will control spastic hypertonia associated with long-standing hemiplegia from acquired brain injury. Six hemiparetic patients (average age, 50 (range, 42-66) yr) with more than 6 mo of disabling lower limb spastic hypertonia on one side caused by either a unilateral traumatic brain injury or a stroke were recruited in a consecutive manner. The setting was a tertiary care outpatient and inpatient rehabilitation center directly attached to a university hospital. Patients were screened via a randomized, double-blind, placebo-controlled, crossover design to receive either an intrathecally administered bolus injection of normal saline or 50 microg of baclofen. Data for Ashworth rigidity scores, spasm scores, and deep tendon reflex scores were collected on the affected upper limb and lower limb side. Those who dropped an average of two points on their affected lower limb side Ashworth scores were then offered computer-controlled pump implantation for continuous intrathecal administration of baclofen. Differences over time were assessed via descriptive statistics and Wilcoxon's signed-rank test. After 3 mo of treatment, the average lower limb Ashworth score on the affected side decreased from 3.7 +/- 1.0 to 1.9 +/- 0.6 standard deviation (SD) (P < 0.0001), the reflex score from 1.8 +/- 1.3 to 0.5 +/- 0.8 SD (P = 0.0208), and the spasm score from 1.3 +/- 1.2 to 0.8 +/- 1.3 SD (P > 0.05). The average upper limb Ashworth score on the affected side decreased from 3.4 +/- 0.9 to 2.1 +/- 0.9 SD (P = 0.0002), the reflex score from 2.3 +/- 0.5 to 1.7 +/- 0.5 SD (P > 0.050, and the spasm score from 0.8 +/- 1.3 to 0 +/- 0 SD (P > 0.05). The average intrathecally administered dose of baclofen that was required to attain these effects was 205.3 microg, which was continuously infused for 24 h. Continuous intrathecal infusion of baclofen is capable of maintaining a reduction in the dystonia on the hemiparetic side without significantly affecting motor strength on the normal side.

Long-term continuously infused intrathecal baclofen for spastic-dystonic hypertonia in traumatic brain injury: 1-year experience

OBJECTIVE

To determine if the long-term use of continuously infused intrathecal baclofen (ITB) over a 1-year period will control spastic-dystonic hypertonia in patients with traumatic brain injury (TBI).

SETTING

Tertiary care outpatient and inpatient rehabilitation center directly attached to a university hospital.

SUBJECTS

Persons with TBI and intractable spasticity and dystonia for more than 6 months' duration recruited in a consecutive manner.

DESIGN

TBI patients were admitted to the study after screening via a bolus injection of either intrathecal normal saline or 50 microg of baclofen. Data for Ashworth rigidity scores, spasm scores, and deep tendon reflex scores were collected for both the upper extremities (UE) and lower extremities (LE). Patients whose LE Ashworth scores decreased an average of 2 points were then offered implantation of a computer-controlled pump for continuous ITB. Changes over time were assessed statistically via Friedman's analysis for ordinal data and ANOVA for linear data. Differences between set points in time were also assessed via Wilcoxon signed rank.

DATA SET

Seventeen patients (average age 29+/-11 yrs) with spasticity and/or dystonia treated over 1 year via a computer-controllable intrathecal delivery system for the delivery of ITB.

RESULTS

After 1 year of continuous ITB treatment the average LE Ashworth score decreased from 3.5+/-1.3 (SD) to 1.7+/-0.9 (p < .0001), spasm score from 1.8+/-1.3 to 0.2+/-0.5 (p< .0001), and reflex score from 2.5+/-1.1 to 0.1+/-0.3 (p < .0001). The average UE Ashworth score decreased from 2.9+/-1.5 to 1.6+/-1.0 (p < .0001), spasm score from 1.2+/-1.5 to 0.2+/-0.6 (p < 0.0001), and reflex score from 2.2+/-0.5 to 1.0+/-0.8 (p < .0001). The average ITB dose required to attain these effects at 1 year was 302 microg continuously infused per day.

CONCLUSION

Continuous intrathecal infusion of baclofen is capable of maintaining a reduction in spasticity and dystonia in both the upper and lower extremities of TBI patients.

Stretch reflex sensitivity: effects of postural and muscle length changes

In this study, a combination of clinical evaluation, laboratory testing, and model simulation of spasticity is performed under various postural conditions to investigate the changes in the sensitivity and specific mechanisms of spasticity. Fifty-nine multiple sclerosis patients participated in the study and received spasticity evaluation based on both the Ashworth scale and the pendulum test. Spasticity was found to increase in the pendulum test when the subjects were tested in a supine posture, compared to when they were sitting. Three patterns of stretch reflex response were seen for similar leg swing trajectories. While it was clear that the increased stretch of rectus femoris in the supine posture contributed to the increased spasticity, the results of modeling showed that other more complex factors were also involved. The supraspinal descending modulation associated with postural control may play a more dominant role in the severity of spasticity. The results suggest that the biomechanical test of spasticity should be performed for several different postures or ranges of movement with muscle activities monitored simultaneously, so that the effect of various factors can be examined. The work also indicates that a neuromusculoskeletal model with detailed muscle dynamics and stretch reflex loops is a valuable tool for investigating the neural mechanisms of spasticity.

"Extensor toe sign" by various methods in spastic children with cerebral palsy

Upper motor neuron lesion in adults is usually associated with spasticity and "extensor toe sign" on plantar stimulation (extensor plantar response). There are various methods of eliciting this sign including the classic method by Babinski. Other methods produce this response when the area of reflexogenic zone is increased due to upper motor neuron lesion. There are varying reports of Babinski positivity in spastic cerebral palsy. This study was undertaken to assess the sensitivity of different methods of eliciting "extensor toe sign." An attempt has also been made to correlate the severity of spasticity with the combined "extensor toe sign" positivity by various methods and with the increase in reflexogenic zone. Eighty-one children with spastic cerebral palsy were examined. Twelve had hemiplegia; therefore, a total of 150 limbs were tested. "Extensor toe sign" was elicited by 12 different methods in each patient. The sensitivity of each method was calculated and compared with each other one. The assessment of spasticity was done using the Ashworth Tone Scale. The severity of spasticity was correlated with "extensor toe sign" positivity using various methods. Classic Babinski reflex was positive in 75% of cases, whereas Gonda-Allen sign was positive in 90% of cases followed by Allen-Cleckley (82%), Chaddock (74%), and Cornell (54%). All other signs had sensitivity of less than 30%. There was no increase in sensitivity after combining them. There was significant negative correlation between the spasticity and the combined "extensor toe sign" positivity (by all the methods). This study, therefore, suggests that the majority of patients with spastic cerebral palsy have positive "extensor toe sign." The Gonda-Allen method is more sensitive than the classic Babinski method. A positive "extensor toe sign" is negatively correlated to the degree of spasticity.

Prospective assessment of continuous intrathecal infusion of baclofen for spasticity caused by acquired brain injury: a preliminary report

Twelve consecutive patients with severe spasticity and hypertonia following acquired brain injury were treated with continuous intrathecal infusion of baclofen via an implanted, programmable infusion pump-catheter system for a minimum of 3 months. In every case intrathecal baclofen therapy resulted in a statistically significant reduction in upper- and lower-extremity tone, spasm frequency, and reflexes, contributing to improved functional abilities. There were no untoward side effects or complications associated with treatment. This preliminary assessment indicates that intrathecal administration of baclofen is effective in treating the disabling spasticity caused by acquired brain injury in selected patients.

A dynamic neuromuscular model for describing the pendulum test of spasticity

Both dynamic and static thresholds, as well as the gain in the stretch reflex loop, affect the sensitivity of motoneurons to muscle stretch. How the variation in each parameter will influence the mechanical behavior of patients with spasticity is not well understood because of the difficulty in experimentally isolating individual parameters. A neuromuscular dynamic model, based on the pendulum test of spasticity, has been developed to study the specific contribution of individual parameter abnormalities in stretch reflex loops to the observed mechanical abnormalities. The model contains detailed nonlinear dynamics of muscle force generation and stretch reflexes. A computer simulation of the model indicates that the stretch reflex thresholds and the gain have different influences on the leg swing in the pendulum test of spasticity. Individual changes in the static stretch reflex threshold, in the dynamic threshold, or in the gain can not stimulate the whole spectrum of spasticity severity. When simultaneous changes in all three parameters of the stretch reflex loop occur, a small variation of the gain coupled with changes in both static and dynamic thresholds can produce increasing severity of spasticity as the thresholds further decrease. The model is also successful in simulating the effect of posture changes on spasticity.

Operant conditioning of H-reflex in spinal cord-injured rats

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of supraspinal control over spinal cord function. Both rats and primates can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) soleus H-reflex magnitude when exposed to an operant conditioning task. This study used H-reflex operant conditioning to assess and modify spinal cord function after injury. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. From 18 to 140 days after injury, background EMG, M response amplitude, and initial H-reflex amplitude were not significantly different from those of normal rats. HRdown conditioning was successful in some, but not all, spinal cord-injured rats. The H-reflex decrease achieved by conditioning was inversely correlated with the severity of the injury as assessed histologically or by time to return of bladder function. It was not correlated with the length of time between injury and the beginning of conditioning. The results confirm the importance of descending control from supraspinal structures in mediating operantly conditioned change in H-reflex amplitude. In conjunction with recent human studies, they suggest that H-reflex conditioning could provide a sensitive new means for assessing spinal cord function after injury, and might also provide a method for initiating and guiding functional rehabilitation.

Age-dependent effects of muscle vibration and the Jendrassik maneuver on the patellar tendon reflex response

OBJECTIVE

To explore possible effects of aging on the excitability of spinal reflexes.

DESIGN

Using a cross-sectional design, the influences of muscle vibration and the Jendrassik maneuver on patellar tendon reflex function were compared between 30 young adults and 15 older adults.

SETTING

Motor control research laboratory.

SUBJECTS

The young adults were volunteers of college age. The older adults (74.5 +/- 4.14 yr) were volunteers from the local community. All subjects were free of medications and neurological conditions that would affect normal neuromuscular responses.

MAIN OUTCOME MEASURES

A force-time curve analysis of the patellar tendon reflex response was used to assess the inhibition and facilitation of spinal reflexes. In the experimental protocol to assess spinal reflex inhibition, 100 Hz vibration was applied to the right quadriceps muscle. In another experimental protocol, spinal reflex facilitation was assessed using the Jendrassik maneuver. To perform the Jendrassik maneuver, subjects were instructed to grasp their hands together and to pull as hard as possible while breathing normally. After a 2-second count, the tendon tap was delivered to the right leg and the subject was instructed to relax. In both experimental protocols, control patellar tendon reflexes were collected.

RESULTS

Analysis of variance for reflex peak force revealed a significant 30% reduction in the amount of vibration-induced reflex inhibition with increasing age, and a similar 33% reduction in the amount of Jendrassik maneuver facilitation observed for the older adults as compared with the younger adults.

CONCLUSION

These results support the hypothesis that inhibitory and excitatory influences acting on the alpha motoneuron pool are different in young and older adults.

Spinal shock

The term "spinal shock" applies to all phenomena surrounding physiologic or anatomic transection of the spinal cord that results in temporary loss or depression of all or most spinal reflex activity below the level of the injury. Hypotension due to loss of sympathetic tone is a possible complication, depending on the level of the lesion. The mechanism of injury that causes spinal shock is usually traumatic in origin and occurs immediately, but spinal shock has been described with mechanisms of injury that progress over several hours. Spinal cord reflex arcs immediately above the level of injury may also be severely depressed on the basis of the Schiff-Sherrington phenomenon. The end of the spinal shock phase of spinal cord injury is signaled by the return of elicitable abnormal cutaneospinal or muscle spindle reflex arcs. Autonomic reflex arcs involving relay to secondary ganglionic neurons outside the spinal cord may be variably affected during spinal shock, and their return after spinal shock abates is variable. The returning spinal cord reflex arcs below the level of injury are irrevocably altered and are the substrate on which rehabilitation efforts are based.

The influence of glycine and related compounds on spinal cord injury-induced spasticity

Spasticity is a frequent and complex sequel to spinal cord injury. The neurochemical basis for the origin of spasticity is largely unknown. Glycine is among the most abundant neurotransmitters in the spinal cord. However, the role of glycine and related compounds in spasticity have received little attention. An ischemic spinal cord injury was created in rabbits, by an intraaortic balloon occlusion technique, which produced lower limb spasticity. A catheter was inserted into the cisterna magna and the spinal cord was bathed with 100 microM solutions of glycine, strychnine, D-serine, beta-alanine, MK-801, or artificial CSF for 4 hours at a rate of 10 microliters/min. H-reflexes were monitored before and during infusion by stimulating the posterior tibial nerve and recording from the plantar surface of the foot. Glycine, D-serine, and MK-801 depressed the H wave, strychnine produced a heightened H wave, and beta-alanine caused no significant changes. These results indicate that glycine and related compounds may influence spasticity.

Normalization of soleus H-reflex recruitment curves in controls and a population of spastic patients

We examined soleus H-reflex recruitment in 30 controls and 33 patients with spinal cord lesions and spastic spinal paresis. H-reflex gain and threshold were determined from recruitment curves after normalization of stimulus intensity as a multiple of the current for a threshold M-response. Reflex gain was expressed as the mean slope of the H-reflex recruitment curve up to the half-maximal response size. Up to this point the curve follows an almost linear trajectory and will mainly reflect Ia afferent stimulation. This slope had a large variability but was clearly correlated with the H/M ratio. The mean gain was equal in controls and patients. The relation between H- and M-thresholds was expressed as a ratio which had a lower mean value in the patients. Though both H- and M-thresholds may be influenced by peripheral factors, this lower ratio suggests an increase in spinal motoneuron excitability in patients.

Mechanisms of tizanidine action on spasticity

This investigation estimated the mechanisms of tizanidine action on spasticity using a battery of neurophysiological methods. Thirty patients with old post-stroke spastic hemiparesis took part in the investigation. They were treated with tizanidine-mean daily dose 15.8 +/- 5.6 mg for a mean of 23.3 +/- 4.8 days. A questionnaire for assessment of subjective improvement after treatment used a 5-point scale. For standardization of the neurological examination 5-point scales were used to assess muscle tone, muscle force and tendon reflexes. A battery of neurophysiological methods was used to analyze different mechanisms of spasticity: for alpha motoneuron excitability--the F wave parameters; for presynaptic inhibition--the ratio of H reflex amplitudes before and after vibration of the achilles tendon (Hvibr/Hmax); for common interneuron activity--the flexor reflex parameters. Our results revealed that tizanidine reduces spastically increased muscle tone, but has no influence on muscle force, tendon reflexes, Babinski sign and ankle clonus. Tizanidine is supposed to act by increasing the presynaptic inhibition and decreasing of alpha motoneuron excitability. When spasticity has decreased presynaptic inhibition and increased motoneuron excitability, it is better to treat with tizanidine.

Glycine: an important potential component of spinal shock

Amino acid neurotransmitters (AANTs) play a major role in maintenance of muscle tone. Abnormal AANT concentrations are associated with hyper- or hypotonic states. Flaccidity from spinal shock commonly occurs after spinal cord injury (SCI) and may be associated with changes in AANT concentrations. Ischemic SCIs created in the lumbar region of rabbits by intraaortic balloon occlusion produced spastic or flaccid injuries. Microdialysis sampling of AANTs from the injured segmental structures was done 3 days after SCI. Evoked potentials were used to monitor spinal cord stability. No significant changes in AANT levels occurred in the spastic or flaccid group after 4 hour sampling. However, flaccid animals had baseline glycine levels 2-3 times higher (p < 0.001) than spastic animals or controls. High concentrations of the inhibitory AANT glycine is associated with flaccidity following SCI, or spinal shock, but not spasticity. Glycinergic compounds directed toward suppression of excess muscle tone deserve further study.

Soleus H-reflex tests and clinical signs of the upper motor neuron syndrome

Soleus H-reflex tests are used for elucidating pathophysiological mechanisms in motor control. The cumulative vibratory inhibition of the soleus H-reflex, the ratio of the reflex to direct muscle potential (H to M ratio) and the recovery curve of the soleus H-reflex were studied in 38 patients with varying signs of the upper motor neuron syndrome for a possible relation with clinical features. The results were compared with those obtained from a group of healthy volunteers. The magnitude of vibratory inhibition decreased with increase of hypertonia. The H to M ratio increased as the activity of the tendon reflex was enhanced and correlated to a lesser degree with muscle tone. Both the H to M ratio and late facilitation of the soleus H-reflex recovery curve were elevated in clonus. The findings suggest that alterations in the results of soleus H-reflex tests relate to specific clinical features of the upper motor neuron syndrome. Possible pathophysiological implications are discussed.

Evidence that alterations in presynaptic inhibition contribute to segmental hypo- and hyperexcitability after spinal cord injury in man

We examined Hoffmann (H) and tendon (T) reflexes in 3 populations of adult subjects: acute SCI (< 2 weeks post injury), controls, and chronic SCI (> 1 year post injury). We further investigated the effects of continuous tendon vibration and different stimulus rates on the size of evoked H reflexes in these subject populations. All reflex amplitudes were expressed as a function of the maximum direct muscle response (M wave), to allow comparison between subjects. Both H and T reflexes were successfully elicited from all subjects examined, including those in 'spinal shock.' Tendon vibration caused a marked attenuation of H reflexes in acute SCI subjects, intermediate attenuation in controls, and relatively little effect in the chronic SCI group. H reflexes showed greatest attenuation for a given stimulus rate in acute SCI subjects compared to controls (intermediate attenuation) or chronic SCI (limited attenuation) subjects. Both rate sensitivity and vibration influence have been linked to presynaptic inhibitory mechanisms. We suggest that spinal cord injury disrupts the supraspinal influence over segmental interneurons mediating presynaptic inhibition, and that the hyporeflexia associated with 'spinal shock' is due in part to a substantial increase in the efficacy of presynaptic inhibition. Conversely, over time the level of presynaptic inhibition of ankle extensor Ia input in SCI subjects declines to levels less than those of control subjects, contributing to the enhancement of spinal reflexes consistent with the clinical state of 'spasticity' seen in chronic SCI.

AAEM Minimonograph #13: H reflexes and F waves: physiology and clinical indications

Motoneurons can be activated both reflexly and antidromically following electrical stimulation of peripheral nerves. These H reflexes and F waves are clinically useful responses which interface at the level of the peripheral nerves and the spinal cord. Because these responses are commonly employed in the electrodiagnostic evaluation of patients, an understanding of their physiology and clinical applications is important. These are reviewed. Reasoning from the physiology, both the value and limitations of H-reflex and F-wave studies are considered for disorders of peripheral nerves, roots, and the central nervous system. Theoretical concepts about the physiology and pathophysiology of the nervous system based on H-reflex and F-wave data are also discussed.

Mechanisms of baclofen action on spasticity

This investigation estimated the mechanisms of baclofen action on spasticity using a battery of electromyographic methods. Thirty patients with old post-stroke spastic hemiparesis took part in the investigation. They were treated with baclofen-mean daily dose 54.3 alpha 11.6 mg for a mean of 26.3 alpha 4.9 days. A questionnaire for assessment of subjective improvement after treatment used a 5-point scale. For standardization of the neurological examination 5-point scales were used to assess muscle tone, muscle force and tendon reflexes. A battery of electromyographic methods was used to analyse different mechanisms of spasticity: for alpha motoneurone activity--the F wave parameters; for gamma motoneurone activity--the T/H reflex amplitude ratio; for presynaptic inhibition--the ratio of H reflex amplitudes before and after vibration on the achilles tendon (Hvibr./Hmax); for common interneurone activity--the flexor reflex parameters. Our results revealed that baclofen reduces spastically increased muscle tone and Babinski sign. It has no influence on muscle force, tendon reflexes and ankle clonus. Baclofen acts by normalizing the altered interneurone activity and decreasing of alpha motoneurone activity. When spasticity has altered interneurone activity and increased motoneurone activity, it is better to treat with baclofen.

A comparative study of methods for estimation of presynaptic inhibition

The influence of vibration on the H-reflex and on the tendon reflex amplitudes was compared and the efficacy of both methods for the assessment of the presynaptic inhibition was studied. One hundred and twenty patients with post-stroke spastic hemiparesis were investigated. Muscle tone, muscle force and tendon reflexes were assessed. The H-reflex and the Achilles tendon reflex (TA) were recorded under identical experimental conditions. Vibration at a frequency of 100 Hz and an amplitude of 2 mm was applied to the TA. Just after vibration the maximal amplitudes of both reflexes were measured. The ratios of reflex amplitudes after vibration to normal maximal reflex amplitudes (Hvibr/Hmax and TAvibr/TAmax) were evaluated. In all patients with hemiparesis the healthy side was used as a control. Our results revealed significantly increased amplitude ratios on the spastic side. Hence it is concluded that presynaptic inhibition is decreased in spasticity. The amplitude ratios on the healthy and the spastic side were consistent. There was good positive correlation between Hvibr/Hmax and TAvibr/TAmax ratios, suggesting that they provide similar and reliable estimates of presynaptic inhibition.

H-reflex modulation during walking in spastic paretic subjects

Hoffman (H) reflexes were elicited from the soleus muscle during treadmill walking in 21 spastic paretic patients. The soleus and tibialis anterior muscles were reciprocally activated during walking in most patients, much like that observed in healthy individuals. The pattern of H-reflex modulation varied considerably between patients, from being relatively normal in some patients to a complete absence of modulation in others. The most common pattern observed was a lack of H-reflex modulation through the stance phase and slight depression of the reflex in the swing phase, considerably less modulation than that of normal subjects under comparable walking conditions. The high reflex amplitudes during periods of the step cycle such as early stance seems to be related to the stretch-induced large electromyogram bursts in the soleus in some subjects. The abnormally active reflexes appear to contribute to the clonus encountered during walking in these patients. In three patients who were able to walk for extended periods, the effect of stimulus intensity was examined. Two of these patients showed a greater degree of reflex modulation at lower stimulus intensities, suggesting that the lack of modulation observed at higher stimulus intensities is a result of saturation of the reflex loop. In six other patients, however, no reflex modulation could be demonstrated even at very low stimulus intensities.

Reciprocal Ia inhibition in patients with spinal spasticity

Reciprocal Ia inhibition from ankle flexors to extensors was studied in five patients with spasticity due to incomplete traumatic spinal cord lesions. Nine healthy subjects were tested as controls. Excitability of the soleus motoneuron pool was estimated by H-reflex testing in the resting state. Ia inhibition was activated by conditioning stimuli to the peroneal nerve. Ia inhibition was detected in all patients tested, the amount of inhibition ranging from 8% to more than 50% of the test H-reflex size. In the control subjects only weak Ia inhibitory effects were present. These findings indicate increased excitability of the Ia inhibitory pathway to ankle extensor motoneurons in patients with spasticity due to spinal cord injury.

Interlimb reflexes following cervical spinal cord injury in man

The reflex interconnection of lower and upper extremity muscles was investigated in subjects with chronic (greater than 1 year post-injury) lesions to the cervical spinal cord. Lower extremity mixed nerves were stimulated with single shocks or with brief trains of high-frequency stimuli of varying intensities. EMG from a number of lower and upper extremity muscles was recorded on magnetic tape for later analysis. In one population of spinal cord injury (SCI) subjects, single stimuli to lower extremity nerves resulted in muscle responses in both ipsi- and contralateral upper extremity muscles. The minimal response latency to a single shock was typically much less in muscles on the ipsilateral side than for contralateral upper extremity muscles. Application of brief trains of stimuli (for example, 2 stimulus pulses at 500 Hz) typically resulted in a large reduction in latency to the contralateral motor response, such that it was now approximately equal to the ipsilateral motor response latency. This decline in response latency was not gradual with increasing afferent input. Instead, the response occurred either early or late, but not at intermediate latencies. Stimuli which were subthreshold for evoking M-waves or H-reflexes were sometimes still adequate to evoke upper extremity motor responses. Once the threshold had been exceeded, the magnitude of the evoked response appeared to be independent of the stimulus magnitude. These reflex interconnections of lower and upper extremities were obtained only from subjects with chronic and motor-complete cervical spinal cord injury. No such interlimb responses were seen in control subjects, or in subjects who had recovered some motor function below the level of their injury, and were now considered to be motor-incomplete quadriplegics.

Selective posterior rhizotomy for the treatment of spasticity: a review

The use of sensory rhizotomy has long been used for the treatment of spasticity. This review outlines the historical development of this treatment, the current surgical technique, and its physiologic rationale. Patient selection, postoperative treatment, and complications are also discussed.

Changes in spinal reflex excitability in brain-dead humans

The excitability of proprio- and exteroceptive spinal reflexes was monitored electrophysiologically and clinically during the occurrence of brain death (BD) in 8 patients. After a period of total reflex unresponsiveness, the soleus H reflex attained a steady-state excitability level in 2-6 h. The recovery cycle of this response regained its normal shape at 10-20 h. The threshold of the cutaneous reflex evoked in the biceps femoris by electrical stimulation of the sural nerve had become normal in 4-13 h, although the response displayed an abnormal multi-component pattern. Digital responses to mechanical stimulation of the foot sole were evident after 6-8 h. Knee and ankle jerks were never evoked during the time of monitoring. The time-courses of the changes in excitability were not directly correlated with the fall in the blood pressure which may occur during BD. It is concluded that the human spinal cord reacts to BD with a spinal shock, characterized by sequential recovery of reflex transmission. The overall timing of this process appears to be much shorter than that previously described for the spinal shock following traumatic transection of the cord, but the latter was never studied in the earliest phases.

FES and spasticity

A model of hemiplegic spasticity based on electromyographical and biomechanical parameters measured during passive muscle stretching is presented. Two components of spasticity can be distinguished--phasic and tonic. This classification depends on the pattern of stretch reflex activity which can be either phasic or tonic as well as on the muscle stretch/tension characteristic. Stretch reflex, as a control loop, is in phasic spasticity characterized by increased sensitivity to velocity of stretching. In tonic spasticity, sensitivity to length of stretching is increased. After the injury, phasic spasticity appears first and invokes monosynaptic reflex pathways. The intensity of tonic spasticity increases with the duration of disability and hence causes changes in muscle fiber biomechanical properties. The model mentioned above has been used to evaluate the effects of FES on spasticity. Hemiplegic patients with implanted peroneal nerve stimulator for gait correction were followed up for one year starting a week before implantation. Long-term use of FES resulted in decrease of tonic spasticity in both ankle joint antagonistic muscle groups. In stimulated tibialis anterior muscle, the phasic type of spasticity increased. To obtain the correlation between changes in spasticity and functional abilities of patients, the maximal voluntary isometric contraction of both muscle groups was also measured. An improvement in voluntary strength was also observed. This can be taken as additional evidence that tonic spasticity is of greater physiological and clinical significance than phasic spasticity. It may be concluded that use of FES can decrease tonic spasticity and, if applied early after the injury, can prevent the appearance of tonic spasticity.

Effects of dorsal bilateral rhizotomy treatment on transmitter systems in the spinal cord of normal and spastic dogs

The high-affinity uptakes of [3H]serotonin, [3H]-glutamate, and gamma-[3H]aminobutyric acid were studied using a myelin-free crude synaptosomal fraction prepared from the spinal cords of normal dogs and spastic dogs following sham treatment or dorsal bilateral rhizotomy surgery. Compared to sham-operated controls, rhizotomy surgery of normal dogs produced, after 1 week, a 30% reduction in the Vmax value of [3H]glutamate, but did not alter the uptake of gamma-[3H]aminobutyric acid. This treatment also produced a 60% decrease in the Vmax value of [3H]serotonin. Comparison of the effect of rhizotomy surgery on normal and spastic dogs revealed that the spastic group had 60% higher Vmax values for uptakes of [3H]glutamate and gamma-[3H]aminobutyric acid. Comparison of sham-operated spastic dogs and rhizotomy-treated spastic animals showed that there was a 25% decrease in the uptake of both amino acids in the rhizotomy-treated spastic group. Overall, the data (a) support the hypothesis that glutamate is the neurotransmitter from some of the primary afferents, and (b) suggest that sprouting of interneuronal amino acid transmitter systems may occur in the spinal cords of spastic dogs.

Motoneuron response to dorsal root stimulation in anesthetized monkeys after spinal cord transection

In preparation for studying the spinal cord alterations produced by operant conditioning of spinal reflexes, we studied peripheral nerve responses to supramaximal dorsal root stimulation in the lumbosacral cord of deeply anesthetized monkeys before and after thoracic cord transection. Except for variable depression in the first few minutes, reflex responses were not reduced or otherwise significantly affected by transection in the hour immediately following the lesion or for at least 50 h. The results suggest that reduction in muscle spindle sensitivity and/or in polysynaptic motoneuron excitation contributes to stretch reflex depression after cord transection.

Serial recording of reflexes after feline spinal cord transection

Implanted nerve cuff and muscle electrodes were used to serially record reflexes after spinal cord transection in cat. Recording of reflexes, in response to both sensory nerve and to mixed motor and sensory nerve stimulation, was accomplished through 2 months after cord section. Serial recording of afferent and efferent nerve volleys was achieved as well. Serial reflex changes that follow cord transection are described. Reflex amplitude to sensory nerve stimulation increased in two phases. The first increase was noted between 1 and 4 days after cord transection; the second increase was recorded between 2 and 4 weeks. These observations suggest that at least two neuronal mechanisms with distinct temporal courses mediate the appearance of spinal hyperreflexia. The animal model described may be useful for further study of the neuronal mechanisms which underlie the hyperreflexia of spinal cord injury.

Presynaptic inhibition of monosynaptic reflexes in the lower limbs of subjects with upper motoneuron disease

Presynaptic inhibition of muscle spindle Ia afferents by group I afferents from the same and other muscles has been studied in the lower limbs of subjects with upper motoneuron lesions. The experiments utilised conditioning of soleus test monosynaptic reflexes during controlled voluntary contraction. The protocol was designed to isolate presynaptic inhibition from postsynaptic components. The relation between estimate of inhibition and test reflex amplitude was examined. The subjects showed less inhibition than controls at all levels of voluntary torque investigated (less than or equal 15 Nm). Two thirds had weak inhibition which did not show the decrease during muscle contraction characteristic of controls. The degree of difference from the normal situation correlated with severity of the clinical sign (weakness of voluntary ankle flexion).

Definition of human reflex excitability by statistical analysis of quantal EMG responses

A precise method has been devised to estimate soleus motoneurone pool excitability by probit analysis of quantal (all-or-none) reflex EMG responses to critical electrical stimulation. The technique is shown to be sensitive to changes induced by weak excitatory or inhibitory inputs and is likely to be useful in the study of monosynaptic proprioceptive reflexes.

Qualitative H-reflex testing in huntington's disease

The occurrence of H-reflexes over both the anterior tibial muscle and the thenar muscle on both sides was investigated in 15 patients suffering from Huntington's disease, 8 clinically inconspicuous offspring, and 30 healthy normal controls. The following results were obtained: 1. An obvious H-reflex over the anterior tibial muscle was found in 12 of 15 patients; there was no H-reflex in only 3 patients. 2. After stimulation on the median nerve there was an H-reflex in 12 of 13 patients investigated. 3. In 5 of 8 clinically inconspicuous offspring there was an H-reflex after peroneal [4] or median [5] nerve stimulation. In 30 normal controls, 1 displayed a weak H-reflex over the anterior tibial muscle, 9 showed a weak H-reflex after median nerve stimulation. 5. The possibility is discussed that an abnormal H-reflex might be an early sign of central reflex disinhibition in otherwise asymptomatic offspring.

The late facilitation in H-reflex recovery cycles in different pyramidal lesions

H-reflex amplitudes were recorded after stimulation of the tibial nerve and different electrical stimuli in 18 normal persons and 26 patients showing pyramidal spasticity (8 spastic spinal paralysis, 6 spastic hemiparesis, 12 spinal lesions). A just subthreshold stimulus of the tibial nerve facilitated the H-reflex in spastic patients slightly after about 300 ms (up to 113%), following an early strong facilitation (10 ms) and a longer lasting depression (20-200ms). Similar postinhibitory facilitation was obtained in spastic patients after ipsilateral stimulation of the plantar surface and after direct stimulation of the dorsal columns. Conditioning by contralateral stimuli of the posterior tibial nerve caused a slight late facilitation in both normal and spastic patients. This late facilitation did not correlate significantly with the severity of spasticity, but it was more pronounced in cerebral pyramidal lesions than in spinal ones. It is assumed that this postinhibitory facilitation is probably generated as a spinal rhythm, similar to the clonus, and that it is modulated from supraspinal structures.

Neurophysiological mechanisms in abnormal reflex activities in cerebral palsy and spinal spasticity

Dorsal root stimulation, carried out during operation in 80 spastic cerebral palsy patients and in one spastic quadriplegic patient, allowed a study of abnormal monosynaptic and polysynaptic reflexes. Frequency-related depression of the monosynaptic reflex was not present; increased activity through non-suppressed polysynaptic pathways was shown.

The management of spinal injuries--past and present

This review paper surveys historical aspects and then proceeds to examine major considerations in the management of spinal injuries. These include neurological sequelae, functional disabilities and expectations, pathology, spinal cord injury in children, management complications (genitourinary, bone, neurological, skin respiratory, cardiovascular, and gastrointestinal), and social aspects. The paper concludes by highlighting the need for comprehensive spinal injury services, noting the bleak future for a reduction in incidence, and emphasizing the goal of care in the community at large, not just in hospital.

[Somatosensory evoked potentials and Hoffmann reflex in acute spinal cord lesions; physiopathological and prognostic aspects]

Twenty-four patients with recent and acute spinal cord lesions were examined. The somatosensory cerebral evoked potential (SEP) following stimulation of the peroneus communis nerve tested spinal conduction, whereas the H reflex showed spinal excitability belowe the lesion. After complete spinal cord section, the SEP was always abolished and the H reflex was absent in most cases tested in the first 24 hours. Into other patients, the recruitment curve and the recovery cycle of the H reflex displayed some abnormalities which progressively disappeared. With partial lesions, SEP could occasionally be altered. Some abnormalities of the H reflex recovery cycle, of the same type as those seen in the late stage of complete sections, were also observed. These data give nre information on the physiopathology of spinal shock; they lead to the distinction of several evolutionary stages after acute spinal lesions and also have prognostic disgnificance.

Discharge pattern of single motor units in the tonic vibration reflex of human triceps surae

Using a single fibre EMG electrode the firing pattern of 46 motor units in the triceps surae has been studied during vibration of the Achilles tendon at frequencies of 25--200 Hz. Potentials activated in the tonic vibration reflex (TVR) were phase-locked to the vibration cycle but tended to become somewhat less so with continued vibration. The firing pattern of voluntarily activated motor units became locked to the waveform by the application of the vibrator. The discharges of 21 motor units were studied during low threshold (sub-M wave) tetanic stimulation of the tibial nerve at 25--100 Hz. No evidence was found of synchronization of potentials activated in the resulting tonic contraction. During weak voluntary contractions, stimulation also failed to regularize voluntarily activated motor units. The findings can be reconciled by postulating that, in normal man, vibration activates monosynaptic and polysynaptic pathways, the latter circuit being adequate to generate reflex contraction, while the former merely affects the temporal patterning of the motor outflow.

Neurophysiological changes following spinal cord lesions in man

A study has been made of the neurophysiological changes that follow spinal cord lesions in man. The Achilles tendon reflex (ATR) is used to estimate transmission in the Ia monosynaptic pathway, and the tonic vibration reflex (TVR) to estimate transmission in the Ia polysynaptic pathway to motoneurons. The inhibition of the H reflex by vibration is used as an estimate of presynaptic inhibition of the Ia monosynaptic pathway. Immediately following a complete lesion of the spinal cord presynaptic inhibition of the Ia monosynaptic pathway appears to be greatly increased. This enhanced inihibition may last several months but it eventually declines and in some instances becomes less than normal. Transmission in the Ia polysynaptic pathway is permanently abolished by a complete spinal lesion. A hypothesis is developed from these findings to explain the evolution of some of the clinical features that follow complete spinal lesions in man. Distinct differences are observed when the spinal lesion is incomplete. Transmission in the Ia polysynaptic pathway may be preserved and there may be no increase in presynaptic inhibition. These differences may depend upon the integrity of certain spinal long tracts which cannot be tested clinically.