Segmental reflex pathways in spinal shock and spinal spasticity in man

Spinal shock in severe SCI dogs and early implementation of intensive neurorehabilitation programs

Spinal shock is complex, paradoxical with sudden presentation, possibly leading to a guarded prognosis. Thus, it is suggested the need for early implementation of intensive neurorehabilitation. This prospective controlled blinded cohort study aims to understand the implication of spinal shock in neurorehabilitation of severe SCI dogs and the importance of its evaluation thought a spinal shock scale (SSS). 371 dogs were randomized by stratification according the presence of spinal shock in the SG (n = 245) or CG (n = 126). The SSS, a punctuation scale (0-7), was evaluated at admission and each 6 h for 3 days, each day for 15 days, each week for 6 weeks, each month until 3 months, followed by 3 monthly follow-ups. All dogs had similar land and underwater treadmill training with functional electrical stimulation. Observational dataset allowed an approximate level of power (1-β) of 0.90 and an α (Type I error) of 0.01, with a total of 11,088 SSS observations between two blinded observers and 18% of disagreement. 75% of the dogs were admitted in 24-48 h after injury, allowing early detection of spinal shock, and dogs admitted at 72 h with SSS ≥ 4 were not able to achieve ambulation. Regarding ambulation rate, there was a significant difference between groups, with 66.9% of ambulation in the SG and 97.6% in the CG. Also, there was a difference in regard to time until ambulation, with a mean of 31.57 days for the SG and 23.02 for the CG. The SSS estimated marginal means had an exponential decrease within the first 6 h, followed by a slower decrease, but always faster in spinal shock dogs diagnosed with non-compressive myelopathies. Thus, early intensive neurorehabilitation in dogs after severe SCI may benefit from SSS classifications at admission and during treatment to establish different therapeutic protocols according to each patient's needs, especially in deep pain negative dogs.

Developing a predictive model for spinal shock in dogs with spinal cord injury

BACKGROUND

Reduced pelvic limb reflexes in dogs with spinal cord injury typically suggests a lesion of the L4-S3 spinal cord segments. However, pelvic limb reflexes might also be reduced in dogs with a T3-L3 myelopathy and concurrent spinal shock.

HYPOTHESIS/OBJECTIVES

We hypothesized that statistical models could be used to identify clinical variables associated with spinal shock in dogs with spinal cord injuries.

ANIMALS

Cohort of 59 dogs with T3-L3 myelopathies and spinal shock and 13 dogs with L4-S3 myelopathies.

METHODS

Data used for this study were prospectively entered by partner institutions into the International Canine Spinal Cord Injury observational registry between October 2016 and July 2019. Univariable logistic regression analyses were performed to assess the association between independent variables and the presence of spinal shock. Independent variables were selected for inclusion in a multivariable logistic regression model if they had a significant effect (P ≤ .1) on the odds of spinal shock in univariable logistic regression.

RESULTS

The final multivariable model included the natural log of weight (kg), the natural log of duration of clinical signs (hours), severity (paresis vs paraplegia), and pelvic limb tone (normal vs decreased/absent). The odds of spinal shock decreased with increasing weight (odds ratio [OR] = 0.28, P = .09; confidence interval [CI] 0.07-1.2), increasing duration (OR = 0.44, P = .02; CI 0.21-0.9), decreased pelvic limb tone (OR = 0.04, P = .003; CI 0.01-0.36), and increased in the presence of paraplegia (OR = 7.87, P = .04; CI 1.1-56.62).

CONCLUSIONS AND CLINICAL IMPORTANCE

A formula, as developed by the present study and after external validation, could be useful for assisting clinicians in determining the likelihood of spinal shock in various clinical scenarios and aid in diagnostic planning.

Comparison of systemic and localized carrier-mediated delivery of methylprednisolone succinate for treatment of acute spinal cord injury

Localized carrier-mediated administration of drugs is a promising approach to treatment of acute phase of spinal cord injury (SCI) as it allows enhanced and/or sustained drug delivery to damaged tissues along with minimization of systemic side effects. We studied the effect of locally applied self-assembling micellar formulation of methylprednisolone succinate (MPS) with trifunctional block copolymer of ethylene oxide and propylene oxide (TBC) on functional recovery and tissue drug content after SCI in rats in comparison with local and systemic administration of MPS alone. Variations in the amplitude of motor evoked responses in the hindlimb muscles induced by epidural stimulation during acute phase of SCI and restoration of movements during chronic period after local vs. systemic application of MPS were evaluated in this study. Results demonstrate that local delivery of MPS in combination with TBC facilitates spinal cord sensorimotor circuitry, increasing the excitability. In addition, this formulation was found to be more effective in improvement of locomotion after SCI compared to systemic administration. LC-MS/MS data shows that the use of TBC carrier increases the glucocorticoid content in treated spinal cord by more than four times over other modes of treatment. The results of this study demonstrate that the local treatment of acute SCI with MPS in the form of mixed micelles with TBC can provide improved therapeutic outcome by promoting drug accumulation and functional restoration of the spinal cord.

Disrupted Ankle Control and Spasticity in Persons With Spinal Cord Injury: The Association Between Neurophysiologic Measures and Function. A Scoping Review

Control of muscles about the ankle joint is an important component of locomotion and balance that is negatively impacted by spinal cord injury (SCI). Volitional control of the ankle dorsiflexors (DF) is impaired by damage to pathways descending from supraspinal centers. Concurrently, spasticity arising from disrupted organization of spinal reflex circuits, further erodes control. The association between neurophysiological changes (corticospinal and spinal) with volitional ankle control (VAC) and spasticity remains unclear. The goal of this scoping review was to synthesize what is known about how changes in corticospinal transmission and spinal reflex excitability contribute to disrupted ankle control after SCI. We followed published guidelines for conducting a scoping review, appraising studies that contained a measure of corticospinal transmission and/or spinal reflex excitability paired with a measure of VAC and/or spasticity. We examined studies for evidence of a relationship between neurophysiological measures (either corticospinal tract transmission or spinal reflex excitability) with VAC and/or spasticity. Of 1,538 records identified, 17 studies were included in the review. Ten of 17 studies investigated spinal reflex excitability, while 7/17 assessed corticospinal tract transmission. Four of the 10 spinal reflex studies examined VAC, while 9/10 examined ankle spasticity. The corticospinal tract transmission studies examined only VAC. While current evidence suggests there is a relationship between neurophysiological measures and ankle function after SCI, more studies are needed. Understanding the relationship between neurophysiology and ankle function is important for advancing therapeutic outcomes after SCI. Future studies to capture an array of corticospinal, spinal, and functional measures are warranted.

Transient depression of pelvic limb reflexes in dogs with acute focal thoracolumbar myelopathy

OBJECTIVE To determine the prevalence of depressed pelvic limb reflexes and changes in those reflexes over time in dogs with acute thoracolumbar myelopathy. DESIGN Prospective study. ANIMALS 34 dogs. PROCEDURES Dogs with acute pelvic limb paralysis caused by acute noncompressive nucleus pulposus extrusion (ANNPE), fibrocartilaginous embolism (FCE), or compressive intervertebral disk herniation (IVDH) within the T3-L3 spinal cord segments were enrolled in the study. Dogs with depressed or absent pelvic limb withdrawal reflexes as determined by 2 examiners were classified as affected and underwent additional testing to rule out multifocal lesions. Pelvic limb reflexes of affected dogs were reassessed every 12 hours until they returned to normal. Neurologic examinations were performed at 4 and 8 weeks after initial examination for some dogs. RESULTS Compressive IVDH, ANNPE, and FCE were diagnosed in 30, 1, and 3 dogs, respectively. Nine (5 with compressive IVDH and all 4 with FCE or ANNPE) of 34 (26%) dogs were classified as affected. Patellar reflexes were depressed in 2 of 9 affected dogs. The median time required for withdrawal reflexes to return to normal was 60 hours (range, 12 to 156 hours). Onset duration of paralysis was negatively associated with the odds of a dog being classified as affected. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that dogs with focal thoracolumbar spinal cord lesions, especially those with peracute onset of paralysis, can develop transient depression of pelvic limb reflexes. Awareness of this phenomenon is important for veterinarians to accurately localize lesions and develop appropriate diagnostic plans and prognoses.

Spontaneous spinal epidural hematoma mimicking Guillain-Barre Syndrome

BACKGROUND

The initial symptoms of Guillain-Barre Syndrome (GBS) can be similar to a case of spontaneous spinal epidural hematoma (SSEH) located at the cervicothoracic junction. Therefore, SSEH may be misdiagnosed as GBS.

CASE REPORT

A previously healthy 6-year-old girl presented with a 2-day history of progressive pain in the lower extremities and an inability to walk. On initial evaluation, she was completely paraparetic in the lower extremities. Deep tendon reflexes were absent in the lower extremities, and Babinski reflexes were positive on both sides. She exhibited reduced response to light touch and pinprick with a sensory level below T10, and experienced difficulty during urination. However, the strength, sensation and flexion of upper extremities were normal. Because her presentation and examinations were consistent with GBS, we initiated intravenous immunoglobulin therapy. The next day, she also developed pain and muscle weakness of the right upper extremity. Three days after admission, respiratory depression progressed rapidly. Spinal MRI showed a mass extending from the level of C7-T3, with spinal cord compression. The patient underwent an emergency laminectomy with evacuation of hematoma, and was diagnosed with SSEH. Sixty days after admission, she was transferred to the rehabilitation hospital with severe neurologic sequelae of paralysis in both legs.

CONCLUSION

SSEH might have severe consequences, including neurologic deficits and risk of death. This case report serves to raise the awareness of SSEH that mimics the initial presentation of GBS.

Afferent stimulation inhibits abnormal cutaneous reflex activity in patients with spinal cord injury spasticity syndrome

BACKGROUND

Tibialis Anterior (TA) cutaneous reflex (CR) activity evoked following cutaneous stimulation of the plantar (Pl) surface (Pl-TA CR) has demonstrated hyperreflexia and damage of inhibitory mechanisms in subjects with spinal cord injury (SCI) and spasticity.

OBJECTIVES

To modulate Pl-TA CR and Soleus H-reflex activity with transcutaneous electrical nerve stimulation (TENS) and vibratory stimulation of the plantar pad during rest and controlled isometric plantarflexion.

METHODS

Non-injured subjects (n = 11) and individuals with incomplete SCI with (n = 14) and without spasticity (n = 14) were recruited. The effect of TENS and vibratory stimuli on Pl-TA CR and soleus H-reflex activity were assessed during rest and controlled ramp-and-hold plantarflexion.

RESULTS

Vibration failed to inhibit H-reflex activity during rest or plantarflexoin following SCI compared to healthy subjects. In contrast, vibration-induced inhibition of Pl-TA CR was specifically detected in SCI spastic subjects during both rest and the hold phase of plantarflexion. TENS inhibited Pl-TA CR activity in the SCI spasticity group only during hold plantarflexion.

CONCLUSIONS

Plantar vibratory stimuli inhibited the pl-TA CR, but not the H reflex, during rest and controlled movement in SCI spastic subjects. Assessment of Pl-TA CR modulation should contribute to the development of modality-specific sensory stimuli programmes for the neurorehabilitation of SCI spasticity.

Revisit Spinal Shock: Pattern of Reflex Evolution during Spinal Shock

When the spinal cord is suddenly severed, all the fundamental functions of the spinal cord below the level of injury including the spinal cord reflexes are immediately depressed, which is referred to as spinal shock. The resolution of spinal shock occurs over a period of days to months, and spinal shock slowly transitions to spasticity. The definition of spinal shock and the pattern of reflex recovery or evolution remains as an issue of debate and controversy. The identification of clinical signs that determine the duration of spinal shock is controversial. The underlying mechanisms of spinal shock are also not clearly defined. Various authors have defined the termination of spinal shock as the appearance of the bulbocavernosus reflex, the recovery of deep tendon reflexes, or the return of reflexic detrusor activity. However, many questions remain to be answered, such as: When should we define spinal shock as the end? What types of reflexes appear first among polysynaptic cutaneous reflexes, monosynaptic deep tendon reflexes, and pathological reflexes? Should it include changes in autonomic reflexes such as a detrusor reflex?

Adjuvant treatments associated with botulinum toxin injection for managing spasticity: An overview of the literature

BACKGROUND AND OBJECTIVE

A wide range of adjunct therapies after botulinum toxin administration have been proposed. The aim of the present paper is to provide an overview of major writings dealing with adjuvant (non-pharmacological) treatments associated with botulinum toxin for managing spasticity in order to provide some up-to-date information about the usefulness of the most commonly used procedures.

METHODS

The literature in PubMed was searched with the MeSH terms botulinum toxins, muscle spasticity, physical therapy modalities, and rehabilitation. The results were limited to studies focusing on adjuvant treatments associated with botulinum toxin for managing spasticity. We excluded papers on the use of non-drug treatments for spasticity not associated with botulinum toxin serotype A (BoNT-A) injection. Relevant literature known to the authors along with this complementary search represented the basis for this overview of the literature.

RESULTS

Adhesive taping and casting effectively improved the botulinum toxin effect in patients with upper- and lower-limb spasticity. There is level 1 evidence that casting is better than taping for outcomes including spasticity, range of motion and gait. However, consensus about their most appropriate timing, duration, target and material is lacking. In terms of physical modalities combined with botulinum toxin injection, we found level 1 evidence that extracorporeal shock wave therapy is better than electrical stimulation for some post-injection outcomes including spasticity and pain. Furthermore, electrical stimulation of injected muscles might be useful to boost the toxin effect. However, the best stimulation protocol has not been defined. In addition, we found level 2b evidence that whole-body vibration therapy might reduce spasticity with cerebral palsy.

CONCLUSION

Future research in this field should focus on investigating the most appropriate post-injection treatment protocol for each goal to achieve.

Comparison of Single-Session Dose Response Effects of Whole Body Vibration on Spasticity and Walking Speed in Persons with Spinal Cord Injury

Spasticity affects approximately 65% of persons with spinal cord injury (SCI) and negatively impacts function and quality of life. Whole body vibration (WBV) appears to reduce spasticity and improve walking function; however, the optimal dose (frequency/duration) is not known. We compared single-session effects of four different WBV frequency/duration dose conditions on spasticity and walking speed, in preparation for a planned multi-session study. Thirty-five participants with motor-incomplete SCI received four different doses of WBV: high frequency (50 Hz)/short duration (180 s), high frequency/long duration (360 s), low frequency (30 Hz)/short duration, and low frequency/long duration, plus a control intervention consisting of sham electrical stimulation. In all conditions, participants stood on the WBV platform for 45-s bouts with 1 min rest between bouts until the requisite duration was achieved. The frequency/duration dose order was randomized across participants; sessions were separated by at least 1 week. Quadriceps spasticity was measured using the pendulum test at four time points during each session: before, immediately after, 15 min after, and 45 min after WBV. Walking speed was quantified using the 10-m walk test at three time points during each session: baseline, immediately after, and 45 min after WBV. In the full group analysis, no frequency/duration combination was significantly different from the sham-control condition. In participants with more severe spasticity, a greater reduction in stretch reflex excitability was associated with the high frequency/long duration WBV condition. The sham-control condition was associated with effects, indicating that the activity of repeated sitting and standing may have a beneficial influence on spasticity.

TRIAL REGISTRATION

NCT02340910 (assigned 01/19/2015).

Limb Segment Load Inhibits the Recovery of Soleus H-Reflex After Segmental Vibration in Humans

We investigated the effects of vertical vibration and compressive load on soleus H-reflex amplitude and postactivation depression. We hypothesized that, in the presence of a compressive load, limb vibration induces a longer suppression of soleus H-reflex. Eleven healthy adults received vibratory stimulation at a fixed frequency (30 Hz) over two loading conditions (0% and 50% of individual's body weight). H-reflex amplitude was depressed ∼88% in both conditions during vibration. Cyclic application of compression after cessation of the vibration caused a persistent reduction in H-reflex excitability and postactivation depression for > 2.5 min. A combination of limb segment vibration and compression may offer a nonpharmacologic method to modulate spinal reflex excitability in people after CNS injury.

Patellar tendon vibration reduces the increased facilitation from quadriceps to soleus in post-stroke hemiparetic individuals

BACKGROUND

Stimulation of the femoral nerve in healthy people can facilitate soleus H-reflex and electromyography (EMG) activity. In stroke patients, such facilitation of transmission in spinal pathways linking the quadriceps and soleus muscles is enhanced and related to co-activation of knee and ankle extensors while sitting and walking. Soleus H-reflex facilitation can be depressed by vibration of the quadriceps in healthy people, but the effects of such vibration have never been studied on the abnormal soleus facilitation observed in people after stroke.

OBJECTIVES

To determine whether vibration of the quadriceps can modify the enhanced heteronymous facilitation of the soleus muscle observed in people with spastic stroke after femoral nerve stimulation and compare post-vibration effects on soleus facilitation in control and stroke individuals.

METHODS

Modulation of voluntary soleus EMG activity induced by femoral nerve stimulation (2×motor threshold) was assessed before, during and after vibration of the patellar tendon in 10 healthy controls and 17 stroke participants.

RESULTS

Voluntary soleus EMG activity was facilitated by femoral nerve stimulation in 4/10 (40%) controls and 11/17 (65%) stroke participants. The level of facilitation was greater in the stroke than control group. Vibration significantly reduced early heteronymous facilitation in both groups (50% of pre-vibration values). However, the delay in recovery of soleus facilitation after vibration was shorter for the stroke than control group. The control condition with the vibrator turned off had no effect on the modulation.

CONCLUSIONS

Patellar tendon vibration can reduce the facilitation between knee and ankle extensors, which suggests effective presynaptic inhibition but decreased post-activation depression in the lower limb of people after chronic hemiparetic stroke. Further studies are warranted to determine whether such vibration could be used to reduce the abnormal extension synergy of knee and ankle extensors in people after hemiparetic stroke.

Whole-body vibration induces distinct reflex patterns in human soleus muscle

The neuronal mechanisms underlying whole body vibration (WBV)-induced muscular reflex (WBV-IMR) are not well understood. To define a possible pathway for WBV-IMR, this study investigated the effects of WBV amplitude on WBV-IMR latency by surface electromyography analysis of the soleus muscle in human adult volunteers. The tendon (T) reflex was also induced to evaluate the level of presynaptic Ia inhibition during WBV. WBV-IMR latency was shorter when induced by low- as compared to medium- or high-amplitude WBV (33.9±5.3msvs. 43.8±3.6 and 44.1±4.2ms, respectively). There was no difference in latencies between T-reflex elicited before WBV (33.8±2.4ms) and WBV-IMR induced by low-amplitude WBV. Presynaptic Ia inhibition was absent during low-amplitude WBV but was present during medium- and high-amplitude WBV. Consequently, WBV induces short- or long-latency reflexes depending on the vibration amplitude. During low-amplitude WBV, muscle spindle activation may induce the short- but not the long-latency WBV-IMR. Furthermore, unlike the higher amplitude WBV, low-amplitude WBV does not induce presynaptic inhibition at the Ia synaptic terminals.

Characterization of Involuntary Contractions after Spinal Cord Injury Reveals Associations between Physiological and Self-Reported Measures of Spasticity

Correlations between physiological, clinical and self-reported assessments of spasticity are often weak. Our aims were to quantify functional, self-reported and physiological indices of spasticity in individuals with thoracic spinal cord injury (SCI; 3 women, 9 men; 19–52 years), and to compare the strength and direction of associations between these measures. The functional measure we introduced involved recording involuntary electromyographic activity during a transfer from wheelchair to bed which is a daily task necessary for function. High soleus (SL) and tibialis anterior (TA) F-wave/M-wave area ratios were the only physiological measures that distinguished injured participants from the uninjured (6 women, 13 men, 19–67 years). Hyporeflexia (decreased SL H/M ratio) was unexpectedly present in older participants after injury. During transfers, the duration and intensity of involuntary electromyographic activity varied across muscles and participants, but coactivity was common. Wide inter-participant variability was seen for self-reported spasm frequency, severity, pain and interference with function, as well as tone (resistance to imposed joint movement). Our recordings of involuntary electromyographic activity during transfers provided evidence of significant associations between physiological and self-reported measures of spasticity. Reduced low frequency H-reflex depression in SL and high F-wave/M-wave area ratios in TA, physiological indicators of reduced inhibition and greater motoneuron excitability, respectively, were associated with long duration SL and biceps femoris (BF) electromyographic activity during transfers. In turn, participants reported high spasm frequency when transfers involved short duration TA EMG, decreased co-activation between SL and TA, as well as between rectus femoris (RF) vs. BF. Thus, the duration of muscle activity and/or the time of agonist-antagonist muscle coactivity may be used by injured individuals to count spasms. Intense electromyographic activity and high tone related closely (possibly from joint stabilization), while intense electromyographic activity in one muscle of an agonist-antagonist pair (especially in TA vs. SL, and RF vs. BF) likely induced joint movement and was associated with severe spasms. These data support the idea that individuals with SCI describe their spasticity by both the duration and intensity of involuntary agonist-antagonist muscle coactivity during everyday tasks.

Intraoperative spinal cord monitoring using low intensity transcranial stimulation to remove post-activation depression of the H-reflex

OBJECTIVE

To investigate whether low intensity transcranial electrical stimulation (TES) can be used to condition post-activation depression of the H-reflex and simultaneously monitor the integrity of spinal motor pathways during spinal deformity correction surgery.

METHODS

In 20 pediatric patients undergoing corrective surgery for spinal deformity, post-activation depression of the medial gastrocnemius H-reflex was initiated by delivering two pulses 50-125ms apart, and the second H-reflex was conditioned by TES.

RESULTS

Low intensity TES caused no visible shoulder or trunk movements during 19/20 procedures and the stimulation reduced post-activation depression of the H-reflex. The interaction was present in 20/20 patients and did not diminish throughout the surgical period. In one case, the conditioning effect was lost within minutes of the disappearance of the lower extremity motor evoked potentials.

CONCLUSION

Post-activation depression was used to detect the arrival of a subthreshold motor evoked potential at the lower motor neuron. The interaction produced minimal movement within the surgical field and remained stable throughout the surgical period.

SIGNIFICANCE

This is the first use of post-activation depression during intraoperative neurophysiological monitoring to directly assess the integrity of descending spinal motor pathways.

Interlimb Reflexes Induced by Electrical Stimulation of Cutaneous Nerves after Spinal Cord Injury

Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.

Functioning of peripheral Ia pathways in leg muscles of newly walking toddlers

Monosynaptic and polysynaptic spinal level reflexes in the leg muscles of infants show significant dispersion across muscles, high variability, and no change in response patterns over the first 10 months. Here we tested the hypothesized relation between early walking experience and the tuning of these responses in three primary gait muscles of participants in four subgroups: cruisers (n=7) and toddlers with one (n=5), two (n=5), or three (n=5) months of walking experience. Reflex responses in multiple Ia pathways - tendon reflex (T-reflex), vibration-induced inhibition of the T-reflex (VIM-T-reflex), and tonic vibration-induced reflex (VIR), were elicited by mechanical stimuli applied to the distal tendons of the quadriceps, gastrocnemius-soleus, and tibialis anterior of both legs. Walking skill was assessed via a GAITRite mat. Generally, walking experience seemed to be related to slowly emerging improvements and, depending on muscle tested and pathway, progress was quite varied. Amplitude and latency of reflex responses were more clearly impacted by age or leg length while the ratio or distribution pattern of reflex response among antagonist pairs of muscles was impacted by walking experience and skill. As walking experience increased, the ratio of reflex responses tended to increase for the stimulated and decrease for the antagonist reflex loops with distribution of the pattern shifting gradually toward a single type of reflex response in all tested muscles. The very slow tuning of these reflexes may underlie the many missteps and falls reported to occur during early walking and suggest that subsequent studies should continue to follow the developmental trajectory through the first year of walking experience.

Recovery of neuronal and network excitability after spinal cord injury and implications for spasticity

The state of areflexia and muscle weakness that immediately follows a spinal cord injury (SCI) is gradually replaced by the recovery of neuronal and network excitability, leading to both improvements in residual motor function and the development of spasticity. In this review we summarize recent animal and human studies that describe how motoneurons and their activation by sensory pathways become hyperexcitable to compensate for the reduction of functional activation of the spinal cord and the eventual impact on the muscle. Specifically, decreases in the inhibitory control of sensory transmission and increases in intrinsic motoneuron excitability are described. We present the idea that replacing lost patterned activation of the spinal cord by activating synaptic inputs via assisted movements, pharmacology or electrical stimulation may help to recover lost spinal inhibition. This may lead to a reduction of uncontrolled activation of the spinal cord and thus, improve its controlled activation by synaptic inputs to ultimately normalize circuit function. Increasing the excitation of the spinal cord with spared descending and/or peripheral inputs by facilitating movement, instead of suppressing it pharmacologically, may provide the best avenue to improve residual motor function and manage spasticity after SCI.

Neuromodulation of evoked muscle potentials induced by epidural spinal-cord stimulation in paralyzed individuals

Epidural stimulation (ES) of the lumbosacral spinal cord has been used to facilitate standing and voluntary movement after clinically motor-complete spinal-cord injury. It seems of importance to examine how the epidurally evoked potentials are modulated in the spinal circuitry and projected to various motor pools. We hypothesized that chronically implanted electrode arrays over the lumbosacral spinal cord can be used to assess functionally spinal circuitry linked to specific motor pools. The purpose of this study was to investigate the functional and topographic organization of compound evoked potentials induced by the stimulation. Three individuals with complete motor paralysis of the lower limbs participated in the study. The evoked potentials to epidural spinal stimulation were investigated after surgery in a supine position and in one participant, during both supine and standing, with body weight load of 60%. The stimulation was delivered with intensity from 0.5 to 10 V at a frequency of 2 Hz. Recruitment curves of evoked potentials in knee and ankle muscles were collected at three localized and two wide-field stimulation configurations. Epidural electrical stimulation of rostral and caudal areas of lumbar spinal cord resulted in a selective topographical recruitment of proximal and distal leg muscles, as revealed by both magnitude and thresholds of the evoked potentials. ES activated both afferent and efferent pathways. The components of neural pathways that can mediate motor-evoked potentials were highly dependent on the stimulation parameters and sensory conditions, suggesting a weight-bearing-induced reorganization of the spinal circuitries.

Lower motor neuron findings after upper motor neuron injury: insights from postoperative supplementary motor area syndrome

Hypertonia and hyperreflexia are classically described responses to upper motor neuron injury. However, acute hypotonia and areflexia with motor deficit are hallmark findings after many central nervous system insults such as acute stroke and spinal shock. Historic theories to explain these contradictory findings have implicated a number of potential mechanisms mostly relying on the loss of descending corticospinal input as the underlying etiology. Unfortunately, these simple descriptions consistently fail to adequately explain the pathophysiology and connectivity leading to acute hyporeflexia and delayed hyperreflexia that result from such insult. This article highlights the common observation of acute hyporeflexia after central nervous system insults and explores the underlying anatomy and physiology. Further, evidence for the underlying connectivity is presented and implicates the dominant role of supraspinal inhibitory influence originating in the supplementary motor area descending through the corticospinal tracts. Unlike traditional explanations, this theory more adequately explains the findings of postoperative supplementary motor area syndrome in which hyporeflexia motor deficit is observed acutely in the face of intact primary motor cortex connections to the spinal cord. Further, the proposed connectivity can be generalized to help explain other insults including stroke, atonic seizures, and spinal shock.

Limb compressive load does not inhibit post activation depression of soleus H-reflex in indiviudals with chronic spinal cord injury

OBJECTIVE

We investigated the effect of various doses of limb compressive load on soleus H-reflex amplitude and post activation depression in individuals with/without chronic SCI. We hypothesized that SCI reorganization changes the typical reflex response to an external load.

METHODS

Ten healthy adults and 10 individuals with SCI received three doses of compressive load to the top of their knee (10%, 25%, and 50% of the body weight, BW). Soleus H-reflexes were measured before (baseline) and during the loading phase.

RESULTS

With persistent background muscle activity across all testing sessions, segment compressive load significantly decreased post activation depression in the control group, but did not change the post activation ratio in the SCI group. Normalized H2 amplitude significantly increased according to load (50%> 25%> 10%) in the control group whereas was minimally modulated to load in those with SCI.

CONCLUSIONS

Segment compressive load inhibits post activation depression in humans without SCI, but minimally modulates the reflex circuitry in people with chronic SCI. These findings suggest that spinal cord reorganization mitigates the typical response to load in people with chronic SCI.

SIGNIFICANCE

Early limb load training may impact the reorganization of the spinal cord in humans with acute SCI.

[Pathophysiology of spasticity]

The term "spasticity" describes the velocity-dependent increase in tonic stretch reflexes. The symptom is commonly seen in patients with injury to the central nervous system. It is rarely isolated but, instead, part of a set of symptoms that is sometimes confusing. However, the pathophysiology of the symptom has evolved over the past three decades, and it is now considered part of a global process that includes not only spinal reflex loop modifications, but also changes in the biomechanical properties of muscle fibers. Finally, recent studies of changes in the membrane properties of motor neurons and the occurrence of plateau potential have opened new perspectives. This review aims to describe these new pathophysiological models.

Limb segment load inhibits post activation depression of soleus H-reflex in humans

OBJECTIVE

We investigated the effect of various doses of limb segment load on soleus H-reflex amplitude and post activation depression in healthy individuals. We also explored the influence of limb segment load on spinal circuitry in one individual with chronic SCI.

METHODS

Twenty-eight healthy adults and one SCI subject received compressive loads applied to the top of their knee at varied doses of load (10%, 25%, and 50% of the body weight). Soleus H-reflexes were measured before (baseline) and during the loading phase.

RESULTS

There were no significant differences in H-reflex amplitudes during the 50% BW load-on phase as compared to either baseline session or the load-off phase. However, the post activation depression was decreased over 9% (p<0.05) during the load-on phase compared to the load-off phase and scaled according to load (50%>25%>10%). The post activation depression ratio also appears less responsive to varying loads after chronic SCI.

CONCLUSIONS

Limb segment load decreases post-activation depression in humans. These findings suggest that the mechanism associated with post activation depression is modulated by limb segment load, and may be influenced by spinal reorganization after SCI.

SIGNIFICANCE

Future studies will determine if various levels of spasticity modulate the response of limb segment load on post activation depression in those with acute and chronic SCI.

Characteristics of lower extremity clonus after human cervical spinal cord injury

Clonus can interfere with self-care and rehabilitation of people with spinal cord injury. Our aim was to characterize clonus and to evaluate factors that influence clonus duration in muscles paralyzed chronically by spinal cord injury. Electromyographic activity was recorded from soleus and 7 other limb muscles (5 ipsilateral, 2 contralateral) during clonus. In 14 subjects, clonus frequency in soleus averaged 5.4±0.9 Hz and was slower when the reflex path was longer. Contraction frequency slowed at the beginning and end of clonus (sometimes by 2 Hz). The magnitude of one cycle changed the timing and magnitude of the next cycle. These data suggest that afferent input influences the frequency and maintenance of clonus. Recording from many muscles revealed that clonus was prolonged (>40 sec) when only ipsilateral triceps surae or triceps surae and tibialis anterior were involved. Therefore, localized inputs to spinal circuits were important to sustain clonus. Clonus was intermediate (median: 21 sec) with activation of three or four ipsilateral muscles and these contractions were associated with greater activation of ipsilateral flexors. Clonus was short (<5 sec) when ipsilateral and contralateral muscles were activated (five or six muscles). Activation of extraneous afferent input, particularly contralateral muscles, may provide a way to shorten clonus after spinal cord injury.

Spasticity mechanisms - for the clinician

Spasticity, a classical clinical manifestation of an upper motor neuron lesion, has been traditionally and physiologically defined as a velocity dependent increase in muscle tone caused by the increased excitability of the muscle stretch reflex. Clinically spasticity manifests as an increased resistance offered by muscles to passive stretching (lengthening) and is often associated with other commonly observed phenomenon like clasp-knife phenomenon, increased tendon reflexes, clonus, and flexor and extensor spasms. The key to the increased excitability of the muscle stretch reflex (muscle tone) is the abnormal activity of muscle spindles which have an intricate relation with the innervations of the extrafusal muscle fibers at the spinal level (feed-back and feed-forward circuits) which are under influence of the supraspinal pathways (inhibitory and facilitatory). The reflex hyperexcitability develops over variable period of time following the primary lesion (brain or spinal cord) and involves adaptation in spinal neuronal circuitries caudal to the lesion. It is highly likely that in humans, reduction of spinal inhibitory mechanisms (in particular that of disynaptic reciprocal inhibition) is involved. While simply speaking the increased muscle stretch reflex may be assumed to be due to an altered balance between the innervations of intra and extrafusal fibers in a muscle caused by loss of inhibitory supraspinal control, the delayed onset after lesion and the frequent reduction in reflex excitability over time, suggest plastic changes in the central nervous system following brain or spinal lesion. It seems highly likely that multiple mechanisms are operative in causation of human spasticity, many of which still remain to be fully elucidated. This will be apparent from the variable mechanisms of actions of anti-spasticity agents used in clinical practice.

Functioning of peripheral Ia pathways in infants with typical development: responses in antagonist muscle pairs

In muscle responses of proprioceptive origin, including the stretch/tendon reflex (T-reflex), the corresponding reciprocal excitation and irradiation to distant muscles have been described from newborn infants to older adults. However, the functioning of other responses mediated primarily by Ia-afferents has not been investigated in infants. Understanding the typical development of these multiple pathways is critical to determining potential problems in their development in populations affected by neurological disease, such as spina bifida or cerebral palsy. Hence, the goal of the present study was to quantify the excitability of Ia-mediated responses in lower limb muscles of infants with typical development. These responses were elicited by mechanical stimulation applied to the distal tendons of the gastrocnemius-soleus (GS), tibialis anterior (TA) and quadriceps (QAD) muscles of both legs in twelve 2- to 10-month-old infants and recorded simultaneously in antagonist muscle pairs by surface EMG. Tendon taps alone elicited responses in either, both or neither muscle. The homonymous response (T-reflex) was less frequent in the TA than the GS or QAD muscle. An 80 Hz vibration superimposed on tendon taps induced primarily an inhibition of monosynaptic responses; however, facilitation also occurred in either muscle of the recorded pair. These responses were not influenced significantly by age or gender. Vibration alone produced a tonic reflex response in the vibrated muscle (TVR) and/or the antagonist muscle (AVR). However, for the TA muscle the TVR was more frequently elicited in older than younger infants. High variability was common to all responses. Overall, the random distribution and inconsistency of muscle responses suggests that the gain of Ia-mediated feedback is unstable. We propose that during infancy the central nervous system needs to learn to set stable feedback gain, or destination of proprioceptive assistance, based on their use during functional movements. This will tailor the neuromuscular connectivity to support adaptive motor behaviors.

Functional evaluation of paraplegic monkeys (Macaca mulatta) over fourteen months post-lesion

We report on the neurological and neurophysiological findings obtained from two adult Macaca mulatta sustaining complete spinal cord transections at T8-T9. We performed periodic neurological exams, recorded motor evoked potentials (MEPs) following transcranial magnetic stimulation (TMS), and recorded electromyograms (EMGs) during the execution of a lower limb motor test. The main observations were: (1) the spinal shock period lasted less than a week; tendon, cutaneous and withdrawal reflexes were uneven in range and occurrence, and Babinski's sign was not observed; (2) a protracted functional lesion in the tibial and common peroneal nerves appeared bilaterally early in the post-lesional period; (3) MEPs were elicited by TMS in the quadriceps muscle of both monkeys; they were recorded as early as the 5th week after lesion in one of the monkeys, and they persisted throughout the post-lesional period in both monkeys; and (4) motor unit action potentials in the quadriceps muscle recorded by EMG were simultaneous with attempts to perform intentional lower limb movements from post-lesion month 11 to 13.5 in both monkeys. The last two sets of observations argue in favor of a partial cortico-spinal functional gain and suggest that spinal cord regeneration can occur after complete spinal cord injury in primates.

Incomplete bladder emptying in patients with stroke: is detrusor external sphincter dyssynergia a potential cause?

OBJECTIVES

To delineate the frequency, clinical risk factors, and urodynamic mechanisms of incomplete bladder emptying (IBE) among patients with recent stroke.

DESIGN

Retrospective study.

SETTING

Inpatient setting in the rehabilitation ward of a university hospital.

PARTICIPANTS

All patients with acute stroke admitted for rehabilitation between January and December 2005, excluding those with a history of lower-urinary tract symptoms and urologic diseases. Eighty-two patients (42 women and 40 men; mean age, 65.5 y) were included.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

We measured postvoid residual (PVRs) by catheterization or by using an ultrasonic bladder scanner. Twenty-five patients (30.5%) had IBE with PVRs greater than 100 mL on 2 consecutive days. Patients with IBE were evaluated by a urologist and subsequently underwent urodynamic studies.

RESULTS

The presence of IBE was significantly associated with urinary tract infection (P<.001) and aphasia (P=.046). The presence of IBE was not related to sex, stroke location, nature of stroke (hemorrhagic or ischemic), history of diabetes mellitus, or previous stroke. Urodynamic studies done on 22 patients with IBE revealed acontractile detrusor in 8 patients (36%) and detrusor underactivity in 3 (14%). Eleven patients (50%) had detrusor-external sphincter dyssynergia (DESD) combined with normative detrusor function (5 patients) or detrusor hyperactivity (6 patients); all but 1 of these patients had a supratentorial lesion. The presence of DESD was associated with a longer onset-to-evaluation interval (P=.018) [corrected] and spasticity of the stroke-affected lower limb (P=.02). [corrected] Diabetes mellitus was associated with the presence of acontractile detrusor or detrusor underactivity (P=.03).

CONCLUSIONS

IBE is common among patients with stroke and is caused by decreased detrusor contractility or DESD. Spasticity of the external urethral sphincter is a possible pathophysiologic mechanism of DESD.

The spinal pathophysiology of spasticity--from a basic science point of view

Spasticity is a term, which was introduced to describe the velocity-sensitive increased resistance of a limb to manipulation in subjects with lesions of descending motor pathways. This distinguishes spasticity from the changes in passive muscle properties, which are often seen in these patients, but are not velocity-sensitive. Increased excitability of the stretch reflex is thus a central component of the definition of spasticity. This review describes changes in cellular properties and transmission in a number of spinal reflex pathways, which may explain the increased stretch reflex excitability. The review focuses mainly on results derived from the use of non-invasive electrophysiological techniques, which have been developed during the past 20-30 years to investigate spinal neuronal networks in human subjects, but work from animal models is also considered. The reflex hyperexcitability develops over several months following the primary lesion and involves adaptation in the spinal neuronal circuitries caudal to the lesion. In animal models, changes in cellular properties (such as 'plateau potentials') have been reported, but the relevance of these changes to human spasticity has not been clarified. In humans, numerous studies have suggested that reduction of spinal inhibitory mechanisms (in particular that of disynaptic reciprocal inhibition) is involved. The inter-subject variability of these mechanisms and the lack of objective quantitative measures of spasticity have impeded disclosure of a clear causal relationship between the alterations in the inhibitory mechanisms and the stretch reflex hyperexcitability. Techniques which make such a quantitative measure possible as well as longitudinal studies where development of reflex excitability and changes in the inhibitory mechanisms are followed over time are in great demand.

Plasticity of spinal cord reflexes after a complete transection in adult rats: relationship to stepping ability

Changes in epidurally induced (S1) spinal cord reflexes were studied as a function of the level of restoration of stepping ability after spinal cord transection (ST). Three types of responses were observed. The early response (ER) had a latency of 2.5 to 3 ms and resulted from direct stimulation of motor fibers or motoneurons. The middle response (MR) had a latency of 5 to 7 ms and was monosynaptic. The late response (LR) had a latency of 9 to 11 ms and was polysynaptic. After a complete midthoracic ST, the LR was abolished, whereas the MR was facilitated and progressively increased. The LR reappeared about 3 wk after ST and increased during the following weeks. Restoration of stepping induced by epidural stimulation at 40 Hz coincided with changes in the LR. During the first 2 wk post-ST, rats were unable to step and electrophysiological assessment failed to show any LR. Three weeks post-ST, epidural stimulation resulted in a few steps and these coincided with reappearance of the LR. The ability of rats to step progressively improved from wk 3 to wk 6 post-ST. There was a continuously improved modulation of rhythmic EMG bursts that was correlated with restoration of the LR. These results suggest that restoration of polysynaptic spinal cord reflexes after complete ST coincides with restoration of stepping function when facilitated by epidural stimulation. Combined, these findings support the view that restoration of polysynaptic spinal cord reflexes induced epidurally may provide a measure of functional restoration of spinal cord locomotor networks after ST.

Soleus H-reflex modulation in response to change in percentage of leg loading in standing after incomplete spinal cord injury

Body weight support (BWS) is frequently used to retrain standing and walking in persons post spinal cord injury (SCI), but the effects of leg unloading using BWS on H-reflex excitability in this population are unknown. The purpose of the study was to assess the effect of two different loading conditions on soleus H-reflex while standing in persons with motor incomplete SCI (i-SCI) and non-injured persons. Eight persons with motor i-SCI (mean age 50.25 years) and five non-injured persons (mean age 48.6 years) participated in the study. Specific control of the loading conditions was achieved using a BWS system. To compare reflex modulation at 40% versus 0% BWS, soleus H-reflexes were evoked during standing and normalized to the maximum M wave amplitude. These studies revealed that (1) H-reflex excitability is significantly greater after SCI and is exhibited even during quiet standing; and (2) no significant modulation in reflex excitability was observed by change in loading conditions in either the non-injured or the i-SCI subjects. These findings suggest that non-injured persons and persons with i-SCI respond similarly to bilateral limb unloading during standing with no change in H-reflex amplitude. Our results suggest that BWS of up to 40% does not produce detectable changes in the excitability of the soleus H-reflex in persons with i-SCI.

Enhanced stretch reflex excitability of the soleus muscle in persons with incomplete rather than complete chronic spinal cord injury

OBJECTIVE

To compare excitabilities of spinal stretch reflex among clinically complete spinal cord injury (SCI), incomplete SCI, elderly healthy, and young healthy subjects.

DESIGN

Case comparison.

SETTING

Research laboratory.

PARTICIPANTS

Volunteer sample of 12 complete SCI, 10 incomplete SCI, 10 elderly, and 11 young subjects.

INTERVENTION

Mechanically induced stretch reflex, H-reflex, and M response in electromyographic activity of the soleus muscle were recorded in all subjects.

MAIN OUTCOME MEASURES

Absolute peak-to-peak stretch reflex amplitude and maximum H-reflex (Hmax), and those values relative to the maximum M response (Mmax) amplitude (relative peak-to-peak stretch reflex amplitude) and H/M ratio.

RESULTS

Both the absolute and relative peak-to-peak stretch reflex amplitudes showed the greatest values in incomplete SCI among the 4 groups. Although absolute and relative peak-to-peak stretch reflex amplitudes of the incomplete SCI group were greater than those of the complete SCI group, the H/M ratios of both groups were comparable, and were greater than those of the younger and elderly groups.

CONCLUSIONS

The results suggest that the greater absolute and relative peak-to-peak stretch reflex amplitudes of incomplete SCI were mostly due to the greater maximum motor potential (Mmax), while the elevated spinal motoneuronal excitability shown by the increased H/M ratio was maintained in the chronic stage after both complete and incomplete SCIs.

Functional plasticity following spinal cord lesions

Spinal cord injury results in marked modification and reorganization of several reflex pathways caudal to the injury. The sudden loss or disruption of descending input engenders substantial changes at the level of primary afferents, interneurons, and motoneurons thus dramatically influencing sensorimotor interactions in the spinal cord. As a general rule reflexes are initially depressed following spinal cord injury due to severe reductions in motoneuron excitability but recover and in some instances become exaggerated. It is thought that modified inhibitory connections and/or altered transmission in some of these reflex pathways after spinal injury as well as the recovery and enhancement of membrane properties in motoneurons underlie several symptoms such as spasticity and may explain some characteristics of spinal locomotion observed in spinally transected animals. Indeed, after partial or complete spinal lesions at the last thoracic vertebra cats recover locomotion when the hindlimbs are placed on a treadmill. Although some deficits in spinal locomotion are related to lesion of specific descending motor pathways, other characteristics can also be explained by changes in the excitability of reflex pathways mentioned above. Consequently it may be the case that to reestablish a stable walking pattern that modified afferent inflow to the spinal cord incurred after injury must be normalized to enable a more normal re-expression of locomotor rhythm generating networks. Indeed, recent evidence demonstrates that step training, which has extensively been shown to facilitate and ameliorate locomotor recovery in spinal animals, directly influences transmission in simple reflex pathways after complete spinal lesions.

Tendon reflexes for predicting movement recovery after acute spinal cord injury in humans

OBJECTIVE

Use the tendon reflex to examine spinal cord excitability after acute spinal cord injury (SCI), relating excitability findings to prognosis.

METHODS

We conducted repeated measures of reflex responses to mechanical taps at the patellar and Achilles tendons of the lower limbs, and the wrist flexor tendons of the upper limbs in persons with acute SCI, beginning as early as the day of injury. The single largest EMG response (peak-to-peak) for each site was recorded. Subjects were compared based on level of injury and final neurologic status of lower limb motor function (i.e. absence of any voluntary recruitment in a lower limb muscle: motor-complete; voluntary recruitment in 1 or more lower-limb muscles: motor-incomplete).

RESULTS

We studied 229 subjects with acute SCI. Persons with injury to the cervical or thoracic spinal cord and who were (or became) motor-incomplete showed large tendon responses, even at the time of initial evaluation. In combination with larger tendon response amplitudes, the presence of the 'crossed-adductor' response to patellar tendon taps at the acute stage was highly predictive of functional motor recovery following SCI. In marked contrast, tendon responses were small (e.g. < 0.1 mV) or absent in persons with acute, motor-complete injury (and which remained motor-complete), and the crossed-adductor response was never seen. Reflex amplitudes and the incidence of the crossed-adductor response increased somewhat over time in persons with motor-complete SCI, but did not approach the values seen in motor-incomplete subjects.

CONCLUSIONS

Taken together, tendon response amplitude and reflex spread were sensitive and specific indicators of preserved supraspinal control over lower limb musculature in subjects with acute SCI. A simple algorithm using these outcome measures predicted a 'motor-complete' status with 100% accuracy, and a motor-incomplete status with accuracy exceeding 91%.

H-reflex and physiologic measures of ejaculation in men with spinal cord injury11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated

OBJECTIVE

To investigate the various physiologic parameters characterizing and predicting ejaculation.

DESIGN

Single case-control study.

SETTING

A referred care center and university setting.

PARTICIPANTS

Two men with spinal cord injury (SCI) and 2 control subjects.

INTERVENTION

Subjects were asked to self-stimulate with a Ferticare vibrator to induce ejaculation over 5 to 8 independent sessions.

MAIN OUTCOME MEASURES

Penile tumescence, blood pressure, heart rate, electromyographic activity of the bulbocavernosus muscles, abdominal muscles, soleus H-reflex, and occurrence of ejaculation.

RESULTS

Changes on all measures were observed, with penile tumescence being more stable in control subjects. Blood pressure increased in both groups, whereas tachycardia was observed in controls and bradycardia in subjects with SCI. H-reflex dropped slightly in controls but increased in subjects with SCI. Muscular patterns differed on ejaculatory success or failure.

CONCLUSIONS

Physiologic changes on all measures can be observed in men with SCI as a function of ejaculation. Changes include hypertension and bradycardia, characteristic of hyperreflexia, and tachycardia in controls. The neural mechanisms underlying these patterns are discussed. H-reflex showed increased spinal cord excitability in subjects with SCI after ejaculation, which suggests spasticity. The results support investigation of the H-reflex to predict ejaculatory success or failure in men with SCI, along with specific analysis of muscular patterns.

Soleus H-reflex recruitment is not altered in persons with chronic spinal cord injury 11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To determine whether spasticity in persons with spinal cord injury (SCI) is associated with elevated monosynaptic reflex excitability.

DESIGN

One-way experimental.

SETTING

Research laboratory.

PARTICIPANTS

Convenience sample of 9 subjects (8 men, 1 woman) with chronic and complete SCI and 20 persons (14 men, 6 women) with no neurologic impairment. Subjects with SCI exhibited lower-extremity spasticity as indicated by velocity-dependent increased resistance to passive muscle stretch, abnormally brisk deep tendon reflexes, involuntary lower-extremity flexion and/or extension spasms, and clonus.

INTERVENTION

Soleus H-reflex recruitment curves were elicited in all subjects.

MAIN OUTCOME MEASURES

Soleus H-reflex threshold (HTH), gain (HGN), and amplitude (HPP).

RESULTS

There was no difference between subjects with and without SCI in HTH, HGN, or HPP.

CONCLUSIONS

Spasticity in people with chronic and complete SCI was not associated with increased excitability of the connections between Ia afferent projections and motoneurons. Factors extrinsic to these connections may have a role in spasticity caused by SCI.

Spinal shock revisited: a four-phase model

Spinal shock has been of interest to clinicians for over two centuries. Advances in our understanding of both the neurophysiology of the spinal cord and neuroplasticity following spinal cord injury have provided us with additional insight into the phenomena of spinal shock. In this review, we provide a historical background followed by a description of a novel four-phase model for understanding and describing spinal shock. Clinical implications of the model are discussed as well.

Recovery from spinal cord injury--underlying mechanisms and efficacy of rehabilitation

Patients with an acute complete spinal cord injury (SCI) present a syndrome called "spinal shock". During spinal shock the loss of tendon reflexes and flaccid muscle tone is associated with a low persistence of F-waves and loss of flexor reflexes while H-reflexes are well elicitable. When clinical signs of spasticity become established, the electrophysiological parameters show little change. The divergent course of clinical signs of spasticity in their possible neuronal correlates indicate the occurrence of non-neuronal changes contributing to spasticity. - When signs of spinal shock had disappeared in patients with incomplete and complete paraplegia a locomotor pattern can be induced and trained under conditions of body unlaoding using a moving treadmill. In complete and incomplete paraplegic patients an increase of gastrocnemius electromyographic activity occurs during the stance phase of a step cycle with a daily locomotor training, coincident with a significant decrease of body unloading. In contrast to this, neither clinical nor electrophysiological examination scores improve. The locomotor pattern depends on the level of lesion: the higher the level of spinal cord lesion the more 'normal' is the locomotor pattern. This suggests that neuronal circuits underlying 'locomotor pattern generation' in man is not restricted to any specific level of the spinal cord, but extends from thoraco-lumbal to cervical levels.

Orally Delivered Baclofen to Control Spastic Hypertonia in Acquired Brain Injury

To determine if oral/systemic delivery of baclofen can effectively decrease spastic hypertonia due to acquired brain injury (traumatic brain injury, stroke, anoxia, or encephalopathy). Tertiary care outpatient rehabilitation center directly attached to a university hospital. Patients were a convenience sample recruited consecutively who had been referred for treatment of their spastic hypertonia to our spasticity clinic over a 5-year period. The spastic hypertonia was due to an acquired brain injury by either traumatic brain injury (TBI), stroke, or anoxic brain injury. All patients were more than 6 months postinjury or illness. Retrospective review of patients before and after initiation of treatment with oral baclofen, per standardized clinical data sheets. Thirty-five patients (22 TBI patients) were started on oral baclofen and were reevaluated between 1 to 3 months after initiation of treatment. Data for motor tone (Ashworth scores), spasm scores (Penn spasm frequency score), and deep tendon reflex scores were collected on the affected upper extremity (UE) and lower extremity (LE) side(s). Normal extremities were not assessed. Differences over time were assessed via descriptive statistics and Wilcoxon signed-rank. After 1 to 3 months of treatment when subjects had reached their maximal tolerated dosage, the average LE Ashworth score in the affected lower extremities (LEs) decreased from 3.5 to 3.2 (P =.0003), the reflex score decreased from 2.5 to 2.2 (P =.0274), and there was no statistical difference in the spasm score (P >.05). When the 22 TBI patients are analyzed separately, the average LE Ashworth score decreased from 3.5 to 3.2 (P =.0044) and the reflex score decreased from 2.7 to 2.0 (P =.0003). There was no statistically significant change in UE tone, spasm frequency, or reflexes after 1 to 3 months of treatment (P >.05). The average dosage at follow-up was 57 mg/day of baclofen (range 15-120 mg/day). There was a 17% incidence of somnolence that limited the maximum daily dosage of the medication. The oral delivery of baclofen is capable of reducing LE spastic hypertonia resulting from acquired brain injury. The lack of effect upon the upper extremities may be due to receptor specificity issues. GABA-B receptors may be less involved in the modulation of UE spastic hypertonia.

H reflexes and F waves. Fundamentals, normal and abnormal patterns

H reflexes and F waves have become integral parts of the electrodiagnostic examination in general, and nerve conduction studies in particular. They supplement the sensory and motor conduction studies by assessing the entire nerve segments including proximal portions of the motor and sensory axons. H reflexes and F waves have their own advantages and limitations, similarities and differences. These "late" responses are useful in patients with radiculopathies, plexopathies, and peripheral polyneuropathies, including the Guillain-Barre syndrome. They are also helpful in spinal cord disorders.

Motoneuron pool excitability of hemiplegic patients: assessing recovery stages by using H-reflex and M response

OBJECTIVES

To compare the excitability of the motoneuron pools of both the spastic and the unimpaired sides of patients with hemiplegia with a new method by using H-reflexes and M responses. The method determines the ratio of the developmental slope of the H-reflex (Hslp) to the slope of the M response (Mslp). We also examined the relation between the Brunnstrom stages and the Hslp/Mslp.

DESIGN

Experiment.

SETTING

Electrophysiologic experimental laboratory in a Japanese medical school.

PATIENTS

Fifteen hemiplegic patients (9 men, 6 women; age range, 48-71yr; mean, 60yr) with spasticity caused by a stroke.

INTERVENTIONS

The subject was instructed to relax while seated in a reclining chair with his foot fixed on an immobile pedal. After the soleus H-reflex and M responses on one side were recorded, the same experimental procedures were carried out on the other side.

MAIN OUTCOME MEASURES

Hslp/Mslp Brunnstrom stages.

RESULTS

Hslp/Mslp had better predictive value than conventional indicators of motoneuron pool excitability. Hslp/Mslp appeared to be a better match for the bell-shaped pattern of the Brunnstrom stages.

CONCLUSION

Hslp/Mslp is the preferred index for evaluating the motoneuron pool excitability of the spastic side of hemiplegic patients.

Prospective assessment of tizanidine for spasticity due to acquired brain injury

OBJECTIVE

To determine if orally delivered tizanidine will control spastic hypertonia due to acquired brain injury.

DESIGN

Randomized, double-blind, placebo-controlled, crossover design, with 2 8-week treatment arms separated by a 1-week washout period at baseline. Patients were randomly assigned to receive tizanidine or a matching placebo.

SETTING

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

PARTICIPANTS

Seventeen persons recruited in a consecutive manner, 9 of whom had suffered a stroke and 8 a traumatic brain injury, and had more than 6 months of intractable spastic hypertonia.

INTERVENTION

Over a 6-week period, subjects were slowly titrated up to their maximum tolerated dose (up to 36 mg/d). Following a 1-week drug taper and 1-week period in which no study drug was administered, patients were then crossed over to the other study medication following an identical titration regime.

MAIN OUTCOME MEASURES

Subjects were evaluated for dose and effect throughout the trial as well as for side effects. Data for Ashworth rigidity scores, spasm scores, deep tendon reflex scores, and motor strength were collected on the affected upper extremity (UE) and lower extremity (LE). Differences over time were assessed via descriptive statistics, Friedman's analysis, and Wilcoxon's signed-rank. Data are reported as the mean +/- 1 standard deviation.

RESULTS

Following 4 weeks of treatment when subjects reached their maximal tolerated dosage, the average LE Ashworth score on the affected side decreased from 2.3 +/- 1.4 to 1.7 +/- 1.1 (p <.0001). The spasm score decreased from 1.0 +/- 0.9 to 0.5 +/- 0.8 (p =.0464), while the reflex score was not statistically significant decreasing from 2.2 +/- 1.0 to 2.0 +/- 1.1 (p =.0883). The average UE Ashworth score on the affected side decreased from 1.9 +/- 1.1 to 1.5 +/- 0.9 (p <.0001). There was no significant change in the UE spasm and reflex scores. While there were positive placebo effects on motor tone, the active drug was still significantly better than placebo for decreasing LE tone (p =.0006) and UE tone (p =.0007). With a reduction in motor tone, there was an increase in motor strength (p =.0089). The average dosage at 4 weeks was 25.2mg/d.

CONCLUSION

Tizanidine is effective in decreasing the spastic hypertonia associated with acquired brain injury, which is dose-dependent. There are limitations on its use due to side effects related to drowsiness.