Does spasticity result from hyperactive stretch reflexes? Preliminary findings from a stretch reflex characterization study

Cannabinoid Activity-Is There a Causal Connection to Spasmolysis in Clinical Studies?

Cannabinoid drugs are registered for postoperative nausea and emesis, Tourette syndrome and tumor-related anorexia, but are also used for spasticity and pain relief, among other conditions. Clinical studies for spasmolysis have been equivocal and even conclusions from meta-analyses were not consistent. This may be due to uncertainty in diagnostic criteria as well as a lack of direct spasmolytic activity (direct causality). In this review we used the Hill criteria to investigate whether a temporal association is causal or spurious. Methods: A systematic literature search was performed to identify all clinical trials of cannabinoids for spasticity. Studies were evaluated for dose dependency and time association; all studies together were analyzed for reproducibility, coherence, analogy and mechanistic consistency. A Funnel plot was done for all studies to identify selection or publication bias. Results: Twenty-seven studies were included in this meta-analysis. The spasmolytic activity (effect strength) was weak, with a nonsignificant small effect in most studies and a large effect only in a few studies (“enriched” studies, low patient numbers). No dose dependency was seen and plotting effect size vs. daily dose resulted in a slope of 0.004. Most studies titrated the cannabinoid to the optimum dose, e.g., 20 mg/d THC. The effect decreased with longer treatment duration (3–4 months). The spasmolytic effect is consistent for different European countries but not always within a country, nor is the effect specific for an etiology (multiple sclerosis, spinal cord injury, others). For other criteria like plausibility, coherence or analogous effects, no data exist to support or refute them. In most studies, adverse effects were frequently reported indicating a therapeutic effect only at high doses with relevant side effects. Conclusions: Current data do not support a specific spasmolytic effect; a general decrease in CNS activity analogous to benzodiazepines appears more likely. Whether individual patients or specific subgroups benefit from cannabinoids is unclear. Further studies should compare cannabinoids with other, nonspecific spasmolytic drugs like benzodiazepines.

On Denny-Brown's 'spastic dystonia' - What is it and what causes it?

In this review, we will work around two simple definitions of two different entities, which most often co-exist in patients with lesions to central motor pathways: Spasticity is "Enhanced excitability of velocity-dependent responses to phasic stretch at rest", which will not be the subject of this review, while Spastic dystonia is tonic, chronic, involuntary muscle contraction in the absence of any stretch or any voluntary command (Gracies, 2005). Spastic dystonia is a much less well understood entity that will be the subject this review. Denny-Brown (1966) observed involuntary sustained muscle activity in monkeys with lesions restricted to the motor cortices . He further observed that such involuntary muscle activity persisted following abolition of sensory input to the spinal cord and concluded that a central mechanism rather than exaggerated stretch reflex activity had to be involved. He coined the term spastic dystonia to describe this involuntary tonic activity in the context of otherwise exaggerated stretch reflexes. Sustained involuntary muscle activity in the absence of any stretch or any voluntary command contributes to burdensome and disabling body deformities in patients with spastic paresis. Yet, little has been done since Denny-Brown's studies to determine the pathophysiology of this non- stretch or effort related sustained involuntary muscle activity following motor lesions and there is a clear need for research studies in order to improve current therapy. The purpose of the present review is to discuss some of the possible mechanisms that may be involved in the hope that this may guide future research. We discuss the existence of persistent inward currents in spinal motoneurones and present the evidence that the channels involved may be upregulated following central motor lesions. We also discuss a possible contribution from alterations in synaptic inputs from surviving or abnormally branched sensory and descending fibres leading to over-activity and lack of motor coordination. We finally discuss evidence of alterations in motor cortical representational maps and basal ganglia lesions.

Changes in correlation between spontaneous activity of dorsal horn neurones lead to differential recruitment of inhibitory pathways in the cat spinal cord

Simultaneous recordings of cord dorsum potentials along the lumbo-sacral spinal cord of the anaesthetized cat revealed the occurrence of spontaneous synchronous negative (n) and negative-positive (np) cord dorsum potentials (CDPs). The npCDPs, unlike the nCDPs, appeared preferentially associated with spontaneous negative dorsal root potentials (DRPs) resulting from primary afferent depolarization. Spontaneous npCDPs recorded in preparations with intact neuroaxis or after spinalization often showed a higher correlation than the nCDPs recorded from the same pair of segments. The acute section of the sural and superficial peroneal nerves further increased the correlation between paired sets of npCDPs and reduced the correlation between the nCDPs recorded from the same pair of segments. It is concluded that the spontaneous nCDPs and npCDPs are produced by the activation of interconnected sets of dorsal horn neurones located in Rexed's laminae III–IV and bilaterally distributed along the lumbo-sacral spinal cord. Under conditions of low synchronization in the activity of this network of neurones there would be a preferential activation of the intermediate nucleus interneurones mediating Ib non-reciprocal postsynaptic inhibition. Increased synchronization in the spontaneous activity of this ensemble of dorsal horn neurones would recruit the interneurones mediating primary afferent depolarization and presynaptic inhibition and, at the same time, reduce the activation of pathways mediating Ib postsynaptic inhibition. Central control of the synchronization in the spontaneous activity of dorsal horn neurones and its modulation by cutaneous inputs is envisaged as an effective mechanism for the selection of alternative inhibitory pathways during the execution of specific motor or sensory tasks.

Electromyographic Response to Manual Passive Stretch of the Hemiplegic Wrist: Accuracy, Reliability, and Correlation With Clinical Spasticity Assessment and Function

Background. The management of spasticity is important in neurorehabilitation and needs to be assessed accurately. The commonly used clinical tools have been criticized for lack of validity and sensitivity. Objective. To investigate the reliability of electromyographic (EMG) response to manual stretches of the hemiplegic wrist and its correlation with clinical assessments of spasticity and physical function. Methods. EMG activity was measured in 10 stroke patients and control participants (53.7 ± 10 and 32 ± 9.1 years respectively, mean ± SEM) during 3 cycles of 10 seconds passive manual movements of the wrist at 60 to 360° • s-1. Isometric maximal voluntary contractions (MVC) strength, range of movement (ROM) of the wrist flexors and extensors, spasticity (Modified Ashworth Scale [MAS]) and hand function (Block and Box Test [BBT]) were also assessed. Results. EMG activity of the stroke patients increased with velocity from 4% to 40% MVC ( P < .001) but there was none in the controls. It was unaffected by repetition and good to moderate reliability occurred at all speeds (ICC, 0.71-0.81). EMG correlated negatively with MVC strength ( r = -.9), active wrist flexion ROM ( r = -.8), and hand function scores ( r = —.7), but not with clinical measures of spasticity except at the lowest velocity ( r = .72). Conclusions. Consistent and accurate stretch velocities and EMG responses can be achieved with manual wrist stretches for the assessment of the neural component of spasticity. These objective tests did not correlate well with the standard clinical assessment of spasticity. They showed significant negative relationships with function, indicating that increased reflex excitability contributes to hand disability after stroke.

Inter- and intrarater reliability of the Modified Modified Ashworth Scale in patients with knee extensor poststroke spasticity

Muscle spasticity is a common motor disorder following upper motor neuron syndrome. A reliable and valid clinical tool is essential to document the effect of therapeutic interventions aimed to improve function by reducing spasticity. The Modified Ashworth Scale (MAS) is the most widely used and accepted clinical scale of spasticity. The MAS has been recently modified. The aim of this investigation was to determine the interrater and intrarater reliability of clinical test of knee extensor post-stroke spasticity graded on a Modified Modified Ashworth Scale (MMAS). Two raters scored the muscle spasticity of 15 patients with ischaemic stroke. For the inter- and intrarater reliability, two raters agreed on 80.1% and 86.6%, respectively. The Kappa values were good (kappa=0.72, SE=0.14, p<0.001) between raters and very good (kappa=0.82, SE=0.12, p<0.001) within one rater. The values of Kendall tau-b correlation were acceptable for clinical use with 0.87 (SE=0.06, p<0.001) between raters and 0.92 (SE=0.05, p<0.001) within one rater. The MMAS demonstrated reliable measurements for a single rater and between raters for measuring knee extensor post-stroke spasticity. The results encourage further study on the reliability and the validity of the scale.

Spinal astrocyte glutamate receptor 1 overexpression after ischemic insult facilitates behavioral signs of spasticity and rigidity

Using a rat model of ischemic paraplegia, we examined the expression of spinal AMPA receptors and their role in mediating spasticity and rigidity. Spinal ischemia was induced by transient occlusion of the descending aorta combined with systemic hypotension. Spasticity/rigidity were identified by simultaneous measurements of peripheral muscle resistance (PMR) and electromyography (EMG) before and during ankle flexion. In addition, Hoffman reflex (H-reflex) and motor evoked potentials (MEPs) were recorded from the gastrocnemius muscle. Animals were implanted with intrathecal catheters for drug delivery and injected with the AMPA receptor antagonist NGX424 (tezampanel), glutamate receptor 1 (GluR1) antisense, or vehicle. Where intrathecal vehicle had no effect, intrathecal NGX424 produced a dose-dependent suppression of PMR [ED50 of 0.44 microg (0.33-0.58)], as well as tonic and ankle flexion-evoked EMG activity. Similar suppression of MEP and H-reflex were also seen. Western blot analyses of lumbar spinal cord tissue from spastic animals showed a significant increase in GluR1 but decreased GluR2 and GluR4 proteins. Confocal and electron microscopic analyses of spinal cord sections from spastic animals revealed increased GluR1 immunoreactivity in reactive astrocytes. Selective GluR1 knockdown by intrathecal antisense treatment resulted in a potent reduction of spasticiy and rigidity and concurrent downregulation of neuronal/astrocytic GluR1 in the lumbar spinal cord. Treatment of rat astrocyte cultures with AMPA led to dose-dependent glutamate release, an effect blocked by NGX424. These data suggest that an AMPA/kainate receptor antagonist can represent a novel therapy in modulating spasticity/rigidity of spinal origin and that astrocytes may be a potential target for such treatment.