Soleus H-reflex measures in patients with focal and generalized dystonia

Segmental Reflex, Long Latency Reflex, and Mixed Nerve Silent Period in Dystonia

We hypothesized that "long latency reflexes" (LLRs), associated segmental reflex (SR), and mixed nerve silent periods (MnSPs) recorded on the distal upper extremity muscles would behave differently in patients with cervical dystonia and focal hand dystonia. We enrolled patients with cervical dystonia, generalized dystonia, focal hand dystonia, and healthy individuals. We recorded SR, LLRs, and MnSPs. The mean amplitude of SR on the affected side of focal hand dystonia was significantly lower (p = 0.010). The parameters related to LLRs and MnSPs were not different between groups. We suggest, using SR, LLRs, and MnSPs, we could not show an electrophysiological signature specific to dystonia.

How can neurophysiological studies help with movement disorders characterization in clinical practice? A review

BACKGROUND

Neurophysiological studies are ancillary tools to better understand the features and nature of movement disorders. Electromyography (EMG), together with electroencephalography (EEG) and accelerometer, can be used to evaluate a hypo and hyperkinetic spectrum of movements. Specific techniques can be applied to better characterize the phenomenology, help distinguish functional from organic origin and assess the most probable site of the movement generator in the nervous system.

OBJECTIVE

We intend to provide an update for clinicians on helpful neurophysiological tools to assess movement disorders in clinical practice.

METHODS

Non-systematic review of the literature published up to June 2019.

RESULTS

A diversity of protocols was found and described. These include EMG analyses to define dystonia, myoclonus, myokymia, myorhythmia, and painful legs moving toes pattern; EMG in combination with accelerometer to study tremor; and EEG-EMG to study myoclonus. Also, indirect measures of cortical and brainstem excitability help to describe and diagnose abnormal physiology in Parkinson's disease, atypical parkinsonism, dystonia, and myoclonus.

CONCLUSION

These studies can be helpful for the diagnosis and are usually underutilized in neurological practice.

Cortical and spinal excitability in patients with multiple sclerosis and spasticity after oromucosal cannabinoid spray

BACKGROUND

Delta-9-tetrahydrocannabinol and cannabidiol (THC:CBD) oromucosal spray (Sativex®) has been recently approved for the management of treatment-resistant multiple sclerosis (MS) spasticity. Although the symptomatic relief of Sativex® on MS-spasticity has been consistently demonstrated, the pathogenetic implications remain unclear and the few electrophysiological studies performed to address this topic yielded controversial results. We therefore aimed to investigate the mechanisms underpinning the modulation of spastic hypertonia by Sativex®, at both central and spinal levels, through an extensive neurophysiological battery in patients with MS.

METHODS

Nineteen MS patients with treatment-resistant spasticity were recruited. Before and after 4weeks of treatment with Sativex® patients were clinically assessed with the Modified Ashworth Scale (MAS) and underwent a large neurophysiological protocol targeting measures of excitability and inhibition at both cortical [e.g., intracortical facilitation (ICF), short (SICI) and long (LICI) intracortical inhibition, cortical silent period (CSP)] and spinal level [e.g., H-reflex, H/M ratio and recovery curve of the H-reflex (HRC)]. A group of 19 healthy subjects served as controls.

RESULTS

A significant reduction of the MAS score after 4weeks of Sativex® treatment was detected. Before treatment, an increase in the late facilitatory phase of HRC was recorded in patients compared to the control group, that normalised post treatment. At central level, SICI and LICI were significantly higher in patients compared to healthy subjects. After therapy, a significant strengthening of inhibition (e.g. reduced LICI) and a non-significant facilitation (e.g. marginally increased ICF) occurred, suggesting a modulatory effect of Sativex® on different pathways, predominantly of inhibitory type. Sativex® treatment was well tolerated, with only 3 patients complaining about dizziness and bitter taste in their mouth.

DISCUSSION

Our results confirm the clinical benefit of Sativex® on spastic hypertonia and demonstrate that it might modulate both cortical and spinal circuits, arguably in terms of both excitation and inhibition. We suggest that the clinical benefit was likely related to a net increase of inhibition at cortical level that, in turn, might have influenced spinal excitability.

A dystonia-like movement disorder with brain and spinal neuronal defects is caused by mutation of the mouse laminin β1 subunit, Lamb1

A new mutant mouse (lamb1t) exhibits intermittent dystonic hindlimb movements and postures when awake, and hyperextension when asleep. Experiments showed co-contraction of opposing muscle groups, and indicated that symptoms depended on the interaction of brain and spinal cord. SNP mapping and exome sequencing identified the dominant causative mutation in the Lamb1 gene. Laminins are extracellular matrix proteins, widely expressed but also known to be important in synapse structure and plasticity. In accordance, awake recording in the cerebellum detected abnormal output from a circuit of two Lamb1-expressing neurons, Purkinje cells and their deep cerebellar nucleus targets, during abnormal postures. We propose that dystonia-like symptoms result from lapses in descending inhibition, exposing excess activity in intrinsic spinal circuits that coordinate muscles. The mouse is a new model for testing how dysfunction in the CNS causes specific abnormal movements and postures.

Abnormal acute changes in upper limb muscle cortical representation areas in the patients with writer's cramp during co-activation of distal and proximal muscles

AIM

We analysed cortical muscle representation areas during single muscle activation and during the co-activation of several upper arm muscles in the patients with writer's cramp to determine the possible occurrence of abnormal dynamic somatotopic changes in M1, in addition to the static map abnormalities already described in this form of dystonia.

METHODS

Using transcranial magnetic stimulation, we assessed cortical representations of medial deltoid, extensor carpi radialis and the first dorsal interosseus muscles in eight patients with writer's cramp and in eight healthy control subjects. Cortical maps were obtained during distal muscles' activation either in isolation or in conjunction with voluntary medial deltoid co-activation.

RESULTS

This study showed a difference in the organization of cortical representations of these muscles between the patients with dystonia and control subjects. The first dorsal interosseus and the extensor carpi radialis cortical representation areas were larger in the dystonic group. The cortical representations became larger when the medial deltoid was simultaneously co-activated, and this effect was not observed in the control group. In the dystonic group, the three cortical muscle representations largely overlapped and their centres of gravity were closer.

CONCLUSION

Patients with dystonia showed not only a different spatial organization of muscle cortical representation areas, but also abnormal acute somatotopic changes during proximal muscle co-activation. Task-specific motor impairment in writer's cramp may result not only from lack of cortical inhibition and the well-known anomalous cortical organization observed in these patients, but also from abnormal patterns of proximo-distal functional muscle coupling.

Writer's cramp: cortical excitability in tasks involving proximo-distal coordination

AIM

The aim of this work was to analyse how writer's cramp patients coordinate each element of the proximal to distal upper arm muscle chain during voluntary movement.

METHODS

Using transcranial magnetic stimulation, we have assessed motor cortex excitability properties in patients by recording motor-evoked potentials and silent periods in both the extensor carpi radialis (ECR) and the first dorsal interosseus muscles (FDI), activated either in isolation, or in conjunction with voluntary medial deltoid (MD) co-activation during performance of precise tasks. Ten dystonic patients and ten healthy controls were tested.

RESULTS

In both test groups, the ECR muscle displayed a similar active motor threshold, but the excitability curves reached higher plateau values, when the proximal MD muscle was co-activated. In the dystonic group, the FDI muscle excitability curves reached higher plateau values when the MD was co-activated, whereas co-activation had no effect on the control group. In the control group, silent periods, in both the ECR and the FDI were longer when the MD was co-activated. This effect was not observed in the dystonic group.

CONCLUSION

In the dystonic group, facilitation of the FDI was observed during a task involving proximo-distal coordination. No differences in silent periods were observed when the muscle was activated alone. Our results suggest that such abnormal facilitation is not only an impairment of the central inhibitory mechanisms reported for dystonic patients, but, in addition, represents true abnormality in cortical muscle activation strategies.

Cervical dystonia: disease profile and clinical management

Cervical dystonia, the most common focal dystonia, frequently results in cervical pain and disability as well as impairments affecting postural control. The predominant treatment for cervical dystonia is provided by physicians, and treatment can vary from pharmacological to surgical. Little literature examining more conservative approaches, such as physical therapy, exists. This article reviews the etiology and pathophysiology of the disease as well as medical and physical therapist management for people with cervical dystonia.

Comparison of Clinical and Neurophysiologic Responses to Intrathecal Baclofen Bolus Administration in Moderate-to-Severe Spasticity After Acquired Brain Injury

OBJECTIVES

To compare clinical and neurophysiologic responses to intrathecal baclofen (ITB) bolus injection in subjects with spasticity after acquired brain injury.

DESIGN

Prospective case series.

SETTING

Tertiary care rehabilitation center.

PARTICIPANTS

Thirty consecutive ITB pump candidates with dysfunctional spasticity caused by traumatic brain injury, hypoxic encephalopathy, or stroke.

INTERVENTION

A single 50-microg ITB bolus.

MAIN OUTCOME MEASURES

Lower-extremity Ashworth Scale score at 2, 4, and 6 hours after ITB bolus; soleus Hoffmann reflex (H-reflex)/M-wave amplitude (H/M) ratio and abductor hallucis F-wave persistence and F/M ratio at 5 hours. Nonparametric repeated-measures analysis of variance and paired t test were used for statistical analyses.

RESULTS

The Ashworth score on the more involved side significantly decreased from 2.4+/-0.7 at baseline to 1.5+/-0.6 and 1.4+/-0.6 at 4- and 6-hour evaluations, respectively (P<.001). H/M ratio significantly decreased bilaterally (more involved side, 62%+/-28% to 14%+/-19%; less involved side, 59%+/-26% to 11%+/-20%; P<.001). F-wave persistence significantly decreased on the more involved side (86%+/-17% to 75%+/-13%, P<.05) with no change in F/M ratio. There was no significant correlation among these outcome measures before or after the ITB bolus injection.

CONCLUSIONS

H/M ratio is more sensitive than the Ashworth score or F-wave persistence in detecting a physiologic response to ITB bolus. H-reflex is useful for verification of ITB bolus administration, as an adjunct to clinical evaluation, particularly among patients with moderate spasticity at rest or with small changes in Ashworth score. However, potential application of the marked sensitivity of the H-reflex to other clinically challenging situations, such as early detection of possible ITB system malfunction, awaits further investigation.

Electrophysiological assessment of the effect of intrathecal baclofen in dystonic children

OBJECTIVE

To evaluate the effect of intrathecal baclofen in a group of dystonic children using electrophysiological procedures previously validated in spastic children.

METHODS

Seven children (aged 2-16 years) with dystonia of various aetiologies (dyskinetic cerebral palsy, pantothenate kinase-associated neurodegeneration and Aicardi-Goutières syndrome) underwent transcranial magnetic stimulation, H-reflex and flexor reflex studies before and after intrathecal injection of baclofen. The Barry-Albright Dystonia Scale (BADS) was used for clinical evaluation of dystonia.

RESULTS

Motor-evoked potentials, present in 2 of 5 patients before baclofen, were preserved after injection. Before baclofen, H reflex was present in 6 of 7 patients (mean H(max)/M(max:) 0.45+/-0.21). It was markedly reduced after the injection (mean H(max)/M(max:) 0.09+/-0.11) (P<0.001). Area of flexor reflex significantly decreased after baclofen (P=0.047), while threshold significantly increased (P=0.01). No significant clinical improvement of the BADS scores was observed (P=0.058).

CONCLUSIONS

These electrophysiological procedures, previously demonstrated to quantify the action of intrathecal baclofen in spastic adults and children, also appear sensitive in dystonic children. The electrophysiological changes are consistent with primarily spinal sites of action of baclofen. They appear more sensitive than clinical evaluation.

Dystonia update

PURPOSE OF REVIEW

Dystonia is a movement disorder with a complex and not fully understood pathophysiology. Its better understanding would enable more focused treatment for the disorder. In this review, we provide an overview of recent studies of the pathophysiology of primary and secondary dystonia, with an emphasis on functional brain imaging. Potential mechanisms underlying the beneficial effects of deep brain stimulation for dystonia are also summarized.

RECENT FINDINGS

The recognition of dysfunction at different levels of the nervous system has extended the classical notions of localized striatal abnormalities in primary dystonia. Recent biochemical studies have revealed evidence of abnormal torsion activity in DYT1 dystonia. Abnormal patterns of brain metabolism have also been identified using functional brain imaging in different dystonia genotypes. These findings, in conjunction with new electrophysiological techniques, can be utilized to help define a common mechanism for the neural dysfunction in dystonia.

SUMMARY

New insights into the pathophysiology of dystonia have been provided by recent studies using electrophysiology, biochemistry and human genetics, as well as functional brain imaging studies. These advances together may create the basis for new therapies for this disorder.