Motor inhibition from the brainstem is normal in torsion dystonia during REM sleep

Sleep disturbance in movement disorders: insights, treatments and challenges

Sleep and circadian rhythm disturbances are central features of many movement disorders, exacerbating motor and non-motor symptoms and impairing quality of life. Understanding these disturbances to sleep is clinically important and may further our understanding of the underlying movement disorder. This review evaluates the current anatomical and neurochemical understanding of normal sleep and the recognised primary sleep disorders. In addition, we undertook a systematic review of the evidence for disruption to sleep across multiple movement disorders. Rapid eye movement sleep behaviour disorder has emerged as the most reliable prodromal biomarker for the alpha synucleinopathies, including Parkinson's disease and multiple system atrophy, often preceding motor symptom onset by several years. Abnormal sleep has also been described for many other movement disorders, but further evidence is needed to determine whether this is a primary or secondary phenotypic component of the underlying condition. Medication used in the treatment of motor symptoms also affects sleep and can aggravate or cause certain sleep disorders. Within the context of movement disorders, there is also some suggestion of a shared underlying mechanism for motor and sleep pathophysiology, with evidence implicating thalamic and brainstem structures and monoaminergic neurotransmission. This review highlights the need for an understanding of normal and abnormal sleep within the movement disorder clinic, an ability to screen for specific causes of poor sleep and to treat sleep disturbance to improve quality of life. Key sleep disorders also act as important biomarkers and have implications in diagnosis, prognosis and the development of future therapies.

Non-motor Symptoms in Chinese Patients With Isolated Generalized Dystonia: A Case-Control Study

Background: Previous studies have indicated that non-motor symptoms are primary problems in focal dystonia, but limited data are available about non-motor problems and their correlation with motor severity in generalized dystonia (GD).

Methods: In the present study, we performed a case-control study and enrolled isolated inherited or idiopathic GD patients and age- and sex-matched healthy controls (HC). Clinical characteristics, motor symptoms, non-motor problems, including psychiatric co-morbidity, sleep problems, fatigue, and quality of life (QoL) were assessed in both groups using various rating scales and assessments.

Results: Thirty-three patients with GD and 33 controls were enrolled. Significant higher scores on depression and anxiety (p < 0.001) were shown in GD compared with HC, whereas the frequency of obsessive-compulsive disorders approached that of HC (p = 0.238). Patients with GD also had significantly higher Pittsburg Sleep Quality Index (PSQI) and fatigue scores than HC, whereas no difference was observed in excessive daytime somnolence. In GD, QoL was more impaired, with statistically lower scores in both physical and mental components. Psychiatric rating scales did not correlate to motor severity or disease duration but might influence quality of sleep. Subgroup analysis suggests non-motor manifestations differ with different etiologies in GD.

Conclusion: This study suggests that non-motor symptoms in GD, such as psychiatric problems, are likely to be primary determinants not correlated to motor severity, which may also affect quality of sleep and fatigue.

Status dystonicus in childhood

PURPOSE OF REVIEW

Dystonia is a common paediatric neurological condition. At its most severe, dystonia may lead to life-threatening complications, a state termed status dystonicus. This review provides an update on the definition, causes, management and outcome of childhood status dystonicus.

RECENT FINDINGS

High-quality studies in childhood status dystonicus are lacking, though an increasing number of case series have been published. Status dystonicus appears to occur more frequently in children compared with adults, with a clear precipitant identified in around two-thirds of cases. Although febrile illness remains the commonest trigger for status dystonicus, unplanned interruption to deep brain stimulation (DBS) is increasingly reported as a precipitant. In parallel with this, neurosurgical intervention for status dystonicus appears to have become more widely used, though optimum timing and patient selection remains unclear. In most cases, a multistaged approach is required; we propose an 'ABCD' approach - Addressing precipitants, Beginning supportive measures, Calibrating sedation and Dystonia specific medications. Outcomes following status dystonicus appear to have slightly improved in recent years, potentially as a consequence of increasing use of DBS, though mortality has remained around 10%.

SUMMARY

Future work is needed to inform evidence-based guidelines for the management of status dystonicus. One of many pressing questions is the precise indication, and timing of interventions such as DBS.

Sleep in patients with primary dystonia: A systematic review on the state of research and perspectives

Patients with primary dystonia, the third most prevalent movement disorder, suffer from a markedly reduced quality of life. This might, at least in part, be mediated by non-motor symptoms, including sleep disturbances. Characterising and treating sleep disturbances might provide new inroads to improve relevant patient-centred outcomes. This review evaluates the state of research on sleep in patients with dystonia and outlines an agenda for future research. A literature search was performed in July 2014 using PubMed, Medline via Ovid, PsycInfo, PsycArticles via Proquest and Embase via Ovid. Search results were screened for eligibility by two independent raters. Peer-reviewed publications reporting on sleep in patients with primary dystonia were included. Of 1445 studies identified through the search strategy, 18 met the inclusion criteria. In total, the included studies reported on 708 patients diagnosed with focal dystonia (cervical dystonia or blepharospasm), torsion dystonia, and dopa-responsive dystonia. The results indicate that at least half of the patients with focal cranial dystonia suffer from sleep disturbances, but excessive daytime sleepiness is uncommon. Sleep disturbance is associated with depressive symptoms. The frequency and duration of dystonic movements is markedly reduced during sleep. Reduced sleep quality appears to persist after treatment with botulinum toxin that successfully reduces motor symptoms. The findings are limited by a high clinical and methodological heterogeneity. Future research is needed to i) further characterize subjective and PSG sleep in patients with different types of dystonia, ii) determine the aetiology of sleep disturbances (e.g., abnormal brain function associated with dystonia, side effects of medication, psychological reasons), and iii) test whether targeted sleep interventions improve sleep and quality of life in patients with primary dystonia.

Cholinergic dysfunction alters synaptic integration between thalamostriatal and corticostriatal inputs in DYT1 dystonia

Projections from thalamic intralaminar nuclei convey sensory signals to striatal cholinergic interneurons. These neurons respond with a pause in their pacemaking activity, enabling synaptic integration with cortical inputs to medium spiny neurons (MSNs), thus playing a crucial role in motor function. In mice with the DYT1 dystonia mutation, stimulation of thalamostriatal axons, mimicking a response to salient events, evoked a shortened pause and triggered an abnormal spiking activity in interneurons. This altered pattern caused a significant rearrangement of the temporal sequence of synaptic activity mediated by M(1) and M(2) muscarinic receptors in MSNs, consisting of an increase in postsynaptic currents and a decrease of presynaptic inhibition, respectively. Consistent with a major role of acetylcholine, either lowering cholinergic tone or antagonizing postsynaptic M(1) muscarinic receptors normalized synaptic activity. Our data demonstrate an abnormal time window for synaptic integration between thalamostriatal and corticostriatal inputs, which might alter the action selection process, thereby predisposing DYT1 gene mutation carriers to develop dystonic movements.

Definition and classification of hyperkinetic movements in childhood

Hyperkinetic movements are unwanted or excess movements that are frequently seen in children with neurologic disorders. They are an important clinical finding with significant implications for diagnosis and treatment. However, the lack of agreement on standard terminology and definitions interferes with clinical treatment and research. We describe definitions of dystonia, chorea, athetosis, myoclonus, tremor, tics, and stereotypies that arose from a consensus meeting in June 2008 of specialists from different clinical and basic science fields. Dystonia is a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. Chorea is an ongoing random-appearing sequence of one or more discrete involuntary movements or movement fragments. Athetosis is a slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture. Myoclonus is a sequence of repeated, often nonrhythmic, brief shock-like jerks due to sudden involuntary contraction or relaxation of one or more muscles. Tremor is a rhythmic back-and-forth or oscillating involuntary movement about a joint axis. Tics are repeated, individually recognizable, intermittent movements or movement fragments that are almost always briefly suppressible and are usually associated with awareness of an urge to perform the movement. Stereotypies are repetitive, simple movements that can be voluntarily suppressed. We provide recommended techniques for clinical examination and suggestions for differentiating between the different types of hyperkinetic movements, noting that there may be overlap between conditions. These definitions and the diagnostic recommendations are intended to be reliable and useful for clinical practice, communication between clinicians and researchers, and for the design of quantitative tests that will guide and assess the outcome of future clinical trials.

[The neurophysiology of cataplexy]

Cataplexy and excessive daytime sleepiness are the leading symptoms of narcolepsy. Electrophysiological studies in humans do not show a clear association between cataplexy and rapid eye movement (REM) sleep. Even a decrement of the H reflex is not specific for cataplexy and may be caused by unspecific triggers such as coughing. Cholinomimetics, which may induce status cataplecticus, do not influence REM sleep, thus evidencing a REM-independent mechanism. Recent studies demonstrate a lack of the neuropeptide hypocretin in the CSF of narcoleptics. Hypocretin controls wakefulness and the motor and autonomous systems. In hypocretin-1 and -2 knockout mice, sudden stops of motor activity could be observed in emotional situations that were accompanied by sudden shifts from wakefulness to REM sleep and could be terminated by application of anticataplectic medication. The lack of hypocretin not only causes a noradrenergic-cholinergic imbalance in the midbrain but also influences motoneurons directly by juxtacellular hypocretin-containing membranes. Intravenous application of hypocretin in a dog with hypocretin deficiency in the CSF caused a dose-dependent decrease of cataplexies. An understanding of the neuronal mechanisms responsible for cataplexies is essential for the development of new anticataplectic medications.

Inhibitory and excitatory intracortical circuits across the human sleep-wake cycle using paired-pulse transcranial magnetic stimulation

Studies using single-pulse transcranial magnetic stimulation (TMS) have shown that excitability of the corticospinal system is systematically reduced in natural human sleep as compared to wakefulness with significant differences between sleep stages. However, the underlying excitatory and inhibitory interactions on the corticospinal system across the sleep-wake cycle are poorly understood. Here, we specifically asked whether in the motor cortex short intracortical inhibition (SICI) and facilitation (ICF) can be elicited at all in sleep using the paired-pulse TMS protocol, and if so, how SICI and ICF vary across sleep stages. We studied 28 healthy subjects at interstimulus intervals of 3 ms (SICI) and 10 ms (ICF), respectively. Magnetic stimulation was performed over the hand area of the motor cortex using a focal coil and evoked motor potentials were recorded from the contralateral first dorsal interosseus muscle (1DI). Relevant data was obtained from 13 subjects (NREM 2: n=7; NREM 3/4: n=7; REM: n=7). Results show that both SICI and ICF were present in NREM sleep. SICI was significantly enhanced in NREM 3/4 as compared to wakefulness and all other sleep stages whereas in NREM 2 neither SICI nor ICF differed from wakefulness. In REM sleep SICI was in the same range as in wakefulness, but ICF was entirely absent. These results in humans support the hypothesis derived from animal experiments which suggests that intracortical inhibitory mechanisms are involved in the control of neocortical pyramidal cells in NREM and REM sleep, but along different intraneuronal circuits. Further, our findings suggest that cortical mechanisms may additionally contribute to the inhibition of spinal motoneurones in REM sleep.

Intracortical inhibition and facilitation upon awakening from different sleep stages: a transcranial magnetic stimulation study

Intracortical facilitation and inhibition, as assessed by the paired-pulse transcranial magnetic stimulation technique with a subthreshold conditioning pulse followed by a suprathreshold test pulse, was studied upon awakening from REM and slow-wave sleep (SWS). Ten normal subjects were studied for four consecutive nights. Intracortical facilitation and inhibition were assessed upon awakening from SWS and REM sleep, and during a presleep baseline. Independently of sleep stage at awakening, intracortical inhibition was found at 1-3-ms interstimulus intervals and facilitation at 7-15-ms interstimulus intervals. Motor thresholds were higher in SWS awakenings, with no differences between REM awakenings and wakefulness, while motor evoked potential amplitude to unconditioned stimuli decreased upon REM awakening as compared to the other conditions. REM sleep awakenings showed a significant increase of intracortical facilitation at 10 and 15 ms, while intracortical inhibition was not affected by sleep stage at awakening. While the dissociation between motor thresholds and motor evoked potential amplitudes could be explained by the different excitability of the corticospinal system during SWS and REM sleep, the heightened cortical facilitation upon awakening from REM sleep points to a cortical motor activation during this stage.

Excessive daytime sleepiness and sleep disturbances in patients with neurological diseases: epidemiology and management

Up to 12% of the general population experience excessive daytime sleepiness (EDS), with increasing prevalence in the elderly. EDS may lead to cognitive impairment, resulting in inattentiveness, poor memory, mood disorders and an increased risk of accidents. As a result, quality of life is reduced in most patients with EDS as well as in their caregiving spouses. There are a variety of causes leading to EDS, including CNS pathology, neurological dysfunction, associated sleep disorders with insufficient or fragmented sleep, and drug therapy. Since EDS accompanies many neurological disorders, such as neurodegenerative and neuromuscular diseases, neurologists should be familiar with the diagnosis, its major causes and with treatment options. The main focus of this article is on movement disorders, neuromuscular diseases, multiple sclerosis, dementia, cerebrovascular diseases, head and brain trauma, pain and epilepsy. General management strategies for EDS in all these neurological diseases include sleep hygiene aspects such as extensions of noctural time in bed and frequent naps during the day. Pharmacological treatment is generally achieved with stimulants such as amphetamine, methylphenidate and pemoline, or newer compounds such as modafinil.

REM sleep atonia: responsible brain regions, quantification, and clinical implication

Muscle tone is profoundly suppressed during rapid-eye-movement sleep. Two indices that quantify this muscle activity suppression were introduced: the tonic inhibition index (TII) and the phasic inhibition index (PII). TII expresses the shortening of phasic chin muscle activity, and PII indicates the degrees of suppression of the occurrence of phasic chin muscle activity in the period of the burst of rapid eye movements. TII increased significantly with age, while PII decreased significantly. TII was found to reach the adult level at 12.3 years of age, while PII decreased to the adult value at 0.4 years. According to this difference in age between their maturation, the human nervous systems involved in muscle activity suppression are hypothesized to comprise at least two independent systems. TII and PII are also hypothesized to be affected by the activity of the brainstem inhibitory centers, which might be implicated in the suppression of muscle activity during wakefulness as well.

Development of REM sleep atonia

OBJECTIVES

To study the functional development of neuronal systems that suppress muscle activity, we quantified the chronological change of atonia in rapid-eye-movement sleep (REMS).

METHODS

REMS atonia was quantified by the tonic and phasic inhibition indices (TII and PII). TII indicates the shortness of chin muscle activity, whereas PII standardizes the simultaneous occurrence of chin muscle activity and bursts of rapid eye movements. TII and PII were calculated in REMS of 135 polysomnographical recordings obtained in healthy humans from premature babies to a 77-year-old man.

RESULTS

TII increased significantly with age, while PII decreased significantly. TII reached an adult level at preadolescence, while PII at early infancy.

CONCLUSION

Human nervous systems involved in both tonic and phasic inhibition in REMS raise their activities with age. Since TII and PII reach adult levels at different ages, suppression of muscle activity is hypothesized to be mediated through at least 2 independent systems in humans.

Maturation of motility and motor inhibition in rapid-eye-movement sleep

OBJECTIVE

To describe the age-related changes in the number of movements in rapid eye movement (REM) sleep, and to quantify the functional maturation of motor inhibition.

STUDY DESIGN

Gross movements, phasic mentalis muscle activity (PMMA), and a new index that expressed the shortness of PMMA (the proportion of short PMMA among all PMMA) were examined cross-sectionally in 87 healthy children from premature babies to preadolescents by means of a single (all-night) polysomnography.

RESULTS

The incidence of gross movements and long PMMA decreased with age, whereas that of short PMMA increased with age. The new index exhibited an age-related increase, with the highest correlation with age among sleep parameters examined, and reached an adult level after 6 years of age.

CONCLUSION

We found that the age-related reduction of PMMA duration, which was expressed by a new index, occurred in parallel with the maturation of the inhibitory system that is tonically activated during REM sleep. We named this index the tonic inhibition index and concluded that the neuronal system involved in motor inhibition during REM sleep was still maturing during early childhood. We propose the tonic inhibition index as a useful quantitative indicator for the maturity of the inhibitory system.

A quantitative assessment of the maturation of phasic motor inhibition during REM sleep

During rapid eye movement (REM) sleep, phasic and further motor inhibition occurs during clusters of REMs besides tonic motor inhibition. We describe the age-related quantitative change of the activity of this REM-related phasic motor inhibition. For this purpose, we introduced the phasic inhibition index (PII). PII is the rate of simultaneous occurrence of bursts of horizontal REMs and phasic mentalis muscle activity during REM sleep. We examined these phasic REM sleep parameters in 87 healthy children from premature babies to preadolescents. The incidence of bursts of REMs showed no age-related change, while that of the phasic mentalis muscle activity increased with age. The simple ratio between the incidence of bursts of REMs and that of phasic mentalis muscle activity showed no significant age-related change, whereas PII decreased rapidly during infancy and reached low constant values thereafter. We concluded that this age-related PII decline reflected the maturation of REM-related phasic motor inhibition. This is the first quantitative description on the development of human motor inhibition. Taken with the neuronal basis underlying REM-related phasic motor inhibition, we hypothesize that a PII value is within the normal low range as far as both the rostral pontine tegmentum and the brainstem inhibitory pathways are functionally intact.

Magnetic stimulation of the human brain during phasic and tonic REM sleep: recordings from distal and proximal muscles

During REM sleep, a powerful postsynaptic inhibition of spinal motoneurons induces a generalized muscle hypotonia. Despite this inhibition, it has been shown that by transcranial magnetic stimulation of the brain (TMS), muscle responses of normal amplitude can be evoked in small hand muscles of humans. Tonic innervation during sleep is different in postural vs. limb muscles, and the spinal inhibition differs during tonic vs. phasic REM episodes, Both phenomena may affect muscle responses to TMS. In this study, muscle responses of 14 healthy subjects were compared to TMS in abductor digiti minimi, lumbar erector spinae, trapezius, and diaphragm during phasic and tonic REM sleep. In all four muscles, the amplitudes of the muscle responses were extremely variable, ranging for example in trapezius from -100% to +473% as compared to wakefulness. There was no systematic difference between the muscles. Moreover, no differences were found for TMS during phasic REM events compared to tonic REM sleep. Thus, responses to TMS during REM sleep may be preserved, with a decreased or increased amplitude. As a likely explanation, the cortical excitability and/or the spinal inhibition fluctuates during REM sleep in humans.