Sleep in the unresponsive wakefulness syndrome and minimally conscious state

Excessive Daytime Sleepiness in Stroke Survivors: An Integrative Review

Excessive daytime sleepiness (EDS) is a prevalent symptom among stroke survivors. This symptom is an independent risk factor for stroke and may reduce stroke survivors' quality of life, cognitive functioning, and daytime functional performance. The lack of a universally accepted definition of EDS makes it difficult to measure EDS and synthesize research. The purpose of this integrative review is to describe poststroke EDS, ascertain conceptual and operational definitions of EDS, identify factors that contribute to EDS in stroke survivors, and explore outcomes associated with EDS in stroke survivors. We searched the following databases: PubMed and MEDLINE (OvidSP 1946-April; Week 2, 2015), Embase (OvidSP 1974-March; Week 1, 2015), and PsycINFO (OvidSP 1967-April; Week 2, 2015). Our search yielded 340 articles, 27 of which met inclusion criteria. The literature reveals EDS to be a multidimensional construct that is operationalized with both subjective and objective measures. Choosing measures that can quantify both the objective and subjective components is useful for gaining a comprehensive understanding of EDS. The antecedents of EDS are stroke, sleep-disordered breathing, reversed Robin Hood syndrome, and depression. The outcomes associated with EDS in stroke patients are serious and negative. Via synthesis of this research, we propose a possible framework for poststroke EDS, which may be of use in clinical practice and in research to identify valid quantifying methods for EDS as well as to prevent harmful outcomes in stroke survivors.

Could combined sleep and pain evaluation be useful in the diagnosis of disorders of consciousness (DOC)? Preliminary findings

BACKGROUND

The diagnosis of Disorders of Consciousness (DOC) is still challenging. Indeed, ~ 40% of patients in vegetative state (VS) are misdiagnosed, suggesting the need of more appropriate diagnostic tools. Emerging data are showing that EEG, including sleep structure evaluation and multimodal evoked potential recording could be helpful in DOC diagnosis. Moreover, pain perception evaluation could further increase diagnosis accuracy in such individuals.

METHODS

Fourteen individuals with DOC, due to severe brain injury, were enrolled and admitted to the Intensive Neurorehabilitation Unit of the Research Institute. All patients were evaluated by means of the Coma Recovery Scale-Revised, a 24(hh)-polysomnography and a Laser Evoked Potential (LEP) paradigm.

RESULTS

Clinically-defined patients in Minimally Consciousness State showed a more preserved sleep structure, physiologic hypnic figures and preserved REM/NREM sleep distribution than subjects in VS. LEP showed increased latencies and reduced amplitudes and were also detectable in patients with more structured sleep.

CONCLUSIONS

The data support previous findings concerning the importance of sleep study in DOC diagnosis, with more specific neurophysiological paradigms. Interestingly, the findings shed some light on the possible correlations among global brain connectivity, sleep structure and pain perception, which are related to the activity of the wide thalamo-cortical and cortico-cortical networks underlying consciousness.

Is Period3 Genotype Associated With Sleep and Recovery in Patients With Disorders of Consciousness?

Background Sleep evaluation is increasingly being used as prognostic tool in patients with disorders of consciousness, but, surprisingly, the role of Period3 (Per3) gene polymorphism has never been evaluated. Objective The aim of this study was to investigate the contribution of Per3 genotype on sleep quantity and consciousness recovery level in patients with disorders of consciousness (DOC). Methods In this observational study, we evaluated 71 patients with DOC classified as vegetative state/unresponsive wakefulness syndrome or minimally conscious state. Demographic and clinical data were collected and a standardised diagnostic workup, including a polysomnographic record, was applied. After informed consent provided by proxy, genomic DNA was obtained and Per3 polymorphism was analysed by polymerase chain reaction to identify 5/5, 4/5, or 4/4 genotype. Results Per3(5/5) genotype was found in 12.7% of our DOC patients. The median total Coma Recovery Scale-revised score in Per3(5/5) carriers was significantly higher than 4/4 genotype (10, range 5-16 vs 7, range 4-11; post hoc P = .036). Moreover, total sleep time seemed to be higher in 5/5 genotype (5/5, 221 minutes, range 88-515 minutes; 4/4, 151.5 minutes, range 36-477 minutes; and 4/5, 188 minutes, range 44-422 minutes). Conclusion For the first time we have shown a possible association between Per3 polymorphism and consciousness recovery level in DOC patients. Even though the exact molecular mechanism has not been defined, we speculate that its effect is mediated by higher total sleep time and slow wave sleep, which would improve the preservation of main cerebral connections.

Persistent vegetative state and minimally conscious state: a systematic review and meta-analysis of diagnostic procedures

BACKGROUND

Acute brain damage can cause major disturbances of consciousness, ranging all the way to the persistent vegetative state (PVS), which is also known as "unresponsive wakefulness syndrome". PVS can be hard to distinguish from a state of minimal preserved consciousness ("minimally conscious state," MCS); the rate of misdiagnosis is high and has been estimated at 37-43%. In contrast, PVS is easily distinguished from brain death. We discuss the various diagnostic techniques that can be used to determine whether a patient is minimally conscious or in a persistent vegetative state.

METHODS

This article is based on a systematic review of pertinent literature and on a quantitative meta-analysis of the sensitivity and specificity of new diagnostic methods for the minimally conscious state.

RESULTS

We identified and evaluated 20 clinical studies involving a total of 906 patients with either PVS or MCS. The reported sensitivities and specificities of the various techniques used to diagnose MCS vary widely. The sensitivity and specificity of functional MRI-based techniques are 44% and 67%, respectively (with corresponding 95% confidence intervals of 19%-72% and 55%-77%); those of quantitative EEG are 90% and 80%, respectively (95% CI, 69%-97% and 66%-90%). EEG, event-related potentials, and imaging studies can also aid in prognostication. Contrary to prior assumptions, 10% to 24% of patients in PVS can regain consciousness, sometimes years after the event, but only with marked functional impairment.

CONCLUSION

The basic diagnostic evaluation for differentiating PVS from MCS consists of a standardized clinical examination. In the future, modern diagnostic techniques may help identify patients who are in a subclinical minimally conscious state.

Across the consciousness continuum-from unresponsive wakefulness to sleep

Advances in the development of new paradigms as well as in neuroimaging techniques nowadays enable us to make inferences about the level of consciousness patients with disorders of consciousness (DOC) retain. They, moreover, allow to predict their probable development. Today, we know that certain brain responses (e.g., event-related potentials or oscillatory changes) to stimulation, circadian rhythmicity, the presence or absence of sleep patterns as well as measures of resting state brain activity can serve the diagnostic and prognostic evaluation process. Still, the paradigms we are using nowadays do not allow to disentangle VS/UWS and minimally conscious state (MCS) patients with the desired reliability and validity. Furthermore, even rather well-established methods have, unfortunately, not found their way into clinical routine yet. We here review current literature as well as recent findings from our group and discuss how neuroimaging methods (fMRI, PET) and particularly electroencephalography (EEG) can be used to investigate cognition in DOC or even to assess the degree of residual awareness. We, moreover, propose that circadian rhythmicity and sleep in brain-injured patients are promising fields of research in this context.

Acute loss of consciousness

Acute loss of consciousness poses a fascinating scenario for theoretical and clinical research. This chapter introduces a simple yet powerful framework to investigate altered states of consciousness. We then explore the different disorders of consciousness that result from acute brain injury, and techniques used in the acute phase to predict clinical outcome in different patient populations in light of models of acute loss of consciousness. We further delve into post-traumatic amnesia as a model for predicting cognitive sequels following acute loss of consciousness. We approach the study of acute loss of consciousness from a theoretical and clinical perspective to conclude that clinicians in acute care centers must incorporate new measurements and techniques besides the classic coma scales in order to assess their patients with loss of consciousness.

Preservation of electroencephalographic organization in patients with impaired consciousness and imaging-based evidence of command-following

OBJECTIVE

Standard clinical characterization of patients with disorders of consciousness (DOC) relies on observation of motor output and may therefore lead to the misdiagnosis of vegetative state or minimally conscious state in patients with preserved cognition. We used conventional electroencephalographic (EEG) measures to assess a cohort of DOC patients with and without functional magnetic resonance imaging (fMRI)-based evidence of command-following, and correlated the findings with standard clinical behavioral evaluation and brain metabolic activity.

METHODS

We enrolled 44 patients with severe brain injury. Behavioral diagnosis was established using standardized clinical assessments. Long-term EEG recordings were analyzed to determine wakeful background organization and presence of elements of sleep architecture. A subset of patients had fMRI testing of command-following using motor imagery paradigms (26 patients) and resting brain metabolism measurement using (18) fluorodeoxyglucose positron emission tomography (31 patients).

RESULTS

All 4 patients with fMRI evidence of covert command-following consistently demonstrated well-organized EEG background during wakefulness, spindling activity during sleep, and relative preservation of cortical metabolic activity. In the entire cohort, EEG organization and overall brain metabolism showed no significant association with bedside behavioral testing, except in a few cases when EEG was severely abnormal.

INTERPRETATION

These findings suggest that conventional EEG is a simple strategy that complements behavioral and imaging characterization of DOC patients. Preservation of specific EEG features may be used to assess the likelihood of unrecognized cognitive abilities in severely brain-injured patients with very limited or no motor responses.

Spectral signatures of reorganised brain networks in disorders of consciousness

Theoretical advances in the science of consciousness have proposed that it is concomitant with balanced cortical integration and differentiation, enabled by efficient networks of information transfer across multiple scales. Here, we apply graph theory to compare key signatures of such networks in high-density electroencephalographic data from 32 patients with chronic disorders of consciousness, against normative data from healthy controls. Based on connectivity within canonical frequency bands, we found that patient networks had reduced local and global efficiency, and fewer hubs in the alpha band. We devised a novel topographical metric, termed modular span, which showed that the alpha network modules in patients were also spatially circumscribed, lacking the structured long-distance interactions commonly observed in the healthy controls. Importantly however, these differences between graph-theoretic metrics were partially reversed in delta and theta band networks, which were also significantly more similar to each other in patients than controls. Going further, we found that metrics of alpha network efficiency also correlated with the degree of behavioural awareness. Intriguingly, some patients in behaviourally unresponsive vegetative states who demonstrated evidence of covert awareness with functional neuroimaging stood out from this trend: they had alpha networks that were remarkably well preserved and similar to those observed in the controls. Taken together, our findings inform current understanding of disorders of consciousness by highlighting the distinctive brain networks that characterise them. In the significant minority of vegetative patients who follow commands in neuroimaging tests, they point to putative network mechanisms that could support cognitive function and consciousness despite profound behavioural impairment.

Significance of multiple neurophysiological measures in patients with chronic disorders of consciousness

OBJECTIVE

The aim of this study was to verify the value of multiple neurophysiological tests in classifying disorders of consciousness (DOCs) in patients in a chronic vegetative or minimal consciousness state categorised on the basis of the Coma Recovery Scale (CRS).

METHODS

The study included 142 patients, all of whom underwent long (18h) EEG-polygraphic recordings including one night. The EEG was scored using the Synek scale and sleep patterns using an arbitrary scale. Absolute total power and relative EEG power were evaluated in different frequency bands. Multimodal evoked potentials (EPs), including auditory event-related potentials, were also evaluated and scored.

RESULTS

The most information came from the combined multimodal EPs and sleep EEG scores. A two-step cluster analysis based on the collected information allowed a satisfactory evaluation of DOC severity. Spectral EEG properties seemed to be significantly related to DOC classes and CRS scores, but did not seem to make any significant additional contribution to DOC classification.

CONCLUSIONS

Multiple electrophysiological evaluations based on EEG, sleep polygraphic recordings and multimodal EPs are helpful in assessing DOC severity and residual functioning in patients with chronic DOCs.

SIGNIFICANCE

Simple electrophysiological measures that can be easily applied at patients' bedsides can significantly contribute to the recognition of DOC severity in chronic patients surviving a severe brain injury.

Nocturnal melatonin regulation in post-traumatic vegetative state: a possible role for melatonin supplementation?

Circadian rhythms were recently proposed as a measure of physiological state and prognosis in disorders of consciousness (DOC). So far, melatonin regulation was never assessed in vegetative state (VS). Aim of our research was to investigate the nocturnal melatonin levels and light-induced melatonin suppression in a cohort of VS patients. We assessed six consecutive patients (four men, age 33.3 ± 9.3 years) with post-traumatic VS and nine age-matched healthy volunteers (five men, age 34.3 ± 8.9 years) on two consecutive nights: one baseline and one light exposure night. During baseline, night subjects were in bed in a dim (<5 lux) room from 10 pm to 8 am. Blood samples were collected hourly 00:30-3:30 am (00:30 = MLT1; 1:30 = MLT2; 2:30 = MLT3; and 3:30 = MLT4). Identical setting was used for melatonin suppression test night, except for the exposure to monochromatic (470 nm) light from 1:30 to 3:30 am. Plasma melatonin levels were evaluated by radioimmunoassay. Magnitude of melatonin suppression was assessed by melatonin suppression score (caMSS) and suppression rate. We searched for group differences in melatonin levels, differences between repeated samples melatonin concentrations during baseline night and light exposure night, and light-induced suppression of melatonin secretion. During baseline night, controls showed an increase of melatonin (MLT4 vs MLT1, p = 0.037), while no significant changes were observed in VS melatonin levels (p = 0.172). Baseline night MLT4 was significantly lower in VS vs controls (p = 0.036). During light-exposure night, controls displayed a significant suppression of melatonin (MLT3 and MLT4 vs MLT2, p = 0.016 and 0.002, respectively), while VS patients displayed no significant changes. The magnitude of light-induced suppression of melatonin levels was statistically different between groups considering control adjusted caMSS (p = 0.000), suppression rate (p = 0.002) and absolute percentage difference (p = 0.012). These results demonstrate for the first time that VS patients present an alteration in night melatonin secretion and reduced light-induced melatonin suppression. These findings confirm previous studies demonstrating a disruption of the circadian system in DOC and suggest a possible benefit from melatonin supplementation in VS.

The Nature of Sleep in 10 Bedridden Elderly Patients With Disorders of Consciousness in a Japanese Hospital

No previous study has satisfactorily clarified the nature of sleep in elderly bedridden people with disorders of consciousness (DOC). The objective of the present study was to clarify the sleep states of 10 elderly bedridden patients with DOC in a Japanese hospital to facilitate provision of evidence-based nursing care and appropriate adjustment of patients’ environments. Nocturnal polysomnography recordings were analyzed according to the standard scoring criteria, and the patients’ sleep stages and quality were investigated. Of the 10 patients, 9 showed slow wave sleep (SWS), 4 showed very high values for sleep efficiency (96–100%), and in 3 of these patients, the percentage of SWS was ≥ 20%. Furthermore, three of these four patients had 200 or more changes in sleep stage. Although the mechanism is unknown, the amount of SWS combined with the value of sleep efficiency suggests that the quality of sleep is poor in elderly bedridden patients with DOC. Further study is needed to determine better indicators of good sleep in this population.

Disorders of consciousness after acquired brain injury: the state of the science

The concept of consciousness continues to defy definition and elude the grasp of philosophical and scientific efforts to formulate a testable construct that maps to human experience. Severe acquired brain injury results in the dissolution of consciousness, providing a natural model from which key insights about consciousness may be drawn. In the clinical setting, neurologists and neurorehabilitation specialists are called on to discern the level of consciousness in patients who are unable to communicate through word or gesture, and to project outcomes and recommend approaches to treatment. Standards of care are not available to guide clinical decision-making for this population, often leading to inconsistent, inaccurate and inappropriate care. In this Review, we describe the state of the science with regard to clinical management of patients with prolonged disorders of consciousness. We review consciousness-altering pathophysiological mechanisms, specific clinical syndromes, and novel diagnostic and prognostic applications of advanced neuroimaging and electrophysiological procedures. We conclude with a provocative discussion of bioethical and medicolegal issues that are unique to this population and have a profound impact on care, as well as raising questions of broad societal interest.

Electroencephalographic profiles for differentiation of disorders of consciousness

Background

Electroencephalography (EEG) is best suited for long-term monitoring of brain functions in patients with disorders of consciousness (DOC). Mathematical tools are needed to facilitate efficient interpretation of long-duration sleep-wake EEG recordings.

Methods

Starting with matching pursuit (MP) decomposition, we automatically detect and parametrize sleep spindles, slow wave activity, K-complexes and alpha, beta and theta waves present in EEG recordings, and automatically construct profiles of their time evolution, relevant to the assessment of residual brain function in patients with DOC.

Results

Above proposed EEG profiles were computed for 32 patients diagnosed as minimally conscious state (MCS, 20 patients), vegetative state/unresponsive wakefulness syndrome (VS/UWS, 11 patients) and Locked-in Syndrome (LiS, 1 patient). Their interpretation revealed significant correlations between patients’ behavioral diagnosis and: (a) occurrence of sleep EEG patterns including sleep spindles, slow wave activity and light/deep sleep cycles, (b) appearance and variability across time of alpha, beta, and theta rhythms. Discrimination between MCS and VS/UWS based upon prominent features of these profiles classified correctly 87% of cases.

Conclusions

Proposed EEG profiles offer user-independent, repeatable, comprehensive and continuous representation of relevant EEG characteristics, intended as an aid in differentiation between VS/UWS and MCS states and diagnostic prognosis. To enable further development of this methodology into clinically usable tests, we share user-friendly software for MP decomposition of EEG (http://braintech.pl/svarog) and scripts used for creation of the presented profiles (attached to this article).