Quantitative assessment of visual behavior in disorders of consciousness

Family caregivers improve the diagnostic accuracy of disorders of consciousness: from remote to near-bed auditory stimulation

BACKGROUND

Family caregivers (FC) contribute to reducing the misdiagnosis rate in patients with disorders of consciousness (DOC). Unfortunately, the recent pandemic of COVID-19 imposed drastic restrictions that limited the access of FC to the sensory/cognitive stimulation protocols. Telemedicine approaches have been implemented to avoid discontinuity in care pathways and to ensure caregivers involvement in rehabilitation programs.

AIM

The aim was to investigate whether the presence of FC remotely connected might help clinicians in eliciting higher cortically mediated behavioral responses in patients with DOC.

DESIGN

Cross-sectional study.

SETTING

Post-acute Unit of Neurorehabilitation.

POPULATION

DOC due to severe brain injury.

METHODS

Consecutive patients with DOC were assessed by means of the Coma Recovery Scale-Revised (CRS-R) by two expert examiners. Each patient underwent to five assessments in two weeks in three different conditions: 1) by the examiner only (standard); 2) with the verbal stimulation given by the FC remotely connected by PC tablet (caregiver in remote); and 3) with the verbal stimulation given by the FC physically present (caregiver in presence).

RESULTS

Thirty patients with DOC (VS/UWS=10; MCS=20; mean age: 51, range: 21-79; vascular: 16; anoxic: 6; TBI=8) and their FC were enrolled. Higher total scores of CRS-R were recorded both in "caregiver in remote" and in "caregiver in presence" than in standard condition (standard vs. remote, Z=2.942, P=0.003; standard vs. presence, Z=3.736, P<0.001). Furthermore, the administration of the CRS-R with a FC, elicited higher levels of behavioral responses in MCS patients, than CRS-R performed in standard condition. In particular, 2 patients out of 30 (6.66%) showed higher scores and better diagnosis when the CRS-R was administered with FC in remote. Similarly, 5 out of 30 patients (16.66%) showed better diagnoses when the CRS-R was administered with FC in presence. Five patients changed diagnosis between standard and presence conditions (3 MCS- were diagnosed as MCS+; 2 MCS+ were diagnosed as conscious).

CONCLUSIONS

Our findings add new evidence regarding the beneficial role of family members in the diagnosis of DOC, even mediated by telemedicine approach.

CLINICAL REHABILITATION IMPACT

In future guidelines, FC should have an active and supporting role in the diagnostic and rehabilitative process of DOC.

The visual stimulation in disorders of consciousness

Severe brain damage usually leads to disorders of consciousness (DOC), which include coma, unresponsive wakefulness syndrome (UWS) and a minimally conscious state (MCS). Visual stimulation is widely used, especially in the diagnosis and treatment and treatment of DOC. Researchers have indicated that tests based on visual stimulation including visual pursuit, when used in conjunction with the Coma Recovery Scale-Revised, are able to differentiate between UWS from an MCS. Recently, targeting patients' circadian rhythms has been proposed to be a possible treatment target for DOC. Indeed, light therapy has been applied in some other fields, including treating seasonal affective disorder, sleep problems, and Parkinson's disease. However, at present, although visual stimulation and light therapy are frequently used in DOC, there is still no international unified standard. Therefore, we recommend the development of an international consensus in regard to the definitions, operational criteria and assessment procedures of visual stimulation and light therapy. This review combines visual stimulation, circadian rhythm recovery, and light therapy in DOC patients and presents the mechanisms and current advances in applications related to light therapy and visual stimulation in an attempt to provide additional ideas for future research and treatment of DOC.

Cerebral Glucose Metabolism in Patients with Chronic Disorders of Consciousness

OBJECTIVE

To measure regional cerebral metabolic rate of glucose (CMRGlu) in patients with chronic disorders of consciousness (DOCs) using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET).

METHODS

This retrospective cohort study examined 50 patients (mean age: 40.9 ± 20.1 years) with traumatic brain injury (TBI)-induced chronic DOCs [minimally conscious state (MCS)+, n = 20; MCS-, n = 15 and vegetative state (VS), n = 15]. We measured FDG-PET-based CMRGlu values in 12 regions of both brain hemispheres and compared those among MCS+, MCS - and VS patients.

RESULTS

In both hemispheres, the regional CMRGlu reduced with consciousness deterioration in 11 of 12 regions (91.7%). In seven right hemisphere regions, CMRGlu values were markedly higher in MCS+ patients than in MCS- patients. Furthermore, CMRGlu was suggestively higher in the left occipital region in MCS- patients than in VS patients.

CONCLUSION

Functional preservation in the left occipital region in patients with chronic DOCs might reflect an awareness of external environments, whereas extensive functional preservation in the right cerebral hemisphere might reflect communication motivation.

Quantitative evaluation of the consciousness level of patients in a vegetative state using virtual reality and an eye-tracking system: A single-case experimental design study

ABSTRACTIt is important to distinguish patients in a minimally conscious state (MCS) from patients in a vegetative state (VS) when assessing disorders of consciousness (DOC) as prognosis, selection of therapy, and drug treatment could differ accordingly. Clinical evaluation of a patient's eye movements, such as visual startle, visual fixation, and visual pursuit, provides valuable evidence but is often subject to misdiagnosis. To minimize such misdiagnosis caused by human judgment, a virtual reality (VR) technology-based quantitative assessment method with an eye-tracking system is proposed in this study. The new VR system presented 3 stimuli to 20 healthy participants, and visual response data were recorded to define valid responses to each stimulus. Further, the newly defined stimuli were presented to five chronic patients in VS, and the system classified three of them as showing visual fixations that could not be verified through clinical assessment beforehand. The proposed system, as verified through such experimentation, suggests quantitative and objective evaluation methods for examining three visual functions of patients with DOC.

Spontaneous eye blinking as a diagnostic marker in prolonged disorders of consciousness

Clinical diagnosis of patients with prolonged disorders of consciousness is very challenging. As spontaneous eye blink rate (EBR) is reliably correlated with cognitive activity in healthy individuals, we investigated whether EBR could serve as a marker of patients' level of consciousness. We assessed ten patients in prolonged Vegetative State/Unresponsive Wakefulness Syndrome (VS/UWS; three females; mean age = 50.3 ± 17.8 years) and fourteen patients in Minimally Conscious State (MCS; three females; mean age = 52.9 ± 17.5 years) at their admission to a rehabilitation unit after the acute phase. During two separate 3-min rest conditions, we recorded patients' EBR by integrating on-line visual and off-line electro-oculographic count. We also assessed EBR during two auditory oddball tasks, i.e. passive listening and active counting of target tones in a sub-group of patients. EBR was significantly higher in MCS than in VS/UWS; moreover, EBR positively correlated with a validated index of responsiveness derived from the Coma Recovery Scale-Revised. Patients' mean EBR showed no significant differences within sessions and across experimental conditions of the oddball task, in both VS/UWS and MCS. Our findings suggest that, at least in the post-acute phase, observing patients' EBR for 3 min at rest could help to discriminate between VS/UWS and MCS, improving accuracy of clinical diagnosis.

Assessment of Language Functions in Patients With Disorders of Consciousness Using an Alternative Communication Tool

This study aimed to describe the percentage of tasks involving language functions that were completed by patients diagnosed with disorders of consciousness, as observed during neurorehabilitation conducted for different periods of time using an alternative communication tool. The project involved six participants, who were observed for 1 month, 6 months, and 1 year. The patients were asked to solve tasks involving language functions with the use of an eye-controlled device. The language functions were evaluated on the basis of the average number of tasks performed by the patients, which was 70.45% for the whole subject group. It is not entirely clear what determined the changes in language functions during the research. It is crucial that patients performed the presented tasks even though their state of consciousness, as confirmed through medical documentation (unresponsive wakefulness syndrome), did not suggest the possibility of establishing any contact with them.

Effect of Retinohypothalamic Tract Dysfunction on Melatonin Level in Patients with Chronic Disorders of Consciousness

OBJECTIVE

The aim of this study is to compare the secretion level of nocturnal melatonin and the characteristics of the peripheral part of the visual analyzer in patients with chronic disorders of consciousness (DOC).

MATERIALS AND METHODS

We studied the level of melatonin in 22 patients with chronic DOC and in 11 healthy volunteers. The fundus condition was assessed using the ophthalmoscopic method.

RESULTS

The average level of nocturnal melatonin in patients with DOC differed by 80% from the level of indole in healthy volunteers. This reveals a direct relationship between etiology, the level of consciousness, gaze fixation, coma recovery scale-revised score and the level of melatonin secretion. Examination by an ophthalmologist revealed a decrease in the macular reflex in a significant number of DOC patients, which in turn correlates negatively with the time from brain injury and positively with low values of nocturnal melatonin.

Visual fixation in disorders of consciousness: Development of predictive models to support differential diagnosis

The visual fixation represents a doubtful behavioral sign to discriminate Vegetative from Minimally Conscious State (MCS). To disentangle its meaning, we fitted univariate and multivariable logistic regression models matching different neurophysiological and neuroimaging data of 54 patients with Disorders of Consciousness to select the best model predicting which visual performance (visual blink or pursuit) was shown by patients and the best predictors set. The best models found highlighted the importance of the structural MRI and the visual evoked potentials data in predicting visual pursuit. Then, a qualitative pilot test was made on four patients showing visual fixation revealing that the obtained models correctly predict whether the patients' visual performance could support/correlate to a cognitively mediated behavior. The present pilot models could help clinicians to evaluate if the visual fixation response can support the MCS diagnosis.

Can Salient Stimuli Enhance Responses in Disorders of Consciousness? A Systematic Review

PURPOSE OF REVIEW

Diagnostic classification of patients with disorders of consciousness (DoC) is based on clinician's observation of volitional behaviours. However, patients' caregivers often report higher levels of responsiveness with respect to those observed during the clinical assessment. Thus, increasing efforts have been aimed at comprehending the effects of self-referential and emotional stimuli on patients' responsiveness. Here we systematically reviewed the original experimental studies that compared behavioural and electrophysiological responses with salient vs. neutral material in patients in vegetative state/unresponsive wakefulness syndrome or in minimally conscious state.

RECENT FINDINGS

Most of the reviewed studies showed that salient stimuli (i.e. patient's own or familiar faces, patient's own name, and familiar voices) seem to elicit a higher amount of behavioural or electrophysiological responses with respect to neutral pictures or sounds. Importantly, a quite high percentage of patients seem to respond to salient stimuli only. The present review could foster use of personally salient stimuli in assessing DoC. However, the low overall quality of evidence and some limitations in the general reviewing process might induce caution in transferring these suggestions into clinical practice.

Human Computer Interface for Tracking Eye Movements Improves Assessment and Diagnosis of Patients With Acquired Brain Injuries

One of the first clinical signs differentiating the minimally conscious state from the vegetative state is the presence of smooth pursuit eye movements occurring in direct response to moving salient stimuli. Glasgow Coma Scale (GCS) is one of the most commonly used diagnostic tools for acute phase assessment of the level of consciousness, together with a neurological examination. These classic measures are limited to qualitative neurological examination without more quantitative measures provided from e.g., tasks with tracking position of the gaze. Among this and other limitations, it is prone to a relatively high rate of misdiagnosis. Here, we developed an interface for gaze tracking to enhance the assessment of consciousness in 10 patients with acquired brain injuries. According to the acute phase GCS assessment, nine of them were considered unaware and below the minimally conscious state. Chronic neurological examination confirmed six of them below the minimally conscious state. Our new Human Computer Interface (HCI) revealed that six patients were conscious enough to complete at least one of the gaze tracking tasks. Among these six patients, one was originally diagnosed as remaining in a vegetative state and one in coma. The patient diagnosed as remaining in a chronic vegetative state scored six GCS points acutely. Following assessment with our HCI the patient was re-diagnosed with a possible locked-in syndrome. Our HCI method provides a new complementary tool for clinical assessment of patients suffering from disorders of consciousness.

Visual pursuit of one's own face in disorders of consciousness: a quantitative analysis

BACKGROUND

Eye behaviour is important to distinguish minimally conscious state (MCS) from vegetative state (VS).

OBJECTIVE

To search for conditions most suitable to characterize patients in MCS and in VS on quantitative assessment of visual tracking.

DESIGN

This is a cross-sectional study.

PARTICIPANTS

In total, 20 patients in VS, 13 in MCS plus and 11 in MCS minus participated in this study.

SETTING

Neurorehabilitation Unit.

METHODS

Evaluation of eye behaviour was performed by infrared system; stimuli were represented by a red circle, a picture of a patient's own face and a picture of an unfamiliar face, slowly moving on a personal computer (PC) monitor. Visual tracking on the horizontal and vertical axes was compared.

MAIN OUTCOME MEASURES

The main outcome measures were proportion of on-target fixations and mean fixation duration.

RESULTS

The proportion of on-target fixations differed as a function of the stimulus in patients in MCS plus but not in other groups. Own face and unfamiliar face elicited a similar proportion of on-target fixations. Tracking along the horizontal axis was more accurate than that along the vertical axis in patients in both MCS plus and MCS minus. Fixation duration did not differ among the three groups.

CONCLUSIONS

Horizontal visual tracking of salient stimuli seems particularly suitable for eliciting on-target fixations. Quantitative assessment of visual tracking can complement clinical evaluation for reducing diagnostic uncertainty between patients in MCS or VS.

Combined Transcranial Direct Current Stimulation and Virtual Reality-Based Paradigm for Upper Limb Rehabilitation in Individuals with Restricted Movements. A Feasibility Study with a Chronic Stroke Survivor with Severe Hemiparesis

Impairments of the upper limb function are a major cause of disability and rehabilitation. Most of the available therapeutic options are based on active exercises and on motor and attentional inclusion of the affected arm in task oriented movements. However, active movements may not be possible after severe impairment of the upper limbs. Different techniques, such as mirror therapy, motor imagery, and non-invasive brain stimulation have been shown to elicit cortical activity in absence of movements, which could be used to preserve the available neural circuits and promote motor learning. We present a virtual reality-based paradigm for upper limb rehabilitation that allows for interaction of individuals with restricted movements from active responses triggered when they attempt to perform a movement. The experimental system also provides multisensory stimulation in the visual, auditory, and tactile channels, and transcranial direct current stimulation coherent to the observed movements. A feasibility study with a chronic stroke survivor with severe hemiparesis who seemed to reach a rehabilitation plateau after two years of its inclusion in a physical therapy program showed clinically meaningful improvement of the upper limb function after the experimental intervention and maintenance of gains in both the body function and activity. The experimental intervention also was reported to be usable and motivating. Although very preliminary, these results could highlight the potential of this intervention to promote functional recovery in severe impairments of the upper limb.

Are visual functions diagnostic signs of the minimally conscious state? an integrative review

Visual pursuit (VP) and visual fixation (VF) have been recognized as the first signs of emerging consciousness and, therefore, are considered indicative of the minimally conscious state (MCS). However, debate exists about their status as they are considered either conscious reactions or reflexes. The aim of this study is to review the evidence of the definition, operationalization, and assessment of VP and VF in unconscious patients. PubMed and EMBASE were searched for relevant papers between May 26, 1994 and October 1, 2016. In addition, an internet search was done to identify other relevant papers, reports and manuals of assessment methods. Papers were included if the definition, operationalization, or assessment method of VP and VF was discussed in patients with disorders of consciousness. We identified 2364 articles, of which 38 were included. No uniform definitions of VP and VF were found. VP and VF were operationalized differently, depending on which scale was used. The Coma Recovery Scale-revised and the Sensory Tool to Assess Responsiveness were the only diagnostic scales found; the other scales were developed to monitor DOC patients. The use of a mirror was the most sensitive method for detecting VP and VF. The literature about the importance VP and VF in relation with consciousness is controversial. This integrative review shows a lack of consensus regarding the definition, operationalization, and assessment of VP and VF. International consensus development about the definition, operationalization, and assessment of VP and VF is recommended.

Mirror efficiency in the assessment of visual pursuit in patients in minimally conscious state

OBJECTIVE

Visual pursuit should be tested with a mirror in patients with disorders of consciousness. This stimulus was indeed more efficient than a person or an object, and the auto-referential aspect was supposed to be the key feature. The present study tested the hypothesis that the mirror was more efficient because of its self-aspect.

METHODS

The mirror was compared (1) to the patient's picture and to the picture of a famous face, in 22 patients in minimally conscious state and (2) to the patient's picture and a fake mirror, which had dynamical and bright aspects of the mirror, without reflecting the face, in 26 other patients in minimally conscious state.

RESULTS

The mirror was more efficient than the patient's picture, which was not statistically different from the famous face. The second part of the study confirmed the statistical difference between the mirror and the picture. However, the fake mirror was neither statistically different from the mirror nor from the picture.

CONCLUSIONS

Although our results suggest that the hypothesis proposed by previous studies was partly wrong, they confirm that the mirror is the best stimulus to use when assessing visual pursuit.

Back to the bedside? Making clinical decisions in patients with prolonged unconsciousness

In 1993, the UK High Court decided that Tony Bland was unaware of himself and his environment, had no interest in medical treatment and allowed withdrawal of treatment. Subsequently, the court has reviewed all cases of stopping feeding and hydration in people with a prolonged disorder of consciousness. Their focus has been on determining whether the person is in the permanent vegetative state, because this avoids considering what is in a person's Best Interests. Consequently, much resource is spent distinguishing the vegetative state from the minimally conscious state and often clinical decisions are delayed or not made because of the requirement to go to court. In this paper, I argue that the neurophysiological basis of consciousness is unknown, and one cannot test whether the necessary structures are functioning. Unconscious people have responsiveness which varies; they may even have brief behaviours suggestive of awareness. No single clinical sign or investigation nor assessment battery can prove the presence (or absence) of consciousness or its permanence. The diagnosis of consciousness is clinical. Furthermore, awareness varies across a spectrum. There is no separate vegetative state. People simply have very limited or absent awareness. Even if there were such a state, it cannot be identified. The ethical and legal issues associated with decisions on treatment of unconscious people are no different from similar decisions in other patients. All decisions should be taken within the Best Interests framework and process. There should be no requirement to take any particular decision to court in this patient group.

Effect of Message Type on the Visual Attention of Adults With Traumatic Brain Injury

PURPOSE

The purpose of this investigation was to measure the effect of message type (i.e., action, naming) on the visual attention patterns of individuals with and without traumatic brain injury (TBI) when viewing grids composed of 3 types of images (i.e., icons, decontextualized photographs, and contextualized photographs).

METHOD

Fourteen adults with TBI and 14 without TBI-assigned either to an action or naming message condition-viewed grids composed of 3 different image types. Participants' task was to select/sustain visual fixation on the image they felt best represented a stated message (i.e., action or naming).

RESULTS

With final fixation location serving as a proxy for selection, participants in the naming message condition selected decontextualized photographs significantly more often than the other 2 image types. Participants in the action message condition selected contextualized photographs significantly more frequently than the other 2 image types. Minimal differences were noted between participant groups.

CONCLUSIONS

This investigation provides preliminary evidence of the relationship between image and message type. Clinicians involved in the selection of images used for message representation should consider the message being represented when designing supports for people with TBI. Further research is necessary to fully understand the relationship between images and message type.

SMART - Recognising the value of existing practice and introducing recent developments: leaving no stone unturned in the assessment and treatment of the PDOC patient

Over the last 25 years there have been a number of papers highlighting the issues of high rates of misdiagnosis in prolonged disorders of consciousness (PDOC) (Andrews, K., Murphy, L., Munday, R., & Littlewood, C. (1996). Misdiagnosis of the vegetative state: Retrospective study in a rehabilitation unit. BMJ, 313(7048), 13-16; Childs, N. L., Mercer, W. N., & Childs, H. W. (1993). Accuracy of diagnosis of persistent vegetative state. Neurology, 43(8), 1465-1467). Surprisingly, these rates still remain at the same level despite defined criteria for diagnosis (Schnakers, C., Vanhaudenhuyse, A., Giacino, J., Ventura, M., Boly, M., Majerus, S.,…Laureys, S. (2009). Diagnostic accuracy of the vegetative and minimally conscious state: Clinical consensus versus standardized neurobehavioral assessment. BMC Neurology, 9(35), 1-5; Van Erp, W., Larvrijsen, J., Vos, P., Bor, H., Laureys, S., & Koopmans, R. (2015). The vegetative state: Prevalence, misdiagnosis and treatment limitations. JAMDA, 85, e9-85.e14. doi: 10.1016/j.jamda.2014.10.014 ). This indicates the continued need for careful standardised assessment by skilled assessors to identify all potential meaningful responses and to establish a correct and incontrovertible diagnosis. The Sensory Modality Assessment and Rehabilitation Technique (SMART) is one of three assessments identified for the assessment of PDOC in the Royal College of Physician guidelines (Royal College of Physicians, 2013). The RCP guidelines and recent publications have highlighted and substantiated the value of some of the existing practices and unique features of the SMART. In recognition of the need to keep SMART current, SMART Version 3 is being developed and will be launched shortly. The interim SMART developments will be introduced in this paper and applied to practice through the illustration of a case study. Evidence suggests that SMART is a current and invaluable tool for the clinical and medico-legal assessment and treatment of the PDOC patient.

A comparative study on assessment procedures and metric properties of two scoring systems of the Coma Recovery Scale-Revised items: standard and modified scores

Objective:

The study compared the metric characteristics (discriminant capacity and factorial structure) of two different methods for scoring the items of the Coma Recovery Scale-Revised and it analysed scale scores collected using the standard assessment procedure and a new proposed method.

Design:

Cross sectional design/methodological study.

Setting:

Inpatient, neurological unit.

Participants:

A total of 153 patients with disorders of consciousness were consecutively enrolled between 2011 and 2013.

Intervention:

All patients were assessed with the Coma Recovery Scale-Revised using standard (rater 1) and inverted (rater 2) procedures.

Main outcome measures:

Coma Recovery Scale-Revised score, number of cognitive and reflex behaviours and diagnosis.

Results:

Regarding patient assessment, rater 1 using standard and rater 2 using inverted procedures obtained the same best scores for each subscale of the Coma Recovery Scale-Revised for all patients, so no clinical (and statistical) difference was found between the two procedures. In 11 patients (7.7%), rater 2 noted that some Coma Recovery Scale-Revised codified behavioural responses were not found during assessment, although higher response categories were present. A total of 51 (36%) patients presented the same Coma Recovery Scale-Revised scores of 7 or 8 using a standard score, whereas no overlap was found using the modified score. Unidimensionality was confirmed for both score systems.

Conclusion:

The Coma Recovery Scale Modified Score showed a higher discriminant capacity than the standard score and a monofactorial structure was also supported. The inverted assessment procedure could be a useful evaluation method for the assessment of patients with disorder of consciousness diagnosis.

Visuo-motor integration in unresponsive wakefulness syndrome: A piece of the puzzle towards consciousness detection?

PURPOSE

The unresponsive wakefulness syndrome (UWS) is characterized by either a profound unawareness or an impairment of large-scale cortico/subcortical connectivity. Nevertheless, some individuals with UWS could show residual markers of consciousness and cognition. In this study, we applied an electrophysiological approach aimed to identify the residual visuomotor connectivity patterns that are thought to be linked to awareness, in patients with chronic disorder of consciousness (DOC).

METHODS

We measured some markers of visuomotor and premotor-motor integration in 14 patients affected by DOC, before and after the application of transcranial direct current stimulation, delivered over the dorsolateral prefrontal cortex and the parieto-occipital area, paired to transorbital alterning current stimulation.

RESULTS

Our protocol induced a potentiation of the electrophysiological markers of visuomotor and premotor-motor connectivity, paired to a clinical improvement, in all of the patients with minimally conscious state and in one individual affected by UWS.

CONCLUSIONS

Our protocol could be a promising approach to potentiate the functional connectivity within large-scale visuomotor networks, thus allowing identifying the patients suffering from a functional locked-in syndrome (i.e. individuals showing an extreme behavioral motor dysfunction although with somehow preserved cognitive functions that can be identified only through para-clinical tests) within individuals with UWS.

Standard EEG in diagnostic process of prolonged disorders of consciousness

OBJECTIVE

This cross-sectional study assessed the ability of standard EEG in distinguishing vegetative state (VS) from minimally conscious state plus (MCS+) or MCS minus (MCS-), and to correlate EEG features with aetiology and level of responsiveness assessed by Coma Recovery Scale-Revised (CRS-R).

METHODS

We analyzed background EEG activity and EEG reactivity to eye opening and closing and to tactile, acoustic, nociceptive stimuli and Intermittent Photic Stimulation (IPS) in 73 inpatients (VS=37, MCS-=11, MCS+=25), with traumatic (n=21), vascular (n=25) or anoxic (n=27) aetiology.

RESULTS

All patients, but one, showed abnormal background activity. EEG abnormalities were more severe in VS than in MCS+ or MCS-, and in anoxic than other aetiologies. MCS+ patients with normal or Mildly Abnormal background activity showed higher scores on CRS-R than patients with moderate to severe EEG abnormalities. Reactivity to IPS, and acoustic stimuli was significantly more frequent in MCS+ and MCS- than in VS patients.

CONCLUSIONS

EEG features differ between VS and MCS- or MCS+ patients and can provide evidence of relative sparing of thalamocortical connections in MCS+ patients. In anoxic patients EEG organization is more severely impaired and provides less discriminative diagnostic information.

SIGNIFICANCE

Conventional EEG can help clinicians to disentangle VS from MCS patients.

Autonomic correlates of seeing one's own face in patients with disorders of consciousness

The ability to recognize one's own face is a hallmark of self-awareness. In healthy subjects, the sympathetic skin response evoked by self-face recognition has a greater area under the curve of the signal than responses evoked by other visual stimuli. We evaluated the sympathetic skin responses evoked by self-face images and by six other visual stimuli (conditions) in 15 patients with severe disorders of consciousness and in 15 age-matched healthy subjects. Under all conditions, the evoked area of the sympathetic skin response was smaller in patients with unresponsive wakefulness syndrome, intermediate in patients in a minimally conscious state, and greater in healthy subjects. In patients with unresponsive wakefulness syndrome, no differences were found between the sympathetic skin response area evoked by self-face images and those evoked by other conditions. In patients in a minimally conscious state, the area of the sympathetic skin response evoked by self-face presentation was greater than those evoked by other conditions, even if statistical significance was reached only in the comparison to other stimuli not involving a real face. This finding may be due to the inability of these patients to differentiate their own face from those of others. Taken together, these results probably reflect a varying level of self-awareness between patients with unresponsive wakefulness syndrome and patients in a minimally conscious state, and suggest that the autonomic correlate of self-awareness may have some diagnostic implications for these patients.

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.

A multicentre study of intentional behavioural responses measured using the Coma Recovery Scale-Revised in patients with minimally conscious state

OBJECTIVE

To investigate which conscious behaviour is most frequently detected using the Coma Recovery Scale-Revised in patients with minimally conscious state.

DESIGN

Multicentre, cross-sectional study.

SETTING

One intensive care unit, 8 post-acute rehabilitation centres and 2 long-term facilities.

SUBJECTS

Fifty-two patients with established diagnosis of minimally conscious state of different aetiology.

MAIN MEASURES

All patients were assessed by the Coma Recovery Scale-Revised.

RESULTS

In most patients (34/52) non-reflexive responses were identified by two or more subscales of the Coma Recovery Scale-Revised, whereas in 14 patients only the visual subscale could identify cortically-mediated behaviours, and in the remaining 4 patients only the motor subscale did so.The clinical signs of intentional behaviour were most often detected by the visual subscale (43/52 patients) and by the motor subscale (31/52), and least frequently by the oromotor/verbal subscale (3/52) of the Coma Recovery Scale-Revised. This clinical pattern was observed independently from time post-onset and aetiology.

CONCLUSIONS

Non-reflexive visual behaviour, identified by the visual subscale of Coma Recovery Scale-Revised, is the most frequently detected intentional sign consistent with the diagnosis of minimally conscious state, independently from aetiology and time post-onset.

Questioning the dichotomy between vegetative state and minimally conscious state: a review of the statistical evidence

Given the enormous consequences that the diagnosis of vegetative state (VS) vs. minimally conscious state (MCS) may have for the treatment of patients with disorders of consciousness, it is particularly important to empirically legitimate the distinction between these two discrete levels of consciousness. Therefore, the aim of this contribution is to review all the articles reporting statistical evidence concerning the performance of patients in VS vs. patients in MCS, on behavioral or neurophysiological measures. Twenty-three articles matched these inclusion criteria, and comprised behavioral, electroencephalographic (EEG), positron emission tomography (PET) and magnetic resonance imaging (MRI) measures. The analysis of these articles yielded 47 different statistical findings. More than half of these findings (n = 24) did not reveal any statistically significant difference between VS and MCS. Overall, there was no combination of variables that allowed reliably discriminating between VS and MCS. This pattern of results casts doubt on the empirical validity of the distinction between VS and MCS.

Eye movement measurement in diagnostic assessment of disorders of consciousness

We review the literature to appraise the evidence supporting or disputing the use of eye movement measurement in disorders of consciousness (DOC) with low levels of arousal or awareness, such as minimally conscious state (MCS), vegetative state (VS), and coma for diagnostic and prognostic purposes. We will focus on the effectiveness of each technique in the diagnostic classification of these patients and the gradual trend in research from manual to computerized tracking methods. New tools have become available at clinicians' disposal to assess eye movements with high spatial and temporal fidelity. The close relationship between eye movement generation and organic dysfunction in the brain allows these tools to be applied to the assessment of severe DOC as a unique supplementary toolset. We posit that eye tracking can improve clinical diagnostic precision for DOC, a key component of assessment that often dictates the course of clinical care in DOC patients. We see the emergence of long-term eye-tracking studies with seamless integration of technology in the future to improve the performance of clinical assessment in DOC.

Assessment of visual fixation in vegetative and minimally conscious states

Background

Visual fixation plays a key role in the differentiation between vegetative state/unresponsive wakefulness (VS/UWS) syndrome and minimally conscious state (MCS). However, the use of different stimuli changes the frequency of visual fixation occured in patients, thereby possibly affecting the accuracy of the diagnosis. In order to establish a standardized assessment of visual fixation in patients in disorders of consciousness (DOC), we compared the frequency of visual fixation elicited by mirror,a ball and a light.

Method

Visual fixation was assessed in eighty-one post-comatose patients diagnosed with a MCS or VS/UWS. Occurrence of fixation to different stimuli was analysis used Chi-square testing.

Result

40 (49%) out of the 81 patients showed fixation to visual stimuli. Among those, significantly more patients (39, 48%) had visual fixation elicited by mirror compared to a ball (23, 28%) and mirror compared to a light (20, 25%).

Conclusion

The use of a mirror during the assessment of visual fixation showed higher positive response rate, compared to other stimuli in eliciting a visual fixating response. Therefore, fixation elicited by a mirror can be a very sensitive and accurate test to differentiate the two disorders of consciousness.

Neuro-ophthalmology update

This review summarizes the most relevant articles from the field of neuro-ophthalmology published in the Journal of Neurology from January 2012 to July 2013. With the advent of video-oculography, several articles describe new applications for eye movement recordings as a diagnostic tool for a wide range of disorders. In myasthenia gravis, anti-Kv1.4 and anti-Lrp4 have been characterized as promising novel autoantibodies for the diagnosis of hitherto 'seronegative' myasthenia gravis. Several articles address new diagnostic and therapeutic approaches to neuromyelitis optica, which further sharpen its profile as a distinct entity. Additionally, 4-aminopyridine has become a standard therapeutic for patients with cerebellar downbeat nystagmus. Finally, revised diagnostic criteria have been proposed for chronic relapsing inflammatory optic neuropathy based on a careful literature review over the last decade.

Corticomotor facilitation in vegetative state: results of a pilot study

OBJECTIVE

To investigate whether corticomotor facilitation induced by transcranial magnetic stimulation (TMS-CF) could evoke a simple purposeful motor behavior in patients with a diagnosis of vegetative state.

DESIGN

Cross-sectional survey.

SETTING

Post-coma and rehabilitation care unit.

PARTICIPANTS

Patients (N=6) with a diagnosis of vegetative state.

INTERVENTIONS

A cascade of consecutive motor-evoked potentials (MEPs) was elicited under 3 different conditions: in the first condition, patients were at rest (Rest); in the second, they were asked to open and close the right hand (Execution); in the third, the examiner modeled a movement of abduction of the thumb in front of the patient who was encouraged in advance to imitate the action (Observation to Imitate).

MAIN OUTCOME MEASURES

Changes in MEP values from the abductor pollicis brevis muscle and improvement in scores on the Coma Recovery Scale-Revised.

RESULTS

TMS-CF alone or combined with verbal instructions did not yield any change; only the combination with imitation caused changes in MEPs (shorter latency and increased amplitude) associated with behavioral improvement in 4 patients.

CONCLUSIONS

Encouraging observation to imitate may favor the transformation of some perceived actions into motor images and performances, probably depending on the activation of mirror motor neurons. In our opinion, combining visual input with TMS-CF might have reinforced the coupling between movement planning and execution, promoting the recovery of elementary motor activities in some patients. The proposed protocol may contribute to unmasking signs of preserved consciousness in patients with latent capacities for recovery.