Disorders of Consciousness, Past, Present, and Future

A scientific approach to diagnosis of disorders of consciousness

Disorder of consciousness (DoC) are the shared clinical manifestation of severe brain injuries resulting from a variety of etiologies. The nosology of DoC, as well as the armamentarium of methods available to diagnose it, has rapidly evolved. As a result, the diagnosis of DoC is complex and dynamic. We offer an evidence-based approach to DoC diagnosis, highlighting the challenges and pitfalls therein. Accordingly, we summarize the contemporary taxonomy of DoC and its development. We discuss the standardized behavioral diagnostic tools that form the foundation of DoC diagnosis, the evidence for their use, and their limitations. We also highlight recent advances in functional MRI (fMRI) and electroencephalography (EEG) techniques to increase the sensitivity and specificity of DoC diagnosis. We discuss the concept of covert consciousness (i.e., cognitive motor dissociation) as a discrete diagnostic category of DoC, as well as its diagnostic implications. Finally, we underscore issues of neuroethics and equity raised by contemporary models of DoC.

Perturbational complexity index in assessing responsiveness to rTMS treatment in patients with disorders of consciousness: a cross-over randomized controlled trial study

BACKGROUND

Disorders of Consciousness (DoC) caused by severe brain injuries represent a challenging clinical entity, which is easy to misdiagnosis and lacks effective treatment options. Repetitive Transcranial Magnetic Stimulation (rTMS) is a non-invasive neuroelectric stimulation method that shows promise in improving consciousness for DoC, especially in minimally conscious state (MCS). However, there is little evidence of its effectiveness, especially in RCT studies.

METHODS

Twenty MCS patients participated in a double-blind, randomized, crossover, sham-controlled clinical study to evaluate the safety and efficacy of rTMS for MCS. Subjects were randomized into two groups: one group received rTMS-active for 10 consecutive days (n = 10), and the other group received rTMS-sham for 10 consecutive days (n = 10). After a 10-day washout period, the two groups were crossed over and received the opposite treatment. the rTMS protocol consisted of 2,000 pulses per day in the left dorsolateral prefrontal cortex (L-DLPFC), sent at 10 Hz. The stimulation intensity was 90% of the resting motor threshold. Coma Recovery Scale Revised (CRS-R), the main evaluation index, was evaluated before and after each phase in a double-blind manner. Meanwhile RS-EEG and TMS-EEG data were acquired and relative alpha power (RAP), and perturbational complexity index based on state transitions (PCIst) were caculated.

RESULTS

One-way ANOVA revealed significantly higher scores in rTMS-active treatment compared to rTMS-sham across various measures, including CRS-R total score, RAP, PCIst (all P < 0.05). Among the 20 MCS patients, 7 (35%) were identified as responders following rTMS treatment. Compared to rTMS-sham, responder scores for CRS-R, RAP, and PCIst (all P < 0.05) were significantly elevated after rTMS-active treatment. Conversely, there was no significant difference observed in non-responders. Furthermore, post-hoc analysis revealed that baseline PCIst was significantly higher in responders than non-responders. Upon a 6-month follow-up, CRS-R scores significantly increased in all 20 patients (P = 0.026). However, the responder group exhibited a more favorable prognosis compared to the non-responder group (P = 0.031).

CONCLUSIONS

Applying 10 Hz rTMS to L-DLPFC significantly increased consciousness level in MCS patients. PCIst is a neurophysiological index that has the potential to evaluate and predict therapeutic efficacy.

TRIAL REGISTRATION

www.

CLINICALTRIALS

gov , identifier: NCT05187000.

Cognitive Motor Dissociation: Gap Analysis and Future Directions

BACKGROUND

Patients with disorders of consciousness who are behaviorally unresponsive may demonstrate volitional brain responses to motor imagery or motor commands detectable on functional magnetic resonance imaging or electroencephalography. This state of cognitive motor dissociation (CMD) may have prognostic significance.

METHODS

The Neurocritical Care Society's Curing Coma Campaign identified an international group of experts who convened in a series of monthly online meetings between September 2021 and April 2023 to examine the science of CMD and identify key knowledge gaps and unmet needs.

RESULTS

The group identified major knowledge gaps in CMD research: (1) lack of information about patient experiences and caregiver accounts of CMD, (2) limited epidemiological data on CMD, (3) uncertainty about underlying mechanisms of CMD, (4) methodological variability that limits testing of CMD as a biomarker for prognostication and treatment trials, (5) educational gaps for health care personnel about the incidence and potential prognostic relevance of CMD, and (6) challenges related to identification of patients with CMD who may be able to communicate using brain-computer interfaces.

CONCLUSIONS

To improve the management of patients with disorders of consciousness, research efforts should address these mechanistic, epidemiological, bioengineering, and educational gaps to enable large-scale implementation of CMD assessment in clinical practice.

Towards modern post-coma care based on neuroscientific evidence

Background

Understanding the mechanisms underlying human consciousness is pivotal to improve the prognostication and treatment of severely brain-injured patients. Consciousness remains an elusive concept and the identification of its neural correlates is an active subject of research, however recent neuroscientific advances have allowed scientists to better characterize disorders of consciousness. These breakthroughs question the historical nomenclature and our current management of post-comatose patients.

Method

This review examines the contribution of consciousness neurosciences to the current clinical management of severe brain injury. It investigates the major impact of consciousness disorders on healthcare systems, the scientific frameworks employed to identify their neural correlates and how evidence-based data from neuroimaging research have reshaped the landscape of post-coma care in recent years.

Results

Our increased ability to detect behavioral and neurophysiological signatures of consciousness has led to significant changes in taxonomy and clinical practice. We advocate for a multimodal framework for the management of severely brain-injured patients based on precision medicine and evidence-based decisions, integrating epidemiology, health economics and neuroethics.

Conclusions

Major progress in brain imaging and clinical assessment have opened the door to a new era of post-coma care based on standardized neuroscientific evidence. We highlight its implications in clinical applications and call for improved collaborations between researchers and clinicians to better translate findings to the bedside.

Effects of 10 Hz individualized repetitive transcranial magnetic stimulation on patients with disorders of consciousness: a study protocol for an exploratory double-blind crossover randomized sham-controlled trial

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS), as a non-invasive brain stimulation technique, has shown potentials for consciousness recovery of patients with disorders of consciousness (DoC), as, to a certain extent, it is effective in regulating the excitability of central nervous system. However, it is difficult to achieve satisfactory effect with "one size fits all" rTMS treatment due to different clinical conditions of patients. There is an urgent need to develop individualized strategy to improve the effectiveness of rTMS on patients with DoC.

METHODS

Our protocol is a randomized double-blind sham-controlled crossover trial that includes 30 DoC patients. Each patient will received 20 sessions, in which 10 sessions will be rTMS-active stimulus, and the other 10 sessions will be sham stimulus, separated by no less than 10 days' washout period. The rTMS-active will include 10 Hz rTMS over the individualized-targeted selection area for each patient according to the different insult regions of the brain. Coma Recovery Scale-Revised (CRS-R) will be used as primary outcome at baseline, after the first stage of stimulation, at the end of the washout period, and after the second stage of stimulation. Secondary outcomes will be measured at the same time, including efficiency, relative spectral power, and functional connectivity of high-density electroencephalograph (EEG). Adverse events will be recorded during the study.

DISCUSSION

rTMS has obtained grade A evidence in treating patients with several central nervous system diseases, and there has been some evidence showing partial improvement on level of consciousness in DoC patients. However, the effectiveness of rTMS in DoC is only 30~36%, mostly due to the non-specific target selection. In this protocol, we present a double-blind crossover randomized sham-controlled trial based on the individualized-targeted selection strategy that aims to study the effectiveness of rTMS therapy for DoC, and the result may provide new insights to non-invasive brain stimulation.

TRIAL REGISTRATION

ClinicalTrials.gov : NCT05187000. Registered on January 10, 2022.

Repetitive transcranial magnetic stimulation over the posterior parietal cortex improves functional recovery in nonresponsive patients: A crossover, randomized, double-blind, sham-controlled study

Background

Recent studies have shown that patients with disorders of consciousness (DoC) can benefit from repetitive transcranial magnetic stimulation (rTMS) therapy. The posterior parietal cortex (PPC) is becoming increasingly important in neuroscience research and clinical treatment for DoC as it plays a crucial role in the formation of human consciousness. However, the effect of rTMS on the PPC in improving consciousness recovery remains to be studied.

Method

We conducted a crossover, randomized, double-blind, sham-controlled clinical study to assess the efficacy and safety of 10 Hz rTMS over the left PPC in unresponsive patients. Twenty patients with unresponsive wakefulness syndrome were recruited. The participants were randomly divided into two groups: one group received active rTMS treatment for 10 consecutive days (n = 10) and the other group received sham treatment for the same period (n = 10). After a 10-day washout period, the groups crossed over and received the opposite treatment. The rTMS protocol involved the delivery of 2000 pulses/day at a frequency of 10 Hz, targeting the left PPC (P3 electrode sites) at 90% of the resting motor threshold. The primary outcome measure was the JFK Coma Recovery Scele-Revised (CRS-R), and evaluations were conducted blindly. EEG power spectrum assessments were also conducted simultaneously before and after each stage of the intervention.

Result

rTMS-active treatment resulted in a significant improvement in the CRS-R total score (F = 8.443, p = 0.009) and the relative alpha power (F = 11.166, p = 0.004) compared to sham treatment. Furthermore, 8 out of 20 patients classified as rTMS responders showed improvement and evolved to a minimally conscious state (MCS) as a result of active rTMS. The relative alpha power also significantly improved in responders (F = 26.372, p = 0.002) but not in non-responders (F = 0.704, p = 0.421). No adverse effects related to rTMS were reported in the study.

Conclusions

This study suggests that 10 Hz rTMS over the left PPC can significantly improve functional recovery in unresponsive patients with DoC, with no reported side effects.

Clinical trial registration

www.ClinicalTrials.gov, identifier: NCT05187000.

How Patients and Families Describe Major Medical Treatments: "They are No Longer Living, Just Existing"

BACKGROUND

As more life-sustaining treatments become available, the need to provide patients and families clarity about what these treatments are and what they do is increasing. Little is known about how patients and families conceptualize life support.

OBJECTIVE

To explore the discourse that patients and families used to describe major medical treatments in their accounts of treatment decision-making.

METHODS

This study is a secondary data analysis of a survey sent to random addresses in Wisconsin regarding experiences with major medical treatment decision-making. This analysis includes the subsample of 366 respondents who specified the type of decision made in the survey's open-ended questions. Inductive content analysis was used to qualitatively analyze the responses to the open-ended questions, with particular attention to how respondents described the treatment in their responses.

RESULTS

Respondents' descriptions showed a conceptualization of engaging in major medical treatments as keeping patients alive, whereas discontinuing or choosing not to engage in such treatments would bring about the patient's death. However, respondents recognized the potential adverse consequences of engaging in major medical treatments, such as their capacity to cause pain or result in an undesirable neurologic state. Additionally, respondents described the limitations of such treatment regarding the uncertainty of the treatments providing the desired outcome or their uselessness in situations in which the patient's death would be inevitable.

CONCLUSION

Understanding how patients and families make sense of major medical treatments can help clinicians during decision-making conversations.

P300 correlates with tDCS response in minimally conscious state patients

BACKGROUND

Several recent studies indicated that transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) showed promising results in patients in a minimally conscious state (MCS). However, the neurological characteristics of patients in MCS considered to be tDCS responders have not been firmly established.

OBJECTIVES

In the current study, we aimed to explore a reliable electrophysiological biomarker of tDCS response before the patients' inclusion in a tDCS protocol.

METHOD

A hierarchical auditory event-related potential (ERP) pattern was applied to thirty-one MCS patients who subsequently received 20 anodal tDCS sessions of the left DLPFC over 10 consecutive working days. The patients were divided into responders and non-responders according to the Coma Recovery Scale-Revised (CRS-R) behavioral evaluation, and the differences in cortical information processing were compared using the P300 component in the ERP pattern.

RESULTS

For the Tone-SON (TO) paradigm, CRS-R score (OR = 2.229, 95% CI: 1.241-4.005, P = .007) at admission was independently associated with tDCS response, while in the SDN-SON (DO) paradigm, CRS-R score at admission (OR = 2.369, 95% CI: 1.143-4.908, P = .020) and P300 (OR = 22.795, 95% CI: 1.823-285.038, P = .015) were independently associated with tDCS response in MCS patients.

CONCLUSION

Our findings showed that higher total CRS-R score and presence of P300 in the hierarchical auditory ERP pattern, especially P300 in the DO paradigm, are associated with tDCS response in MCS patients. We speculate that P300 in the DO paradigm indicates patients with more preserved semantic processing abilities, and a priority to recover. The results provide important information for guidelines on the use of tDCS in MCS patients.

Update on neuroimaging in disorders of consciousness

PURPOSE OF REVIEW

Neuroimaging has acquired a prominent place in the assessment of disorders of consciousness (DoC). Rapidly evolving technologies combined with state-of-the-art data analyses open new horizons to probe brain activity, but selecting appropriate imaging modalities from the plethora of available techniques can be challenging for clinicians. This update reviews selected advances in neuroimaging that demonstrate clinical relevance and translational potential in the assessment of severely brain-injured patients with DoC.

RECENT FINDINGS

Magnetic resonance imaging and high-density electroencephalography provide measurements of brain connectivity between functional networks, assessments of language function, detection of covert consciousness, and prognostic markers of recovery. Positron emission tomography can identify patients with preserved brain metabolism despite clinical unresponsiveness and can measure glucose consumption rates in targeted brain regions. Transcranial magnetic stimulation and near-infrared spectroscopy are noninvasive and practical tools with promising clinical applications.

SUMMARY

Each neuroimaging technique conveys advantages and pitfalls to assess consciousness. We recommend a multimodal approach in which complementary techniques provide diagnostic and prognostic information about brain function. Patients demonstrating neuroimaging evidence of covert consciousness may benefit from early adapted rehabilitation. Translating methodological advances to clinical care will require the implementation of recently published international guidelines and the integration of neuroimaging techniques into patient-centered decision-making algorithms.

Ethical and legal considerations related to disorders of consciousness

PURPOSE OF REVIEW

The purpose of this review is to describe ethical and legal issues that arise in the management of patients with disorders of consciousness ranging from the minimally conscious state to the coma state, as well as brain death.

RECENT FINDINGS

The recent literature highlights dilemmas created by diagnostic and prognostic uncertainties in patients with disorders of consciousness. The discussion also reveals the challenges experienced by the disability community, which includes individuals with severe brain injury who are classified as having a disorder of consciousness. We review current guidelines for management of patients with disorders of consciousness including discussions around diagnosis, prognosis, consideration of neuropalliation, and decisions around life sustaining medical treatment.

SUMMARY

In the setting of uncertainty, this review describes the utility of applying a disability rights perspective and shared decision-making process to approach medical decision-making for patients with disorders of consciousness. We outline approaches to identifying surrogate decision makers, standards for decision-making and decision-making processes, specifically addressing the concept of futility as a less useful framework for making decisions. We also highlight special considerations for research, innovative and controversial care, brain death, organ donation, and child abuse and neglect.

Disorders of Consciousness and Disability Law

In 2018, the American Academy of Neurology, the American Congress of Rehabilitation Medicine, and the National Institute on Disability, Independent Living, and Rehabilitation Research published a systematic evidence-based review and an associated practice guideline for improved assessment, treatment, and rehabilitation of patients with disorders of consciousness. Patients with disorders of consciousness include individuals in the vegetative and minimally conscious states, as well as others with covert consciousness and cognitive motor dissociation. These landmark publications (concurrently published in Neurology and Archives of Physical Medicine and Rehabilitation) supplant the 1994 New England Journal of Medicine Multi-Society Task Force report on the vegetative state and the 2002 criteria establishing minimally conscious states. The guideline re-designates the permanent vegetative state as chronic. In our article, we consider the legal and ethical implications of the practice guideline for clinical practice and explain the vulnerability of these patients who suffer from high rates of misdiagnosis, inadequate medical surveillance, undertreatment of pain, inadequate rehabilitation, and segregation in chronic care. We argue that these deficiencies in medical care are inconsistent with our growing appreciation of the dynamic nature of these brain states and an emerging standard of care as articulated by the national guideline. These deficiencies also violate domestic and international disability law. To substantiate this latter claim, we apply disability law to this population, focusing on key Americans with Disabilities Act mandates, the relevance of the 1999 Supreme Court, Olmstead v. L.C., and the utility of Olmstead enforcement actions to integrate the care of these individuals into the medical mainstream.