Disorders of Consciousness, An Issue of Neurologic Clinics , livre ebook

Saunders - G. Bryan Young

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This issue of Neurologic Clinics addresses the cognitive impact of various forms of brain injury.

Sujets

Neurology

Informations

Publié par	Saunders
Date de parution	28 mai 2011
Nombre de lectures	0
EAN13	9781455712434
Langue	English
Poids de l'ouvrage	2 Mo

Informations légales : prix de location à la page 0,6457€. Cette information est donnée uniquement à titre indicatif conformément à la législation en vigueur.

Extrait

Neurologic Clinics , Vol. 29, No. 4, November 2011
ISSN: 0733-8619
doi: 10.1016/S0733-8619(11)00096-X

Contributors
Neurologic Clinics
Disorders of Consciousness
GUEST EDITOR: G. Bryan Young, MD
University of Western Ontario, London, ON, Canada
CONSULTING EDITOR: Randolph W. Evans, MD
ISSN 0733-8619
Volume 29 • Number 4 • November 2011

Contents
Cover
Contributors
Forthcoming Issues
Preface
Consciousness: Its Neurobiology and the Major Classes of Impairment
A Clinical and Investigative Approach to the Patient with Diminished Responsiveness
Delirium in the Intensive Care Unit: A Review
Impaired Consciousness and Herniation Syndromes
The Vegetative and Minimally Conscious States: Diagnosis, Prognosis and Treatment
Neurologic Determination of Death
Epilepsy and the Consciousness System: Transient Vegetative State?
Anoxic-Ischemic Encephalopathy and Strokes Causing Impaired Consciousness
Metabolic Encephalopathies
Trauma and Impaired Consciousness
Syncope
Infectious Diseases and Impaired Consciousness
Central Nervous System Complications After Transplantation
Coma in the Pregnant Patient
Psychogenic Unresponsiveness
Nontraumatic Coma in Children and Adolescents: Diagnosis and Management
Transient Global Amnesia
Ethical Aspects of Disordered States of Consciousness
Index
Neurologic Clinics , Vol. 29, No. 4, November 2011
ISSN: 0733-8619
doi: 10.1016/S0733-8619(11)00098-3

Forthcoming Issues
Neurologic Clinics , Vol. 29, No. 4, November 2011
ISSN: 0733-8619
doi: 10.1016/j.ncl.2011.08.005

Preface

G. Bryan Young, MD, FRCP(C) ,
Division of Neurology, Department of Clinical Neurological Sciences, University of Western Ontario, London Health Sciences Centre, 339 Windermere Road, London, ON N6A 5A5, Canada
E-mail address: bryan.young@lhsc.on.ca

G. Bryan Young, MD, FRCP(C), Guest Editor
Neurologists and neurosurgeons are practical people. We don’t often gaze at our navels and wonder if consciousness is “real or an illusion.” 1 We accept that “being conscious” includes an essential alertness and an awareness of ourselves and the world, however imperfectly we do this, and that such awareness arises as a function of brain activity. Admittedly, we do not fully understand how awareness and awareness that we are aware happen, but presumably such functions are the net result of neuronal processing and integration of activity of numerous modules and centers. The “whole is more than the sum of its parts” is probably a fair statement.
Our ability to determine whether consciousness is present or not was revolutionized by the work of Adrian Owen and colleagues, who showed that a patient who was declared “vegetative” was able to generate different brain responses, detected by functional magnetic resonance imaging (fMRI), to imagine she was playing tennis or walking through rooms of her house. 2 Although not able to show any motor response, upon which we have traditionally depended, she was able to show evidence of language comprehension and processing with a sophisticated level of imagining. Indeed, such patients, who amount to about 10% of those previously declared “vegetative,” are able to generate accurate binary responses to various questions using the above imagining technique. 3
This should serve as a wake-up call for us to do better, to more accurately determine whether there is the innate capacity or potential for consciousness, ie, the ultimate prognosis for patients. We should be able to do this without relying on fMRI for each unresponsive patient. 4
This monograph is devoted to disorders of consciousness, both reversible and irreversible. The neurological basis of consciousness is reviewed by Drs Goldfine and Schiff. A clinical approach is given by Drs Hocker and Rabinstein. The impairment of consciousness by mass lesions, anoxic-ischemic encephalopathy, stroke, seizures, central nervous system infections and inflammatory diseases, general metabolic disorders, intoxications (to appear in a forthcoming issue), trauma, and syncope are dealt with in excellent articles by experts in their respective fields. In addition, causes of impaired consciousness in childhood diseases, pregnancy, and transplantation are discussed. Various states of impaired consciousness, including psychogenic unresponsiveness, delirium, transient global amnesia, stupor, coma, and brain death, are addressed by experts in individual articles. Finally, the all important ethical issues involving end-of-life decision-making fall to Drs Rubin and Bernat. Ethical discussions take us back to the philosophy of what consciousness is and how important it is in human existence. However, ethical considerations go beyond consciousness to quality-of-life issues. Perhaps “being conscious” is not enough when all other aspects of life are denied. Also, the processing of information to command, which we can to some extent assess with technology, is not equivalent to the generation of spontaneous thought. Can we ever truly assess the higher aspects of “thinking” in the absence of a motor action?
We hope you enjoy this volume and that it will update your knowledge and stimulate you to think about consciousness in a more comprehensive and meaningful way.

References

   1. S. Blackmore. Consciousness: A Brief Insight . New York: Sterling; 2010.
   2. A.M. Owen, M.R. Coleman, M. Boly, et al. Detecting awareness in the vegetative state. Science . 2006;313(5792):1402.
   3. M.M. Monti, A. Vanhaudenhuyse, M.R. Coleman, et al. Willful modulation of brain activity in disorders of consciousness. N Engl J Med . 2010;362:579-589.
   4. A.H. Ropper. Cogito ergo sum by MRI. N Engl J Med . 2010;362:348-349.
Neurologic Clinics , Vol. 29, No. 4, November 2011
ISSN: 0733-8619
doi: 10.1016/j.ncl.2011.08.001

Consciousness: Its Neurobiology and the Major Classes of Impairment

Andrew M. Goldfine, MD a , b , * , Nicholas D. Schiff, MD a
a Department of Neurology and Neuroscience, Weill Cornell Medical College, LC 803, 1300 York Avenue, New York, NY 10065, USA
b Burke Medical Research Institute, Weill Cornell Medical College, 785 Mamaroneck Avenue, White Plains, NY 10605, USA
* Corresponding author. Burke Medical Research Institute, Weill Cornell Medical College, 785 Mamaroneck Avenue, White Plains, NY 10605.
E-mail address: andygoldfine@gmail.com

Abstract
Human consciousness requires brainstem, basal forebrain, and diencephalic areas to support generalized arousal, and functioning thalamocortical networks to respond to environmental and internal stimuli. Disconnection of these interconnected systems, typically from cardiac arrest and traumatic brain injury, can result in disorders of consciousness. Brain injuries can also result in loss of motor output out of proportion to consciousness, resulting in misdiagnoses. The authors review pathology and imaging studies and derive mechanistic models for each of these conditions. Such models may guide the development of target-based treatment algorithms to enhance recovery of consciousness in many of these patients.

Keywords
• Consciousness • Vegetative state • Minimally conscious state • Traumatic brain injury • Arousal
Disorders of consciousness encompass a wide range of syndromes whereby patients demonstrate a globally impaired ability to interact with the environment. We briefly review the subset of disorders of consciousness that result from permanent brain injury, such as ischemic stroke, global ischemia, and traumatic brain injury (TBI). Disorders of consciousness may also arise as functional (rather than structural) disturbances of consciousness, including generalized and complex partial seizures as well as metabolic and toxic delirium. These functional disturbances are not discussed here but have been reviewed by Posner and colleagues. 1
In this review, we first review brain structures that support the normal conscious state to develop a framework to demonstrate how their dysfunction can lead to disorders of consciousness. We then present the nosology of the different disorders of consciousness, including coma, vegetative state (VS), the minimally conscious state, and akinetic mutism. The pathology and brain imaging data that give insight into the pathophysiology associated with each diagnostic category are reviewed. Knowledge of the underlying mechanisms of the disorders can enhance the ability to prognosticate and promote recovery from these devastating conditions.

Biologic basis of consciousness: mechanisms of arousal and cerebral integrative function

A Clinically Relevant Definition of Consciousness
Normal human consciousness is defined as the presence of a wakeful arousal state and the awareness and motivation to respond to self or environmental events. In the intact brain, arousal is the overall level of responsiveness to environmental stimuli. Arousal has a physiologic range from stage 3 non–rapid eye movement (REM) sleep during which strong stimuli are required to elicit a response, to states of high vigilance, during which subtle stimuli can be detected and acted upon. 2 Whereas arousal is the global state of responsiveness, awareness is the brain’s ability to perceive specific environmental stimuli in different domains, including visual, somatosensory, auditory, and interoceptive (eg, visceral and body position). The focal loss of awareness, such as language awareness in aphasia or spatial awareness in left-sided neglect, does not significantly impair awareness in other modalities. Motivation is the drive to act on internal or external stimuli that have entered conscious awareness. In the next section, we describe the brain regions that support these three aspects of consciousness and show that they are not independent, but rather interact extensively with each other.

Underlying Substrates of Arousal and Conscious Awareness
The initial discovery that specific brain areas could drive overall