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Moreover, Norton et al. This study shows that the presence of a default mode network does not prove a patient is conscious, although it may serve as a predictor of good outcome. For example, Qin et al. Rodriguez Moreno et al. This indicates that those patients were trying to move their hand, although this was not translated into motor activity.
However, in a similar mental imagery experiment by Bardin et al. Diffusion tensor imaging is a relatively recent addition to the analysis of structural data acquired with MRI and is employed to measure axonal integrity. It analyses the direction of water protons travelling along nerve fibers, thereby visualizing white matter nerve tract structure and orientation. Finally, magnetic resonance spectroscopy may be used for the detection of creatine, choline, N-acetylaspartate, and lactate in predefined regions of interest.
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One of the main shortcomings of PET and fMRI is the relatively bad temporal resolution, which is generally in excess of 1. Cognitive processes usually take place on a much shorter timescale, in the order of milliseconds. Electroencephalography is the method of choice to fill this niche in DOC diagnosis. Similarly, occurrence of sleep spindles during periods of assumed sleep in DOC patients has been associated with better outcome [ 62 ]. In a recent EEG sleep study, all tested MCS patients showed characteristic sleep patterns resembling those of healthy subjects [ 63 ]. These included alternating periods of rapid eye movement and non-rapid eye movement sleep, as well as the phenomenon of shorter periods of slow-wave sleep at the end of the night than at the beginning of the night this is a normal sleep development also occurring in healthy controls and thought to be related to neural plasticity.
Chapter 2 Disorders of Consciousness : Coma , Vegetative and Minimally Conscious States
However, other studies did show significant differences in EEG patterns during sleep as compared to wakefulness for a review, see [ 62 ]. However, patient entropy measurements at more than one month post injury did not have this diagnostic potential. In DOC patients, the occurrence of event-related potentials that are thought to be a result of cognitive functioning e. This technique was also used to detect consciousness in a case of total locked-in syndrome [ 37 ], whereby a patient is fully conscious but completely unable to communicate by bodily movements or even eye-blinking.
These potentials were similar to normal in three patients, indicating that they were misdiagnosed as a result of their behavioral unresponsiveness. Lastly, transcranial magnetic stimulation TMS , in combination with EEG recording, can also be used for the assessment of residual brain function of DOC patients [ 68 ]. TMS is a method used to stimulate a region of the cortex, while EEG recordings make it possible to visualize changes in effective connectivity in response to this stimulation.
Therefore, TMS-EEG can be used to analyze the intactness of neural circuits and can offer important clues about the state of consciousness a patient is in. TMS-EEG has been tested in healthy controls during midazolam-induced unconsciousness [ 69 ] and non-rapid eye movement sleep [ 70 ].
In these conditions, the cortical response following TMS remained more local and lasted for a shorter period of time than during wakefulness. A variety of other diagnostic tools is currently in development and is being tested on DOC patients. Electromyography has been used to study the occurrence of subthreshold muscle activity in response to verbal command. Sniffing can provide a control interface that is fast, accurate, robust and highly conserved following severe injury. It is therefore possible that this can be used as a diagnostic tool in DOC, although more research is needed.
When studying the brain, fMRI has the advantage of showing with high precision the brain areas that are involved in cognition and consciousness. As mentioned before, this information can be used to communicate via brain modulation by the patient. However, although attempts for such fMRI-based communication have been successful in a number of cases [ 19 ], it has the disadvantage of being dependent on expensive and immobile fMRI scanning equipment. The technique capitalizes on the changing optical characteristics of blood in the visible and near-infrared light range, when oxygenated hemoglobin in the blood becomes deoxygenated due to oxygen extraction by brain tissues.
Although initial fNIRS studies have been performed in several neurological and psychiatric disorders [ 74 ], validation of the technique in DOC is still awaited.
A limitation of fNIRS is the fact that it cannot measure activity in deep brain structures. However, the technique offers the possibility of continuous scanning for longer periods of time than would be possible with fMRI and can include patients that have physiological limitations that make fMRI scanning impossible.
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After years of study, precise characterization of DOC remains elusive. When is minimal consciousness enough to call a patient conscious? This problem is emphasized in the renaming of the vegetative state into unresponsive wakefulness syndrome, reminding physicians to remain careful when making inferences regarding conscious awareness based on behavioral assessment of motor responsiveness.
Correct diagnosis of the level of remaining consciousness in a DOC patient is important for multiple reasons. First, it helps to ensure that appropriate caretaking can take place, tailored to the specific needs of each patient. These needs may include treatment for pain, and access to rehabilitation support and methods for motor-independent or motor signal-enhancing communication as mentioned in this review.
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Second, knowing the actual state of the patient can aid in prognosis. The experiments and their accompanying behavioral assessment, which was usually the CRS-r, mentioned in this review were performed from five days after brain injury to This shows that no general consensus exists on the time since injury at which to conduct differential diagnosis. However, the implications for palliative care and prognosis mean that behavioral assessment and neuroimaging should be administered as soon as the patient is stabilized and shows signs of brain arousal i.
As the condition of DOC patients is more prone to being transitional during the acute phase, caretakers should retest during the subacute phase. Third, the ongoing subcategorisation of DOC might have societal, ethical and legal consequences. Care of DOC patients is costly, and insurance companies might base payment of insurance money for this care on the presence of consciousness in the patient. As for now, the CRS-r is still considered to be the best behavioral scale that exists for differential diagnosis of DOC. A robust training in applying the scale and experience in conducting the scale is definitely recommended.
Furthermore, it should be noted that the trust in the CRS-r to deliver good differential diagnosis is not based on validation with a gold standard, as no such standard exists. Rather, credibility for the differential capabilities of the scale comes from proven good interrater reliability, test-retest reliability, internal consistency, the fact that it includes all of the Aspen Workgroup criteria for good standardized administration and scoring, as well as its consistency with neuroimaging results.
Disorders of consciousness
Brain imaging techniques based on passive paradigms, as well as other ancillary methods, are being validated for accuracy. Please enter User Name Password Error: Please enter Password Forgot Username? Use this site remotely Bookmark your favorite content Track your self-assessment progress and more! Otherwise it is hidden from view. About MyAccess If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.
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Search within a content type, and even narrow to one or more resources. You can also find results for a single author or contributor. Durcan L Durcan, Liam. The intensivist should consider general categories of pathologic states that can lead to coma. This obviously occurs once the patient is confirmed to have adequate oxygenation, ventilation, and hemodynamic function i. Categories in the differential diagnosis of coma include:. Pseudo-coma residual neuromuscular blockade, psychogenic coma, locked-in syndrome.
The locked-in syndrome is another condition that resembles coma. It usually results from ventral pontine damage with sparing of the reticular activating system and cerebral hemispheres. N Eng J Med. No sponsor or advertiser has participated in, approved or paid for the content provided by Decision Support in Medicine LLC.
Description of the problem What every clinician should know Key management points 2. Diagnosis Pathophysiology Epidemiology Special considerations for nursing and allied health professionals. Description of the problem What every clinician should know Coma is a condition in which a patient cannot be aroused to consciousness. Key management points Initial assessment of the comatose patient focuses on basic life support: Diagnosis Coma is a medical emergency. Categories in the differential diagnosis of coma include: Pharmacologic such as anesthesia or opioid induced.
Toxic such as alcohol, methanol, etc. Metabolic hyponatremia, hyperammonemia, hypoglycemia. Vascular stroke, subarachnoid hemorrhage. Hydrocephalus usually acute rather than chronic. Neoplastic carcinomatous meningitis, brain tumor causing mass effect. Seizure post-ictal state or ongoing non-convulsive seizures.
Neurodegenerative such as advanced Alzheimer's dementia. Epidemiology Coma is very common, as can be ascertained from the various etiologic entities. Special considerations for nursing and allied health professionals. Powered By Decision Support in Medicine. You must be a registered member of Cancer Therapy Advisor to post a comment.