Elsevier

The Lancet

Volume 367, Issue 9517, 8–14 April 2006, Pages 1181-1192
The Lancet

Seminar
Chronic disorders of consciousness

https://doi.org/10.1016/S0140-6736(06)68508-5Get rights and content

Summary

The vegetative state and the minimally conscious state are disorders of consciousness that can be acute and reversible or chronic and irreversible. Diffuse lesions of the thalami, cortical neurons, or the white-matter tracts that connect them cause the vegetative state, which is wakefulness without awareness. Functional imaging with PET and functional MRI shows activation of primary cortical areas with stimulation, but not of secondary areas or distributed neural networks that would indicate awareness. Vegetative state has a poor prognosis for recovery of awareness when present for more than a year in traumatic cases and for 3 months in non-traumatic cases. Patients in minimally conscious state are poorly responsive to stimuli, but show intermittent awareness behaviours. Indeed, findings of preliminary functional imaging studies suggest that some patients could have substantially intact awareness. The outcomes of minimally conscious state are variable. Stimulation treatments have been disappointing in vegetative state but occasionally improve minimally conscious state. Treatment decisions for patients in vegetative state or minimally conscious state should follow established ethical and legal principles and accepted practice guidelines of professional medical specialty societies.

Section snippets

Background

Coma, a pathological state of eyes-closed unconsciousness from which patients cannot be aroused to wakefulness by stimuli, is caused by a structural, metabolic, or toxic disturbance of the reticular system and its thalamic projections.5 In most survivors of comas who do not spontaneously achieve awareness, coma progresses after several weeks to a state of eyes-open wakefulness without awareness, called the vegetative state.5 True coma rarely persists for longer than a month in the absence of

Vegetative state

The essence of the vegetative state is wakefulness without awareness. Patients in vegetative state lie with their eyes open while awake and closed while asleep. They breathe spontaneously, have preserved autonomic function, and intact limb tendon and cranial nerve-innervated reflexes. They blink, have roving eye movements, and facial movements and expressions. They have limb spasticity, non-purposeful limb movements, and pseudobulbar palsy. But to the fullest extent determinable, they lack

Assessment and differential diagnosis

The diagnosis of vegetative state and minimally conscious state can be made only after a careful assessment of the patient's level of awareness. The Glasgow coma scale, which was developed, validated, and used widely to assess the level of consciousness and prognosis of patients with acute traumatic brain injuries49, 50 and non-traumatic causes of coma,51 is insufficient for the assessment of vegetative state and minimally conscious state because of its crude measurement of awareness and its

Cause and epidemiology

The most common cause of vegetative state and minimally conscious state is traumatic brain injury.75 Non-traumatic causes in adults include acute hypoxic-ischaemic neuronal injury suffered during cardiopulmonary arrest, stroke, and meningoencephalitis.76 Although a few patients with endstage neurodegenerative diseases, such as Alzheimer's, Huntington's, and Parkinson's, might reach minimally conscious state if they survive long enough,77 it is rare for them to progress to true vegetative state.

Pathology

Vegetative state and minimally conscious state are clinical syndromes that can be caused by several pathological processes. The pathology of vegetative state is more completely described than that of minimally conscious state. The latter usually represents less severe pathological changes than the former with less thalamic injury and less high-grade diffuse axonal injury.85

The pathology of vegetative state can be described anatomically and histologically. Anatomically, vegetative state is

Neuroimaging

Anatomical brain imaging discloses few features of diagnostic specificity for vegetative state and minimally conscious state, but functional brain imaging reveals findings of importance in understanding how consciousness is mapped in the brain that will become diagnostically useful in the near future. Brain imaging with CT and MRI in vegetative state shows widespread cortical and thalamic atrophy that increases in severity after months to years.12 Anatomical MRI sequences at 6 weeks after

Electrophysiology

Electroencephalography discloses non-specific findings in vegetative state and minimally conscious state. Most patients in vegetative state have profound generalised slowing of background activity with delta rhythms that do not react to stimuli,127, 128 but that desynchronise with sleep.28 Patients with the most severe forms of vegetative state show electrocerebral silence.9 Recovery of awareness is associated with re-establishment of the alpha rhythm.127 There are few systematic data on EEG in

Prognosis

Patients might be in a vegetative state or minimally conscious state temporarily as a stage during recovery from a traumatic brain injury or a non-traumatic brain insult, or might reside in the state chronically and permanently. The issue of prognosis for recovery of awareness is a crucial but difficult clinical determination. The Multisociety Task Force devoted nearly half of its effort to reviewing published data on recovery and proposing guidelines for estimation of prognosis.28 They

Medical treatment

After discharge from the intensive care unit, patients in vegetative state require the same level of medical and nursing care as comatose patients, including, positioning, range of motion exercises, pulmonary toilet, skin care, bowel and bladder care, and optimum nutrition.152 All patients require gastrostomy for tube feedings and nearly all have a tracheostomy for airway protection, but no longer require mechanical ventilation. Treatment in a neurorehabilitation unit that specialises in brain

Ethical and legal issues

Management of patients in vegetative state or minimally conscious state inevitably raises ethical and legal questions about the appropriate degree of life-sustaining treatment. Most ethical analyses conclude that the decision to treat aggressively or passively should be guided by reliable information about how the patient would wish to be treated in this condition,10, 12, 173 in accordance with the principles of patient-centred medicine.174 Physicians can seek this information in advance

Future directions

Several areas are ready for further research. The intensive study of additional patients in vegetative state and minimally conscious state by PET, fMRI, cortical ERPs, and magnetoencephalography will probably yield information of sufficient specificity about how consciousness is mapped in the brain to quantify the extent of awareness, help confidently discriminate between vegetative state and minimally conscious state, and improve predictions with respect to recovery.125 Further trials of

Search strategy and selection criteria

For this Seminar, I searched articles on PubMed in, or translated into, English published since 1990, using the terms “vegetative state” and “minimally conscious state”. I also searched the reference lists from these articles, and analysed articles I have previously summarised.10

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