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Vegetative State and Minimally Conscious State
A vegetative state is absence of responsiveness and awareness due to overwhelming dysfunction of the cerebral hemispheres, with sufficient sparing of the diencephalon and brain stem to preserve autonomic and motor reflexes and sleep-wake cycles. Patients may have complex reflexes, including eye movements, yawning, and involuntary movements to noxious stimuli, but show no awareness of self or environment. A minimally conscious state, unlike a vegetative state, is characterized by some evidence of awareness of self and/or the environment, and patients tend to improve. Diagnosis is clinical. Treatment is mainly supportive. Prognosis for patients with persistent deficits is typically bleak.
The vegetative state is a chronic condition that preserves the ability to maintain BP, respiration, and cardiac function, but not cognitive function. Hypothalamic and medullary brain stem functions remain intact to support cardiorespiratory and autonomic functions and are sufficient for survival if medical and nursing care is adequate. The cortex is severely damaged (eliminating cognitive function), but the reticular activating system (RAS) remains functional (making wakefulness possible). Midbrain or pontine reflexes may or may not be present. Patients have no awareness of self and interact with the environment only via reflexes. Seizure activity may be present but not be clinically evident.
Traditionally, a vegetative state that lasts > 1 mo is considered to be a persistent vegetative state. However, a diagnosis of persistent vegetative state does not imply permanent disability because in very rare cases (eg, after traumatic brain injury), patients can improve, reaching a minimally conscious state or a higher level of consciousness.
The most common causes are traumatic brain injury and diffuse cerebral hypoxia. However, any disorder that results in brain damage can cause a vegetative state. Typically, a vegetative state occurs because the function of the brain stem and diencephalon resumes after coma, but cortical function does not.
In the minimally conscious state, unlike the vegetative state, there is evidence that patients are aware of themselves and/or their environment. Patients also tend to improve (ie, gradually become more conscious), but improvement is limited. This state may be the first indication of brain damage or may follow a vegetative state as people recover some function. Patients can transition between the vegetative state and minimally conscious state, sometimes for years after the original brain damage.
Patients show no evidence of awareness of self or environment and cannot interact with other people. Purposeful responses to external stimuli are absent, as are language comprehension and expression.
Signs of an intact reticular formation (eg, eye opening) and an intact brain stem (eg, reactive pupils, oculocephalic reflex) are present. Sleep-wake cycles occur but do not necessarily reflect a specific circadian rhythm and are not associated with the environment. More complex brain stem reflexes, including yawning, chewing, swallowing, and, uncommonly, guttural vocalizations, are also present. Arousal and startle reflexes may be preserved; eg, loud sounds or blinking with bright lights may elicit eye opening. Eyes may water and produce tears. Patients may appear to smile or frown. Spontaneous roving eye movements—usually slow, of constant velocity, and without saccadic jerks—may be misinterpreted as volitional tracking and can be misinterpreted by family members as evidence of awareness.
Patients cannot react to visual threat and cannot follow commands. The limbs may move, but the only purposeful motor responses that occur are primitive (eg, grasping an object that contacts the hand). Pain usually elicits a motor response (typically decorticate or decerebrate posturing) but no purposeful avoidance. Patients have fecal and urinary incontinence. Cranial nerve and spinal reflexes are typically preserved.
Rarely, brain activity, detected by functional MRI or EEG, indicates a response to questions and commands even though there is no behavioral response. The extent of patients' actual awareness is not yet known. In most patients who have such brain activity, the vegetative state resulted from traumatic brain injury, not hypoxic encephalopathy.
A vegetative state is suggested by characteristic findings (eg, no purposeful activity or comprehension) plus signs of an intact reticular formation. Diagnosis is based on clinical criteria. However, neuroimaging is indicated to rule out treatable disorders.
The vegetative state must be distinguished from the minimally conscious state. Both states can be permanent or temporary, and the physical examination may not reliably distinguish one from the other. Sufficient observation is needed. If observation is too brief, evidence of awareness may be overlooked, resulting in a false-positive diagnosis. Some patients with severe Parkinson disease are misdiagnosed as being in a vegetative state.
CT or MRI can differentiate an ischemic infarct, an intracerebral hemorrhage, and a mass lesion involving the cortex or the brain stem. MR angiography can be used to visualize the cerebral vasculature after exclusion of a cerebral hemorrhage. Diffusion-weighted MRI is becoming the preferred imaging modality for following ongoing ischemic changes in the brain. PET and SPECT can be used to assess cerebral function (rather than brain anatomy). If the diagnosis of persistent vegetative state is in doubt, PET or SPECT should be done. EEG is useful in assessing cortical dysfunction and identifying occult seizure activity.
Prognosis varies somewhat by cause and duration of the vegetative state. Prognosis may be better if the cause is a reversible metabolic condition (eg, toxic encephalopathy) than if the cause is neuronal death due to extensive hypoxia and ischemia or another condition. Also, younger patients may recover more motor function than older patients but not more cognition, behavior, or speech.
Recovery from a vegetative state is unlikely after 1 mo if brain damage is nontraumatic and after 12 mo if brain damage is traumatic. Even if some recovery occurs after these intervals, most patients are severely disabled. Rarely, improvement occurs late; after 5 yr, about 3% of patients recover the ability to communicate and comprehend, but even fewer can live independently; no patients regain normal function.
If a vegetative state persists, most patients die within 6 mo of the original brain damage. The cause is usually pulmonary infection, UTI, or multiple organ failure, or death may be sudden and of unknown cause. For most of the rest, life expectancy is about 2 to 5 yr; only about 25% of patients live > 5 yr. A few patients live for decades.
Most patients tend to recover consciousness but to a limited extent depending on how long the minimally conscious state has lasted. The longer it has lasted, the less chance of patients recovering higher cortical function. Prognosis may be better if the cause is traumatic brain injury.
Rarely, patients regain clear but limited awareness after years of coma, called awakenings by the news media.
Supportive care is the mainstay of treatment and should include the following:
Vegetative state has no specific treatment. Decisions about life-sustaining care should involve social services, the hospital ethics committee, and family members. Maintaining patients, especially those without advanced directives to guide decisions about terminating treatment (see page Advance Directives), in a prolonged vegetative state raises ethical and other (eg, resource utilization) questions.
Most patients in a minimally conscious state do not respond to specific treatments. However, rarely, treatment with zolpidem can cause dramatic and repeated improvement in neurologic responsiveness for as long as the drug is continued.
Vegetative state is typically characterized by absence of responsiveness and awareness due to overwhelming dysfunction of the cerebral hemispheres, intact brain stem function, and sometimes the simulation of awareness despite its absence.
Minimally conscious state differs from vegetative state in that patients have some interaction with the environment and tend to improve over time.
Diagnosis requires exclusion of other disorders and often prolonged observation, particularly to differentiate vegetative state, minimally conscious state, and Parkinson disease.
Prognosis tends to be poor, particularly for patients in a vegetative state.
Treatment is mainly supportive.
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