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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. Diagnosis is clinical. Treatment is supportive. Prognosis with persistent deficits is bleak, and withdrawal of care should be discussed with family members.
The vegetative state is a chronic condition that preserves the ability to maintain BP, respiration, and cardiac function, but not cognitive function. Although medullary brainstem functions remain intact to support cardiorespiratory functions, the presence of midbrain or pontine reflexes may be variable.
A vegetative state occurs when the reticular activating system (RAS) remains functional (making wakefulness possible), but the cortex is severely damaged (eliminating cognitive function). The patient has no awareness of self and interacts with the environment only via reflexes. Hypothalamic and brain stem autonomic function are preserved and sufficient for survival if medical and nursing care is adequate. A vegetative state is considered persistent if it lasts > 1 mo.
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.
Symptoms and Signs
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.
Diagnosis
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, which results from less severe but sometimes widespread cerebral damage. Fragments of awareness may be observed in patients in a minimally conscious state; they may reach for objects or visually fixate or speak a word or gesture in response to a command. 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.
CT or MRI can differentiate an ischemic infarct, an intracerebral hemorrhage, and a mass lesion involving the cortex or the brainstem. MR angiography can be used to visualize the cerebral vasculature following the exclusion of a cerebral hemorrhage. Additionally, diffusion-weighted MRI is becoming the desired imaging modality to follow ongoing ischemic changes in the brain. PET and SPECT provide an alternative method of imaging that assesses 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 the presence of occult seizure activity.
Prognosis
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 injury. 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.
Most patients in a persistent vegetative state 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; a few patients live for decades.
Treatment
There is no specific treatment, but supportive care should include the following:
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 Medicolegal Issues: Advance Directives), in a prolonged vegetative state raises ethical and other (eg, resource utilization) questions.
Last full review/revision January 2008 by Kenneth Maiese, MD
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