Vegetative state and minimally conscious state

[Michiko]

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 blood pressure (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 gt; 1 month 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 of a vegetative state and minimally conscious state are

Traumatic brain injury
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.