Prognosis
Comas can last from several days to several weeks. In more severe cases a coma may last for over five weeks, while some have lasted as long as several years. After this time, some patients gradually come out of the coma, some progress to a vegetative state, and others die. Some patients who have entered a vegetative state go on to regain a degree of awareness. Others remain in a vegetative state for years or even decades (the longest recorded period being 42 years).
The outcome for coma and vegetative state depends on the cause, location, severity and extent of neurological damage. A deeper coma alone does not necessarily mean a slimmer chance of recovery, because some people in deep coma recover well while others in a so-called milder coma sometimes fail to improve.
People may emerge from a coma with a combination of physical, intellectual and psychological difficulties that need special attention. Recovery usually occurs gradually—patients acquire more and more ability to respond. Some patients never progress beyond very basic responses, but many recover full awareness. Regaining consciousness is not instant: in the first days, patients are only awake for a few minutes, and duration of time awake gradually increases. This is unlike the situation in many movies where people who awake from comas are instantly able to continue their normal lives. In reality, the coma patient awakes sometimes in a profound state of confusion, not knowing how they got there and sometimes suffering from dysarthria, the inability to articulate any speech, and with many other disabilities.
Predicted chances of recovery are variable owing to different techniques used to measure the extent of neurological damage. All the predictions are based on statistical rates with some level of chance for recovery present: a person with a low chance of recovery may still awaken. Time is the best general predictor of a chance of recovery: after four months of coma caused by brain damage, the chance of partial recovery is less than 15%, and the chance of full recovery is very low.
The most common cause of death for a person in a vegetative state is secondary infection such as pneumonia which can occur in patients who lie still for extended periods.
Occasionally people come out of coma after long periods of time. After 19 years in a minimally conscious state, Terry Wallis spontaneously began speaking and regained awareness of his surroundings. Similarly, Polish railroad worker Jan Grzebski woke up from a 19-year coma in 2007.
A brain-damaged man, trapped in a coma-like state for six years, was brought back to consciousness in 2003 by doctors who planted electrodes deep inside his brain. The method, called deep brain stimulation (DBS) successfully roused communication, complex movement and eating ability in the 38-year-old American man who suffered a traumatic brain injury. His injuries left him in a minimally conscious state (MCS), a condition akin to a coma but characterized by occasional, but brief, evidence of environmental and self-awareness that coma patients lack.
Coma lasting seconds to minutes results in post-traumatic amnesia (PTA) that lasts hours to days; recovery plateau occurs over days to weeks. Coma that lasts hours to days results in PTA lasting days to weeks; recovery plateau occurs over months. Coma lasting weeks results in PTA that lasts months; recovery plateau occurs over months to years.
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