Vegetative State, Minimally Conscious State, and Locked-In Syndrome
These terms refer to conditions of exceedingly severe neurological disabilities. A common feature is that there is little if any voluntary motor function, for example in the form of functional hand use, head lifting in prone, or rolling over.
The clinical definition of vegetative state that we have used in our research includes the inability to communicate, on a consistent basis, with speech, hand gestures, etc. There are additional criteria; a formal definition is given in our published work.6
The minimally conscious state applies to persons whose cognitive function is slightly above the VS. It includes, for example, persons who are able to speak and understand a few simple words.
The term locked-in syndrome is generally applied to persons with minimal, if any, voluntary motor function and no ability to speak but at least relatively well-preserved cognitive function. Such persons may be able to communicate with, for example, eye blinking.
Life expectancy in the persistent VS. Early research8 suggested that life expectancy in this condition was 2-5 years, with survival for 10 years being uncommon. More recent work suggests a somewhat better prognosis for survival. The reasons are summarized in Reference 6 below. See reference 8 for an extensive bibliography of research up to 1994. See reference 10 for the latest findings on life expectancy.
Life expectancy of immobile persons in the MCS,5 or of those in LIS,1 may be only slightly better than that of those in the VS, other factors being equal. This is because motor function, rather than cognitive function, and the need for a feeding tube, are the critical factors for morbidity and mortality.
Does the etiology of the condition matter? It does to a limited extent. Obviously, persons in the VS as a result of a degenerative disease, such as Alzheimer's disease, tend to die sooner than those with a static brain injury. Further, other things being equal an acquired injury, such as a traumatic brain injury, is associated with longer survival than a congenital condition such as cerebral palsy. Among persons with acquired static conditions, however -- for example, traumatic brain injuries or anoxic injuries following cardiorespiratory arrest -- no major difference in prognosis for survival has been documented.
The studies referenced above are available on the articles page.