Monday, March 21, 2005

Terri Schiavo and the definition of persistent vegetative state

I've written a rather long essay on the neurological definition and implications of the persistent vegetative state. I've also included some observations that bear on the specifics of the Terri Schiavo case.

Click here for the complete essay.
Terri Schiavo has been the focus of incredible public interest because of the many emotional and ethical issues her case raises.

I thought that a discussion of just what persistent vegetative state (PVS) means would help make sense of the multitude of conflicting and confusing statements propagating through the news media and the internet.

Hopefully, this discussion will act as a step-off point to promote a more informed debate regarding the circumstances surrounding this unfortunate patient. I find such an exposition essential because frankly, I'm amazed about the misunderstandings, the misstatements and the general misrepresentations I've seen in both the MSM and the blogosphere regarding this case.

Sources

The most authoritative American guideline regarding PVS is "Medical Aspects of the Persistent Vegetative State" published in 1994 by the New England Journal of Medicine (Part I, Part II). (You'll need a subscription to NEJM to download the actual papers.) Another good reference that you can download for free is the British Guideline entitled "The Vegetative State: guidance on diagnosis and management" published by the Royal College of Physicians in 2003. Do not assume that the British version is more accurate because it was published more recently. It is very similar and draws heavily from the older American version but is not as comprehensive.

For the layperson, I would recommend the British guideline as it is much more easily understood.

Wakefulness and Awareness

In discussing altered levels of mental status, two concepts are very important: wakefulness and awareness.

Wakefulness means, not surprisingly, the state of being awake: the eyes are open and significant movement is possible. During sleep, the eyes are closed and movement is generally much curtailed. Normally, people exhibit a sleep-wake cycle passing from one state to the other in a contrived pattern. This sleep-wake cycle is often rather easy to observe in patients.

Awareness on the other hand is much more difficult to evaluate and our descriptions of it become almost philosophical in nature. Basically, it refers to an awareness of self and environment in the form of sensations, memories and experiences. As physicians, we infer awareness by patients' actions. Actions can be as obvious as speech or as subtle as the flicker of an eyelid. When more subtle actions are used to infer awareness, they must be purposeful, that is they must be directed to some conscious end.

The quivering of an eyelid during a seizure does not reflect purposefulness. On the other hand, a patient who can only move a single fingertip can manifest his awareness by moving that fingertip purposefully in response to questions. In medicine, the word consciousness is sometimes used synonymously with awareness. I say this because it is easy to confuse consciousness with wakefulness.

Physicians are generally materialists. Under a medical paradigm, physicians think of wakefulness and awareness as occurring in certain, relatively well-circumscribed areas of the brain. A tremendous body of knowledge exists on just where these different functions localize to and yet there is overlap and uncertainty.

Much of what we know about the localization of various mental functions is derived from observing victims of brain trauma. Often, such victims have damage to very specific areas and careful observation of the ensuing deficits has allowed the brain to be functionally mapped.

As a first approximation, wakefulness is a function of the upper brainstem called the reticular activating system and the thalamus. Awareness is not as well localized but primarily involves multiple areas in the cerebral cortex.

Coma and Vegetative State

Obviously, a normal person has both wakefulness (alternating of course with sleep) and awareness. The question is, how does a patient respond and what is his prognosis when one of these two functionalities is damaged? This is certainly possible given that they reside primarily on different parts of the brain.

If a patient doesn't exhibit typical sleep-wake patterns with periods of sleep (eyes closed, notable paucity of movement) followed by wakeful periods (eyes open, activation of movement) he is said to be in a coma. What is noteworthy about coma is that the sense of awareness cannot be evaluated. In fact it can be argued that the concept of awareness is meaningless in the setting of coma.

When a patient exhibits wakefulness and the absence of awareness he is said to be in a vegetative state (VS). A person in a vegetative state is able to move spontaneously when awake. These movements may have the appearance of being purposeful but in a true vegetative state where awareness is lacking, they are not. Such patients may withdraw from painful stimuli. These withdrawal responses are reflexes and do not involve the higher areas of the brain i.e. the cerebral cortex where awareness occurs.

Diagnosis of Vegetative State

Patients in a VS may track objects with their eyes. Again, such eye tracking which may very well appear to demonstrate conscious awareness is in fact mediated by much more primitive areas of the brain (predominantly the brainstem and midbrain). It becomes a diagnostic dilemma when a patient otherwise felt to be in a VS is able to track objects. Such behavior may be seen in patients with awareness and who are therefore not in a VS.

The main discriminating behavior in such a circumstance is consistency of visual tracking. Patients with awareness are consistently able to track objects. The visual tracking mechanisms are driven by the cerebral cortex (though executed by lower levels) and are therefore under conscious control. In VS, without such direction from higher centers, the tracking behavior is hit and miss. It is very inconsistent and not easily reproduced from minute to minute.

A particularly upsetting behavior observed in some patients in VS is what appears to be emotional expression. Such patients may occasionally be seen to smile, cry, frown, grimace, in other words demonstrate some or all of the usual outward signs of emotion. Family and friends may be convinced that such behavior implies awareness and be filled with a false sense of hope. The problem is that the physical outlet of emotional expression is in fact mediated by subcortical areas of the brain and a patient with a completely destroyed cerebral cortex can exhibit such behaviors.

As with visual tracking, the key to making the distinction of isolated emotional expression and emotional expression due to awareness is context. Do the various expressions appear to correlate with what is currently happening in the patient's room or do they seem to occur at random? If a patient smiles whenever he is provoked, that would tend to argue against awareness. On the other hand, a patient that consistently smiled only when his wife entered the room more likely then not is exhibiting cortical awareness and is probably not in a VS despite other physical findings that may be present.

Time-Course of Vegetative State

At this stage, it is time for some more nomenclature. For the first four weeks following a VS, this condition is referred to as an acute VS (AVS). After that, it is referred to as a persistent VS (PVS). These two terms are diagnoses. There is a third term that is sometimes used called permanent VS. This isn't so much a diagnosis as a prognosis, the implication being that such a patient will never recover awareness.

I generally prefer to use the term persistent VS and consider permanent VS as a subset of it determined not so much by definition as by what is known about the overall prognosis of PVS patients.

Use of Laboratory or Imaging Studies

In light of the tremendous amount of misinformation being disseminated about the Schiavo case, this point needs to be made: Nowhere in the guidelines are laboratory or imaging studies felt to be necessary for the diagnosis of PVS. They do discuss CT scans, MRI's and PET scans as being useful in determining the etiology of PVS or in situations where the diagnosis is uncertain on the basis of purely clinical grounds.

I've read a number of reports in the press where claims have been made that an MRI or PET scan is necessary for the diagnosis and hasn't yet been done in Schiavo's case. It is extremely unlikely that such studies will shed any light on her case at this time nor are they medically mandated.

Prognosis in PVS

Prognosis is determined by several different factors, most importantly, the underlying cause of the PVS. The two main causes are divided as traumatic (e.g. head injury) and nontraumatic (myocardial infarction, anoxia, metabolic derangement, vascular, etc.)

Patients in a PVS due to a nontraumatic cause (as is the case of Terri Schiavo) have a much grimmer prognosis. A number of studies have demonstrated this. The data generally suggests that a PVS is permanent for traumatic causes after a twelve month period. For nontraumatic causes, three months of PVS implies permanence (the British guideline is more conservative and states six months).

How rare is recovery of awareness after being in a PVS for longer than the periods defined by these guidelines? As of 1994 when the U.S. guidelines were published, the authors were able to find documentation of eight cases where patients regained awareness after twelve months in PVS. Of these only four were of nontraumatic etiology. Several other cases occurred in children (who are known to have a much better prognosis than adults). Another study reveals several cases of recovery of some awareness after four months but none after twelve months.

As of 1994, this leaves a total of four known cases of recovery of some degree of awareness in adult, nontraumatic PVS after greater than twelve months. Each of these cases was associated with severe or moderate disability afterwards. Clearly, the likelihood of reversal of PVS is dismal. Another literature review that looked for additional cases came to the same conclusion as of 1998.

What does this mean for Terri Schiavo?

I hope that this rather lengthy description of PVS helps put some things into perspective regarding the overall prognosis of Ms. Schiavo. If the diagnosis is correct, and I have no reason to believe otherwise, then after 15 years in a PVS, she is most assuredly not going to regain awareness. In essence, she will never again be a sentient being.

A lot has been made of some videos of her appearing to visually track a balloon as well as smile. Obviously, I have not examined her but as compelling as such videos may seem to the layperson, nothing I've seen rules out the diagnosis of PVS.

As I have attempted to convey, visual tracking and physical expressions of emotionality alone are not diagnostic of awareness. What matters is the overall consistency and reproducibility of such findings. I have read several accounts of her case suggesting that these videos have been taken completely out of context and that more complete video footage of Ms. Schiavo show her movements to be completely inconsistent and random.

An excellent summary of these and other details of her case can be found in the very good website Abstract Appeal. This blog is run by a lawyer with a passionate interest in Florida law and in the Eleventh Circuit Court of Appeals.

The details surrounding the misfortunes of this woman and her family have captivated the people of this country and the world. That so much misinformation is being propagated by people on both sides of this issue is truly disappointing and has at times been reprehensible.

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1 Comments:

Anonymous Anonymous said...

thanks

March 23, 2005 9:35 PM  

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