Pure Pedantry

A very sad story, and I wish Kate the best in her recovery.

However, I do have a comment about how this story is being presented.

Some people are likely to frame this case as a recovery from a persistent vegetative state. I want to make clear that I don't think that is what happened here. Rather, the much more likely event is that she was mis-diagnosed as being in a persistent vegetative state when she was in fact in a minimally conscious state (more on this in a second). Part of that misdiagnosis has to do with limitations in our ability to get an accurate diagnosis -- something Dr. Owen is trying to address.

First thing, you have to understand the diagnostic criterion for different types of unconscious states. The table below is from here. It compares the different symptoms of various unconscious states (click to enlarge).

Note that neurologists draw a clear distinction between minimally conscious (MC) and persistent vegetative states (PVS). Partly, this distinction rests on different clinical findings. For example, to what degree does the patient track different visual stimuli? To what degree does the patient respond to noxious (painful) stimuli? These are the types of clinical findings that a neurologist would look for in a clinical exam to differentiate between the two states.

Partly, and more important in relation the patient shown above, this distinction rests are the relationship between clinical findings and whether we think the patient is completely unconscious (PVS) or only intermittently or partially conscious (MC). However, the relationship between clinical findings and consciousness isn't clear cut. There isn't a clear relationship between the responsiveness to pain and the existence of consciousness. It is something that we have to infer. Because we don't have access to what the patient is thinking (or not thinking) it is really hard to tell whether they are conscious or not.

This is in part a problem with the term PVS. Neurologists are often loath to use it because it basically rests on the failure of the patient to get better. Because the vegetative state persists, we call it PVS. Unfortunately, at present we really don't have a better system.

Thus, without justifying what may well have been physician error, I can see how this patient may have been mis-diagnosed. She says in the video above that she could perceive pain and did have intermittent consciousness of what was happening to her. This means that she was not in a PVS as I understand the term. The problem is that even a very good diagnostician may have missed the signs of that intermittent consciousness.

This is why Dr. Owen's research is so important. (More on his research here.) In using fMRI to determine whether the activity associated with consciousness is present in these patients, he is giving us a much more powerful diagnostic test. Before, we had EEGs and clinical exam, but if you can do an fMRI or a PET scan and show that conscious-like activity exists, we can be much more certain about the patients diagnosis. And this is not a trivial problem in a couple of isolated cases. Some estimate that as many as 40% of these patients are diagnosed as being in PVS when they are in fact in MC.

The distinction between PVS and MC is also critical in terms of prognosis. I never want to say never, but it is exceedingly rare to see some with PVS recover. In fact, I might go so far as to argue that one of the clinical criterion for PVS is the near impossibility of recovery. PVS is generally caused by anoxic brain injuries where nothing remains intact but the housekeeping functions of the brain -- breathing, orienting to light, sleep cycles, etc. There is nothing left of the higher functions to recover. By contrast, MC (which is much more commonly caused by trauma or infectious disease) can spare a greater deal of the brain. What is impaired is often the reticular activating system (RAS) -- a sort of neurological on-off switch without which none of these higher centers can be active. (Some clinical interventions may be possible to reactivate the RAS, using drugs or deep-brain stimulation, which is why you sometimes read about coma "recoveries." Whenever you read that, I want you to remember that the patient was probably in a MC rather than a PVS).

These are rough distinctions. Individual patients are rarely clear cut with these issues. But the take home is that PVS patients will probably never get better and MC patients -- though they are likely to have significant continuing impairment -- might.