The Disorders of Consciousness Spectrum

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What is the spectrum of disorders of consciousness?
With Joseph Giacino, PhD

Lower Third
Joseph Giacino, PhD
Project Director,
Spaulding-Harvard Traumatic Brain Injury Model System

When we think about disorders of consciousness, we can think about these syndromes from along two dimensions, arousal and awareness. By arousal we mean wakefulness. Is the person literally awake? Are the eyes open? Are they processing sensory information at a very basic level? On the awareness part of the equation: is the individual demonstrating signs of interaction with the environment? Or is there some evidence of self-awareness? Are they attending to their body?

Disorders of consciousness can be viewed really on a continuum. So in coma: no wakefulness, no awareness. Eyes are continuously closed, no purposeful behavior, really no movement, and the person is in need of life support because those vital systems of the brain that control breathing and heart rate and temperature can’t perform those functions on their own. Once the eyes open, if nothing else changes, we have wakefulness without awareness. That is the so-called vegetative state, also referred to as unresponsive wakefulness syndrome. They mean the same thing. The term vegetative state has become pejorative. People are referred to as a vegetable. That's not what its intent was. The vegetative functions of the body are those base functions like respiration and cardiac control, et cetera. So the idea is that when a person is in a vegetative state, those vegetative functions are coming back online. They're not in need of external support. But the bottom line is … in vegetative state, we have wakefulness without awareness.

The next transition is to the minimally conscious state. So in minimally conscious state, there's at least one behavioral sign of consciousness. So that can be … the person's beginning to follow some simple commands. At the lowest level, they're able to track people or objects moving around with their eyes. So if somebody enters the room, that person may be laying in bed, make eye contact with that individual and follow movement. That's a very important sign. That will not happen in an unconscious state.

Other behavioral signs of consciousness are communication. It can be verbal or it can be gestural. It doesn't have to be accurate, but the person is signaling in a way that's communicative. And then other kinds of purposeful behavior: they may move something that's gotten on their face and brush it off. We start to see those purposeful behaviors come back. But minimally conscious state is when at least one of these signs is present and reproducible. I gotta be convinced it's there. It's definitive.

The tricky part about diagnosing a minimally conscious state is that that condition fluctuates. So one moment, clear sign of consciousness is present. I tell the person to follow some simple instruction like open your mouth or raise your hand. They do it. And then five minutes later, I give the same instruction … I get nothing at all. It's why we don't want to do a one-off examination because if you happen to grab the person when they're sort of downregulated, in a downregulated state, you're not going to find the sign of consciousness that's super important, that’s going to drive decision making. So we need to do repeated assessments over time to capture that person when that brain state is at its maximum.

There's two subdivisions of the minimally conscious state. One is called MCS-, where these, at least one behavioral sign of consciousness is present, but it doesn't include language function. So these are individuals who don't follow commands, don't have any speech or communication, but do have one of these other signs of consciousness. MCS+ is a conscious state that includes evidence of language function, and now we have growing evidence suggesting that, especially early on, if somebody is an MCS+, is showing signs of language function, it's a more favorable prognostic sign for better downstream functional recovery than if they did not have language function as they were regaining consciousness.

After the MCS+ state, persons get to the point where they're able to either communicate in a reliable manner — simple yes/no questions. Is your name Jim? Is your name Bob? They're now demonstrating the ability to use objects in a functional manner. They're combing their hair, they're self-feeding, doing the kinds of overlearned behaviors that we do routinely or automatically. They're now back online.

Either functional communication or functional object use brings you out of the minimally conscious state into the last rung on the ladder of disorders of consciousness, which is the post-traumatic confusional state or, if it's not a traumatic injury, acute confusional state. So these are individuals now — they're alert, they're awake, they're able to follow instructions, but typically disoriented to time and place. They can engage in an appropriate manner in a conversation or an environmental interaction. And then in the next moment sort of be in left field. They're completely off target, talking about something that has nothing to do with the immediate circumstances, maybe agitated during that state or prone to episodes of agitation, may even have so-called psychotic features where there are delusions or hallucinations or paranoia that arise again from that stage of brain injury recovery. It's sort of a delirium that they may be experiencing in this confusional state. And then once they become reoriented, disorders of consciousness are a thing of the past.