Disorders of Consciousness (DOC)
What are disorders of consciousness?
Disorders of consciousness can be described in a two dimensional scale. The figure below depicts them on a two dimensional scale. Consciousness is dependent on two components: arousal and awareness. Arousal is also described as wakefulness or vigilance. Awareness is the level of perception and recognition of the person himself and of the environment. People in coma have no arousal and no awareness and could be found in the bottom left corner of the figure. In the top right corner, one can find people in the locked-in syndrome (LIS): their levels of arousal and awareness is the same as for other healthy people, they are just unable to perform voluntary motor movements. People with unresponsive wakefulness syndrome (UWS) or in MCS are the most challenging in terms of diagnoses and treatment. The arousal of these people could be very high, although the awareness is not existent (UWS) or at a low level (MCS). One is tempted to believe that a UWS patient has still consciousness, because of obvious arousal level.
Classification of DOC
The next figure shows the flowchart of different conditions of cerebral insult. The coma is the first state after a severe brain injury. The cause of brain injuries could be traumatic or non-traumatic. Traumatic brain injury is mainly caused by road accidents, falls or violence. Reasons for non-traumatic brain injury could be, amongst others, tumors, strokes, aneurysms or hemorrhages. After the coma, the patient can evolve into LIS, UWS, brain death or chronic coma. Most people who survive coma, start to awaken and recover gradually within the next weeks, so that chronic coma is a rare state.
Locked-in state (LIS)
This state can be defined as follows:- the presence of sustained eye opening
- aphonia or hypophonia
- quadriplegia or quadriparesis
- a primary mode of communication that uses vertical or lateral eye movement or blinking of the upper eyelid to signal yes/no responses
Completely Locked-In Syndrome (CLIS)
A person in the completely locked-in syndrome (CLIS) has lost all motor functions. The cause for both, LIS and CLIS may be neurological diseases or traumatic brain injuries. People suffering neurological diseases undergo a transition from LIS to CLIS. People seemed to lose their ability to control BCIs, based on visual or tactile stimulation, as well as on MI, during this transition. It has been hypothesized that this is due to the reduced sensory information flow to the brain, leading to an "extinction of thought".Unresponsive wakefulness (UWS)
People with UWS are people awakened from coma. In UWS, people show complete unawareness of themselves and the environment, but show sleep-wake cycles with some preservation of autonomic brain-stem functions. They show eye opening, yet remain unresponsive. In other words, these people show periods of wakeful eye opening with lack of any evidence of a working mind, either receiving or projecting information. The emphasis should lay here in the lack of evidence, which does not necessarily mean that the patient’s mind is unconscious. Furthermore, one should carefully distinguish between reflex responses in UWS patients and voluntary responses. Even for visual responses the American Taskforce on Persistent Vegetative State concluded: "One should be extremely cautious in making a diagnosis of the vegetative state when there is any degree of sustained visual pursuit or consistent and reproducible visual fixation." The diagnosis of UWS should be questioned when there is any degree of sustained visual pursuit, consistent and reproducible visual fixation, or response to threatening gestures. The UWS was named vegetative state until 2010. The cause for renaming was mainly because medical professionals felt uncomfortable referring to patients as vegetative, which sounds vegetable like.Permanent UWS
The term permanent vegetative state was introduced by the Multi-Society Task Force on Persistent Vegetative State, to denote irreversibility after three months following a nontraumatic brain injury and 12 months after traumatic injury. The same is true for permanent UWS. There are though some very few patients who showed some degree of recovery after such long time periods.
Brain death
Person with brain death have permanently lost all brainstem functions. In clinical assessment, brain death is defined by the loss of brainstem reflexes and the demonstration of continuing apnoea in a persistently comatose patient.
Coma and chronic coma
Coma is characterized by the absence of arousal and thus also of consciousness. The patient lies with eyes closed or, at best, eye opening to painful stimuli. To be clearly distinguished from transient unconsciousness, coma must persist for at least one hour. Most of the surviving comatose patients begin to awaken and recover within 2 to 4 weeks, to a state of higher consciousness. If no recovery happened, the person could stay in chronic coma.Minimal conscious state (MCS)
Patients in MCS show limited but clearly discernible evidence of consciousness of themselves or the environment, but are unable to communicate. MCS is diagnosed by at least one of the following behaviours:- following simple commands
- gestural or verbal yes/no response (regardless of accuracy)
- intelligible verbalization
- purposeful behaviour (e.g. movement or behaviour that is not reflexive behaviour)