Vegetative state versus minimally conscious state versus locked-in syndrome
The vegetative state, minimally conscious state and locked-in syndrome are compared by wakefulness (being awake), awareness (knowing yourself and your surroundings) and ability to respond.
Remember
Wakefulness with reflex responses but no behavioural sign of awareness is a vegetative state; inconsistent but reproducible purposeful responses mean a minimally conscious state; full awareness with almost complete paralysis (loss of voluntary movement) is locked-in syndrome.
Memory aid
the mind is awake, the body is locked
Use it to recall locked-in syndrome, where awareness is preserved despite severe paralysis.
Consciousness has two parts: arousal (being awake) and awareness (knowing about oneself and the surroundings). The three states are compared by wakefulness, awareness and ability to respond, and they are not a single ladder of severity.
In a vegetative state, also called unresponsive wakefulness syndrome, the patient is awake, with eye opening and sleep-wake cycles, but there is no behavioural evidence of awareness. Reflex and spontaneous movements can still occur, such as withdrawing a limb from a painful stimulus. Repeated careful assessment is needed to tell these from purposeful responses.
In a minimally conscious state, awareness is limited but demonstrable. It shows as inconsistent yet reproducible purposeful responses, such as following commands. One isolated movement is not enough, so the diagnosis needs careful repeated assessment. Reliable communication or intelligent use of objects indicates that the patient has emerged from this state.
In locked-in syndrome, awareness is preserved despite severe paralysis and inability to speak. The damage classically involves the ventral (front) part of the pons, which is the middle part of the brainstem, while the arousal networks are spared. Vertical eye movements or blinking may allow purposeful communication. Because the patient cannot move or speak, the condition is easy to mistake for coma (where wakefulness and awareness are both absent), so the eyes must be tested.
Key facts
- Vegetative state
- wakefulness, including eye opening and sleep-wake cycles, without behavioural evidence of awareness.
- Minimally conscious state
- limited but demonstrable awareness, shown by inconsistent yet reproducible purposeful responses such as following commands.
- Locked-in syndrome
- awareness is preserved despite severe paralysis and inability to speak.
- Cause of locked-in syndrome
- often a blockage of the basilar artery (the main artery of the back of the brain), damaging the front of the pons.
- Communication in locked-in syndrome
- vertical eye movements or blinking may be the only way to communicate.
- Coma
- wakefulness and awareness are both absent.
Exam traps
- Inconsistent command following and purposeful reaching after a brain injury do not mean locked-in syndrome, because that syndrome is full awareness with almost complete paralysis, usually after damage to the ventral pons.
- Inconsistent yet reproducible purposeful responses on repeated assessment, such as following simple commands or reaching purposefully, are a sign of awareness, so a patient who shows them has moved beyond a vegetative state.
- Communicating yes or no with vertical eye movements and blinking does not fit a vegetative state, because that state has no behavioural evidence of awareness, whereas reliable communication shows awareness.
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