-A normal level of consciousness depends on the interaction between the cerebral hemispheres and the rostral reticular activating system.
-Anatomical bilateral hemispheric lesions or brainstem lesions may result in an altered level of consciousness.
-Large unilateral hemispheric lesions may produce impairment of consciousness by compression of the upper brainstem.
-Metabolic processes may result in coma from interuption of energy substrate delivery or alteration of neuronal excitability.
Disorder of consciousness are characterized by an alteration of either the level or content of consciousness.
1. Consciousness - an awake individual demonstrates full awareness of self and environment.
2. Confusion - Inability to think with customary speed and clarity, associated with inattentiveness, reduced awareness and disorientation.
3. Delirium - Confusion with agitation and hallucination.
4. Stupor - Unresponsiveness with arousal only by deep and repeated stimuli.
5. Coma - unarousable unresponsiveness.
6. Locked in syndrome - total paralysis below third cranial nerve nuclei; normal or impaired mental function.
7. Persistant vegetative state - Prolonged coma > 1 month, some preservation of brainstem and motor reflexes.
8. Akinetic mutism - Prolonged coma with apparent alertness and flaccid motor tone.
9. Minimally conscious state - Preserved wakefulness, awareness and brainstem reflexes but poorly responsive.
Coma -like syndromes and related states:
1. Locked in syndrome
Features: alert and aware, vertical eye movements present, and able to blink. Quadriplegic, lower cranial nerve palsies (below CNIII nerve nuclei). No speech, facial or pharyngeal movements.
Site of lesion: bilateral anterior pontine lesion which transects all descending motor pathways bu spares ascending sensory and RAS.
Normal EEG. 90-100% of normal metabolism.
Similar state seen with severe polyneuropathies, MG and NMB.
2. PVS (apallic syndrome, neocortical death)
Features: Previously comatose, who now appear to be awake. Spontaneous limb movements, eye movements and yawning seen. However patient is inattentive, no speech, no awareness of environment and total inability to respond to commands.
Site of lesion: Extensive damage to both cerebral hemispheres with relative preservation of the brainstem.
EEG: polymorphic delta or theta waves, sometimes alpha. 40-60% of normal metabolism.
When vegetative state lasts longer than 4 weeks, it is termed persistent. PVS lasting for longer than 2 weeks implies a poor prognosis.
3. Akinetic mutism (coma vigile)
Features: Partially of fully awake patient, immobile and silent.
Site of lesion: Lesion is bilateral frontal lobes or hydrocephalus or third ventricular masses.
EEG: diffuse slowing. $0-80% normal metabolism.
'Abulia' is the tern applied to milder forms of akinetic mutism.
4. Catatonia
Features: awake patients, sometimes a fixed posture, muteness with decreased motor activity.
Site: usually of psychiatric origin.
EEG: non specific EEG patterns associated with associated medical conditions. Variable metabolic changes in prefrontal cortex.
May be mimicked by frontal lobe disease and drugs.
5. Minimally conscious state
Features: Globally imparied responsiveness, limited but discernible evidence of self and environment.
Site: Global neuronal damage.
EEG: theta and alpha waves. 40-60% normal metabolism.
Differs from PVS in that patients diagnosed with minimally conscious state have some level of awareness.
-Anatomical bilateral hemispheric lesions or brainstem lesions may result in an altered level of consciousness.
-Large unilateral hemispheric lesions may produce impairment of consciousness by compression of the upper brainstem.
-Metabolic processes may result in coma from interuption of energy substrate delivery or alteration of neuronal excitability.
Disorder of consciousness are characterized by an alteration of either the level or content of consciousness.
1. Consciousness - an awake individual demonstrates full awareness of self and environment.
2. Confusion - Inability to think with customary speed and clarity, associated with inattentiveness, reduced awareness and disorientation.
3. Delirium - Confusion with agitation and hallucination.
4. Stupor - Unresponsiveness with arousal only by deep and repeated stimuli.
5. Coma - unarousable unresponsiveness.
6. Locked in syndrome - total paralysis below third cranial nerve nuclei; normal or impaired mental function.
7. Persistant vegetative state - Prolonged coma > 1 month, some preservation of brainstem and motor reflexes.
8. Akinetic mutism - Prolonged coma with apparent alertness and flaccid motor tone.
9. Minimally conscious state - Preserved wakefulness, awareness and brainstem reflexes but poorly responsive.
Coma -like syndromes and related states:
1. Locked in syndrome
Features: alert and aware, vertical eye movements present, and able to blink. Quadriplegic, lower cranial nerve palsies (below CNIII nerve nuclei). No speech, facial or pharyngeal movements.
Site of lesion: bilateral anterior pontine lesion which transects all descending motor pathways bu spares ascending sensory and RAS.
Normal EEG. 90-100% of normal metabolism.
Similar state seen with severe polyneuropathies, MG and NMB.
2. PVS (apallic syndrome, neocortical death)
Features: Previously comatose, who now appear to be awake. Spontaneous limb movements, eye movements and yawning seen. However patient is inattentive, no speech, no awareness of environment and total inability to respond to commands.
Site of lesion: Extensive damage to both cerebral hemispheres with relative preservation of the brainstem.
EEG: polymorphic delta or theta waves, sometimes alpha. 40-60% of normal metabolism.
When vegetative state lasts longer than 4 weeks, it is termed persistent. PVS lasting for longer than 2 weeks implies a poor prognosis.
3. Akinetic mutism (coma vigile)
Features: Partially of fully awake patient, immobile and silent.
Site of lesion: Lesion is bilateral frontal lobes or hydrocephalus or third ventricular masses.
EEG: diffuse slowing. $0-80% normal metabolism.
'Abulia' is the tern applied to milder forms of akinetic mutism.
4. Catatonia
Features: awake patients, sometimes a fixed posture, muteness with decreased motor activity.
Site: usually of psychiatric origin.
EEG: non specific EEG patterns associated with associated medical conditions. Variable metabolic changes in prefrontal cortex.
May be mimicked by frontal lobe disease and drugs.
5. Minimally conscious state
Features: Globally imparied responsiveness, limited but discernible evidence of self and environment.
Site: Global neuronal damage.
EEG: theta and alpha waves. 40-60% normal metabolism.
Differs from PVS in that patients diagnosed with minimally conscious state have some level of awareness.
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