Lecture 41: Coma Flashcards
What is consciousness?
States of consciousness can range from confounded, stuporous to minimally conscious and vegetative
What is coma (working definition)?
Transient state in which the patient’s eyes are closed;
No response to external stimuli other than reflex
Eyes are closed and sleep-wake cyclers are absent
Usually prolonged (hours to days) but rarely permanent
What are the two interconnected systems necessary to maintain normal consciousness?
- The cerebral cortices
- Ascending Reticular Activating system/thalami (ARAS)
(located in the midbrain, mesenchepahlic nucleus, thalamic intralaminar nucleus, dorsal hypothalamus and tegmentum…which is the middle point of brain stem)
So what causes coma?
Dysfunction in Cerebral Cortices or Ascending Reticular activating system (ARAS), which includes the thalamus
What are coma mimics in you DDx?
i. locked in syndrome
ii. Severe neuromuscular disease
iii. Psychiatric disease: catatonia
iv. Akinetic mutism
What is the most important goal coma exam?
To distinguish between diffuse cortical dysfunction and brainstem dysfunction
That’s why you have the eye exams and shit!
What is the significance if your coma exam localizes to brainstem?
Most likely a structural (focal) lesion
What is the significance if your coma exam localizes to hemispheres?
Systemic abnormality
What are the 4 elements focused upon in a neurological exam?
i. pupillary response
ii. eye movements
iii. position or movement of the limbs
iv. breathing patterns
Where are the nuclei for CNIII, IV and MLF located? Significance?
Amid the neurons of the ARAS
When coma is caused by brainstem dysfunction, distrubances of ocular motility and pupil size may help localize lesion to specific brainstem level
What is responsible for the parasympathetic innervation to the eye? Lesion would result in
Oculomotor
-efferent limb of pupillary reflex
Optic nerve is afferent limb
Lesion to CN III results in dilation of the eye or “abnormal constriction…dumbass term”
What is responsible for sympathetic innervation to the eye? Lesion causes?
Hypothalamic tract, pregang (superior cervical ganglion) post gang in nasociliary ganglion
What happens when you have a horners?
You get aberrant pupillary constriction
This guy really likes the term “abnormal dilation” or ability to dilate is abnormal/dysfunctional
What are eye fields and what are their function?
Frontal Eye fields = motor area of cortex that controls muscular movement
Each eye field is wired to drive the eyes to the opposite side
Each eye field connects to the contralateral PrePontine Reticular Formation
In a patient with coma, if you see eyes look toward a particular direction, what does that mean?
If an eye field is damaged on one side, the eyes will look toward the IPSILATERAL side due to unopposed activity of the contralateral eye fields
Therefore injury is ipsilateral to where eyes are pointing
What does the PPRF innervate?
Ipsilateral abducens and contralateral oculomotor (through MLF)
PPRF = paramedian pontine reticular formation
Functions to carry out conjugate horizontal gaze
What happens if the eye is roving in a patient with coma?
Coma is likely due to diffuse cortical dysfunction and NOT brainstem dysfunction
This is because the eye fields (cortices) normally exhibit tonic inhibition to prevent eyes from roving
What is the oculocephalic reflex?
With the head turning, the ipsilateral horizontal semicircular canal sends impulses to the ipsilateral vestibular nucleus
-vestibular synapses in the contralateral abducens to ipsilateral CN III
-results in conjugate eye deviation in the opposite direction of head turn
COUNTERROTATION
What is the oculovestibular reflex?
In a normal person, the eyes deviate slowly toward the side of the cold water. The cortex then tries to correct the deviation and the eyes jerk back toward midline
COWS refers to FAST phase of nystagmus that you see with cold/warm water
However, slow tonic movement is opposite of the COWS mnemonic
What is papilledema?
Swelling of the optic disc caused by increased intracranial pressure
What is the optic disc?
The location where the ganglion cell axons exit the eye to form the optic nerve
How can you tell if there is normal intracranial pressure?
The presence of spontaneous venous pulsations
What is purposeful vs. non-purposeful behavior?
Purposeful movements are not stereotyped and require complex motor input?
Exmple of purposeful: scratching, grimacing
Example of non-purposeful: response to painful stimuli
What is decerebrate rigidity?
Abnormal extension
Injury below the level of the red nucleus
Think extension points palm inferior to your body or inferior to red nucleus
