Lecture 41: Coma

Question 1

What is consciousness?

Answer 1

States of consciousness can range from confounded, stuporous to minimally conscious and vegetative

Question 2

What is coma (working definition)?

Answer 2

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

Question 3

What are the two interconnected systems necessary to maintain normal consciousness?

Answer 3

1. The cerebral cortices
2. 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)

Question 4

So what causes coma?

Answer 4

Dysfunction in Cerebral Cortices or Ascending Reticular activating system (ARAS), which includes the thalamus

Question 5

What are coma mimics in you DDx?

Answer 5

i. locked in syndrome
ii. Severe neuromuscular disease
iii. Psychiatric disease: catatonia
iv. Akinetic mutism

Question 6

What is the most important goal coma exam?

Answer 6

To distinguish between diffuse cortical dysfunction and brainstem dysfunction
That’s why you have the eye exams and shit!

Question 7

What is the significance if your coma exam localizes to brainstem?

Answer 7

Most likely a structural (focal) lesion

Question 8

What is the significance if your coma exam localizes to hemispheres?

Answer 8

Systemic abnormality

Question 9

What are the 4 elements focused upon in a neurological exam?

Answer 9

i. pupillary response
ii. eye movements
iii. position or movement of the limbs
iv. breathing patterns

Question 10

Where are the nuclei for CNIII, IV and MLF located? Significance?

Answer 10

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

Question 11

What is responsible for the parasympathetic innervation to the eye? Lesion would result in

Answer 11

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”

Question 12

What is responsible for sympathetic innervation to the eye? Lesion causes?

Answer 12

Hypothalamic tract, pregang (superior cervical ganglion) post gang in nasociliary ganglion

Question 13

What happens when you have a horners?

Answer 13

You get aberrant pupillary constriction

This guy really likes the term “abnormal dilation” or ability to dilate is abnormal/dysfunctional

Question 14

What are eye fields and what are their function?

Answer 14

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

Question 15

In a patient with coma, if you see eyes look toward a particular direction, what does that mean?

Answer 15

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

Question 16

What does the PPRF innervate?

Answer 16

Ipsilateral abducens and contralateral oculomotor (through MLF)
PPRF = paramedian pontine reticular formation
Functions to carry out conjugate horizontal gaze

Question 17

What happens if the eye is roving in a patient with coma?

Answer 17

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

Question 18

What is the oculocephalic reflex?

Answer 18

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

Question 19

What is the oculovestibular reflex?

Answer 19

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

Question 20

What is papilledema?

Answer 20

Swelling of the optic disc caused by increased intracranial pressure

Question 21

What is the optic disc?

Answer 21

The location where the ganglion cell axons exit the eye to form the optic nerve

Question 22

How can you tell if there is normal intracranial pressure?

Answer 22

The presence of spontaneous venous pulsations

Question 23

What is purposeful vs. non-purposeful behavior?

Answer 23

Purposeful movements are not stereotyped and require complex motor input?
Exmple of purposeful: scratching, grimacing
Example of non-purposeful: response to painful stimuli

Question 24

What is decerebrate rigidity?

Answer 24

Abnormal extension
Injury below the level of the red nucleus
Think extension points palm inferior to your body or inferior to red nucleus

Question 25

What is decorticate posturing?

Answer 25

Abnormal flexion
Injury above level of red nucleus
Think flexion points palm superiorly or towards a direction superior to red nucleus

Question 26

What does Stereotyped movement mean?

Answer 26

Movement in which no matter how many times you give the stimulus, you will always give the same response

Question 27

What are the five types of respiratory patterns in coma patients?

Answer 27

1. Cheyne-Stokes: lots of breaths followed by periods of silence
   -demonstrates bilateral thalamic injury
2. Central neurogenic hyperventilation
   -pontomesencephalic region (midbrain)
3. Apneustic
   -pons
4. Ataxic (Biots) breathing
   -lower dorsomedial medulla
5. Respiratory arrest
   Spinal cord C3-5

Question 28

What are the potential types of herniations?

Answer 28

1. Subfalcine herniation
2. Uncal herniation
3. Diencephalic herniation
4. External herniation
5. Tonsilar herniation
   Caused by hematoma

Question 29

What is subfalcine herniation? What are the symptoms

Answer 29

Subfalcine = herniation of the cingulate cortex under the falx
Symptoms: think of homunculus
IPSILATERAL lower extremity weakness (because herniation is compressing opposite M1 at foot homunculus

Question 30

What are the symptoms of uncal herniation?

Answer 30

i. ipsilateral CN III palsy
ii. contralateral hemiparesis
iii. ipsilateral hemiparesis
Uncus compresses BOTH CNIII and ipsilateral cerebral peduncle so that gives you contralateral weakness
However, the false localizing sign is that there may also be weakness IPSILATERALLY because by pushing one cerebral peduncle, you are pushing the other cerebral peduncle towards the rigid tentorium, which is actually more damaging than pushing ipsilateral peduncle towards midline

Question 31

What is diencephalic (central) herniation? What are the symptoms?

Answer 31

Mechanism: when large frontal or parietal mass lesions compress the diencephalon (thalamus) which in turn shifts downward and compresses midbrain and pons
-leads to rostrocaudal progression of brainstem signs

Early
-Small pupils, somnolence, Cheyne stokes respirations (bilateral thalamic lesion), decorticate posturing (flexor)

Intermediate
-Pupils become midsize and non-reactive, breathing is hyperventilation, then apneusis (midbrain then pons), and decerebrate posturing (extensor, below red nucleus)

Late
-the oculovestibular/oculocephalic reflexes disappear, ataxic breathing (medulla) to respiratory arrest

Question 32

What are symptoms of tonsilar herniation?

Answer 32

Fuck with C3-5…so talk and die

Sudden respiratory arrest