13 - Vestibular Disorders

Question 1

What is the vestibular system,?

Answer 1

The apparatus of the inner ear, made of the semicircular canals, the ampullae, and the cochlea.

Question 2

What parts of the vestibular system sense angular acceleration? What about linear acceleration?

Answer 2

Angular: semicircular canals can detect pitch (up and down), yaw (side to side), and roll (tilt left to tilt right).

Linear: otolith organs detect up/down, front/back, left/right.

Question 3

How does your brain sense that you’re moving?

Answer 3

By detecting activity from both ears and comparing. If they’re the same, you’re not moving.

Your vestibular nerve is constantly firing, and when you move it either increases or decreases activity.

Question 4

What is the function of the vestibular ocular reflex (VOR)? What can happen if this reflexing isn’t working properly? How do you tell that it’s not working as a doctor?

Answer 4

Maintains eye position during motion.

Disturbances in this reflex can be seen on eye examination. Eye movements that are inappropriate cause sensation of dizziness and nausea.

Question 5

What is one test that can be done to test someones vestibular ocular reflex?

Answer 5

The head thrust test: tell pt to look at a single spot while you thrust their head to one side. They should be able to keep their eyes on the spot despite you thrusting their head.

Question 6

What is Ewald’s first Law?

Answer 6

Nystagmus is toward the more active side.

Nystagmus is in the plane of the more active canal.

Question 7

Which semicircular canal creates which eye movement?

Answer 7

Horizontal canal: L and R movement

Superior canal: up and over movement

Posterior canal: down and over movement

Question 8

What is Nystagmus? How is it named?

Answer 8

A corrective mechanism that is opposite the direction evoked by canal excitation.

It rapidly brings eyes back to where they belong and is named for the fast direction of movement ie left-beating or downward-beating, clockwise beating.

Question 9

What is the direction of nystagmus?

Answer 9

Occurs when they are inappropriately stimulated.

The direction is the opposite of what normally occurs when the associated canal is stimulated.

Question 10

Describe the race car analogy for nystagmus.

Answer 10

When you have a flat tire and you’re trying to drive straight you will periodically jerk the wheel the other way (towards the good tire) to keep it on track.

This is the way nystagmus works–it beats towards the more active canal.

Question 11

What are the two things that can result in nystagmus?

Answer 11

When a canal is inappropriately stimulated, or when the other canal has lost its function.

Question 12

What is acute unilateral hypofunction?

Answer 12

When one vestibular system is functioning at a lower level then the other.

Question 13

What is Alexander’s Law?

Answer 13

Looking toward the more active side increases nystagmus.

And looking away from it decreases the nystagmus.

Question 14

What is ewald’s second law?

Answer 14

Excitatory responses for the angular VOR are greater than inhibitory responses.

Head shake can bring out an asymmetry causing nystagmus to the stronger side.

Question 15

What does Ewald’s second law mean in terms of the head turn test?

Answer 15

Turning toward a side activates that side greater than turning away from a side inhibits that side.

Question 16

Activation and inhibition of semicircular canals close together ______.

Answer 16

Add up.

This is why you stay dizzy after spinning in a chair for a while even after you stop.

Question 17

How do you perform a head shake exam?

Answer 17

Shake patients head back and forth vigorously for 10-15 seconds.

If one side is weak, the excitation on the stronger side will predominate and eye movements will mimic unilateral canal excitation (fast beat to the better side).

Question 18

What does a normal head shake test look like?

Answer 18

No nystagmus.

Question 19

Why does nystagmus beat toward the “stronger” side?

Answer 19

Because the other side is damaged, or because the strong side is inappropriately stimulated.

Question 20

How would you know if someone’s dizziness is not an inner ear problem?

Answer 20

If they don’t have nystagmus it’s not of ear origin.

If they have vertical nystagmus it’s not ear related because ear canals can’t generate vertical nystagmus.

If their nystagmus changes directions it’s not ear related.

Question 21

What is benign paroxysmal positional vertigo?

Answer 21

When otoconia get displaced into one of the semicircular canals. These are what sense inertia.

85% of the time they go into the posterior canal when they get loose (posterior canal canalithiasis).

Question 22

What happens in posterior canal canalithiasis?

Answer 22

Posterior canal is activated by movement because the otoconia move in the canal and inappropriately simulate movement.

Nystagmus is toward the affected ear and rotary in nature because the crystals stimulate the verve, making it the more active side.

Question 23

How would you test for benign paroxysmal positional vertigo (BPPV)?

Answer 23

Dix-Hallpike testing: Turn their head 45 degrees to align the posterior canal with the spine, then tilt the head back to get the canal hanging down relative to gravity.

If there’s crystals in the canal, they will settle at the bottom of the canal and cause the nystagmus.

Question 24

What is superior canal dehiscence? What are some symptoms that patients will experience?

Answer 24

The superior canal sticks up and is only separated from the brain by a thin layer of bone; when this bone is eroded through patients will get dehiscence, or an opening into the superior canal.

This allows pressure, sound, and exercise can stimulate the canal.

Pts may experience autophony: hypersensitivity to internal body sounds.

Question 25

How can you tell that the superior canal is being activated, such as when a patient has superior canal dehiscence?

Answer 25

The superior canal does rotary up and over movements.

Question 26

What is Meniere’s disease? What are symptoms?

Answer 26

Too much endolymphatic pressure and it builds up and can cause membrane rupture that results in mixing of the high Na and K fluids.

This causes a neural discharge in the inner ear, making it more active (nystagmus) and people feel acute attacks of vertigo that lasts 4-12 hours.

Membrane can repair itself and the process can repeat.

Question 27

What are characteristics of Meniere’s disease?

Answer 27

Entire labyrinth is affected: hearing and vestibular components both affected.

Usually unilateral, so you should be able to elicit unilateral signs with the head shake and head thrust.

Question 28

What is vestibular neuritis/labryrinthitis?

Answer 28

Inflammation of the vestibular nerve of of the labyrinth.

The acute phase is like cutting the nerve: sudden loss of function and nystagmus beats away from affected ear.

Chronic phase causes loss of unilateral VOR seen with the head thrust and head shake.

Question 29

What is the likely cause of vertigo if the dizziness duration is long and there is hearing loss? What about if the dizziness is long but there’s no hearing loss?

Answer 29

Long duration dizziness with hearing loss: Labyrinthisis

Long duration dizziness with no hearing loss: vestibular neuronitis.

Question 30

What is the likely cause of vertigo if the duration of dizziness is short and there’s hearing loss? What is the duration is short and there’s no hearing loss?

Answer 30

Short duration with hearing loss: Meneire’s disease (20 min to 12 hours)

Short duration with no hearing loss: benign paroxysmal positional vertigo (BPPV) (like 30 seconds).

Question 31

What should you be thinking if vertigo can’t be associated with a physical pathology of the vestibular system?

Answer 31

MIGRAINE.

Vertigo is a prominent manifestation and lo longer an aura symptom.

1% of the population will have vestibular migraine at some point.

Question 32

What are common symptoms of people with migraines?

Answer 32

30-50% experience episodes of true vertigo with migraines.

50-75% experience dizziness, lightheadedness, or unsteadyness.

25% experience vestibular symptoms during headache-free intervals. (vestibular symptoms are more common in pts suffering from migraine with aura).