Third Nerve Palsy

Question 1

Third nerve palsy, also known as oculomotor nerve palsy, is a neurological condition characteriwed by weakness or paralysis of the muscles innervated by the third cranial nerve (CN III). What is the incidence of this?

1 - 4000 cases per 100,000
2 - 400 cases per 100,000
3 - 40 cases per 100,000
4 - 4 cases per 100,000

Answer 1

4 - 4 cases per 100,000

Affects men and women equally

Question 2

What age does the incidence of third nerve palsy, also known as oculomotor nerve palsy occur?

1 - >40
2 - >50
3 - >60
4 - >70

Answer 2

4 - >70

Question 3

Third nerve palsies can be categorised into 2 main groups. Which 2 of the following are those groups?

1 - ischemic (microvascular)
2 - compressive (mass lesion)
3 - autoimmune
4 - infective

Answer 3

1 - ischemic (microvascular)
2 - compressive (mass lesion)

Question 4

There are 2 broad categories of third nerve palsy: ischaemic and compressive. Which of the following is NOT a characteristic feature of ischaemic (microvascular) third nerve palsy?

1 - always presents with pupillary involvement
2 - associated with diabetes mellitus
3 - associated with hypertension
4 - associated with vascular risk factors
5 - benign course

Answer 4

1 - always presents with pupillary involvement

Normally presents WITHOUT pupillary involvement

Question 5

There are 2 broad categories of third nerve palsy: ischaemic and compressive. Ischaemic (microvascular) third nerve palsies are typically benign and typically resolve over what time period?

1 - minutes to hours
2 - hours to days
3 - days to weeks
4 - weeks to months

Answer 5

4 - weeks to months

Question 6

There are 2 broad categories of third nerve palsy: ischaemic and compressive. Which of the following is NOT a characteristic feature of compressive (mass lesion) third nerve palsy?

1 - typically present with pupillary involvement
2 - can be caused by aneurysms, tumours, or other space-occupying lesions
3 - benign course
4 - require urgent referral

Answer 6

3 - benign course

These are not benign and need urgent referral to evaluate and managed to prevent life-threatening complications.

Can also cause diplopia (double vision)

Question 7

The oculomotor nerve arises from the oculomotor nucleus in the midbrain and traverses through the cavernous sinus before entering the orbit through the superior orbital fissure. Which of the following muscles does this nerve NOT innervate?

1 - Superior rectus
2 - Medial rectus
3 - Lateral rectus
4 - Inferior rectus
5 - Inferior oblique

Answer 7

3 - Lateral rectus

Question 8

The oculomotor nerve arises from the oculomotor nucleus in the midbrain and traverses through the cavernous sinus before entering the orbit through the superior orbital fissure. This nerve is responsible for innervating all of the following:

• Superior rectus
• Medial rectus
• Inferior rectus
• Inferior oblique

What else does CN III innervate?

1 - levator palpebrae superioris muscle
2 - parasympathetic fibres controlling the pupillary sphincter
3 - ciliary muscle regulating pupil constriction and lens accommodation
4 - all of the above

Answer 8

4 - all of the above

• palpebrae superioris muscle = responsible for elevating the upper eyelid

pupillary sphincter = CN III constricts pupils during rest and digest

ciliary muscle = CN III contracts, causing the lens to become more spherical, and thus more adapted to short range vision, as per the accommodation reflex

Question 9

In patients with a third nerve palsy, do they typically present with a partial of complete ptosis?

Answer 9

can be both

BUT a partial ptosis can mean the cause is evolving and could get worse

Question 10

In patients with a third nerve palsy, what direction is the eye typically facing?

1 - up and out
2 - up and in
3 - down and out
4 - down and in

Answer 10

3 - down and out
Sounds like a boxer or alcoholic

Only left with lateral rectus and superior oblique functioning

Question 11

Movement of the eye is limited in all directions, EXCEPT which direction?

1 - up
2 - down
3 - lateral
4 - medial

Answer 11

3 - lateral

This is because this is innervated by CN VI (abducens) nerve which is responsible for lateral movement

Question 12

If pupil dilation and reactivity is affected in third nerve palsy, is this more likely to be ischaemic or compressive in its cause?

Answer 12

• compressive

Pupil dilation is one of the 1st signs of a compressive cause

Question 13

Which 2 imaging modalities should ALL patients have done urgently to identify if there is a compressive or ischaemic event causing the third nerve palsy?

1 - head x-ray
2 - MRI
3 - CT angiography
4 - eye ultrasound

Answer 13

2 - MRI
3 - CT angiography

Question 14

Which blood vessel is most likely the cause the cause of a third nerve palsy due to its close proximity with CN III?

1 - posterior cerebral artery
2 - anterior cerebral artery
3 - anterior communicating artery
4 - posterior communicating artery

Answer 14

4 - posterior communicating artery