III Nerve Palsy - Oculomotor Flashcards
Which muscles are supplied by which division of IIIrd nerve palsy
- Clinical signs are quite characteristic
- Superior division – supplies superior rectus and levator palpebrae muscle
- Inferior division – supplies medial rectus, inferior rectus & inferior oblique
o Much larger than superior division
o Splits into 3 parts in orbit
1 branch passing under optic nerve & entering MR muscle on its lateral aspect or ocular aspect
Another branch enter IR on its upper aspect
Final branch supplies inferior oblique (& ciliary ganglion by a short stout branch before relay to sphincter pupillae & ciliary muscle) - Motor nerve only – so no sensory input
- Close anatomical links with afferent & efferent pupillary pathway along with control of ciliary body & accommodation
How are IIIrd nerve palsies classified?
- They are classified into 3 specific categories
o Partial (paresis, not a palsy)
o Complete (palsy) WITHOUT pupillary involvement (=pupil sparing)
o Complete (palsy) WITH pupillary involvement
What is the definition of IIIrd nerve palsy?
- One or more of EOM innervated by 3rd nerve are not affected or when there is only paresis of one or more of these muscles
The more nerves/muscles affected the closer the lesion is to the eye
The less nerves/muscles affected the further back the lesion is from the eye
Inferior division supplies IO, IR, MR & pupil – so unlikely to have lesion that just affects one of these
What are the two categories of complete 3rd nerve palsy?
a. Complete with pupillary involvement
b. Complete with pupil sparing
Complete 3rd nerve palsy – eye is out & down – ptosis, SR affected, IR, IO & MR
Only muscles which are working are LR & SO
Describe a “pupil-sparing” IIIrd nerve palsy?
- Refers only to a complete 3rd nerve palsy in which all EOMs it serves are w/o any activity & in which pupil remains of normal size & reactivity
If 3rd nerve is not affecting pupil likely to be vascular in aetiology (but can never be sure & px needs to be scanned)
Microvascular 3rd nerve palsy is not going to give a dilated pupil but will have a 3rd nerve palsy
Diabetics commonly get 3rd & 6th nerve palsies
If px is >50 years old then thinking vascular causes – unless told otherwise that they were in a traffic accident or had trauma etc
Describe a IIIrd nerve palsy with an affected pupil?
If pupil is affected, px has ptosis & eye is out and down – this is a 999 emergency – if BV swells (aneurysm) & BV wall becomes too thin then it can pop (if aneurysm bursts) – called a subarachnoid haemorrhage (the px can die)
Symptoms of aneurysms = headaches that feel like head is going to explode
Compressive 3rd nerve palsy is going to give a dilated pupil
Pupillary fibres of 3rd nerve are travelling on exterior walls of 3rd nerve – if something is pressing on it (e.g. enlarged BV) will give px a dilated pupil – 999 straight up in ambulance
Could also be due to trauma but px will report history about this
Which tests should be done in a px with IIIrd nerve palsy?
- BP
- Blood glucose – checking if diabetic – v important now with rise of type 2
- ESR – Erythrocyte Sedimentation Rate (sign of inflammation/infection) – how RBCs sediment – inflammation could be MS, granulomatous disease, rheumatoid arthritis
- CRP – C-reactive protein test measures the level of C-reactive protein (another sign of inflammation) – looking at protein that liver produces
- MRI w/ MRA (MR angiography) or CTA & often catheter angiography as aneurysms or cranial arteries are the concern -> looking for signs of aneurysms – these can be quite dangerous to perform
- If pupil is not involved then do these checks – if pupil is involved then they must have a scan
o If px presents with associated headache then MUST BE SCANNED
What are the most common causes of isolated “pupil-sparing” IIIrd nerve palsy?
- Microvascular ischaemia
- Diabetes
- Other vascular risk factors
- Myasthenia Gravis – can mimic anything
How long does microvascular IIIrd nerve palsy take to recover?
- ~3-4 months
o If has not resolved then likely need a scan
Always err on side of caution - 1st thing that lifts is the eyelid – levator is first to resolve – px then has constant diplopia (horizontal & vertical) – hard to solve with prisms so probably need to occlude
- If not starting to resolve then MRI/MRA
Describe aberrant regeneration and the signs?
- Only happens in two forms of 3rd:
o Compressive 3rd
o Traumatic 3rd
o Slightly in congenital but these pxs will be in the hospital already - Compressive or traumatic – nerve is so damaged than when it starts to regenerate, new nerve fibres starts to grow & they start to supply random muscles – synkinesis
o Pupillary mioses on adduction & lid may go up too (upper lid retraction) - Elevation of upper lid on adduction (gaze-eyelid synkinesis)
- Retraction & elevation of upper eyelid on downgaze (Pseudo Von-Graefe Sign)
- Signs:
o “Pseudo Von-Graefe Sign”: elevation of upper eyelid on downward gaze or adduction
o Adduction of eye on attempted upward or downward gaze
o Limitation of elevation & depression of eye with retraction of globe on attempted vertical movement
o “Pseudo- Argyll Robertson Pupil” – greater constriction of pupil to convergence than to light & gaze-evoked pupillary constriction
Describe the IIIrd nerve nucleus?
- The nucleus of 3rd nerve is a collection of sub-nuclei – one for each of the muscles it supplies
- Isolated IR palsy – may be nuclear – congenital (nucleus has not formed properly)
- R SR subnucleus supplies L SR
- L SR subnucleus supplies R SR
- Both lids are supplied by the one nucleus
- Edinger-Westphal nucleus sits above all other nuclei
o Becomes part of the pupillary fibres
Describe the signs seen with a unilateral lesion of entire IIIrd nerve nucleus?
a. Complete ipsilateral 3rd nerve palsy with pupil involvement
b. Bilateral ptosis
c. Bilateral elevation deficit
Once see someone with a ptosis then can assume SR under action on both sides
MS is an e.g. of inflammatory lesion aged 21-40 years
Describe fascicular IIIrd nerve palsy?
- 3rd nerve palsy results in ipsilateral paresis of following:
o Adduction (MR)
o Elevation (SR & IO)
o Depression (IR)
o Ptosis (levator palpebrae)
o Pupillary dilation (parasympathetic)
o Accommodation paralysis (parasympathetic)
Describe the IIIrd nerve pathway?
- 3rd nerve exits midbrain near medial aspect of cerebral peduncle
- It enters subarachnoid space, where it travels between superior cerebellar artery & posterior cerebral artery (PCA) next to tip of basilar artery, then travels medially along the PCA & lateral to internal carotid artery
- It enters cavernous sinus where it is enclosed within lateral wall, superior to 4th nerve
- It then enters orbit through superior orbital fissure & annulus of Zinn, at which point it divides into 2 divisions
How do you check if VIth and IVth nerves are still working in a IIIrd nerve palsy?
To check a px with a 3rd to see if the 6th is working – get them to abduct their eye – then to check 4th is working, get them to look down & if you see intorsion then 4th nerve is working too
