Week 4 - 3rd nerve Palsy Flashcards
How are 3rd nerve dysfunctions classified?
They are classified into 3 specific categories:
a. partial (paresis, not a palsy)
b. complete (palsy) WITHOUT pupillary involvement (= pupil sparing)
c. complete (palsy) WITH pupillary involvement.
What is the definition of a partial 3rd nerve palsy?
A partial 3rd nerve palsy is when one or more of the extraocular muscles innervated by the 3th nerve are not affected or when there is only paresis of the one or more of these muscles.
What are the two categories of complete 3rd nerve palsies?
a. complete with pupillary involvement
b. complete with pupil sparing
What is meant by “a pupil-sparing 3rd nerve palsy”?
A “pupil-sparing 3th nerve palsy” refers only to a complete 3th nerve palsy in which all the extraocular muscle it serves are without any activity and in which the pupil remains of normal size and reactivity.
What tests should be done when a px over 50 presents with isolated incomplete 3rd nerve palsy AND the pupil is involved?
• BP
• Blood Glucose
• ESR - (sign of inflammation/infection)
• CRP - (C reactive protein test, sign of inflammation)
• MRI with MR angiography
What tests should be done when a px over 50 presents with isolated incomplete 3rd nerve palsy AND the pupil is NOT involved?
• BP
• Blood Glucose
• ESR - (sign of inflammation/infection)
• CRP - (C reactive protein test, sign of inflammation)
Most common cause of isolated “pupil-sparing 3rd nerve palsy”?
• Microvascular ischaemia
• Diabetes
• Other Vascular risk factors
Don’t forget Myasthenia Gravis can mimic too!
How long does it take for microvascular 3rd nerve palsy to resolve?
• Approx 3-4 months
- If not starting to resolve then MRI/MRA
How does Aberrant Regeneration develop?
This will only develop of the aetiology of the 3rd is
• Traumatic
• Compressive
What are the 4 signs of Aberrant regeneration?
• “Pseudo Von-Graefe Sign.” elevation of upper evelid on downward gaze/adduction
• Adduction of the eye on attempted upward or downward gaze
• Limitation of elevation and depression of the eye with retraction of the globe on attempted vertical movement
• “Pseudo-Argyll Robertson pupil”: greater constriction of pupil to convergence than to light and gaze-evoked pupillary constriction
What are the findings when there is a unilateral lesion of the entire 3rd nerve
a. Complete ipsilateral 3rd nerve palsy with pupil involvement.
b. Bilateral ptosis
c. Bilateral elevation deficit.
What results from the 3rd nerve Palsy - Fascicular? (6 total)
Ipsilateral Paresis:
• Adduction (medial rectus)
• Elevation (superior rectus and inferior oblique)
• Depression (inferior rectus)
• Ptosis (levator palpebrae)
• Pupillary dilation (parasympathics)
• Accommodation paralysis (parasympathics)
What is the 3rd Nerve Pathway?
• Exits midbrain near medial aspect of cerebral peduncle
• Enters subarachnoid space, travels between superior cerebellar artery, posterior cerebral artery next to tip of basilar artery, then medially along posterior communicating artery and lateral to internal carotid artery
• Enters cavernous sinus where enclosed within lateral wall, superior to forth nerve
• Enters orbit through superior orbital fissure and annulus of zinn, which point divides into 2 divisions
What is the difference between pupillary involvement, and why is it so important?
• Dilated pupil : Internal carotid artery aneurysm compressing third nerve
• Normal pupil : Distal ischaemia
• Pupillary Fibers run on the surface of the nerve
• Compression therefore is the aetiology and a medical emergency
• Microvascular aetiologies will reduce the blood supply to the muscle fibers running
deep inside the nerve.
