Third nerve palsy

Background

• Third (oculomotor) nerve, innervates eyelid muscles and external ocular muscles (except lateral rectus and superior oblique)
• Nerve also carries parasympathetic fibers on external surface allowing for pupillary constriction
• Palsy causes diplopia except in lateral gaze (lateral rectus innervated by CN VI)
• Ptosis, headache

Causes

• Posterior Communicating Artery Aneurysm
  • Compresses nerve
• Ischemia
  • Diabetes
• Trauma
  • Temporal lobe herniation through tentorium
• Myasthenia Gravis
• Cavernous Sinus Thrombosis
  • often associated with other cranial nerve defecits
• Neurosyphillis
• Autoimmune vasculitis (Lupus)

Clinical Features

• Eye deviates laterally and down
• Pupil exam:
  • If dilated/nonreactive likely secondary to space occupying lesion
  • If pupil is spared likely ischemic etiology
• Loss of accommodation

DDx

• Aneurysm
• Carotid Cavernous Fistula
• Mass
• Ischemia
• Myasthenia Gravis
• Thyroid associated orbitopathy
• Internuclear opthalmoplegia
• Giant Cell Arteritis

Work-up

1. If complete CNIII involvement with ptosis, mydriasis, and ophtalmoplegia:

assume a compressive etiology from an intracraneal anurysm.

Proceed to a CTA brain

1. If complete oculomotor nerve palsy without pupil involvement then strongly favor an ischemic process

Consider a CTA brain

Coronal reconstruction on CT will allow visualization of orbits to rule out compressive process

1. If associated with other neurologic deficits:

CTA brain followed by MRI/MRA brain

Dispo

• If ischemic cause
  • Medical management with most self resolving in 6-8 wks
  • Ophthalmology f/u
• If aneurysm/mass
  • Neurosurgery consult
• If diplopia, no driving or operating heavy machinery

Source

Harwood and Nuss, Rosen's, Emedicine