Third Cranial Nerve Palsy

Palsy of the oculomotor nerve causes ptosis, a "down and out" eye and, if the parasympathetic fibres are involved, a dilated non-reactive pupil.

• The pupillary fibres lie superficially on the nerve, so compressive lesions (posterior communicating artery aneurysm, uncal herniation) usually affect the pupil early, while microvascular ischaemia affects the central fibres and spares the pupil.
• Other causes: trauma, cavernous sinus lesions (tumour, thrombosis, carotid cavernous fistula, infection), brainstem infarction, midbrain tumour, giant cell arteritis, meningitis, diabetes, ophthalmoplegic migraine in children, and congenital palsy.

• Complete: ptosis, eye abducted and depressed, loss of adduction, elevation and depression, dilated pupil (6 to 8 mm), loss of accommodation.
• Pupil sparing palsy: ptosis and ophthalmoplegia with a normal reactive pupil, often painful, in patients over 50 with diabetes or hypertension.
• Intorsion on attempted downgaze is preserved because the fourth nerve is intact.
• Painful palsy with a dilated pupil: expanding posterior communicating aneurysm until proven otherwise.
• Aberrant regeneration: lid elevation on adduction or downgaze, pupil constriction on adduction (pseudo-Argyll Robertson), indicating chronic compressive or traumatic cause; not seen in microvascular palsy.
• Associated features locate the lesion: contralateral hemiparesis (Weber), contralateral tremor (Benedikt), cavernous sinus involvement (fifth and sixth nerve signs, proptosis, chemosis).

• Detailed exam of ptosis, pupil size in light and dark, motility, fundus, other cranial nerves, and neurological signs. Exclude myasthenia (fatigability, ice pack test).
• Pupil involving or incomplete palsy with a pupil abnormality, any age: urgent CT angiography or MR angiography, followed by catheter angiography if non-diagnostic. Contrast MRI brain and orbits for cavernous sinus or mass lesion.
• Pupil sparing complete palsy in age over 50: blood pressure, glucose and HbA1c, ESR, CRP and platelets (giant cell arteritis), lipid profile. Imaging if no improvement at 3 months, or earlier if any additional sign.
• Children and young adults: neuroimaging always.
• CSF with MRI if meningitis or infiltrative disease suspected. Acetylcholine receptor antibodies if variable.

• Aneurysm: neurosurgical or interventional referral urgently for endovascular coiling or clipping. Maintain blood pressure below 140 mmHg systolic, nimodipine 60 mg 4-hourly if subarachnoid haemorrhage.
• Giant cell arteritis: methylprednisolone 1 g IV daily for 3 days then prednisolone 1 mg/kg (maximum 60 to 80 mg) daily with gastric and bone protection, before temporal artery biopsy.
• Microvascular: control diabetes, blood pressure and lipids; stop smoking; aspirin 75 mg daily. Expect recovery in 8 to 12 weeks (diabetic palsy can take 3 to 6 months).
• Diplopia: occlusion (patch or frosted lens) or Fresnel prism in the early phase.
• Persistent palsy after 6 months of stable measurements: botulinum toxin (2.5 to 5 units) to the lateral rectus in some, then surgery. Large angle exotropia: lateral rectus recession with medial rectus resection, or superior oblique transposition to the medial aspect of the globe. Ptosis surgery (frontalis suspension or levator procedures) is done after strabismus is corrected, with care for corneal exposure; avoid if Bell phenomenon is poor.
• Corneal protection: lubricants, ointment at night, moisture chamber.