Third Nerve Palsy

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | References

Definition

Third nerve palsy, also known as oculomotor nerve palsy, is a neurological condition characterised by the dysfunction of the third cranial nerve, which affects eye movements, pupil constriction, and eyelid elevation.

Aetiology

Third nerve palsy can be caused by various factors, including:

• Vascular causes (e.g., diabetes, hypertension)
• Aneurysms, particularly of the posterior communicating artery
• Trauma to the head
• Infections (e.g., meningitis)
• Neoplasms (e.g., brain tumours)
• Inflammatory conditions (e.g., multiple sclerosis)
• Idiopathic (unknown cause)

Pathophysiology

The third cranial nerve controls several eye muscles, including the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles, as well as the levator palpebrae superioris muscle. Dysfunction of this nerve can lead to impaired eye movements, ptosis (drooping eyelid), and pupil abnormalities. Ischaemic causes often spare the pupil, whereas compressive causes (like aneurysms) frequently involve the pupil.

Risk Factors

• Diabetes
• Hypertension
• Atherosclerosis
• Smoking
• Head trauma
• Infections and inflammation

Signs and Symptoms

Common signs and symptoms of third nerve palsy include:

• Ptosis (drooping eyelid)
• Diplopia (double vision)
• Eye deviated down and out
• Pupil dilation (if the pupil is involved)
• Difficulty moving the eye inwards, upwards, or downwards

Investigations

• Clinical history and physical examination
• Pupil examination to assess involvement
• Blood tests to check for diabetes, hypertension, and other systemic conditions
• Imaging studies:
  • MRI or CT scan of the brain to identify structural causes such as aneurysms or tumours
  • Magnetic resonance angiography (MRA) or CT angiography (CTA) to assess for vascular abnormalities
• Lumbar puncture if an infectious or inflammatory cause is suspected

Management

Primary Care Management

• Immediate referral to a neurologist or ophthalmologist: For further evaluation and management
• Management of underlying conditions: Such as controlling blood sugar levels in diabetes or blood pressure in hypertension
• Pain management: Oral analgesics such as paracetamol or ibuprofen if there is associated pain

Specialist Management

• Treatment of the underlying cause:
  • Surgical intervention for aneurysms
  • Antibiotics for infections
  • Immunosuppressive therapy for inflammatory conditions
• Prism glasses or occlusion therapy: To manage diplopia
• Strabismus surgery: In cases of persistent eye misalignment
• Regular follow-up to monitor recovery and manage any complications

References

1. NICE. (2024). Oculomotor Nerve Palsy: Diagnosis and Management. Retrieved from NICE
2. NHS. (2023). Third Nerve Palsy. Retrieved from NHS
3. British Medical Journal (BMJ). (2022). Third Nerve Palsy: Diagnosis and Management. Retrieved from BMJ
4. American Academy of Ophthalmology (AAO). (2021). Clinical Practice Guidelines: Third Nerve Palsy. Retrieved from AAO

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