Third-nerve palsy
Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management
Definition
Third-nerve palsy (oculomotor nerve palsy) is a neurological condition characterised by impaired function of the oculomotor nerve, leading to ptosis, ophthalmoplegia, and pupillary abnormalities.
Aetiology
- Vascular causes: diabetes mellitus, hypertension, aneurysms (e.g., posterior communicating artery aneurysm).
- Trauma: head injury leading to nerve compression or shearing.
- Neoplastic: compressive lesions such as brainstem tumours, meningiomas.
- Inflammatory: multiple sclerosis, sarcoidosis.
- Infectious: meningitis, tuberculosis, syphilis.
Pathophysiology
- The oculomotor nerve supplies most extraocular muscles, the levator palpebrae superioris, and the pupillary sphincter.
- Lesions affecting the nerve lead to impaired eye movement, ptosis, and, in some cases, pupillary dilation.
- Compression of the nerve (e.g., by an aneurysm) often affects the pupillary fibres, while ischemic causes (e.g., diabetes) typically spare the pupil.
Risk Factors
- Diabetes mellitus.
- Hypertension.
- Atherosclerosis.
- Head trauma.
- Intracranial aneurysms.
- Brain tumours.
Signs and Symptoms
- Ptosis: drooping of the upper eyelid.
- Ophthalmoplegia: limited eye movements, particularly affecting adduction, elevation, and depression.
- Pupillary involvement: fixed, dilated pupil in compressive lesions.
- Diplopia: due to impaired eye alignment.
- Headache: in aneurysmal or neoplastic causes.
Investigations
- Neuroimaging: urgent MRI/MRA or CT angiography if an aneurysm is suspected.
- Blood tests: glucose, HbA1c for diabetic aetiology.
- LP (lumbar puncture): if infectious or inflammatory causes are considered.
- Electromyography (EMG): in suspected neuromuscular junction disorders.
Management
1. Medical Management:
- Glycaemic and blood pressure control: for microvascular causes.
- Corticosteroids: if inflammatory conditions are suspected.
- Antibiotics: in cases of infectious causes.
2. Surgical Management:
- Aneurysm repair: via coiling or clipping if vascular pathology is identified.
- Strabismus surgery: for persistent ophthalmoplegia.
3. Supportive Care:
- Prism glasses for diplopia.
- Ophthalmological follow-up for monitoring recovery.
4. Referral:
- Neurology: for suspected aneurysmal or neurological causes.
- Ophthalmology: for persistent diplopia or ptosis.
- Neurosurgery: if surgical intervention is required for a compressive lesion.