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13th February 2025
Cranial nerve palsy
| Cranial nerve | Third (oculomotor) | Fourth (trochlear) | Sixth (abducens) |
|---|---|---|---|
| Cause | Intracranial aneurysm: posterior communicating artery most common
Microvascular disease Trauma: significant injury Malignancy |
Congenital
Trauma: can occur following mild injury Microvascular disease: but less commonly affects CN IV compared to III and VI |
Microvascular disease
Malignancy Trauma: significant injury, e.g. basal skull fracture Increased intracranial pressure |
| Symptoms | Horizontal, vertical or oblique diplopia
Pain at the onset of symptoms is common |
Vertical diplopia and/or torsional diplopia which is worse at gaze towards the paretic superior oblique muscle
Head tilt towards the unaffected side reduces diplopia |
Horizontal diplopia which is worse at distance and at gaze towards paretic lateral rectus muscle
Head turned towards the affected side reduces diplopia |
| Examination | 
Primary position ipsilateral abduction, depression and intorsion. Fixed dilated pupil and ptosis may also be present if a complete palsy |
Primary position ipsilateral hypertropia and extorsion, more pronounced in ipsilateral head tilt |
Primary position esotropia with an ipsilateral abduction deficit |
| Prognosis | Most will recover over weeks to months
Lack of pupil involvement suggests a benign cause which can be observed |
Patients are often observed for several months before treatment is considered as symptoms may improve | Majority will recover spontaneously (3-6 months), more common if unilateral and non-traumatic |
Table 6 Summary of cranial nerve palsies
Figures adapted from icons through The Noun Project, CC BY 3.0
Eyes – Alone forever https://thenounproject.com/icon/eye-1436483/
Cranial nerve palsies are often investigated with neuroimaging, ideally MRI, to identify an underlying cause. This is essential in third nerve palsies with pupillary involvement to exclude an underlying intracranial aneurysm.
Management of cranial nerve palsies includes addressing the underlying cause as well as managing symptoms of diplopia with patching, prisms, strabismus surgery and/or botulinum toxin.
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