Causes of 6th Nerve Palsy
The most common causes of 6th nerve palsy in adults are vasculopathic conditions (particularly diabetes and hypertension), trauma, and neoplasms, with specific etiologies varying by age group and clinical presentation. 1
Anatomical Considerations
Understanding the anatomical pathway of the 6th cranial nerve helps identify potential causes based on location:
- The 6th nerve originates in the abducens nucleus of the pons 1
- Within the pons, it courses through corticospinal tracts 1
- It ascends in the subarachnoid space and passes underneath the petroclinoid ligament to enter the cavernous sinus 1
- In the cavernous sinus, it lies in proximity to the intracavernous carotid artery, ocular sympathetics, and cranial nerves III, IV, and V1 1
- Finally, it passes through the superior orbital fissure into the orbit 1
Common Causes by Location
Brainstem (Nuclear/Fascicular)
- Demyelinating diseases (e.g., multiple sclerosis) - often with ipsilateral facial palsy due to 7th nerve involvement 1
- Pontine infarction - may present with contralateral hemiparesis 1
- Brainstem tumors 1
Subarachnoid Space
- Increased intracranial pressure - can cause bilateral 6th nerve palsies 1
- Meningeal processes (infection, inflammation) 1
- Clival chordoma - associated with bilateral involvement 1
Cavernous Sinus
- Carotid artery aneurysms 1
- Inflammatory cavernous sinus processes 1
- Other structural lesions - may present with concomitant Horner's syndrome, 3rd and 4th nerve palsies, or facial pain 1
Orbit
Major Etiologic Categories
Vasculopathic (Most Common in Adults >50)
- Diabetes mellitus 1
- Hypertension 1
- Giant cell arteritis - presents with scalp tenderness, jaw claudication; requires immediate treatment 1
Neoplastic
- Intracranial tumors - presentation may be insidious or acute 1
- Skull base tumors - can cause remitting/relapsing 6th nerve palsy 2
- Most common cause in children and young adults 3, 4
Traumatic
- Head injury with basilar skull fracture 1
- Acute rise in intracranial pressure from intracranial hemorrhage 1
Other Causes
- Demyelinating diseases (e.g., multiple sclerosis) - most common cause of isolated 6th nerve palsy in young adults 4
- Post-viral - diagnosis of exclusion, reported with COVID-19 infection and vaccination 1
- Congenital - rare 5
- Idiopathic - approximately 5% of cases 3
Age-Related Considerations
- In children: Neoplasms are the most common cause (45%), followed by elevated intracranial pressure (15%), trauma (12%), and congenital causes (11%) 3
- In young adults (20-50 years): CNS mass lesions and multiple sclerosis are most common 4
- In adults >50 years: Vasculopathic causes predominate 6
Clinical Pearls and Pitfalls
- Isolated 6th nerve palsy in children is uncommon (9%) but still warrants neuroimaging due to high risk of neoplasm 3
- Spontaneous recovery does not rule out neoplastic origin - skull base tumors can cause remitting 6th nerve palsies 2
- If no recovery is apparent by 6 months, approximately 40% of patients demonstrate serious underlying pathology 1
- Most vasculopathic palsies resolve within 6 months, with about one-third resolving within 8 weeks 1
- Bilateral 6th nerve involvement should raise suspicion for clival chordoma, increased intracranial pressure, or meningeal processes 1
Diagnostic Approach
- Neuroimaging is recommended for all young patients or any patient with other cranial neuropathies, neurologic changes, elevated IOP, or absence of vasculopathic risk factors 1
- In elderly patients with vasculopathic risk factors, evaluation may initially focus on blood pressure, glucose levels, and HbA1c 1
- For elderly patients with temporal tenderness or jaw claudication, check ESR and CRP immediately and consider temporal artery biopsy 1
- Evidence of increased intracranial pressure warrants lumbar puncture (after neuroimaging) 1