====== 6th Nerve Palsy ======
The sixth cranial nerve has the longest intracranial course of any cranial nerve, making it vulnerable to a wide range of pathologies at multiple anatomical sites (brainstem, subarachnoid space, Dorello's canal, cavernous sinus, and orbit).

===== Causes in Adults =====

=== Microvascular / Ischemic ===

  * Microvascular ischemia (diabetes mellitus, hypertension, atherosclerosis) — the most common cause in adults, accounting for ~37–46% of cases. Typically presents as an acute, isolated palsy that resolves spontaneously over 8–12 weeks  
  * Brainstem infarction (pontine stroke)

=== Neoplastic ===

  * Primary brain tumors (pontine glioma, [meningioma](/rare-disease/meningioma), schwannoma)
  * Clivus tumors (chordoma, chondrosarcoma)
  * Cerebellopontine angle tumors
  * Metastatic disease / leptomeningeal carcinomatosis
  * Nasopharyngeal carcinoma with skull base invasion 

=== Raised Intracranial Pressure (False Localizing Sign) ===

  * Space-occupying lesions (tumor, hemorrhage, abscess)
  * Hydrocephalus
  * Idiopathic intracranial hypertension (pseudotumor cerebri)
  * Cerebral venous sinus thrombosis
  * Meningeal infiltration 

=== Decreased Intracranial Pressure ===
  * Post–lumbar puncture
  * Spontaneous intracranial hypotension (CSF leak)

=== Traumatic ===
  * Head trauma / skull base fracture (~4–7% of cases)

=== Inflammatory / Autoimmune ===

  * Neurosarcoidosis
  * Granulomatosis with polyangiitis (Wegener)
  * IgG4-related disease
  * Tolosa-Hunt syndrome (painful ophthalmoplegia)
  * Giant cell arteritis
  * Systemic lupus erythematosus
  * [[sjogren_syndrome|Sjögren syndrome]]
  * Neuro-Behçet syndrome

=== Demyelinating ===

  * Multiple sclerosis (demyelinating plaque in pons or medial longitudinal fasciculus)

=== Infectious ===
  * Bacterial meningitis
  * Tuberculous meningitis
  * Neurosyphilis
  * Lyme disease
  * HIV
  * Cryptococcal meningitis
  * Varicella-zoster virus
  * Aspergillus

=== Cavernous Sinus Pathology ===

  * Cavernous sinus thrombosis
  * Cavernous sinus infection
  * Cavernous sinus tumors (meningioma, pituitary adenoma, metastasis)
  * Carotid-cavernous fistula

=== Vascular Anomalies ===
  * Aneurysm (posterior circulation)
  * Dural arteriovenous fistula
  * Vascular malformation / hemorrhage

=== Neuromuscular Junction / Muscle ===
  * [[ocular_myasthenia_gravis|Myasthenia gravis]] (may mimic CN VI palsy)
  * Thyroid eye disease (restrictive myopathy)
  * Miller Fisher syndrome (anti-GQ1b antibody)

=== Other ===
  * Wernicke encephalopathy
  * Post-surgical (e.g., after neurosurgical procedures)
  * Idiopathic (~18–23% of cases)

===== Causes in Children =====

The etiologic spectrum in children differs significantly from adults. Microvascular ischemia is rare; neoplasia and raised intracranial pressure are proportionally more common.

=== Neoplastic (Most Common Serious Cause) ===

  * Posterior fossa tumors (medulloblastoma, ependymoma, brainstem glioma)
  * Pontine glioma (diffuse intrinsic pontine glioma)
  * [Acute lymphoblastic leukemia](/rare-disease/acute-lymphoblastic-leukemia) (CNS involvement)
  * Other CNS tumors
  * ~10% of isolated acquired pediatric CN6 palsies are associated with a newly diagnosed brain tumor

=== Raised Intracranial Pressure ===
  * Brain tumors (secondary effect)
  * Hydrocephalus
  * [[pediatric_iih|Idiopathic intracranial hypertension]] (pseudotumor cerebri)
  * Dural sinus thrombosis

=== Post-Infectious / Immune-Mediated ===
  * Anti-GQ1b syndrome (Miller Fisher spectrum)
  * Guillain-Barré syndrome
  * Post-viral (following upper respiratory infection or other viral illness)
  * Post-vaccination
  * These account for ~50% of isolated cases in children

=== Infectious === 
  * Bacterial meningitis
  * Lyme disease
  * Mycoplasma infection
  * Viral infections

=== Demyelinating ===
  * Multiple sclerosis
  * MOG antibody–associated disease

=== Inflammatory ===
  * Neurosarcoidosis
  * Other granulomatous disease

=== Traumatic ===
  * Head trauma / skull base fracture

=== Idiopathic ===
  * No identifiable cause in ~5–30% of pediatric cases
  * Recurrent isolated sixth nerve palsy — rare; young females with left-sided palsy and recent immunization are at higher risk of recurrence. Complete recovery is typical

===== Key Differences: Adults vs. Children =====

^ Feature ^ Adults ^ Children ^
| Most common cause | Microvascular ischemia (~37–46%) | Neoplasia and post-viral/immune-mediated |
| Neoplasia prevalence | ~14% | ~20–25%; ~10% even in isolated palsies |
| Microvascular ischemia | Very common | Very rare |
| Post-viral / post-vaccination | Uncommon | Common (~50% of isolated cases) |
| Spontaneous resolution | ~82% overall | ~59% overall; less likely with tumor etiology |
| Neuroimaging recommendation | Based on clinical context | Recommended in all pediatric cases |

===== References =====

  - [[https://pubmed.ncbi.nlm.nih.gov/35356946|Oh SY. Clinical Outcomes and Etiology of Acquired Sixth Cranial Nerve Palsy. Medicine (Baltimore). 2022]]
  - [[https://pubmed.ncbi.nlm.nih.gov/37154347|Kim HJ, Kim HJ, Choi JY, et al. Etiologic Distribution of Isolated Abducens Nerve Palsy: Analysis of 807 Patients and Literature Review. Eur J Neurol. 2023]]
  - [[https://pubmed.ncbi.nlm.nih.gov/34537871|Hörner S, et al. Sixth Cranial Nerve Palsy: Etiology and Outcome. J Neurol. 2022]]
  - [[https://doi.org/10.1212/WNL.0000000000004330|Meyer C, Wynn DP, Pulst SM, Chen R, Digre K. Clinical Reasoning: A 22-Year-Old Man With Diplopia. Neurology. 2017]]
  - [[https://doi.org/10.1212/01.wnl.0000284607.49249.24|Buracchio T, Rucker JC. Pearls and Oy-Sters of Localization in Ophthalmoparesis. Neurology. 2007]]
  - [[https://doi.org/10.1212/WNL.0000000000207543|Giacobbe A, et al. Clinical Reasoning: Sixth Nerve Palsy. Neurology. 2023]]
  - [[https://doi.org/10.1212/WNL.0000000000012093|Munro NA, Fernandez RL. Clinical Reasoning: Cranial Nerve Palsies. Neurology. 2018]]
  - [[https://pubmed.ncbi.nlm.nih.gov/34417775|Chang MY, Borchert MS. Etiology and Outcomes of Acquired Pediatric Sixth Nerve Palsies. J Neuroophthalmol. 2022]]
  - [[https://pubmed.ncbi.nlm.nih.gov/30760897|Park KA, Oh SY, Min JH, Kim BJ, Kim Y. Acquired Onset of Third, Fourth, and Sixth Cranial Nerve Palsies in Children and Adolescents. Eye (Lond). 2019]]
  - [[https://pubmed.ncbi.nlm.nih.gov/34879720|Hanna FA, Jabaly-Habib H, Halachmi-Eyal O, et al. Sixth Nerve Palsy in Children: Etiology, Long-Term Course, and a Diagnostic Algorithm. J Child Neurol. 2022]]
  - [[https://pubmed.ncbi.nlm.nih.gov/25806679|Teksam O, et al. Sixth Cranial Nerve Palsy in Children. J Pediatr Ophthalmol Strabismus. 2016]]
  - [[https://pubmed.ncbi.nlm.nih.gov/34991161|Kingma HJ, Ceulemans B. Recurrent Isolated Sixth Nerve Palsy in Children. Eur J Paediatr Neurol. 2022]]

{{tag>strabismus ddx}}