CN VI Palsy Flashcards by Sarah W

In order to be considered comitant, what is the tolerance in different fields of gaze?

5 PD

decompensating phorias and congenital phorias tent to be comitant

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what kind of problem is associated with noncomitant deviation?

muscle or nerve

“n”oncomitant= “n”erve

devation is largest in direction of action of the affected muscle

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What are 2 ways to test for comitance?

ACT 9-Diagnostic Action Fields; Maddox Rod

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when quantifying versions

What is the +/- scale?

(+)= overacting muscle
(-)= underacting muscle

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When quantifying versions

What is the 1-4 scale?

1= minimal OA/ UA
4= gross/ marked OA/ UA

UA: does not cross midline; OA: iris buried under eyelid

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What are the potential causes of an underacting EOM?

(-)UA

Mechanical, Paresis secondary to trauma, Innervational

Mechanical: tendon/ligament abnormality; faulty EOM insertion; scar formation s/p EOM Sx; Paresis: neurologic/ cranial nerve damage; direct trauma to muscle; innervational: impairments to CN III, IV, VI

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What are the potential causes of an overacting EOM?

(+) OA

Mechanical; Idiopathic, Hering’s Law

Mechanical: faulty EOM insertion

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If palsy improves when affected eye is fixating (normal eye is covered) is it paretic or mechanical?

Paretic

ductions>versions

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If Palsy does not improve when affected eye is fixating (normal eye covered), is it paretic or mechanical?

Mechanical

ductions = versions

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What does forced duction testing determine?

If limitation is mechanically restrictive

(-) FDT = no resistance: paretic
(+) FDT = resistance: mechanical

mechanical: tumor, graves disease, muscle entrapment

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What does Force Generation Testing assess?

Active movement of the globe

determines potential force of the muscle

(+) FGT: can’t break resistance: paretic
(-) FGT: can break resistance: mechanical
inversely related to FDT

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FGT/FDT testing has the patient look toward the restricted gaze

FDT

FGT has patient loook in opposite direction of restriction

FGT is testing strength while FDT is passive

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What EOM does CN VI innervate? What is its action?

Lateral rectus; abduction

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Where is the abducens nucleus?

Pons on the floor of the fourth ventricle

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CN VI arises at the pontomedullary junction medial to CN VII

What 2 structures does CN VI pass between?

anterior inferior cerebellar artery and internaly auditory artery

trigeminal nerve also close

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What opening does CN VI travel through to innervate the lateral rectus?

superior orbital fissure

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What 4 structures are involved in abduction and horizontal gaze?

CN VI nucleus, PPRF, MLF, CN VI fascicles

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What is it called when there is an inability to move both eyes in the SAME direction?

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Gaze palsy

What is the signature motility of CN VI palsy?

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Eso deviation at distance

D>N

worse in gaze direction of affected eye; head turns toward direction of paretic muscle to compensate

What are the 6 syndromes of CN VI?

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brainstem syndrome
subarachnoid space syndrome
petrous apex syndrome
cavernous sinus syndrome
orbital apex syndrome
isolated CN VI palsy

In Brainstem syndrome, there is a(n) ipsilateral/ contralateral gaze palsy with ipsilateral/ contralateral facial weakness

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ipsilateral; ipsilateral

Brainstem Syndrome

A lesion to the abducens nucleus causes a ipsilateral/ contralateral gaze palsy due to its proximity to what structure?

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ipsilateral/ paramedian pontine reticular formation

What 3 neurologic signs is fascicular sixth nerve palsy associated with?

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Foville’s syndrome; Raymond syndrome; Millard-Gubler syndrome

What are the three causes of Foville’s syndrome?

Foville’s: CN V, VI, VII and VIII palsies; oculosympathetic denervation and contralateral hemiparesis

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Stroke (older adults)
Demyelination/ MS (younger patients)
Tumor (any age)

What are the 3 causes of Subarachnoid space syndrome?

* anterior inferior cerebellar artery aneurysm * Trauma * Elevated ICP ## Footnote elevated ICP: subarachnoid hemorrhage; hydrocephalus, IIH; Post-LP or Post epidural

# CN VI courses across the bony clivus as it enteres the cavernous sinus If trauma occurs or ICP increases, what happens to CN VI?

It can become compressed and lead to 6th nerve palsy | Once ICP reduces, palsy improves

# (subarachnoid syndrome) What is the most common neurological structural condition?

Chiari malformation | brainstem shifts forward w/ cerebellar tonsils at foramen magnum entranc ## Footnote Flow and reabsorption of CSF blocked: HA and papilledema

What can happen at the Petrous apex that can cause CN VI palsy?

Gradenigo's syndrome; petrous bone fracture; inferior petrosal sinus infection/ thrombosis; tumors (nasopharyngeal carcinoma)

What causes Gradenigo's syndrome?

Otitis Media: middle ear infection

What are the symptoms of Gradenigo's syndrome?

* Recent onset CN VI palsy with earache and facial pain; ipsilateral facial palsy, fever, headache, vomiting, vertigo * Ipsilateral CN VI palsy * V1, V2: ipsilateral facial pain or numbness, decreased corneal sensation * +/- facial nerve: ipsilateral facial palsy

What is the management of Gradenigo's Syndrome?

* MRI imaging (T2 weighted) * Culture ear drainage * CBC with diff * CRP | Tx: high-dose Ab treatment ## Footnote cases of high-risk inflammation: mastoidectomies and petrosectomies

When a tumor erodes through the petrous bone and affects CN VI and the SPG, what else is affected?

parasympathetic fibers of CN VII | innervation of lacrimal gland ## Footnote cause decreased tearing on ipsilateral side

If Cavernous Sinus syndrome is caused by Aneurysm of the ICA, what nerve is affected first?

CN VI

What are ocular signs of Orbital Apex Syndrome? ## Footnote seen in assocation with other CN palsies and vision loss due to CN II

ptosis, proptosis, conjunctival chemosis/ injection

What is the typical patient profile of an isolated CN VI Palsy?

Patient over 50 years old with history of DM or HTN

What is the onset and prognosis of Isolated CN VI Palsy?

Sudden onset; resolves within 3 months

What is the management of isolated CN VI Palsy?

* Manage systemic risk factors * GCA more common than CN Palsy over 50 years old: Run ESR/ CRP * No Improvement/ worsening: MRI of brain and orbits; MRA/ CTA if vascular process suspected * Under 50: post-viral infection most common * R/o mass lesions or MS: MRI | CN VI most common cranial nerve affected by MS

What is the agenesis of CN VI known as?

Duane's retraction syndrome | congenital: familial motility disorder of horizontal gaze; F>M ## Footnote Aberrant regeneration d/t CN VI not developing properly; LR innervation by CN III: co-contraction of MR and LR

Is Duane's Retraction Syndrome unilateral or bilateral?

Unilateral (80%) | left eye predominance ## Footnote associated with other congenital anomalies: Moebius syndrome; Morning Glory Syndrome and Goldenhar syndrome

Which Duane's type is most common?

Type I | abduction defecit; ET common ## Footnote Type II: adduction defecit; XT common; Type III: abduction and adduction; XT common

In all 3 types of Duane's retraction syndrome, there is a _narrowing/ widening_ of the palpebral fissure

Narrowing

Why does the globe retract with Duane's Retraction Syndrome?

Co-contraction of MR and LR | eye "sucks back" into the globe ## Footnote Right Duane's Type I: right globe retraction when patient looks to the LEFT (Abduction defecit)

What is the management for Duane's Retraction Syndrome?

* No cure: provide education and reassurance * Surgery: reduce angle of strabismus to reduce/ stop compensatory head posture

CN VI Palsy Flashcards

(43 cards)