Sixth Nerve Palsy Flashcards
Neurogenic
What deviation is present in a sixth nerve palsy?
Esotropia that increases in distance + far distance, and increases in lateral versions
What’s the pathway for 6th nerve palsy?
- Abducens nucleus in the pons
- Exits the brainstem at the junction between the pons and medulla
- Enters the subarachnoid space and runs along dorello’s canal
- Passes above the tip of the petrous temporal bone
- Enters the cavernous sinus where it runs along side the internal carotid artery
- Enters the lateral aspect of the superior orbital fissure and passes anteriorly to innervate the lateral rectus
Whats the most likely Aeitiology for a 6th nerve palsy in over 50 y/o?
Microvascular Risk Factors (HBP, High Chol, Dia, Age), Stroke, GCA (emergency!!!), Trauma and myasthenia gravis
What’s the most likely Aeitiology for a 6th nerve palsy in adults under 50 y/o?
< 50: Multiple Sclerosis (demyelination), Raised ICP, Space-Occupying lesion, Viral Infection, Trauma, myasthenia gravis, subarachnoid haemorrhage
What’s the most likely Aeitiology for a 6th nerve palsy in children?
Congenital, Space occupying lesion, Viral, Hydrocephalus (need a new shunt!), Gradenigo Syndrome: infection petrous temporal bone, ear discharge from otitis media (infection of middle ear), viral or idiopathic.
What does fascicular damage to the 6th nerve cause ( 2 conditions)
-Demyelination, vascular disease and tumours are likely causes of fascicular damage. The sixth nerve is closely related to the seventh nerve and pyrami dal tracts. Lesions in this region result in:
-Foville’s syndrome with damage to the pontine tegmentum, resulting in partial sixth nerve palsy, ipsilateral facial weakness, loss of taste of the anterior two-thirds of the tongue, ipsilateral Horner’s syndrome, ipsilateral facial sensory loss and ipsilateral peripheral deafness.
-Millard–Gubler syndrome with damage to the ventral pons, resulting in sixth nerve palsy and contralateral hemiplegia, with or without ipsilateral facial paralysis.
Differential Diagnosis:
for a sixth np
- Myasthenia Gravis
- High myopia
- Decompensating distance esophoria
- Duane’s RS – Type 1 (congenital + mechanical)
- Infantile Esotropia (latent nystagmus + DVD)
- Mobeius Syndrome – combined 6th and 7th nerve palsy (facial nerve = no facial expression)
- Medial Wall Fracture (cant abduct)
Extra Clinical Tests:
for a sixth nerve palsy
- Assess Far Distance @ 20m + (cover test and measurements)
- Lateral Version measurements to compare varying size of esotropia (incomitance)
- Smooth Pursuits will show limitation of abduction of affected eye
- Saccades may show hypometria or lag of affected eye
- Lee’s screen will support smooth pursuit findings and allow comparison of palsy at future visits
Symptoms and signs: - Uncrossed diplopia worse to affected side and in distance
- Esotropia increasing in size in dis and on attempted abduction
*Face turn to affected side (R 6th = R face turn) - Field of BSV moved towards unaffected eye
- Long-standing palsies contracture of the MR, often preventing abduction to the midline in total palsy
Non surigcal treatment of sith np
- Prism/Occlusion and wait 4 weeks, if gets worse or swaps to other side = IMMEDIATE SCAN!
- Unless patient has high risks factors indicating microvascular incident then patient most likely requires neuro-imaging to determine cause of palsy. Need to rule out anything sinister like space occupying lesion or multiple sclerosis.
- Allow 6/12 for recovery“
-Prisms split between both eyes, or just put on top section if diplopia only in distance
-Sector occlusion of nasal Prt of specs relieves diplopia on lateral gaze
-Short-term re-establishment of BSV in adults and children. The use of botulinum toxin early in the course of a sixth nerve palsy is effective in re-establishing BSV and relieving symptoms in a significant proportion of patients (Occasionally the effects of the botulinum toxin spill over to affect the superior oblique or inferior rectus muscles, fur ther complicating observation of change. In view of this we routinely perform neuroim aging on all patients in whom the cause is unknown when botulinum toxin injection is planned)
-Achievement of long-term cure. The use of bot ulinum toxin in patients with a relatively con comitant esotropia after good recovery of lateral rectus function can result in good align ment, which is maintained long after the effects of the toxin have worn off; the patient appar ently ‘locks-on’ to BSV - Late-stage treatment The nonsurgical management options in patients with chronic sixth nerve palsy are: maintenance of an AHP; the use of Fresnel prisms or of prisms incorporated in the spectacles; repeat injections of botulinum toxin.
what is the most likely cause a sixth nerve palsy along the pathway, if it was trauma or tumour/compression?
When the sixth nerve travels over the petrous temporal bone
what is the sixth nerve next to in the cavernous sinus?
Below the internal carotid artery and near the ophthalmic branch of the 5th nerve + slightly below the 4th nerve
what type of head posture might a longstanding 6th nerve palsy have?
Face turn to affected side; R 6th = to right?
when is surgical tx for 6th np warranted and important factors?
- When esotropia is not improving and becomes stable for at least 6 months, surgical intervention is warranted.
- Whether the palsy is unilateral or bilateral
- Whether the palsy is total or partial (still some function- FDT).
- Presence or absence of demonstrable binocular single vision (BSV).
surgery for partial 6th np
Type 1: Concomitant deviation: PP <= to 30 Δ: Recession of MR and resection of LR.
PP angle > 30 Δ = surgery on 3 or 4 muscles
Type 2: Incomitant deviation in PP: (to reduce lateral incomitance)
- NO MR contracture: Recession of MR and resection of LR combined with posterior fixation suture (PFS) to contralateral MR
- OR if MR contracture = Ipsilateral MR recession +/- LR resection
Type 3: Incomitant deviation in lateral gaze (no sig angle in PP + no MR contracture): Contralateral MR recession with affected LR resection
surgery for total 6th np
Low risk ASI Preferred option: Full-width lateral transposition of vertical rectus muscles.
- For mild/moderate MR contracture: use botulinum toxin to weaken ipsilateral MR and avoid operating on three rectus muscles simultaneously.
Or use foster suture. (In px < 20 yrs old, rather than using botox, we routinely recess the ipsilateral MR 6 mm)
- For absent MR contracture: no augmentation required to transposition
- For severe MR contracture: staged MR recession
High risk ASI - Outcome: Hummelsheim and Jensen operations reserved for patients at risk of anterior segment ischemia. (Hummelsheim’s operation: lateral transposition of part of the vertical recti; Jensen’s operation: postinsertion union of the vertical recti to the LR ; dissection of anterior ciliary vessels from the vertical recti prior to transposition)
- Use full-width transposition procedure combined with recession or botulinum toxin of medial rectus muscle.
- Botulinum toxin to MR can lead to favourable postoperative 15-20 Δ exo, resulting in long-term alignment.
- Avoid overcorrection by using Foster suture with caution in patients without significant ipsilateral medial rectus contracture.
- Can establish central area of BSV with degree of abduction beyond the midline.
- Postoperative vertical deviation may result from surgical technique, botulinum toxin side-effects, or failure to identify fourth nerve palsy.
