IV Nerve Palsy - Trochlear Flashcards
1
Q
Describe a IVth nerve palsy - which muscle is affected?
A
- IV CN Palsy causes a palsy of SO muscle
o 4th CN only supplies ONE MUSCLE - Purely a motor muscle
- Unilateral/bilateral
o More commonly bilateral - Congenital/acquired
o Can sometimes be congenital but not found until later teen or early adulthood
2
Q
What are the features of a IVth nerve palsy?
A
- Loss of depression so affected eye is sitting higher
o Deviation is a hyper deviation that may or may not be controlled – more eso than exo - Loss of incyclotorsion
- Loss of relative abduction
SO works at near – if issue with SO – will have bigger vertical & bigger ESO at near than at distance
Convergence should be completely fine
3
Q
Describe the anatomy of the IVth nerve?
A
- Dorsal midbrain at level of inferior colliculus ventral to cerebral aqueduct
- Decussation – R nucleus becomes L nerve, L nucleus becomes R nerve
- Moves posterior
- Fibres cross over
- Leaves midbrain
- Sweeps round midbrain
- Runs between posterior cerebral artery & superior cerebellar artery
- Enters cavernous sinus below IIIrd & ophthalmic division of Vth
- Enters Superior Orbital Fissure above annulus of Zinn
- Innervates SO
- SO is a complex muscle – lots can happen to it
4
Q
What is the aetiology of acquired IVth nerve palsy?
A
- Closed head trauma accounts for most acquired bilateral palsies & many unilateral
o Due to anatomy bashing head off floor, decelerating injury e.g. traffic accident (whiplash)
o In a child, trauma would be quite common
If have teenager w/ 4th nerve palsy – will not know if congenital or through childhood trauma
If adult develops it with no trauma then could be a vascular reason - Microvascular – hypertension, DM, high cholesterol
- Midbrain stroke
- Intracranial tumours – not common cause of 4th palsy (so not really looking for these pxs to be scanned unless other things ruled out)
- Myasthenia Gravis – can mimic anything – if px has this they will have other signs & symptoms too (ALWAYS WRITE THIS IN THE EXAM!!)
Think off aetiology in age groups – what could apply to this px?
5
Q
What is the aetiology of congenital IVth nerve palsy?
A
- 38.3% unilateral – 10% bilateral
- Anatomical anomaly of SO tendon, complete absence, abnormal insertion or excessively lax tendon
o If due to lax tendon then needs different management - Autosomal dominant form of inherited congenital SO palsy
o Can be familial
6
Q
Describe a congenital unilateral IVth nerve palsy?
A
- Px usually presents w/ an AHP (abnormal head position) in childhood but that can also be detected quite late in life
o AHP needs investigated, look at old photos - All children w/ an AHP should have a full orthoptic/ophthalmological examination to rule out an ocular cause
- AHP in unilateral form:
o Will tilt to unaffected side
o Vertical deviation: e.g R>L –> will always tilt to lower eye
o Head tilt to left – probably have a R 4th nerve palsy
7
Q
Describe a congenital bilateral IVth nerve palsy?
A
- Usually a V-pattern Esotropia with hyperdeviation of non-fixing eye
- Chin depression
- +ve BHTT on either side confirms a bilateral palsy
o Reversal of hypertropia on R & L tilt - No torsional symptoms but obvious torsion on fundoscopy
o No torsional symptoms since brain suppresses it
8
Q
Describe Abnormal Head Posture and facial asymmetry?
A
- Head tilt unaffected side
- Head turn to unaffected side
- Chin depression
- If acquired AHP then will have vertical diplopia
- Longstanding problems will have a compensatory head posture & new problems will not
Facial asymmetry – head tilt, chin depression – head tilt/head posture is what is allowing child to see clearly (not have diplopia) - Facial asymmetry is common in congenital palsies – it develops secondary to torticollis (shortening of neck) – facial asymmetry due to parts of face growing at different rates
- Reduction in distance between lateral canthus & corner of mouth on side of head posture
9
Q
What is intermittent diplopia? Where will the deviation in a IVth nerve palsy be larger? How will you see excylcotorsion deviation?
A
- Intermittent diplopia (at times can fuse, at other times cannot) can be 1st sign of decompensation as child ages – huge ability to have vertical fusion
- Large hyperphoria w/ AHP & larger hypertropia w/o AHP
- Deviation will usually be greater at near
- Horizontal deviation of 8Δ occurs in 10% of cases will be based on what they had before – more common is ESOphoria but if they already had an EXOphoria then they will still have this
- Excyclodeviation can be seen on fundoscopy – will see the discs is tilted in comparison to macula – will barely see this deviation on cover test
10
Q
Compare normal vertical fusion to IVth nerve palsy vertical fusion?
A
A normal px will have 3 dioptres of vertical fusion
Pxs w/ a longstanding or congenital 4th nerve palsy will often have increased vertical fusion (much more than 3 degrees)
Longstanding – could get this nerve palsy at 10 years old then have had it whole life
11
Q
Describe the Bielschowsky Head Tilt Test (BHHT) in IVth Nerve Palsy?
A
- Performed at 3 metres
o This is to not isolate any muscles – if at 6m then favouring distance, if do it a lot closer then favouring near - Target: kay picture or letter on logMAR chart
- Want know which direction the deviation is biggest in
- Head is tilted 30° to affected side & if hypertropia increases then a SO palsy is present
o If head tilted to affected side – eye shoots up – deviation gets bigger (SR now acting unopposed (do not have SO to keep eyes level) - Head tilt to unaffected side should show v little difference in deviation suggesting a contralateral SR under action
- +ve result should be minimum 5Δ difference from tilting right to left
o For it to be a +ve result then would have to measure with prism bars
12
Q
Describe Parks 3 Step Test?
A
- Cover test performed in primary position
- Alternate cover test performed on dextroversion (BEs to R) & laevoversion (BEs to L) to assess the greater vertical deviation – looking left & looking right to see if there is a vertical deviation
- BHHT is then performed tilting 30° right & left & noting the increase in hyperdeviation
13
Q
Describe acquired IVth nerve palsy?
A
- Recent onset of vertical diplopia
- No evidence of enlarged vertical fusion ranges
- Subjective awareness of AHP – px will know it
- BHHT will be +ve if px tilts to affected side
- History of trauma (most common aetiological factor)
14
Q
Describe unilateral IVth nerve palsy?
A
- Torsion is rarely complained of in unilateral palsies
- Examination is as before w/ a positive BHHT
- Hypertropia
- Excyclophoria/tropia
Can fuse ~3 degrees of excyclotorsion/incyclotorsion
Pxs do not know how to complain about torsion – often cannot tell if things are tilted or not
Cannot correct torsion optically – these pxs need surgery – REFER THE PX
15
Q
Describe a bilateral IVth nerve palsy?
A
- Torsional diplopia is main symptom – this prevents fusion
- Excyclodeviation may exceed 10° in PP
- Marked chin depression may be seen
o More likely to be ESO looking down - Reversal of hypertropia on R & L gaze – w/ a +ve BHHT
- V Eso pattern
o The more eso further down you get them to look because SO has no function on abduction anymore - Bilateral palsy biggest issue is the torsion
o Torsion cannot be relieved by prism – occlude one eye (to allow px to have comfortable viewing) – then consider surgery
16
Q
What are the investigations into IVth nerve palsy?
A
- As w/ all neurogenic palsies
- Detailed history – microvascular causes (DM, hypertensive), ask about viruses (could be COVID - more likely causes a 6th palsy but could cause a 4th palsy), enquire about trauma
- Hx of significant trauma – skull# (skull trauma), loss of consciousness, subdural haematoma
- Full blood count, blood sugar levels, serum lipids
17
Q
What is the key presenting sign in a IVth nerve palsy?
A
Vertical problem and a head tilt then think 4th
18
Q
Describe the orthoptic investigation into a IVth nerve palsy?
A
- VA N+D – always in log MAR
- CT N+D w/ & w/o AHP
o Looking to see if AHP helps them – does deviation get bigger?? - OM – record diagrammatically
- BHHT
- PCT N+D+9 positions of gaze
o Measure of angle of deviation (prism cover test) - Less/Hess
- Bagolini Glasses (striated lenses)
o Measuring sensory fusion – checking how they fuse
o If binocular vision then they’ll see 1 light
o If suppressing – will see 1 line - PFR – horizontal & vertical
o Prism Fusion Range
o Concerned if this is increased in Incomitant
o Normal is 3 dioptres - Stereoacuity – TNO/Frisby
19
Q
State Hering’s Law and Sherrington’s Law?
A
Hering’s Law: Law of equal innervation
* When an impulse goes to muscle, causing it to contract, a simultaneous & equal impulse goes to its contralateral synergist to contract by an equal amount
Sherrington’s Law: Law of reciprocal innervation
* When increased innervation is sent to a muscle to cause it to contract – decreased innervation goes to its direct antagonist which is therefore relaxed
20
Q
What is the pattern of muscles affected in IVth nerve palsy and how does this help you determine onset?
A
- Overaction of contralateral synergists according to Hering’s Law of equal innervation: IMMEDIATE
o Know it’s happened within a week - Overaction of ipsilateral antagonist according to Sherrington’s Law of reciprocal innervation: TIME
o week or 2 to a few weeks - Secondary inhibition of contralateral antagonist w/ Hering’s Law – this happens because overaction of antagonist in affected eye requires less innervation: MORE TIME
21
Q
What is the muscle sequelae of a IVth nerve palsy?
A
- Underaction of ipsilateral SO
- Overaction of contralateral IR
- Overaction of ipsilateral IO
- Inhibitional palsy of contralateral SR
If not all steps of muscle sequelae occurred then know it is recent onset
22
Q
What are the four steps of muscle sequelae?
A
- Underaction of ipsilateral agonist (muscle affected)
- Overaction of contralateral synergist
- Overaction of ipsilateral antagonist
- Inhibitional palsy (underaction) of contralateral antagonist
23
Q
What is the difference between SR palsy and SO palsy?
A
SR palsy - ptosis & bigger in distance
SO palsy - no ptosis & bigger at near
24
Q
What are the investigations into a longstanding IVth with sequelae?
A
- Relative concomitance from muscle sequelae – field look similar
- Investigations: Cover test, Ocular motility, prism cover test (D&N – to prove which distance it is bigger in), measure palpebral aperture to assess for proptosis
25
Describe how to investigate torsion?
* Can be measures subjectively or objectively
* Double Maddox rod (cylinders vertical so px has lines horizontal, red/green, give px diplopia w/ prism, get the px to turn trial frame axis until lines appear straight 10° if bilateral, 5° if unilateral – degrees of movement from 0 on trial frame) , Synoptophere, Torsionometer, Dulley Adaptation on Lees Screen
* Synoptophore allows you to measure deviation & torsion together in 9 positions of gaze
* Cyclodeviation is worse on depression & a barrier to fusion
26
How much torsion do unilateral palsies produce vs bilateral palsies?
- Unilateral palsies may produce 5/6 degrees of excyclotorsion which can be fused
- Bilateral palsies typically produce excyclotorsion of 15 degrees & this cannot be fused
27
What is the biggest problem in bilateral IVth? Will a child have a AHP?
- Torsion is biggest problem in bilateral 4th nerve palsy
- Bilateral 4th nerve palsy often asymmetrical
- 4th nerve palsy & superior division 3rd nerve palsy present v similarly
- Children who develop squints & have suppression then they have no reason to develop an AHP
28
Comparing unilateral vs bilateral IVth nerve palsy - describe AHP, BHHT, Hypertropia, Excyclotropia and V Pattern - ?
UNILATERAL:
AHP: contralateral head tilt (face turn, chin depression)
BHHT: +ve (on one side)
Hypertropia: no reversal on versions & >5Δ (bigger, no swap)
Excyclotropia: not symptomatic & less than 10 degrees
V Pattern: uncommon
BILATERAL:
AHP: chin depression
BHHT: +ve (on both sides)
Hypertropia: reversal no versions and <5Δ (swaps from R to L)
Excyclotropia: symptomatic & greater than 10 degrees in acquired palsies
V Pattern: common
29
Comparing congenital vs acquired IVth nerve palsy - describe Facial Asymmetry, AHP, Cyclotropia, Vertical Fusion
CONGENITAL:
Facial Asymmetry: common (more than normal)
AHP: present in photographs
Cyclotropia: not a symptom - no torsion (suppression)
Vertical Fusion: increased
ACQUIRED:
AHP: aware of holding head in an awkward position
Cyclotropia: symptomatic
Vertical Fusion: normal (3Δ - px cannot cope & get diplopia all time)
