Week 3 - 4th Nerve palsy (trochlear) Flashcards
What is IV Nerve palsy trochlear?
• IV Cranial Nerve Palsy causes a palsy of the Superior Oblique muscle.
• Purely a motor nerve
• Unilateral/Bilateral
• Congenital/Acquired
What are the features of IV Nerve palsy?
• Loss of depression
• Loss of incyclotorsion
• Loss of relative abduction
does Superior oblique work at near or distance?
Near! Therefore there will be a larger deviation at near cover test.
What is the anatomy of IV Nerve Palsy? NEEDS FINISHED (SLIDE 6)
• Exits midbrain at dorsal
• Right nucleus becomes left nerve, decussation
- vice versa
aetiology for acquired 4th nerve palsy?
• Closed head trauma accounts for most acquired bilateral palsies and many unilateral
• Microvascular
• Midbrain stroke
• Intracranial tumours
• Myasthenia Gravis
aetiology for CONGENITAL 4th nerve palsy?
• 38.3% Unilateral and 10% Bilateral
• Anatomical anomaly of Superior Oblique Tendon, complete absence, abnormal insertion or excessively lax tendon
• Autosomal dominant form of inherited congenital superior oblique palsy
How does congenital unilateral IVN Palsy present?
• Patient usually presents with an Abnormal head posture in childhood but this can also be detected quite late in life
• All children with an Abnormal head posture should have a full orthoptic/ophthalmological examination to rule out an ocular cause
How does the abnormal head posture present? (unilateral)
• Head tilt unaffected side
• Head turn to unaffected side
• Chin depression
• Facial asymmetry is common in congenital
- secondary torticollis
How does IV nerve palsy present with signs, symptoms and deviations?
• Intermittent diplopia can be the first sign of decompensation as the child ages
• Large Hyperphoria with the Abnormal head posture and larger
- Hypertropia without the Abnormal head posture
• Deviation will usually be greater at near
• Horizontal Deviation of 8^ occurs in 10% of cases
• Excyclodeviation can be seen on fundoscopy
How is the Bielschowsky head tilt test done?
• Performed at 3 metres: not isolate muscle
• Head tilted 30 Degrees to affected side; if the hypertropia increases then SO palsy is present
• Head tilt to the unaffected side should show very little difference in the deviation suggesting a Contralateral Superior rectus under action
• Positive result should be minimum 5^ difference from tilting right to left
What is the Parks 3 step?
• Cover test performed in primary position
• Alternate Cover Test performed on extroversion and laevoversion to assess the greater vertical deviation
• BHHT is then performed tilting 30 degrees right and left and noting the increase in hyper deviation
How to differentiate if the RSO/LSR Palsy?
• Tilt right - right eye is intorted by the superior oblique and the superior rectus
• The depressing action of the SO is balanced by the elevating action of the SR and the eye remains level
• If there is a SO Palsy the elevating action of the SR is unopposed and the hyperdeviation increases
• This is a positive result
How does congenital Bilateral IVN palsy present?
• Usually a V-Pattern Esotropia with Hyperdeviation of the non fixing eye
• Chin depression
• +ve Bielschowsky on either side confirms a bilateral palsy. Reversal of the hypertropia on right and left tilt
• No torsional symptoms but obvious torsion on fundoscopy
What is the presentation acquired IVN palsy?
• Recent onset of vertical diplopia
• No evidence of enlarged Vert Fusion ranges
• Subjective awareness of AHP
• History of trauma
Unilateral palsy symptoms?
• Torsion is rarely complained of in unilateral palsies
• Examination is as before with a positive BHHT
• Hypertropia
• Excyclophoria/tropia
Bilateral palsy symptoms?
• Torsional diplopia is the main symptom. This prevents fusion.
• Excyclodeviation may exceed 10 degrees in PP
• Marked chin depression may be seen
• Reversal of the hypertopia on right and left gaze. With a +ve BHHT on either side
• V Eso pattern
What do you look for during the history symptoms of palsies?
• As with all Neurogenic palsies
• Detailed History - microvascular causes
• History of significant trauma - skull#, loss of consciousness, subdural hematoma
• Full blood count, blood sugar levels, serum lipids
Definition of muscle sequelae?
• When one muscle is weak or limited muscle sequelae develops determined by Hering’s Law of equal innervation and Sherington’s Law of reciprocal innervation
Definition of Hering law?
• When an impulse goes to a muscle, causing it to contract, a simultaneous and equal impulse goes to its contralateral synergist to contract by an equal amount
Definition of Sherringtons law?
• When increased innervation is sent to a muscle to cause it to contract, decreased innervation goes to it’s direct antagonist, which is therefore relaxed.
How does muscle sequelae develop?
• Overaction of the Contralateral synergists according to Hering’s Law of equal innervation. - Immediately
• Overaction of the Ipsilateral antagonist according to Sherrington’s Law of reciprocal innervation - Time
• Secondary inhibition of the Contralateral Antagonist with Hering’s Law. This happens because the overaction of the antagonist in the affected eye requires less innervation -
More Time
What are the muscle sequelae in a 4th nerve palsy?
• Under-action of ipsilateral SO
• Over-action of contralateral IR
• Over-action of ipsilateral IO
• Inhibitional palsy of contralateral SR
How do you Investigate Torsion?
• Can be measured Subjectively or Objectively
• Double Maddox Rod, Synoptophore, Torsionometer, Dulley Adaptation on Lees Screen
• Synoptophore allows you to measure the deviation and torsion together in 9 positions of gaze
•Cyclodeviation is worse on depression and a barrier to fusion
Difference between unilateral palsies and bilateral palsies torsions?
• Unilateral palsies may produce 5/6 degrees of excyclotorsion, which can be fused
• Bilateral palsies typically produce excycotorsion of 15 degrees and this cannot be fused
