Central Nervous system - 7th Cranial nerve palsy

Question 1

What are the salient histories of CN7 PALSY?

Answer 1

• Onset: whether abrupt followed by worsening over the following day (Bell’s palsy).
• Pain preceding or accompanying the weakness (Bell’s palsy).
• The face itself feels stiff and pulled to one side.
• Ipsilateral restriction of eye closure.
• Difficulty with eating.
• Disturbance of taste (due to chorda tympani fibres).
• Hyperacusis (involvement of stapedius muscle in the inner ear

Question 2

What are the important findings in the examination for the CNS7 Palsy?

Answer 2

• Weakness of muscles of one half of the face - patient is unable to screw her eyes tightly shut or move the angle of the mouth on the affected side.
• Loss of facial expression.
• Widened palpebral fissure.

Proceed as follows:
• Look for the following when the patient is unaware of being observed:
-Flatter nasolabial folds on the affected side.
-Mouth on the affected side droops and participates manifestly less while talking.
-The eyelid on the affected side closes just after the opposite eyelid.
• Look at the external auditory meatus for herpes zoster (Ramsay Hunt syndrome).
• Look for parotid gland enlargement.
• Examine for taste (loss of taste with the involvement of chorda tympani).
• Check for hearing (for hyperacusis resulting from involvement of the nerve to stapedius muscle).
• Examine the tympanic membrane for otitis media.
• Tell the examiner that you would like to do the following:
- Test the urine for sugar (diabetes).

Question 3

How would you differentiate between upper and lower motor neuron palsy?

Answer 3

In lower motor neuron palsy the whole half of the face on the affected side is involved.
In upper motor neuron palsy the upper half of the face (the forehead) is spared.

Question 4

What are the causes of bilateral facial nerve palsy?

Answer 4

• Guillain-Barre syndrome.
• Sarcoidosis in the form of uveoparotid fever (Heerfordt’s disease).
• Melkersson-Rosenthal syndrome, which is a triad of facial palsy, recurrent facial oedema and plication of the tongue

Question 5

What are the causes of unilateral facial nerve palsy?

Answer 5

Lower motor neuron (all the muscles of one half of the face are affected):
• Bell's palsy (idiopathic). Recent studies using a polymerase chain reaction have implicated herpes simplex viral infection in Bell's palsy. The incidence of Bell's palsy is 23 per 100 000 individuals per year or about 1 in 60-70 individuals per year. Men and women are equally affected and the peak incidence is between the ages of 10 and 40. Both the right and left sides are affected with equal frequency.
• Herpes zoster.
• Cerebellopontine angle tumours.
• Parotid tumours.
• Old polio.
• Otitis media.
• Skull fracture
Stroke

Question 6

Is the facial nerve a motor nerve or a sensory nerve?

Answer 6

• The facial nerve is predominantly a motor nerve and supplies all muscles concerned with facial expression and the stapedius muscle.
• Uncommonly, it may have a sensory component which is small - the nervus intermedius of Wrisberg. It conveys taste sensation from the anterior two thirds of the tongue and, probably, cutaneous impulses from the anterior wall of the external auditory canal.

Question 7

What do you know of nervus intermedius?

Answer 7

is the sensory or the parasympathetic root of the facial nerve, and is lateral and inferior to the motor root.
- Inside the internal auditory meatus it lies between the motor root and the eighth cranial nerve. The sensory cells are located in the geniculate ganglion (at the bend of the facial nerve in the facial canal) and their nerve fibres enter the pons with the motor root.
- The geniculate ganglion is continued distally as the chorda tympani, which carries taste and preganglionic parasympathetic fibres.
- This nerve consists of contributions from three areas:
• Superior salivary nucleus (in the pons) supplies secretory fibres to the glands.
• Gustatory or solitary nucleus (in the medulla) receives taste fibres via the chorda tympani.
• Dorsal part of the trigeminal nerve receives cutaneous sensation from the external auditory meatus and the skin behind the ear (distributed with the facial nerve proper).

Question 8

How would you manage Bell’s palsy?

Answer 8

• About 50-60% of patients recover spontaneously without deficits,
• others have considerable improvement and
• about 10% have permanent residual deficits.
• Therefore many physicians tend to initiate treatment with steroids only in those with clinically complete deficit or when there is severe pain.
  Treatment includes:
  • Physiotherapy: massage, electrical stimulation, splint to prevent drooping of the lower part of the face.
  • Protection of the eye with lubricating eye drops and a patch during sleep.
  • A short course of dexamethasone 2 mg three times a day for 5 days and tapered over the next 5 days (should be given within 48 hours of onset). (Can used prednisone 50mg daily too)
  • Acyclovir & prednisone is more effective in improving volitional muscle activity and in preventing partial nerve degeneration as compared to placebo & prednisone treatment (Ann Otol Rhinol Laryngol 1996; 105: 371).

Question 9

What are the branches of the facial nerve?

Answer 9

• Greater superficial petrosal nerve (supplies lacrimal, nasal and palatine glands).
• Nerve to stapedius muscle.
• Chorda tympani (supplies taste to anterior two thirds of tongue, submaxillary and sublingual glands).
• Motor branches (exit from the stylomastoid foramen).

Question 10

How would you localize facial nerve palsy?

Answer 10

• Involvement of the nuclei in the pons - associated ipsilateral sixth nerve palsy.
• Cerebellopontine angle lesion - associated fifth and eighth nerve involvement.
• Lesion in the bony canal - loss of taste (carried by the lingual nerve) and hyperacusis (due to involvement of the nerve to stapedius).

Question 11

Mention reflexes involving the facial nerve

Answer 11

• Corneal reflex.
• Palmomental reflex.
• Suck reflex.
• Snout reflex.
• Orbicularis oculi reflex or glabellar reflex.
• Palpebral-oculogyric reflex.
• orbicularis oris reflex

Question 12

Mention a few examples of facial synkinesis

Answer 12

Facial synkinesis means that attempts to move one group of facial muscles result in contraction of associated muscles. It may be seen during anomalous regeneration of the facial nerve. For example:
• If fibres originally connected with muscles of the face later innervate the lacrimal gland, anomalous secretion of tears (crocodile tears) may occur while eating.
• If fibres originally connected with the orbicularis oculi innervate the orbicularis oris, closure of the eyelids causes retraction of the mouth.
• Opening of the jaw may cause closure of the eyelids on the corresponding side (jaw-winking)