Seventh cranial nerve palsy: Lower motor neuron type

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53 Seventh cranial nerve palsy

Lower motor neuron type

Instruction

Look at this patient’s face.

Examine the cranial nerves.

Salient features

History

• Onset: whether abrupt followed by worsening over the following day (Bell’s palsy)

• Pain over the 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 (caused by chorda tympani fibres)

• Hyperacusis (involvement of stapedius muscle in the inner ear).

Examination

• Weakness of muscles of one half of the face; the patient is unable to screw his or her eyes tightly shut or move the angle of the mouth on the affected side (Fig. 53.1)

• Loss of facial expression

• Widened palpebral fissure.

image

Fig. 53.1 Facial weakness: central (A) and peripheral (B).

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 tympanic membrane for otitis media

• Tell the examiner that you would like to test the urine for sugar (diabetes).

Diagnosis

The patient has lower motor neuron seventh cranial nerve palsy (lesion), which is idiopathic (aetiology). She is distressed because the condition causes severe disfigurement while talking and has House Brackman grade VI facial palsy (functional status).

Questions

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

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 (Fig. 53.1).

How is facial palsy graded?

House Brackman grades:

I: normal

II: mild dysfunction, slight weakness, slight synkinesis

III: moderate dysfunction, obvious weakness, incomplete eye closure, normal symmetry only at rest

IV: moderately severe dysfunction

V: severe dysfunction, barely perceptible movement, asymmetry at rest

VI: total paralysis.

Advanced-level questions

What are the causes of bilateral facial nerve palsy?

• Guillain–Barré syndrome (p. 338)

• 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 (Hygiea 1928;90:737–41, Z Neurol Psychiatr 1931;131:475–501).

Note: Myasthenia may mimic bilateral facial nerve palsy.

What are causes of unilateral facial nerve palsy?

Causes can be idiopathic (Bell’s palsy; 65%), infective (associated with Bell’s palsy), trauma (25%), neoplasms (5%), metabolic and toxic, plus other rate causes.

Lower motor neuron

All the muscles of one half of the face are affected:

• Bell’s palsy. Recent studies using a polymerase chain reaction (PCR) 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 or women are affected equally and the peak incidence 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.

Upper motor neuron

The forehead is spared:

• Stroke (hemiplegia).

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

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.

What do you know of nervus intermedius?

Nervus intermedius or pars intermedia of Wrisberg 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).

How would you manage Bell’s palsy?

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 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

• early treatment (within 72 h) with prednisolone significantly improves the chances of complete recovery at 3 and 9 months (N Engl J Med 2007;357:1598)

• aciclovir–prednisone is more effective in improving volitional muscle activity and in preventing partial nerve degeneration than placebo–prednisone treatment (Ann Otol Rhinol Laryngol 1996;105:371).

What are the branches of the facial nerve?

• 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).

How would you localize facial nerve palsy?

• 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 (caused by involvement of the nerve to stapedius).

Mention reflexes involving the facial nerve

• Corneal reflex (p. 156)

• Palmomental reflex (p. 204)

• Suck reflex

• Snout reflex (p. 204)

• Orbicularis oculi reflex or glabellar reflex (p. 194)

• Palpebral–oculogyric reflex

• Orbicularis oris reflex.

Mention a few examples of facial synkinesis

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 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).

Have you heard of Möbius syndrome?

It consists of congenital bilateral facial palsy associated with third and sixth nerve palsies and comprises congenital facial diplegia, congenital oculofacial paralysis and infantile nuclear aplasia.

What is the relationship between diabetes and Bell’s palsy?

Diabetes is said to be an important cause in about 10% of cases of Bell’s palsy. In one study, Bell’s palsy was associated with abnormal glucose tolerance in two-thirds of patients (Lancet 1971;i:108, Arch Otolaryngol 1974;99:114).

What parts of the facial nerve must be imaged when facial nerve palsy is suspected?

Both MRI and CT of the temporal bone are used when the facial nerve must be examined.

The following anatomic areas must be imaged when the facial nerve is studied:

• The brain and pons (precentral, postcentral and central gyrus; posterior limb of the internal capsule)

• The cerebellopontine angle

• The internal auditory canal

• The labyrinthine part of the facial nerve canal (VII-1) and geniculate ganglion

• The tympanic part of the facial nerve canal (VII-2)

• The mastoid part of the facial nerve canal (VII-3)

• The stylomastoid foramen and the parotid gland.

Does the facial nerve communicate with other cranial nerves or cervical spinal nerves?

Yes, the facial nerve demonstrates clinically relevant communications with other cranial and cervical spinal nerves.

Site Communication
Internal acoustic meatus Vestibulocochlear nerve
Geniculate ganglion Splenopalatine nucleus, otic ganglion, sympathetic nerves around the middle meningeal artery
Facial canal Auricular branche of the vagus nerve
Splenomastoid foramen Glossopharnyngeal, vagus, great auricular, and auricular temporal nerves
Behind the ear Lesser occipital nerve
On the face Trigeminal
In the neck Cutaneous cervical nerve

Sir Charles Bell (1774–1842) was Professor of Surgery in Edinburgh and a founder member of the Middlesex Hospital in London. He discovered that the anterior and posterior spinal nerve roots were motor and sensory respectively.

James Ramsay Hunt (1874–1937), Professor of Neurology in New York.

PJ Möbius (1853–1907), a German neurologist.

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