All you need to know about facial nerve palsy
Facial nerve is the seventh cranial nerve. Its motor fibers originate in the brainstem between the medulla and pons and enter a bony canal in the skull known as internal auditory canal (IAC). It exits the skull in front of the ear to finally reach the facial muscles, where is splits into several branches.
Why we need intact facial nerve?
Following are the major functions of facial nerve:
- Movement of facial muscles
- Controls expressions
- It carries fibers that give taste and sensation to the tip of the tongue.
- It also carries nerve fibers to tear glands.
As facial nerve serves several functions, we can now imagine its importance. It is also known as the “nerve of face” because it controls our facial expressions and movements. Our expressions represent our feelings.
What is facial nerve palsy?
Palsy is a complete or partial paralysis of any body part. Facial nerve palsy is complete or partial paralysis of facial muscles resulting in expressionless and asymmetric face.
Levels of facial nerve palsy
The chief or principal part of facial nerve is its nucleus. This nucleus lies in the pons. Nucleus is actually group of cell bodies of facial nerve. So, we divide facial nerve palsy on the basis of its nucleus level, as follows:
- Supranuclear palsy
- Infranuclear palsy
The supra nuclear palsy or paralysis means the lesion lies above the nucleus of facial nerve in pons. It causes weakness of lower part of the face and Upper part is spared because of its bilateral representation in the cerebral cortex.
Characteristic signs of supra nuclear palsy includes:
- There is a paralysis of the face of muscles, opposite to the side of lesion.
- Muscles of the forehead are spared, so the patient is able to make furrows over the forehead on looking upward.
In Infranuclear palsy the lesion lies below the nucleus of facial nerve. It means involvement of facial nerve in pons or along its path from pons to its exit. The lesion must be either in the pons, or outside the brainstem (bony canal, posterior fossa, middle ear or outside skull).
- The muscles of facial expression get completely paralyzed on one side.
- The face seems asymmetrical and on the normal side it seems drawn up.
- Loss of movements and expressions of affected side.
- Disappearance of wrinkles from the forehead. On smiling the mouth deviates towards normal side.
It is an Idiopathic facial nerve paralysis which is usually unilateral or bilateral, self-limiting and is of rapid onset. Bell’s palsy is characterized by inflammation of the facial nerve or its nerve sheath. Rapid onset of paralysis (that often occurs overnight) is its hallmark. It is the most commonly seen facial nerve palsy.
Mostly cause of Bell’s palsy is unknown.
Bacterial and viral infections can cause palsy. These include:
- Herpesvirus (type 1)
- Herpes zoster virus (Ramsay Hunt syndrome)
- Lyme disease
- Otitis media or cholesteatoma
Head or face injuries can lead to paralysis of facial nerve. For example:
- Fractures of the skull base
- Fracture of temporal bone
- Hematoma after acupuncture
Tumors of face and brain (whether benign or malignant) can be responsible for facial nerve palsy. Such tumors include:
- Facial neuromas
- Congenital cholesteatomas
- Acoustic neuromas
- Parotid gland neoplasms
- Metastases of other tumours
- Posterior fossa tumours
- Parotid gland tumours
- Facial schwannomas
- Intracranial tumours
Diseases involving brain can lead to facial nerve paralysis in brain. Possible diseases are listed as follows:
- Multiple sclerosis
- Guillain-Barre syndrome
- Diabetes Mellitus
Cerebrovascular disease like stroke is one of the main causes. Infarction can affect facial nerve fibers or its nucleus.
- Sjogren’s syndrome
- Melkersson's syndrome.
- Facial weakness
- Loss of taste
- Hypersensitivity to some sounds
- Dryness of face and mouth
- Change of taste on the affected side
- Rarely, drooling/drooping of saliva
- Difficulty in closing eyes
- Difficulty in making expression
- Difficulty in eating
- Weakness or Twitching of the muscles in the face
- Inability to blow cheeks
- Pain behind the ear or on one side of face
- Irreversible blindness can be prevented by using lubricating drops hourly or eye ointment at night.
- Botulinum toxin may also be required temporarily
Steroids increase recovery. They are beneficial if given within 72hours. The usual amount is one milligram per kilogram body weight of prednisolone (a steroid) per day for 7 to 14 days. Use of steroid is of less value in children.
Antivirals like acyclovir given in conjunction with steroids increase recovery. Doses of the antivirals will vary with the drug chosen.
Physiotherapy is beneficial to some individuals with Bell’s palsy as it helps to maintain muscle tone of the affected facial muscles and stimulate the facial nerve. Physiotherapy techniques help to prevent permanent contractures of the paralyzed facial muscles. In order to reduce pain heat can be applied to affected side.
Surgical decompression can be done for those patients not responding to above line treatments; however, there is substantial risk of hearing loss with this surgery.
Followings are the possible surgeries:
- Cosmetic surgery helps to elevate mouth.
- Nerve repair or nerve grafts: Facial nerve regenerates at a rate of 1mm/day. In this procedure we do direct microscopic repair of damaged or cut nerve.
- Nerve transposition: In nerve transposition hypoglossal nerve is connected (12th cranial nerve) to the existing facial nerve. The patients can then train themselves to move their face by moving their tongue.
- Sling procedure: In muscle transposition the temporalis muscle or masseter muscle is moved down and connected to the corner of the mouth to allow movement of face.
- Other procedures: In reconstructive surgery following facial nerve palsy these procedures (a brow lift or facelift, partial lip resection, eyelid repositioning, lower eyelid shortening, upper eyelid weights, or eyelid springs) can also be done.
Tests for facial nerve
- Ask the patient to look towards ceiling with head kept in front and unmoved by the examiner. If the patient is having lower motor neuron palsy he will be unable to raise the eyebrows and to wrinkle the forehead.
- Ask the patient to whistle, affected person will not be able to do.
- Ask him to smile; the mouth is then drawn towards healthy side.
- Ask him to shut his eyes as tightly as he can, affected eye will not close.
Mouth inflation test
Ask him to inflate his mouth. Tap with the finger in turn on each inflated cheek. Air easily escapes out from the affected side.
- Fasting glucose level. These tests are done to rule out diabetes, lyme disease, ramsay hunt syndrome.
In first three days no changes are detected by electrodiagnostic study but over the next weeks a steady decline of electrical activity occurs.
Maximum stimulation test (MST)
In this a device “Hilger Monitor” is used. The test determines the amount of current that can be tolerated on the normal side.
In this test electrical stimulus is given across the skin and electrical activity of muscle is recorded. The response of two sides is measured, and should be within 3% in normal people.
EMG is a technique that amplifies and records the voluntary muscle electrical responses. EMG fibrillations occur in lower motor palsy.
Evoked electromyography (EEMG)
EEMG is decreased or absent in infranuclear palsy.
Motor unit action potential (MUAP)
MUAP is decreased or absent in infranuclear palsy.
MRI and CT-Scans
These are done to rule out tumors.
These tests help to diagnose Lyme disease, herpes and Zoster disease if these are the cause.
Schimer’s tear test
This test reveals a reduced flow of tears on the side of palsy.
It is an audiological test, it will be absent if the stapedius muscle is affected (as facial nerve also supplies stapedial muscle).
This reflex involves consensual blinking of both eyes in response to stimulation of one eye. It will be present only if facial nerve is working properly.
- 70% of people with facial nerve palsy recover completely. Improvement starts after 2-3 weeks however full recovery occurs in 3-6months.
- In 20-30% of people nerve damage is severe and these people are left with a certain degree of permanent facial paralysis.
- In 5% of people complete and permanent damage occurs.
Poor prognostic features
- Severe degeneration of the nerve.
- No signs of recovery by three weeks.
- Age >60 years.
- Severe pain.
- Ramsay Hunt syndrome (herpes zoster virus).
- Association with hypertension, diabetes, or pregnancy.
About 1-2 in 10 experience long term complications of Bell’s palsy, which may include one of the following:
- Chronic loss of taste (ageusia): This can happen if damaged nerve does not repair properly.
- Chronic facial spasm (contracture): If facial muscles remain permanently tense, facial disfigurement occurs called as contracture. In this eye become smaller, the cheek become bulky, or the facial line between the nose and the mouth become deeper.
- Speech complications: This can occur as a result of damage to facial muscles.
- Eye-Mouth Synekinesias: When the person blinks his eyes, the angle of mouth rises
- Eye Drying and Corneal Ulceration: Corneal ulceration can occur when the eyelid is too weak to close completely. It can also occur as a result of reduced tear production, which can lead to infection and can cause blindness.
- Crocodile Tear Syndrome: It is defined as “tears when eating”. This is due to improper regeneration of facial nerve.
- Arterial thrombosis occurs in 5%
- Venous thrombosis occurs in 3%
- Complete arterial and venous occlusion occurs in 1%
- Hematoma occurs in 3%
- Failure of muscle transplantation in occurs 4%
- Muscle necrosis occurs in 1%
|Michal Vilímovský (EN)
|March 24, 2014 at 10:48 AM
|Next scheduled update:
|March 24, 2016 at 10:48 AM