Facial nerve palsy causes weakness or paralysis of the muscles on one side of the face and can significantly affect facial expression, eye closure, speech, and everyday functioning. The most common form of acute peripheral facial nerve palsy is Bell’s palsy, in which facial weakness develops suddenly without another specific cause being identified. However, sudden facial asymmetry is not always caused by Bell’s palsy. It may be associated with other disorders affecting the facial nerve or, in some cases, with a central nervous system lesion such as a stroke. For this reason, appropriate neurological assessment is particularly important.
Facial Nerve Palsy and Bell’s Palsy
The facial nerve is the seventh cranial nerve and controls most of the muscles responsible for facial expression. It is also involved in other functions, including taste in the anterior part of the tongue and regulation of certain glands. Through a small muscle in the middle ear, it also influences the perception of sound intensity. When the facial nerve becomes dysfunctional, weakness or complete paralysis may develop on one side of the face. In Bell’s palsy, symptoms usually develop rapidly, often within hours, and progress over a relatively short period of time.
Symptoms of Facial Nerve Palsy
The clinical presentation depends on the severity and location of the nerve lesion.
The most common symptoms include:
- sudden weakness or paralysis on one side of the face
- facial asymmetry
- drooping of the corner of the mouth
- difficulty smiling
- inability to raise the eyebrow
- flattening of forehead wrinkles on the affected side
- difficulty or inability to close the eye completely
- dry eye or excessive tearing
- leakage of liquids from the corner of the mouth
- difficulty chewing
- changes in taste
- increased sensitivity to sounds (hyperacusis)
- pain around or behind the ear in some patients
The severity can range from mild muscle weakness to complete paralysis of one side of the face.
Causes of Facial Nerve Palsy
Facial nerve palsy can have a variety of causes. In Bell’s palsy, no other clear cause is identified. Inflammation and swelling of the facial nerve, possibly associated with reactivation of a viral infection, are thought to play a role in its development.
Other causes of peripheral facial nerve palsy may include:
- infections, including herpes zoster
- Lyme disease in an appropriate epidemiological setting
- trauma or skull fractures
- middle ear disorders
- tumors or other lesions along the course of the facial nerve
- neurological or systemic disorders
The underlying cause should be investigated particularly when the clinical presentation is not typical of Bell’s palsy.
Diagnosis of Facial Nerve Palsy
The diagnosis of facial nerve palsy is primarily based on the patient’s medical history and a detailed neurological examination. During the examination, the function of different facial muscles is assessed.
The patient may be asked to:
- raise the eyebrows
- close the eyes tightly
- smile
- show the teeth
- puff out the cheeks
The other cranial nerves, muscle strength in the limbs, sensation, coordination, and other neurological signs are also assessed to identify features that may suggest an alternative cause.
Differences Between Bell’s Palsy and Stroke
Sudden facial asymmetry may raise concern about a possible stroke. In typical peripheral facial nerve palsy, both the upper and lower parts of one side of the face are usually affected. The patient may therefore have difficulty raising the eyebrow, closing the eye, and smiling. In some central nervous system lesions, such as a stroke, weakness may be more prominent in the lower part of the face. However, this distinction should not be used alone to exclude a stroke. If facial asymmetry is accompanied by weakness or numbness in an arm or leg, speech disturbance, double vision, severe imbalance, altered consciousness, or other sudden neurological symptoms, immediate emergency medical evaluation is required.
Tests for Facial Nerve Palsy
In a typical case of Bell’s palsy, the diagnosis is usually clinical and extensive investigations are not always necessary. However, further investigation may be required when there are atypical features, recurrent episodes, gradual progression, other neurological symptoms, or inadequate recovery.
Depending on the individual case, investigations may include:
Brain Magnetic Resonance Imaging (MRI): Used to evaluate the course of the facial nerve and exclude other neurological or structural causes.
Computed Tomography (CT): May be used in specific situations, such as when there is a history of trauma or suspected pathology involving bony structures.
Laboratory investigations: These may be performed when the medical history or clinical presentation raises suspicion of a specific infectious, metabolic, or systemic cause.
Treatment of Bell’s Palsy
The treatment of Bell’s palsy should ideally begin as early as possible after the onset of symptoms. Corticosteroids are the main pharmacological treatment and provide the greatest benefit when started early, usually within the first 72 hours after symptom onset, provided there are no contraindications. In selected patients, particularly those with severe or complete facial paralysis, the addition of antiviral therapy to corticosteroid treatment may be considered. When a specific cause is suspected, such as herpes zoster or another underlying condition, treatment is adjusted accordingly.
Eye Protection
Inability to close the eyelid completely is one of the most important problems associated with facial nerve palsy. When the eye does not close fully, the cornea may remain exposed, increasing the risk of dryness, irritation, and corneal injury.
Depending on the severity, management may include:
- artificial tears
- lubricating eye ointment
- appropriate eye protection during the night
- ophthalmological assessment when there is significant corneal exposure or ocular symptoms
Eye protection is an essential part of treatment and should not be neglected.
Rehabilitation of Facial Movement
Most patients with Bell’s palsy experience significant improvement, although the time required for recovery varies. In patients with persistent weakness or incomplete recovery, specialized facial neuromuscular retraining may be beneficial, using exercises adapted to the stage and type of facial dysfunction. Rehabilitation should be individualized. The indiscriminate use of intensive electrical stimulation of the facial muscles is not considered routine treatment for all patients.
Course and Prognosis of Facial Nerve Palsy
The prognosis of Bell’s palsy is generally good, and many patients experience significant or complete recovery of facial nerve function.
The course of recovery depends, among other factors, on the severity of the initial paralysis and the extent of nerve injury.
In some patients, residual problems may include:
- persistent facial weakness
- facial asymmetry
- involuntary muscle contractions
- a sensation of tightness or tension
- synkinesis, in which a voluntary facial movement simultaneously causes an unwanted movement of other facial muscles
Follow-up allows these problems to be identified early and the rehabilitation program to be adjusted accordingly.
Neurological Follow-Up
Reassessment is particularly important when the paralysis is severe, when atypical symptoms are present, or when the expected improvement is delayed. In these situations, reconsideration of the diagnosis, neurophysiological testing, or further imaging may be necessary. Early diagnosis and treatment of facial nerve palsy, appropriate eye protection, and neurological follow-up can contribute to the best possible recovery of facial function and symmetry.