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Facial Asymmetry: Not Always a Stroke Indicator

Mr. Wong was alarmed one morning when he noticed his mouth muscles uncontrollable, drooling involuntarily, and his face asymmetrical in the mirror, fearing he had a stroke.

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Upon consultation and medical imaging by a neurosurgeon, Mr. Wong discovered his condition was facial paralysis caused by paralysis of the seventh cranial nerve, responsible for controlling facial muscles. After over a month of treatment, he was able to show his "true face" again. Sudden facial droop indeed causes concern. The facial nerve, the seventh pair out of the twelve cranial nerves, can lead to facial paralysis or palsy when damaged, including damage to the brain stem, cerebral cortex's facial motor area, or any associated neural circuits.

Central Facial Palsy Induced by Stroke

Indeed, strokes can cause facial paralysis, with one type being "central" facial palsy, where strokes damage neurons in the cerebral cortex brain stem, or other related neural circuits, rendering them unable to command the facial nerve. However, stroke symptoms are rarely limited to the facial nerve and usually include other localised neurological symptoms such as weakness or numbness in the limbs on the same or opposite side, and swallowing or speech difficulties.


Patients typically have risk factors for cerebrovascular diseases, such as hypertension, diabetes, high cholesterol, atrial fibrillation, or arrhythmias. Moreover, central-type facial paralysis or palsy, indicating damage above the facial nerve nucleus in the brain stem, mainly causes paralysis in the lower half of the face on the opposite side, but the forehead remains active, less affecting eyebrow furrowing.


Central-type facial palsy seldom affects the entire face at once. Another type is "peripheral" facial palsy, with Bell's palsy being the most common, caused by damage to the seventh cranial nerve below the brain stem nucleus, leading to paralysis of the facial nerve on the same side. This results in complete paralysis of the face on the affected side, making it impossible to make facial movements. "Idiopathic facial nerve paralysis," also known as "Bell's Palsy," is the most common form, with statistics showing about 1,000 to 3,000 cases annually among Hong Kong's 7 million population.

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The onset of "Bell's Palsy" progresses rapidly, usually peaking within two to five days, causing paralysis or stiffness in the face, tearing due to the inability to close the eye, and altered taste sensation.

Viral Infection Damages the Nerve

Although "Bell's Palsy" has been described for over 150 years, its exact cause remains unclear, with viral infections damaging the nerve, particularly herpes virus and EB virus, being most commonly associated. Some scholars also believe it could be due to autoimmune disorders.

Peripheral facial palsy occurs indiscriminately regarding gender, age, day or night, or season, but those with viral infections, compromised immunity, or diabetes are indeed at higher risk. Despite the seemingly unavoidable and frightening symptoms of peripheral facial palsy, its recovery outlook is generally good, with about 80 to 85% of patients fully recovering if treated with medication within the first few days of onset. However, about 10% of patients, especially those who delay treatment, may suffer permanent sequelae or not fully recover.

Treatment for facial nerve paralysis typically involves taking high-dose oral corticosteroids for over seven days to reduce inflammation. The use of antiviral medications remains controversial, although some reports suggest faster recovery with their use. However, most patients can heal through the body's natural repair mechanisms without medication. Recovery varies among individuals, generally beginning two weeks after onset, with the recovery period possibly extending over one to two months or longer.

Firefly generate a diagraphm of human brain nerve, with a human hand supporting the bottom
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