Conditions: Facial Weakness or Paralysis

A problem anywhere along the facial nerve may create weakness or paralysis of one or more muscles of the face—a situation with many potential causes, from temporary inflammation to infection, tumor, injury, or stroke.

Facial nerve weakness in general

The left or right facial nerve as a whole may become weak or paralyzed due to trauma, infection, inflammation, tumor, or stroke. Weakness may be complete (paralysis), with no movement at all on the affected side, or partial (paresis), in which some movement remains but is diminished. With complete paralysis of the entire nerve, the forehead does not wrinkle, the eye cannot close, and the corner of the mouth does not move. Individual branches of the facial nerve allow for blinking and closing of the eyelids, moving the lips for speech and eating, and facial expression, so weakness of one or more individual branches affects only the specific muscles the affected branch(es) control. Involvement of a single branch may be a clue that a localized problem, such as a tumor or an injury, is affecting one part of the nerve rather than the whole nerve.

Example of complete Right facial nerve paralysis (all branches) under different expressions and efforts:

Individual branch(es) of the facial nerve

One or more branches of the facial nerve may be dysfunctional, leading to specific muscular weaknesses. While variable from individual to individual, the facial nerve branches are conceptualized as follows: temporal, zygomatic, buccal, marginal mandibular, and cervical.

1. The temporal branch innervates the frontalis muscle, which raises the eyebrows and furrows the brow.

2. The zygomatic branch innervates the orbicularis oculi muscle, which closes the eyelids and holds the lower eyelid snugly against the eyeball.

3. The buccal branches innervate the muscles of the mid-cheek, including those used in smiling, squeezing the cheeks inward toward the teeth, dilating the nostril, and moving the upper lip.

4. The marginal mandibular branch innervates muscles controlling the lower lip, used to hold the lower lip up against the teeth, purse the lips as if to blow out a candle, smile, and make a watertight seal of the lips when eating and drinking.

5. The cervical branch innervates the platysma muscle in the neck. This muscle is less important than others innervated by the facial nerve and causes neck bands that may be considered cosmetically undesirable.

Effects of facial nerve weakness

Depending on how much of the nerve is affected, facial weakness may cause:

• The eye: Difficulty closing the eyelid, drooping of the lower lid, and either watering or dryness. When the eye cannot blink and close normally, its surface may become dry and irritated. The clear front window of the eye (the cornea) may be scratched or damaged, and prolonged dryness can lead to loss of vision in the affected eye.

• The mouth: Drooping at the corner of the mouth, drooling, and difficulty smiling or pursing the lips.

• Speech: Sounds made with the lips, such as “b,” “p,” and “m,” may be harder to pronounce clearly.

• Eating and drinking: Food and liquid may collect in the cheek or spill from the weak corner of the mouth, and chewing may be messier.

• Taste: Taste may be reduced or altered on the front part of the tongue on the affected side (see conditions affecting taste).

• Sound sensitivity: Ordinary sounds may seem uncomfortably loud on the affected side (hyperacusis) because the small ear muscle that normally softens sound is not working. This differs from hearing loss (see conditions affecting hearing).

• Pain: Aching around the ear or jaw is common with some causes.

Bell’s palsy

The most common cause of sudden one-sided facial nerve weakness, but by no means the only cause, is Bell’s palsy. Other conditions that can cause facial weakness include brain tumor, stroke, Ramsay Hunt syndrome, trauma, and Lyme disease.

Bell's palsy is one type of facial nerve weakness or paralysis that results in a temporary inability to move the facial muscles on the entire affected side of the face. Symptoms usually come on quickly, over hours to a few days, and the weakness may be mild or may be complete paralysis. The time from initial symptoms to maximal symptoms occurs within 72 hours, or else the problem is not Bell’s palsy. Along with facial droop, people may notice difficulty closing the eye, changes in taste, increased sensitivity to sound, and pain around the ear. In most cases, the weakness is temporary and improves significantly over weeks to months.

The cause of Bell's palsy is called idiopathic, meaning no specific cause is identified, although it is thought to involve inflammation and swelling of the facial nerve, possibly triggered by a common virus such as the one that causes cold sores. Bell’s palsy can occur at any age and affects men and women about equally. Risk factors include a recent upper respiratory infection, diabetes, and pregnancy. Bell’s palsy is a diagnosis reached after other causes have been considered, and not all facial weakness is due to Bell’s palsy.

Stroke (cerebrovascular accident, CVA)

A stroke, or cerebrovascular accident, is an emergency resulting from lack of blood flow to brain tissue or from bleeding within the brain. Facial weakness is one potential way a stroke may manifest, though other signs may include difficulty speaking (finding the right words or having slurred speech), weakness or numbness of an arm or leg, visual impairment, headache, or confusion.

Because a stroke happens in the brain, the resulting facial weakness differs from a problem with the facial nerve itself (a peripheral cause). The key difference is the forehead. With a stroke (a central cause), the forehead is usually spared: the person can still wrinkle the forehead and close the eye on the weak side, because the brain controls the upper face from both sides. With peripheral facial nerve palsy, such as Bell’s palsy, the whole side of the face is weak, including the forehead. Because sudden facial weakness may be a sign of stroke, it is regarded as a possible medical emergency, particularly when accompanied by weakness elsewhere in the body, difficulty speaking or understanding speech, severe headache, vision changes, or confusion.

Trauma and temporal bone fracture

Injury can damage the facial nerve directly. A blow to the head that fractures the temporal bone (the part of the skull surrounding the ear) may injure the nerve within its bony canal, and deep cuts or penetrating injuries of the face may bruise or sever the nerve or its branches. Weakness may appear immediately or may develop over the following hours to days. When facial weakness appears right after an injury, the timing points to trauma as the cause.

Surgical injury

The facial nerve may be injured during operations near its path, such as surgery on the ear, the parotid salivary gland, or tumors near the hearing and balance nerve. Surgeons take great care to protect the nerve, but because of its location, weakness can sometimes result from these procedures. Depending on the site of the injury, the entire nerve or only certain branches may be affected, as described for zygomatic branch weakness and lower lip (marginal mandibular) weakness. Weakness after surgery is sometimes temporary, from bruising or stretching of a nerve that remains intact, and sometimes lasting, when the nerve has been cut or more severely damaged.

Congenital and other causes

• Congenital facial weakness: Some babies are born with facial weakness, sometimes from pressure on the nerve during delivery and sometimes from conditions present from birth.

• Moebius syndrome: A rare condition present from birth that affects the facial nerves on both sides, limiting facial expression and side-to-side eye movement.

• Sarcoidosis: An inflammatory condition that may affect nerves and cause facial weakness, sometimes on both sides.

• Diabetes: Associated with facial nerve palsy, possibly through effects on the small blood vessels that supply the nerve.

• Guillain-Barré syndrome: An immune condition that causes widespread nerve weakness, often beginning in the hands and feet and moving upward; it may affect the facial nerves, sometimes on both sides.

• Other conditions: Certain other infections (such as HIV, infectious mononucleosis, and syphilis), other inflammatory and autoimmune conditions, and rare inherited conditions may also be involved.

Features that help distinguish the causes

Several clues help separate one cause of facial weakness from another:

• Speed of onset: Sudden onset over hours to days is characteristic of Bell’s palsy, Ramsay Hunt syndrome, and stroke, whereas slowly progressive weakness raises the possibility of a tumor or cholesteatoma.

• Forehead involvement: Weakness of the whole side of the face, including the forehead, points to a problem with the facial nerve itself, whereas forehead sparing with other body symptoms points toward a stroke.

• One side or both sides: Weakness on both sides may be seen with Lyme disease, sarcoidosis, and Guillain-Barré syndrome.

• Accompanying signs: A painful ear rash suggests Ramsay Hunt syndrome; ear pain, fever, and hearing loss suggest an ear infection; a tick bite or expanding rash suggests Lyme disease; and other nerve or body symptoms suggest a stroke or a broader condition.

• Recent events: A head injury or recent surgery near the ear points toward a traumatic or surgical cause.

• Part of the face involved: Weakness limited to a single branch may point toward a tumor or a localized injury.

Typical course, recovery, and complications

The course of facial weakness depends heavily on its cause:

• Bell’s palsy generally has a good outlook. Many people begin to improve within about two to three weeks, and most recover over two to three months, although a portion do not recover completely and have some lasting weakness.

• Ramsay Hunt syndrome tends to be more severe, and recovery is often less complete than with Bell’s palsy.

• Tumors, trauma, and ear disease follow the course of the underlying condition, and recovery varies widely.

• Stroke-related facial weakness recovers along with the stroke and depends on its size and location.

Possible lasting complications of facial nerve weakness include:

• Incomplete recovery, with some permanent weakness or facial asymmetry, which may affect appearance, confidence, and emotional well-being

• Synkinesis: As the nerve heals, its fibers may reconnect to the “wrong” muscles so that movements become linked, such as the eye narrowing when smiling or the mouth twitching when blinking

• “Crocodile tears”: Tearing of the eye while eating, from nerve fibers that have reconnected to the tear gland instead of a salivary gland

• Dry eye and corneal injury: When the eyelid cannot close well, the surface of the eye may become irritated, scratched, or ulcerated, which may harm vision

• Ongoing sound sensitivity or taste changes in some cases