Diagnosing Facial Nerve Paralysis

Facial nerve paralysis is an inability to move the muscles that control smiling, blinking, and other facial movements. This condition can affect a person’s ability to convey emotion. Most of the time, facial paralysis is limited to one side of the face.

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Paralysis can occur if any part of the facial nerve, called the seventh cranial nerve, becomes inflamed or damaged. The facial nerve has branches throughout both sides of the face and controls many muscle groups, including those in the brow, eyelid, cheek, and lips. A person may also experience paralysis if the area of the brain that sends electrical signals to facial muscles is damaged.

NYU Langone otolaryngologists—also known as ear, nose, and throat (ENT) doctors—specialize in diagnosing facial nerve paralysis. An early diagnosis can dramatically improve the chances that doctors can restore muscle function.

Symptoms and Causes

Symptoms of facial nerve paralysis include drooping skin around the brow, eye, cheek, and mouth. When a muscle loses motor function, it relaxes completely, and the skin above the muscle relaxes as well. Some people may still have partial control over facial muscles or experience muscle spasms or twitching, while others cannot move any muscle on the affected side of the face.

Because the condition may prevent you from closing your eyelid, you may develop dry eye and other eye problems. Facial nerve paralysis may also interfere with eating and talking.

Facial nerve paralysis can be congenital, meaning a person is born with it. But most of the time, the condition occurs in adults as the result of damage to the facial nerves.

One of the most common causes is Bell’s palsy. This type of facial paralysis usually develops suddenly and affects only one side of the face. The cause may be swelling in the facial nerve, which temporarily restricts its blood supply. The nerve almost always recovers, and facial paralysis typically goes away on its own within a year.

Other causes of sudden one-sided facial nerve paralysis include a traumatic head injury, which may damage the seventh cranial nerve; a stroke, which occurs as a result of a loss of blood supply to the brain stem; a viral infection, such as herpes simplex or herpes zoster; or, more rarely, Lyme disease.

Sometimes, facial nerve paralysis develops slowly. Muscles on one side of the face gradually lose movement over a period of weeks or months. In this instance, the cause may be a growth on the seventh cranial nerve, such as a facial nerve schwannoma. This slow-growing, noncancerous tumor may press on the nerve and cause increasing paralysis in facial muscles.

Rarely, a cancerous tumor located near the facial nerve or in the area of the brain that sends signals to facial muscles causes paralysis. In some circumstances, surgery to remove a growth may result in facial nerve paralysis.

Less commonly, a neurological disorder or virus may cause complete paralysis by damaging nerve tissue on both sides of the face. Guillain-Barré syndrome, in which the body’s immune system attacks nerve tissue, is one example.

Diagnostic Tests

Doctors at NYU Langone may use one or more diagnostic tests to determine the cause of your symptoms. Based on the results of these tests, your doctor decides if further evaluation is necessary.

Physical Examination

Your doctor visually examines your face to assess the extent of paralysis. He or she asks when you first noticed symptoms, how quickly paralysis developed, and whether you have any muscle control of the affected area of your face. The doctor also asks whether you have any other symptoms, such as hearing loss or tinnitus, a persistent ringing in the ears. The seventh cranial nerve travels through parts of the skull alongside the eighth cranial nerve, which controls hearing, so these symptoms may occur at the same time.

Tell your doctor if you’ve had any recent insect bites, have spent time in areas known to have ticks, or have been recently diagnosed with a viral infection.  

MRI Scan

MRI scans use radio waves and a magnetic field to create computerized, three-dimensional images of soft tissues in the body. Doctors use an MRI to examine the entire facial nerve. This imaging test also allows a doctor to identify swelling or a growth on or near the nerve.

Your doctor may recommend a type of MRI that uses a contrast agent, or dye, called gadolinium. When the dye is injected into the bloodstream, it travels to the facial nerve, highlighting areas of inflammation.  

Stapedius Reflex Test

The stapedius reflex test is a type of hearing test that audiologists—specialists who study hearing loss, balance problems, and related disorders—use to assess damage to the seventh cranial nerve.

During the test, an audiologist uses noise to stimulate the stapedius muscle, a tiny muscle in the middle ear. The nerve that controls facial muscles also controls the stapedius muscle. A doctor may be able to pinpoint the location of a problem on the facial nerve based on whether the stapedius muscle responds to the test. If this muscle does not respond, it may indicate that the area of the facial nerve that controls the stapedius is affected.


Electroneurography is a test used to evaluate the function of peripheral nerves, which include the facial nerve. Ideally, this test is performed within 14 days of the onset of paralysis. The results help doctors determine whether further testing or intervention may be required.

To perform this test, an audiologist places several electrodes on the face and at the base of the ear on both sides of your face. The electrodes are flat, adhesive discs that stick to the skin and are attached to a machine that produces a low electrical current. The sensation may tingle but is not painful.

A doctor stimulates the facial nerves and measures the muscle response to stimulation. The results help doctors determine whether the nerves can return to full function without intervention. If the paralyzed muscles display less than 10 percent of the function that healthy muscles show on the other side, this may suggest that the paralysis may be permanent.

Your doctor may conduct this test two or three times during the weeks after diagnosis to assess whether nerve function is improving.


An electromyogram measures the electrical impulses transmitted along nerves and muscle tissue. This test helps doctors evaluate weakness or paralysis in the facial muscles or nerves.

During an electromyogram, a doctor inserts small, thin needle electrodes through the skin and into facial muscles that correspond to specific nerves. He or she then asks you to move these muscles if you can. The signals recorded when each muscle contracts can indicate which nerves are affected and whether a nerve injury has caused muscle paralysis. The test is also occasionally used after paralysis to determine whether a nerve is recovering.

Blood Test

Occasionally, a doctor may recommend a blood test to determine if a virus or an infection may be the cause of facial nerve paralysis. A specialist draws a small amount of blood and sends the sample to a laboratory for testing. Test results are usually available in a few days.

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