Bell's palsy - Diagnosing Bell's palsy

There is no specific test to diagnose Bell’s palsy. But tests can be used to rule out other conditions that cause facial paralysis.

If someone experiences sudden facial paralysis, visit your nearest A&E department immediately or call 999 for an ambulance. It's important to see a doctor to determine the cause.

Studies have also shown that treatment for Bell's palsy is most effective if it's started quickly, within 72 hours of symptoms developing.

Ruling out other conditions

Bell's palsy is diagnosed using a process known as diagnosis by exclusion. Your doctor will look for any evidence that might suggest your symptoms are caused by a different health condition, such as:

stroke
Lyme disease – a bacterial infection caused by ticks
a tumour – an abnormal tissue growth
Moebius syndrome – a rare condition that is present from birth (congenital)
middle ear infection
cholesteatoma (an abnormal collection of skin cells in the middle ear)
head injury

Your doctor will examine your head, ears and neck. They will also check the muscles in your face to determine whether it's only the facial nerve that has been affected.

If your doctor is unable to find evidence of symptoms associated with other conditions, Bell's palsy may be diagnosed.

Further testing

If your doctor is still uncertain, or there are no signs of symptoms improving after a month, you may be referred to an ear, nose and throat (ENT) specialist for further testing. You may have electromyography or an imaging scan. These are explained below.

Electromyography

During electromyography (EMG), a thin needle electrode is inserted through the skin and into your muscle. A machine called an oscilloscope is then used to measure the electrical activity in your muscles and nerves. The information provided by an EMG can be used to assess the extent of any nerve damage.

Imaging scans

Imaging scans such as magnetic resonance imaging (MRI) may be used to determine the cause of the pressure on your facial nerve. MRI scans use radio waves and a strong magnetic field to produce a detailed image of the inside of your body.

A computerised tomography (CT) scan may also be used to detect other causes of your symptoms, such as an infection or tumour. A facial CT scan may also be carried out to rule out facial fractures.