What Is the Difference Between Myasthenia Gravis and Bell’s Palsy?

Myasthenia gravis (MG) and Bell’s palsy share a few common symptoms. However, they are different conditions with distinct underlying causes. MG is an autoimmune disease that results in weakness in the muscles you can voluntarily control.¹

What causes these conditions

Normally, nerves send chemical messages that fit neatly into receptor sites in the muscles. In some people with MG, the immune system mistakenly targets receptor sites for a chemical messenger called acetylcholine. As the receptor sites are destroyed, the muscles receive fewer nerve signals. This leads to muscle weakness.²

In other people with MG, the immune system disrupts the function of a protein that is key to forming the nerve-muscle junction. Researchers are still trying to find all the different kinds of antibodies that may cause various types of MG.²

While MG can affect many parts of the body, Bell’s palsy affects only the face. This is because Bell’s palsy is caused by injury to or inflammation in the facial nerve. This condition is sometimes associated with MG.³

Symptoms of MG

MG generally affects women younger than 40 and men older than 60. However, it can affect anyone of any age, even children. People with MG experience rapid fatigue and weakness of their muscles. This worsens with activity but gets better with rest.^2,4

MG can affect muscles in the face, neck, arms, and legs. It can cause:²

• Double vision
• Drooping of 1 or both eyelids
• Problems talking, chewing, and swallowing
• Problems breathing

In some people with MG, the thymus gland may become enlarged or develop tumors. The thymus is a small gland in the upper chest that is part of the immune system.²

Symptoms of Bell’s palsy

Bell’s palsy affects men and women equally, usually between the ages of 15 and 60. Symptoms may improve within 2 weeks. However, it may take 3 to 6 months to fully resolve.^3,5

People with Bell’s palsy experience symptoms on 1 or both sides of their face or head. It can cause:^5,6

• Facial weakness, paralysis, or pain
• Sagging eyebrow and eyelid
• Dropping lower part of the face, especially the corner of the mouth
• Drooling and/or trouble swallowing

The onset of Bell’s palsy may be linked to:^3,5,6

• Stress
• Viral infection
• Restricted blood flow the nerve
• Diabetes
• High blood pressure
• Autoimmune disorders

The exact trigger for the inflammation or injury that leads to Bell’s palsy may be unclear. But as the facial nerve swells, its sheath breaks down and this disrupts the ability of the nerve and surrounding muscles to communicate.^5,6

How are they diagnosed?

MG is diagnosed with a variety of tests:⁴

• A physical and neurological examination is given to evaluate muscle strength and tone, coordination, sense of touch, and eye function.
• A blood test will be given to look for abnormal immune markers.
• Electrodiagnostics will be used to repeatedly stimulate nerves and evaluate the response of specific muscles
• Diagnostic scans of the chest will image the soft tissues to evaluate the thymus gland.
• Pulmonary function testing will measure breathing strength.

Bell’s palsy is easier to diagnose. A doctor will perform a physical exam and note whether the person has trouble moving their facial muscles. A test that measures the electrical conductivity of the nerve may also be used to confirm the diagnosis or assess nerve damage.5

What are the treatment options?

Treatment options for Bell’s palsy are usually simple: rest and massage. In some cases, a doctor may prescribe a steroid to reduce inflammation of the facial nerve. People who have trouble fully closing their eye may need special eye drops or protective eyewear. Most people with Bell’s palsy recover their full facial strength.^3,5

MG is long-lasting and there is no cure, but treatments can help. These include:^2,7

• Acetylcholinesterase inhibitors
• Steroids and other drugs that suppress the immune system
• Plasmapheresis
• Intravenous immunoglobulin (IVIG)
• Lifestyle and alternative treatments
• Biologics

Surgically removing the thymus gland (thymectomy) is also a treatment option. This might be recommended whether or not a tumor or enlargement is present.⁷

The good news is that people with MG who get treatment improve over time. Some may experience remission with no symptoms, and they may or may not need continued medicine. Others stabilize with no symptoms but a doctor may still be able to find clinical signs of MG. This is usually weakness in an eye muscle or hip flexor, which may not fully heal.^1,7