Causes of myasthenia gravis

Myasthenia gravis is caused by a problem with the transmission of nerve signals to the muscles.

It's an autoimmune condition, which means the body's immune system (specific antibodies) attacks its own tissues.

Nerve signals

Nerve signals travel down the nerves and stimulate the nerve endings to release a chemical substance called acetylcholine.

When acetylcholine comes into contact with specific receptors on the muscle membrane, the receptors are activated and cause the muscles to contract (tighten).

However, in myasthenia gravis the immune system produces antibodies (proteins) that block or damage the muscle acetylcholine receptors, which prevents the muscles contracting.

The disruption between your nerves and muscles means your muscles become weak and easily tired.

The thymus gland

It's not fully understood why some people's immune systems produce antibodies that act against the muscle receptors.

However, it's thought the thymus gland, which is part of the immune system, may be linked to the production of the antibodies.

During infancy, the thymus gland is large and gradually increases in size before getting smaller during adulthood.

However, some adults with myasthenia gravis develop abnormal enlargement of the thymus gland. In around 10% of people, there's evidence of a thymus gland tumour (thymoma). This is more common in older people.

Content supplied by the NHS Website

Medically Reviewed by a doctor on 26 Mar 2015