Myasthenia gravis

What is myasthenia gravis?

Myasthenia gravis (MG) is a neuromuscular disorder that affects the nerves that control the voluntary muscles in our bodies. It's a rare condition that causes muscle weakness – most commonly, in the muscles controlling the eyes, facial expressions, chewing, swallowing and speaking. But it can also make the muscles in the diaphragm and chest weaker, causing shortness of breath and occasionally, serious breathing difficulties.

What causes myasthenia gravis?

Myasthenia gravis is an autoimmune condition which means your immune system mistakenly attacks the healthy tissue in your body. In people with myasthenia gravis, proteins called antibodies which usually fight harmful substances in the body, like infections, start attacking the healthy muscles, making them tired and weak.

Doctors don't understand why this happens, but it's linked to a gland in the chest called the thymus gland. In many people with myasthenia gravis, the thymus gland is bigger than usual. Around one in 10 people have an abnormal growth on their thymus gland called a thymoma.

Myasthenia gravis symptoms

Common symptoms of myasthenia gravis include:

• Drooping of one or both eyelids

• Double vision

• Changes or difficulties with facial expressions

• Problems swallowing

• Slurred speech

• Hoarse voice

• Shortness of breath

• Weakness in the arms, legs or neck

• Tiredness

Not everyone will have all the symptoms above. The muscle weakness can change from day to day. Symptoms will increase over time if the condition is left untreated.

How is myasthenia gravis diagnosed?

Myasthenia gravis can be challenging to diagnose. The doctor will ask about your symptoms and your medical history.
They will carry out a physical examination which may involve:

• Checking your reflexes

• Looking at your muscle tone and checking for weaknesses

• Checking your eye movements

• Testing your motor functions, e.g. touching your finger to your nose

• Checking what sensation you have in different areas of your body

Tests for myasthenia gravis may include:

• Blood test – to look for a type of antibody that stops the signals sent between the nerves and muscles. A high level of these antibodies (made by the immune system) usually means you have myasthenia gravis.

• Nerve tests – known as electromyography, it involves inserting small needles into your muscles to measure electrical activity. The recordings show whether signals sent from the nerves to the muscles are being disrupted, which could be a sign of myasthenia gravis.

• CT or MRI scans – to check if the thymus gland in the chest is larger than usual or has an abnormal growth (called a thymoma). Sometimes the brain is scanned to rule out any problems with the brain.

• Edrophonium test – this involves injecting a medicine called edrophonium chloride into the muscle. If you get a sudden, temporary improvement in muscle strength, you likely have myasthenia gravis. There are serious risks associated with this test (like a slow heartbeat and breathing problems), so it's rarely used. If the doctor decides you need an edrophonium test, it will take place at a hospital.

Treatment for myasthenia gravis

There's no cure for the condition, but myasthenia gravis treatments can help keep the symptoms under control. Some people with myasthenia gravis need ongoing treatment, and sometimes may require emergency treatment in a hospital, if their symptoms suddenly worsen.
Myasthenia treatments include:

Medication

A medication, called pyridostigmine, is usually given. This helps the electrical signals between the nerves and muscles, reducing muscle weakness. The effect may only last for a few hours, so it needs to be taken several times a day.

If pyridostigmine doesn't help, the doctor may suggest steroid tablets. Steroids work by stopping the immune system from attacking the signals between the nerves and muscles.

If you're taking steroid medication, you'll be carefully monitored because they can cause side-effects like weight gain, mood swings and a greater risk of infection.

Sometimes steroids are unsuitable for some people. They might not control myasthenia gravis symptoms or may have unpleasant side effects. The GP may suggest an immunosuppressant medication instead which reduces the immune system's activity. But it can take at least nine months for immunosuppressants to take full effect. So you'll also need to take the other medicines listed above at first.

Surgery

Surgery to remove the thymus gland, called a thymectomy, may be recommended. This can improve myasthenia gravis symptoms in some people with a larger thymus than usual.

Symptoms usually improve a few months after the surgery, but it may take as long as two years to get the full benefit.

There are several benefits of surgery, including:

• Reducing the dose of steroids you need to take

• Reducing the chances of needing immunosuppressants

• Reducing the risk of needing hospital treatment due to worsening symptoms

Emergency treatment

Sometimes people with myasthenia gravis find their symptoms get suddenly worse and they may find it difficult to breathe or swallow. This is known as a myasthenic crisis, and it can be life-threatening. When this happens, urgent treatment in hospital is needed and may include:

• An oxygen mask to provide fresh oxygen to the body

• A ventilator to help with breathing

• Intravenous immunoglobulin therapy – donated blood to improve muscle strength

• Plasmapheresis – the blood is circulated through a machine to filter out the harmful antibodies attacking the messages between the nerves and muscles