Myasthenia Gravis

What is Myasthenia Gravis?

Myasthenia gravis is a rare chronic condition that affects the muscles. It contributes to weakness and affects muscle control, especially in terms of voluntary movements such as moving the eyes, swallowing and making facial expressions.

What causes myasthenia gravis?

Myasthenia gravis is an autoimmune condition, which means that it affects the way the immune system works. Normally, when the body perceives that it is under threat, an immune response is triggered and this helps you to fight off illness and recover. In cases of autoimmune conditions, there is no threat, but the response is still triggered. With myasthenia gravis, antibodies are produced, which cause the muscle receptor cells to become damaged and this prevents signals from the nerves from reaching the muscles. When the signals are not delivered properly, this prevents muscle contraction.

It is not fully understood why autoimmune conditions occur, however there is a belief that the thymus gland may play a part. This gland is part of the immune system and abnormal growth may result in an elevated risk of autoimmune diseases. Tumours known as thymoma can also develop in the gland. This is thought to affect around 10 percent of people with myasthenia gravis.

How is myasthenia gravis diagnosed?

It can be complex to diagnose myasthenia gravis because it is a rare condition and weakness in the muscles can be symptomatic of many different conditions and syndromes. If your GP believes that your symptoms may suggest a risk of myasthenia gravis, you will be referred to a neurologist for further tests.

Tests conducted to either confirm or rule out a diagnosis of myasthenia gravis include:

• Blood tests: blood tests are used to detect antibodies. In cases of myasthenia gravis, the levels of acetylcholine receptor antibodies may be much higher than normal.
• Electromyography (EMG): this test is used to detect issues with the delivery of nerve signals to the muscles and it involves placing an electrode into the muscle.
• Edrophenium test: for this test, an injection of edrophenium chloride is used to prevent acetylcholine from being processed by the body. This produces a sudden spike in muscle power in people who have myasthenia gravis. Usually, other tests are preferred as this test can produce side-effects, including breathing difficulties and an irregular heartbeat.
• Imaging scans: if problems with the thymus gland are suspected, imaging scans such as MRI can be beneficial.

What are the symptoms?

The dominant symptom of myasthenia gravis is weakness in the muscles. It mainly affects the facial muscles, the muscles that control the eyes and the swallowing action. Although the onset of symptoms can be sudden, it can take a long time to diagnose the condition.

Weakness around the eye muscles is usually the first symptom. However, additional symptoms can become apparent in the early days, including difficulty with swallowing, slurred speech and weakness in the neck, arms or legs.

Loss of strength and control around the eye muscles can cause drooping in one or both eyes, blurred vision and double vision. Symptoms tend to be worse towards the end of the day when you feel tired. The eye muscles are affected in around 90 percent of cases of myasthenia gravis. Occasionally, they may be the only muscles affected. If the facial muscles are affected, this can change the way you form facial expressions.

If weakness affects the muscles in the throat, this can make swallowing difficult and affect speech and voice tone. If dysphagia (difficulty swallowing) occurs, this can increase the risk of choking and make you more susceptible to chest infections. Some people may also develop breathing difficulties. However, this is less common.

If the limbs are affected by myasthenia gravis, this can affect movement and mobility and make day to day tasks more difficult. Muscle weakness in the promixal muscles can make it difficult to get up from a sitting position, go up the stairs and clean the teeth.

Treating myasthenia gravis

Treatment can make a very positive difference to muscle weakness and improve symptoms such as pain and reduced mobility. Many people are able to live a normal life, but in more severe cases, ongoing treatment may be required.

Treatments used to ease symptoms of myasthenia gravis include:

• Medication: medications can help to prevent the body from breaking down acetylcholine, which helps the muscles to contract. The most commonly used drug is pyridostigmine. Medication is usually most effective in milder cases and is used temporarily. Possible side-effects include nausea, diarrhoea, muscle twitches and abdominal cramps. Steroid medication may be prescribed if pyridostigmine is unsuccessful.
• Immunosuppressants: if other medications such as pyridostigmine and steroids are ineffective or unsuitable, immunosuppressants may be recommended. Initially, medication may be combined with steroids so that the dose can be gradually lowered.
• Surgery: if the thymus gland is enlarged, a surgical procedure called thymectomy may be carried out to remove the gland. Symptoms tend to improve shortly after treatment and the procedure is effective in the majority of cases. Only around 25% of people experience no benefit from treatment. Research shows little benefit for those who have thymoma (a tumour on the thymus gland). However, surgery may be recommended to prevent cells from spreading.
• Plasmapheresis and IV immunoglobulin therapy: these treatments are recommended for people with severe myasthenia gravis. Plasmapheresis involves using a machine to remove plasma from the blood. Immunoglobulin therapy involves injecting donor immunoglobulin into the blood. This helps to alter the way the immune system acts. Although treatment tends to be effective, the benefits are short-lived and they are not suitable long-term options.