Myasthenia Gravis: What is it?
Myasthenia gravis is an autoimmune disease characterised by muscle weakness. The immune system produces abnormal antibodies which attack the junction between the nerves and muscles. This affects the transmission and causes the symptoms. There is currently no cure. However, symptoms can be managed with treatment to suppress the activity of the immune system.
Myasthenia Gravis Awareness Month happens in June every year. Read on to find out more about this immune disease.
What is myasthenia gravis?
Myasthenia gravis is an autoimmune neuromuscular disorder affecting the neuromuscular junction of the skeletal muscles. Myasthenia gravis can occur at any age but is more common in females less than 40 years of age and in males older than 60 years of age. In some Asian countries, this disease is peculiarly common in children less than 15 years old, where they make up about half of patients.
What is the cause of myasthenia gravis?
This condition is not inherited, nor contagious. However, there is an increased risk of developing the condition if another autoimmune disease runs in the family. Classically, in autoimmune diseases, the immune system produces antibodies (also known as autoantibodies) that targets parts of the body that are not foreign.
In myasthenia gravis, the antibodies attack the junction between the nerves and muscles. This causes a breakdown in the transmission of signals between the nerves and muscles, and subsequently the inability for the muscles to carry out their functions. This leads to muscle weakness and other symptoms related to myasthenia gravis.
What are the symptoms of myasthenia gravis?
Symptoms usually manifest as muscle weakness. Muscle weakness in the affected muscles can worsen with as the disease progresses over time, but is usually improved with rest. Therefore, symptoms may fluctuate but eventually progress over the years.
First signs of people who develop myasthenia gravis include:
- Double vision (diplopia)
- Eye deviation and/or
- Drooping of either or both eyelids (ptosis)
Face and throat muscles are also affected in 10% of patients which may include:
- Trouble talking
- Difficulties in chewing and swallowing
Other common symptoms include weakness in the arm and legs and neck where posture is affected, presence of difficulty in holding up one’s neck, and problems with walking up the stairs. In children, symptoms may present at the beginning of childhood.
How to diagnose myasthenia gravis?
Diagnosis is clinically defined as muscle weakness, with or without eye involvement. Alongside a history of muscle weakness, further tests and scans can be done to confirm diagnosis.
- Blood test: Detection of antibodies against the acetylcholine receptor or MuSK
- Tensilon test: Injection of a drug that temporarily improves muscle strength in patients
- CT scan or MRI to detect abnormalities in the thymus gland
- Electromyography: Electrodes are used to evaluate muscle function. Weak muscle contractions could suggest myasthenia gravis.
How to classify myasthenia gravis?
Classification is dependent on the type of antibodies present and clinical features associated:
- Early-onset MG: Age at onset less than 50 years old with increased thymic cell growth
- Late-onset MG: Age at onset greater than 50 years old with thymic atrophy
- Juvenile MG
- Thymoma-associated MG
- Oculate MG: Symptoms only from eye muscles
- MG with no detectable antibodies
How to treat myasthenia gravis?
Currently, there is no cure for myasthenia gravis. However, symptoms can be managed. Non-clinical treatments include changes in lifestyle to minimise physical exertion.
This disease can also be treated by interfering with immune function to suppress immune cell activity. This can reduce the movement of the immune cell through the body and block the effects of the cell such as inflammation.
Acetylcholinesterase inhibitors such as neostigmine and pyridostigmine are most used. They help to increase the accumulation of acetylcholine and prevent acetylcholine destruction, helping muscles to contract more effectively. However, side effects such as involuntary muscle twitching (fasciculation) and excessive salivation may be present in some patients.
Drugs such as prednisone (or prednisolone) help to suppress antibodies that destroy the neuromuscular junction. Corticosteroids have shown to largely help to improve symptoms and may be prescribed to be taken daily at low dosage. Side effects include weight gain, osteoporosis and the formation of gastric ulcers.
These drugs are also called immunosuppressants, including azathioprine or mycophenolate. They are also usually administered as first-line treatments and may present with fewer side effects.
In more severe cases, plasmapheresis is used to clear antibodies from the blood. Plasmapheresis is administered in myasthenic crises and in patients who require long-term treatment.
In some cases, the thymus gland is also surgically removed. Benefits usually peak years after removal but have a higher rate of drug-free remission.
In juvenile myasthenia gravis, the first line of treatment is symptomatic management with pyridostigmine. Immunosuppression management is then administered with oral prednisolone if symptomatic management is not achieved. In a myasthenic crisis, children must be admitted to the hospital immediately.
Article is written in conjunction with Myasthenia Gravis Awareness Month, which happens in June every year.