What is Myasthenia Gravis?
Myasthenia gravis (commonly called “MG”) is a condition that causes some muscles to weaken. These muscles usually include:
- Eyelids and muscles around the eyes – If MG only affects these muscles, doctors call it “ocular MG”. About half of all MG patients fall into this category.
- Jaw and pharyngeal muscles.
- Arm and neck muscles.
- Muscles for breathing.
The cause of MG is due to problems in the body’s immune system. The immune system usually produces a protein called “antibody” that helps to prevent and fight against infections. However, the immune system of MG patients produces antibodies that mistakenly attack the junction between nerves and muscles, affecting normal muscle function.
What are the symptoms of MG?
The commonest symptom is muscle weakness that varies over the day, particularly worsens in the afternoon or evening. Doctors call it “fatigable weakness” because the muscle weakness is often further worsened after repeated use and temporarily improved after rest. It may result in:
- Eyelid drooping (Figure 1)
- Blurred vision or double vision
- Difficulty in chewing food – The jaw muscles may feel tired when eating.
- Difficulty in swallowing (dysphagia)
- Speaking problems – Patients may speak in a lower voice than usual, or they may have a heavy nasal sound.
- Reduced facial expression
- Head feeling heavy or dropping forward
- Difficulty in breathing – Patients may feel shortness of breath, and need extra breaths.
- Weakness – It may be difficult to raise your arms or legs.
Will I need test?
Your doctor will first learn about your symptoms and then do appropriate physical examination. If the condition is suspected, you may have some of these tests:
- Ice pack test (see video clip)-
During this test, the doctor will place a cool bag on your closed and weak eyelid for 2 minutes. When you open your eyes again and the eyelid drooping disappears temporarily (Figure 2), it may be a sign of MG.
- Drug injection test – Your doctor will inject a diagnostic drug into your vein (edrophonium) or arm muscle (neostigmine) before testing your weak muscles. These drugs temporarily improve the signal transmission at the neuromuscular junction in the muscles. If the test result is positive, there will be a brief but significant improvement in the muscle strength of your eyelids and other affected muscles. Since the first drug (edrophonium) used in the test was brand-named “Tensilon®,” this test is often referred to as the “Tensilon test.”
- Blood tests to look for certain antibodies that may cause MG.
- Electrical tests of nerves and muscles (Electromyography or “EMG”) – These can show whether the nerves transmit electrical signals normally and whether the muscles produce abnormal signals.
- Imaging tests, such as computerized tomography (CT) or magnetic resonance (MRI) scans – Thymus is a gland inside the chest and behind the sternum. It is part of the immune system. Many MG patients have lesions in the thymus, such as hyperplasia or tumors. The scan can help to look for the above conditions.
How is MG treated?
(1) Treatment options:
Doctor will decide a treatment plan based on the individual circumstances of the patient, which may include:
- Drugs that temporarily improve symptoms of muscle weakness, such as pyridostigmine (common brand name: Mestinon®)
- Drugs that inhibit or regulate the immune system over time- commonly used ones include corticosteroids such as prednisolone or antimetabolite such as azathioprine (common brand name: Imuran®)
- Fast-acting treatments of the immune system:
- Intraveous immunoglobulin (IVIg) – This medicine is extracted from the blood of many blood donors and requires intravenous injection. The treatment course is two to five days.
- Plasma exchange, also known as “plasma replacement” – the doctor will first insert a catheter into a large blood vessel (such as the jugular vein in the neck) of the patient so that the machine can draw blood from the body and remove substances from the blood that attack the nerves and muscles. The machine then pumps the blood back to the body.
IVIg or plasma exchange generally stabilize the MG condition within a few days, but the effect can only last for several weeks, and there are potential harms associated with them. Based on risks and cost-effective considerations, these treatments are reserved for the patients in critically ill or life-threatening conditions.
- Surgical removal of the thymus – only for some MG patients. The doctor will make recommendations based on the individual circumstances of the patient.
(2) Myasthenic crisis:
- This refers to a serious state of the MG condition. At the onset time, the patient will have worsening symptoms in a short period of time, especially leading to severe dysphagia and respiratory failure, and even death. If MG patients have these symptoms, they should seek medical advice as soon as possible. In addition to the above-mentioned treatments, the medical team may also need to put a tube in the patient’s airway and use machine to help breathing.
- In general, patients with stable MG have a very low risk of developing myasthenic crisis. The most common predisposing factors are infections (such as flu) and rapid reduction of immunosuppressive drugs. Other factors include surgery, pregnancy, childbirth, certain drug effects, and so on.
(3) Children with myasthenia gravis:
Children with MG can take the same medication as adults, and the dose will be adjusted accordingly. However, if used for a long time, some drugs used to treat MG may cause problems in children’s development. Surgical removal of the thymus is generally safe for children and usually works well. Please discuss the appropriate treatment plan with your doctor.
What if I want to get pregnant?
If you want to get pregnant, you should consult your doctor to learn more about your condition to make the most appropriate treatment plan.
What else should I know about MG?
MG patients may have worsening symptoms or even serious problems if they get the flu or pneumonia. Therefore, regular vaccinations for them are recommended.
Moreover, some drugs may make MG worse. Before taking any new medications (including over-the-counter ones), please consult your doctor if they are safe.
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