Myasthenia Gravis

What Is Myasthenia Gravis?

Myasthenia gravis (MG) is a Latin word meaning “grave (serious) muscle weakness.” It is an autoimmune neuromuscular junctional disease, caused by an antibody-mediated blockade of neuromuscular transmission resulting in skeletal muscle weakness. The first muscles to be affected are the ones around the eyes, which makes the eyelids droop and double vision. All functions performed by voluntary muscles like chewing, swallowing, speaking, and breathing and shoulder and hip girdle muscles can get affected. It results when the communication between nerve cells and muscles is affected. MG is the most common disorder caused by neuromuscular transmission.

How Does Myasthenia Gravis Affect the Body?

The weakness of voluntary muscles and rapid fatigue is the most common symptom. Voluntary muscles are muscles that are under our control, however, certain groups of muscles are more common. These muscles fail to respond to the nerve impulses, which prevents muscles from contracting. As the transmission between the nerve and muscle is affected, the muscles do not

function properly, which results in muscle weakness. Muscle weakness caused by myasthenia gravis worsens on use, and it improves on rest. This muscle weakness can come on and off. As it is a progressive disorder, the symptoms worsen with age.

What Are the Symptoms of Myasthenia Gravis?

Muscle weakness gets worse with activity, and it gets better with rest. The symptoms include:

• Fatiguability.

• Drooping eyelids.

• Difficulty in speaking or speech problems.

• Problems climbing stairs and lifting objects.

• Facial paralysis.

• Tiredness.

• Breathing problems.

• Voice hoarseness.

• Double vision.

• Drooping eyelids.

• Chewing becomes difficult.

• Limb weakness.

In most patients, the muscles in the eyes, face, and throat are affected first, but in some patients, it may affect shoulder and hip muscles also. All symptoms become worse during periods of activity.

What Causes Myasthenia Gravis?

MG is caused by an autoimmune problem, which results in a neuromuscular junction disorder. An autoimmune reaction occurs when the immune system mistakenly attacks healthy cells in the body. Here, instead of the antibodies attacking the harmful substances in the body, it attacks the acetylcholine receptors, which are located at the neuromuscular junction. Nerves communicate with muscles by releasing chemicals (neurotransmitters) that fit precisely into receptor sites on the muscle cells at the nerve-muscular junction. The effect of neurotransmitter substance acetylcholine reduces when the immune system damages the neuromuscular membrane, which results in muscle weakness. Acetylcholine is crucial for communication between nerve cells and muscles.

The exact cause is still not known. Some studies show that virus or bacteria induces molecularmimicry with acetylcholine receptor (AChR) and provokes immunity to attack AChR. It commonly affects people over 40 years of age.

Some believe that the thymus gland triggers the production of antibodies that block the chemical acetylcholine transmission through AChR.

What Are the Risk Factors for Myasthenia Gravis?

Some factors that worsen the condition are:

• Stress.

• Other illness.

• Fatigue.

• Medications like beta-blockers (Propranolol), antibiotics (Aminoglycosides, Fluoroquinolones, Macrolides), anti-malarial drugs, anesthetic drugs, and Magnesium.

• Menstrual periods.

• Pregnancy.

How Is Myasthenia Gravis Diagnosed?

On your visit, your doctor will perform a physical examination and take a complete medical history. Then the doctor will perform neurological exams like checking your eye movements, assess your speech and swallowing, checking your strength of different muscle groups, muscle tone, reflexes, muscle twisting, and thinning of muscles. And also, he or she will examine the sensations balance of body like touch, pain, and coordination to rule out any other possibilities.

After these initial examinations, your doctor might suggest you do the following tests:

• Edrophonium test - The rapid and temporary improvement in muscle strength (especially eyelid drooping or slurred speech) after injecting the chemical edrophonium chloride indicates myasthenia gravis. This chemical blocks the enzyme acetylcholine esterase that breaks down acetylcholine. (Edrophonium is not available in some countries, in such cases, injection Neostigmine is used).

• Ice pack test - The doctor will place an ice pack on your drooping eyelid, and after two minutes check for signs of improvement.

• Blood analysis - Looks for acetylcholine receptor antibodies. In some cases, AChR antibodies are negative. In such cases, check anti-MuSK and anti-LRP4 (Lipoprotein Related Protein - 4) antibodies.

• Repetitive nerve stimulation - Electrodes are attached to your skin over the muscles to be tested (around the eyes or over the shoulder), and electric stimulations are given to the particular nerve and small pulses measure the nerve’s ability to send a signal to your muscle.

• Single-Fiber Electromyography (EMG) - It is the gold standard test to diagnose MG. This test measures the electrical activity traveling between the nerve and muscle. A fine wire electrode is inserted into a muscle through your skin to test a single muscle fiber.

• CT or MRI scan - To check for thymus enlargement or to rule out lung tumors or other

• abnormality.

• Pulmonary function tests - To check your breathing capacity.

How Is Myasthenia Gravis Treated?

There is no cure for myasthenia gravis, but the symptoms can often be controlled with medications. Myasthenia gravis is a lifelong medical condition. Early detection is the key to managing the condition. Treatment may include:

Medications:

Oral Therapy

• Cholinesterase inhibitors - Pyridostigmine and Neostigmine enhance communication between nerves and muscles.
• Corticosteroids - Prednisone inhibit the immune system.
• Immunosuppressants – Modulates the immune response - Azathioprine, Mycophenolate mofetil, Cyclosporine, and Methotrexate. These drugs, which can take months to work, might be used with corticosteroids. Side effects of immunosuppressants, such as the increased risk of infection and liver or kidney damage, can be serious. Hence needed timely monitoring of blood count, liver function and kidney functions test as per your doctor’s protocol.

Intravenous therapy - To treat sudden worsening of symptoms, the following therapies are used:

• Plasmapheresis - This procedure uses a filtering process similar to dialysis. Antibodies that block the transmission is removed by passing blood through a machine.
• Intravenous immunoglobulin (IVIg) - It adds normal antibodies to the blood, which improves the immune system response. Benefits are usually seen in less than a week and can last four to six weeks.
• Monoclonal antibody - Rituximab and Eculizumab. These drugs are usually used for people who do not respond to other treatments.

Surgery:

If there is a tumour in the thymus, the gland has to be removed. The surgical removal of the thymus gland is called thymectomy. The types of thymectomy are:

• Open surgery - The doctor splits the sternum and removes the thymus gland.

• Video-assisted thymectomy - A small incision is made on the neck, and then with the help of an endoscope, the thymus gland is removed.

• Robot-assisted thymectomy - Here, the thymus gland is removed using a robotic system, which has a camera and mechanical arms.

Lifestyle modifications:

• Modify your eating habits - Eat soft foods and avoid food that needs a lot of chewing. Chew your food properly, and take breaks in-between bites.

• Use safety precautions at home or office - Install grab railings or bars in places where you need support, such as next to the bathtub or next to steps.

• Take the support of technology and power tools - Try using an electric toothbrush, electric can openers, and other electrical tools to perform tasks, etc., for maintenance of your energy.

• Plan - If you have a necessary task or shopping to do, then plan the activity for when you have the most energy.

What Are the Complications of Myasthenia Gravis?

The complications are:

• Myasthenia crisis - It is a life-threatening condition, where the breathing becomes impaired due to weakness in the muscles that control breathing.

• Some patients may need intravenous therapy and long term ventilatory and feeding support muscle strength returns with treatment.

• Reactivation of latent diseases like tuberculosis, herpes zoster and many rare diseases because of long term use of immunosuppressants.

Other Condition May Be Associated with MG:

• Thymus tumors.

• Hyperthyroidism or hypothyroidism.

• Other autoimmune conditions like rheumatoid arthritis.

Conclusion

Some patients develop mild symptoms, while others ability to walk and perform other activities is affected so much that they become confined to a wheelchair. To relieve symptoms and lead an almost normal life, consult a doctor now.