Summary

Myasthenia Gravis is an auto-immune disorder that impairs the functioning of the skeletal muscles. This happens when the nerve signals to these muscles are not received properly. It affects younger women and older men. The condition can neither be cured nor prevented. The symptoms can be managed well so that the person can live a fairly normal life. In this article, we will learn more about the condition.

Introduction

Nerves are the carriers of communication signals between the Central Nervous System and muscle-groups located anywhere in the body. This is true of skeletal muscles as well, which are involved in our movement. In Myasthenia Gravis (MG), this communication gets impaired due to reasons explained in the next section. As a result of MG, the person is not able to voluntarily control his/her muscles. The muscles become weak or tired. The person is unable to control movement of muscles in the eyes, face, neck and limbs.

MG is quite common and affects 20 persons in every 1 lakh people. Women are generally diagnosed with MG in the age group of 20-40 years, while men are diagnosed with MG between 60 and 80 years of age. Juvenile MG affects a tiny percentage of youngsters. MG cannot be cured but its symptoms managed through medication, so as to sustain the quality of life.

Causes

The communication between nerves and muscles happens over a connection called synapse, at the neuromuscular junction. The nerves release a molecule called acetylcholine. The skeletal muscles have sites called acetylcholine receptors on them. The acetylcholine sent out by the nerves binds to these receptors. In response to that, the muscle fibres contract and movement happens. This is how the normal cycle of nerve-muscle communication. It is seamless in most people and rarely fails.

However, in people with MG, the immune system produces antibodies that attack and destroy the acetylcholine receptors in the muscles. Some or all of the receptors may be destroyed. As a result, the nerve to muscle communication becomes slow or sluggish. Since muscles are not contracting instantly, the movement is impaired. The person can no longer control his movements leading to various symptoms.

Antibodies also can block a protein called muscle-specific receptor tyrosine kinase, referred to as MuSK. This protein is crucial to form the nerve-muscle junction. Antibodies produced by the immune system can destroy this protein, leading to myasthenia gravis.

Another antibody that attacks a protein called lipoprotein-related protein 4 (LRP4), is also known to play a part in causing MG.

Research is uncovering other antibodies and newer ones may emerge with time, all of which have a role to play in causing and sustaining MG.

There is another aspect to MG, which is the connection to the thymus gland. The thymus is a butterfly-shaped gland present in the upper chest region closer to the throat. It is part of the lymphatic system and is responsible for producing antibodies that fight infections and pathogens. It is also known to produce antibodies that block acetylcholine. In two-thirds of people with MG, it is found that the thymus gland is larger than usual and also overactive, the condition being called thymic hyperplasia. In some cases, the thymus gland may have a tumour on it which is benign or not cancerous.

In some infants, there is neonatal MG that was passed on by the mother. However, this is a temporary condition that disappears in 3 months’ time.

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Risk Factors

• Fatigue
• Illness or infection
• Surgery or surgical procedures
• Chronic stress
• Medications for cancer, arrhythmias and malaria. This includes beta blockers, quinine (Qualaquin), quinidine gluconate, quinidine sulfate, phenytoin (Dilantin), some anaesthetics and some antibiotics. Other medication includes narcotic drugs, muscle relaxants, penicillamine, anaesthesia and magnesium
• Menstrual periods
• Pregnancy
• A personal or family history of other autoimmune diseases such as rheumatoid arthritis, lupus and thyrotoxicosis
• Thyroid disease

Symptoms

• Vision problems such as double vision (diplopia) and drooping eyelids (ptosis). The double vision can be vertical or horizontal and improves or goes away when one eye is closed.
• Muscle weakness and fatigue that vary with time and worsen with usage
• Abnormal facial expressions: for example, a smile that appears like a snarl
• Weakness of the neck or limbs
• Difficulty in moving the neck up or holding up the head (drooping head)
• Difficulty in holding the gaze
• Difficulty in speaking: the speech might sound soft or nasal, depending on specific muscles that are affected
• Difficulty with swallowing: So, eating, drinking and swallowing medication becomes difficult. The person may choke easily and sometimes liquids that are swallowed come out the nose.
• Difficulty in chewing: The muscles involved in chewing get tired halfway through the meal. This is especially true if the food being chewed is tough (hard vegetables or tough meat)
• Shortness of breath (dyspnoea) and difficulty in breathing
• Weakness in the diaphragm and chest muscles
• Difficulty in walking up the stairs or lifting objects
• Weakness of facial muscles leading to facial paralysis
• Constant fatigue
• Hoarseness or change in voice

Diagnosis

• Genetic tests: These tests are done to determine a genetic predisposition for MG in the family. Or to look for any other autoimmune disorder in the family.
• Neurological examination: The person’s reflexes, balance, muscle strength, coordination, senses of touch and sight, and muscle tone, are all tested.
• Ice pack test: For patients with droopy eyelids, a bag filled with ice is kept on the eyelids. After a couple of minutes, the bag is removed and the patient observed to see if the droopy-eyelid condition improves.
• Blood analysis: This will show all those irregular antibodies that interrupt receptor sites on muscles where the nerve signal arrives to prompt a movement.
• Repetitive nerve stimulation: This is a nerve conduction study. In this, electrodes are attached to the skin over the muscles which are being tested. Small pulses of electricity are sent through the electrodes. These pulses measure if the nerve can send a signal to the muscle or not. Fatigue test is then done. That is, the nerve is tested several times to see if its ability to send signals diminishes with fatigue.
• Single-fibre electromyography (EMG): In this, a fine-wire electrode is inserted through the skin and into a muscle to test a single muscle fibre. The electrical signals traveling between the brain and muscle are measured.
• Imaging: An MRI or CT scan is done to see if there’s a tumour or any growth in the thymus, which is creating problems.
• Pulmonary function tests: This test reveals how good is the breathing and whether MG is affecting the breathing or not.
• Edrophonium (Tensilon) test: This observes how the body reacts to this drug, that is, to see if MG symptoms will improve in the short run or not.

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Also Read: What are autoimmune diseases?

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Treatment

Medications

• Cholinesterase inhibitors: These improve communication between nerves and muscles and include yridostigmine (Mestinon, Regonal)
• Corticosteroids: These suppress the immune system, thereby reducing its ability to produce antibodies, and includes prednisone (Rayos).
• Immunosuppressants: Similar to the above. Includes azathioprine (Azasan, Imuran), tacrolimus (Astagraf XL, Prograf, others), mycophenolate mofetil (Cellcept), methotrexate (Trexall) and cyclosporine (Sandimmune, Gengraf, others)

Intravenous therapy

• Plasmapheresis (plaz-muh-fuh-REE-sis): In this, the plasma is separated from the blood using a machine. Thereafter, healthy plasma taken from another donor is injected into the body.
• Intravenous immunoglobulin (IVIg): In this, desired antibodies are injected into the body in order to correct the immune system.
• Monoclonal antibodies: These are medication that is given through a vein and include Eculizumab (Soliris) and Rituximab (Rituxan).

Surgery

• Surgery is done to remove a tumour in the thymus gland, called a thymoma.
• Thymectomy: In this, the entire thymus gland is removed irrespective of whether there is a tumour in it or not. The surgery may be open incisional or minimally invasive. Options for minimally invasive surgery includes video-assisted thymectomy and robot-assisted thymectomy.

Lifestyle and home remedies

• Adjustments to the eating routine: The person must consume small and multiple meals throughout the day. He/she must consume soft foods that do not require too much chewing. He/she must chew the food thoroughly and eat slowly to prevent fatigue in the muscles.
• Increasing precautions at home: To prevent falls at home, grab bars or railings must be installed wherever necessary. Floors must be clean and dry, rugs and carpets must be removed, and all obstructions including leaves and snow outside must be removed.
• Use electric appliances and power tools: Electric toothbrush, electric can openers, etc help save energy and prevent muscle fatigue.
• Use an eye patch: This helps people with double-vision. To prevent fatigue in one eye, the patch must be changed between the 2 eyes.
• Planning: Activities that require doing some chores or going out must be planned in such a way that they are accomplished when the person is feeling energetic and not tired.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai (Alwarpet & Vadapalani), Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

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