Myasthenia Gravis is a chronic disorder characterized by rapid fatigue and weakness of voluntarily controlled muscles caused by the breakdown of normal transmission of impulses between nerves and muscles. This disorder that affects muscular function improves with rest. The symptoms include double vision, drooping eyelids, limb weakness and difficulty with chewing, swallowing, speech and breathing. Myasthenia Gravis may occur at any age but is more common in women below the age of 40 years and above the age of 70 years. It is also more common in men above the age of 50 years. There is no cure but medication is available to help control the signs and symptoms.
Myasthenia Gravis may affect any of the muscles that are under voluntary control. Certain muscles are more commonly affected and these include the muscles of the face, eyes, arms and legs as well as muscles used for speaking, chewing and swallowing. Other muscles that may be involved include those that control breathing and movement of the head. When affected, the symptoms that may result include Drooping eyelids, Facial muscle weakness, Double Vision and Fatigue brought on by repetitive motion. The fatigue worsens with each movement and in rare cases, breathing and swallowing problems may lead to a medical emergency.
Under normal conditions, specialised areas in the muscles known as nueromuscular junctions have receptor sites that receive nerve impulses that signal them to contract. These nerve impulses are transmitted by the chemical Acetylcholine. In Myasthenia Gravis, there is a breakdown in communication between the nerves and muscles. For poorly understood reasons, the immune system
produces antibodies that destroy or block several Acetylcholine receptor sites in muscle. As a result, the muscles recieve fewer nerve signals leading to weakness.
The thymus gland (part of the immune system) which is located in the upper chest beneath the sternum (breastbone) is thought to be responsible for triggering or maintaining the production of these antibodies. The thymus gland is usually large in infancy and small in adulthood. In some adults with Myasthenia Gravis the thymus is abnormally large and others have benign (non-cancerous) tumours of the thymus.
Myasthenia Gravis may be aggravated by illness, stress, extreme heat and certain medications including beta blockers, calcium channel blockers, botox, quinine and some antibiotics. If any of the symptoms of Myasthenia Gravis are suspected a doctor should be consulted. Diagnosis may be confirmed through a series of tests and a detailed clinical history. The symptoms of Myasthenia Gravis usually improve with rest. A Neurological Examination may be performed to test reflexes, muscle tone, muscle strength, sensory perception, co-ordination, balance, posture and mental skills. A Blood Test may show the presence of antibodies that disrupt the receptor sites. An Edrophonium Test may be performed by injecting the chemical Edrophonium (Tensilon) which leads to a sudden temporary increase in muscle strength in patients with Myasthenia Gravis. Edrophonium blocks the enzyme that breaks down Acetylcholine which is the chemical that transmits signals from the nerve endings to the muscle receptor sites.
The strength of muscle contractions may be tested by a Nerve Conduction Study where a small electrical impulse is applied to the skin to stimulate muscle contractions. A Single – Fibre Electromyography may be carried out by inserting a thin needle electrode into a muscle to measure patterns of electrical activity at rest and with slight muscle contraction.
A variety of treatments are available to relieve the symptoms of Myasthenia Gravis. These may be administered alone or in combination. Medications known as cholinesterase inhibitors such as Neostigmine (Prostigmine) and Pyridostigmine (Mestinon)Â improve the communication between nerves and muscles. These drugs don’t treat the underlying condition but help improve muscle contraction and muscle strength. Corticosteroids may be given to inhibit the immune system thus limiting the production of antibodies. Long term cortiosteroid use may lead to serious side effects such as osteoporosis (thinning of the bones), weight gain, diabetes, increased risk of some infections and redistribution of body fat. Other drugs that suppress the immune system may also be prescribed such as Azathiprine (Imuran), Cyclophosphamide (Cytoxan), Cyclosporine (Neoral or Sandimmune) and Mycophenolate
Surgical removal of the Thymus gland (Thymectomy), recommended for patients under the age of 60 years, may be performed to alleviate symptoms. About 25% of patients who have had surgery go into remission within a year and significant improvement is often delayed for years. Plasmapharesis may be performed in life threatening cases of Myasthenia Gravis. In this procedure the offending antibodies are removed from the blood by passing it through a filter and returning it to the body. Intravenous Immune Globulin may be administered to provide the body with normal antibodies to alter the immune system’s response. Physical therapy and occupational therapy may also be instituted.
Patients with Myasthenia Gravis may better cope with symptoms by making the most of their available energy. Eating when there is good muscle strength is advised possibly after taking Cholinesterae inhibitors. They should take smaller meals, avoid foods that require a lot of chewing and rest between bites. Energy may be conserved by using power tools and electrical appliances. Use of an eye patch may help relieve double vision. Safety precautions should be taken. Rails and grab bars should be installed in the home in places where support may be needed such as in the bathroom. The home should also be clutter free to prevent tripping. Emotional stress should be managed as stress worsens the condition.