Myasthenia gravis

What is it?

Myasthenia gravis is a neuromuscular disease characterized by varying degrees of weakness and rapid fatigue of the skeletal (voluntary) muscles of the body. The name myasthenia gravis, which is Latin and Greek in origin, literally means "grave muscle weakness." With current therapies, however, most cases of myasthenia gravis are not as "grave" as the name implies. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest. Certain muscles such as those that control eye and eyelid movement, facial expression, chewing, talking, and swallowing are often, but not always, involved. The muscles that control breathing and neck and limb movements may also be affected.

What are the causes?

Myasthenia gravis is a defect in which the transmission of nerve impulses to muscles is affected. Normally, when impulses travel down the nerve, the nerve endings release a neurotransmitter substance called acetylcholine. Acetylcholine travels through the neuromuscular junction and binds to receptors which are activated and generate a muscle contraction. In myasthenia gravis, antibodies block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction which prevents the muscle contraction from occurring. These antibodies are produced by the body's own immune system.

What are the symptoms?

Although myasthenia gravis may affect any voluntary muscle, muscles that control eye and eyelid movement, facial expression, and swallowing are most frequently affected. The onset of the disorder may be sudden and the symptoms often are not immediately recognized. In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness involved in myasthenia gravis varies greatly among patients, ranging from a localized form limited to eye muscles to a severe or generalized form in which many muscles - sometimes including those that control breathing - are affected. Symptoms may include drooping of one or both eyelids (ptosis), blurred or double vision (diplopia) due to weakness of the muscles that control eye movements, unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, difficulty in swallowing and shortness of breath, and impaired speech (dysarthria).

What are the risk factors?

Myasthenia gravis may occur in all ethnic groups and both genders. Most commonly it affects women under 40 and older men (over 60), but it can occur at any age. Myasthenia gravis is not directly inherited nor is it contagious.

How is the diagnosis made?

A delay in diagnosis of one or two years is not unusual in cases of myasthenia gravis. Because weakness is a common symptom of many other disorders, the diagnosis is often missed in people who experience mild weakness or in those individuals whose weakness is restricted to only a few muscles. The first steps of diagnosing myasthenia gravis include a review of the individual's medical history, and physical and neurological examinations. This may include testing of muscle reflexes, muscle strength and tone, senses of touch and sight, gait, posture, coordination, balance and mental skills. A special blood test can detect the presence of immune molecules or acetylcholine receptor antibodies. Most patients with myasthenia gravis have abnormally elevated levels of these antibodies. Injection of a chemical edrophonium chloride (Tensilon) may result in a sudden, although temporary, improvement in muscle strength, an indication of myasthenia gravis. Edrophonium chloride blocks the enzyme that inhibits the transmission of signals from nerve endings to muscle receptor sites. Electromyography (EMG) is a test in which single muscle fibres are stimulated by electrical impulses, which detects impaired nerve-to-muscle transmission. EMG measures the electrical potential of muscle cells. Muscle fibres in myasthenia gravis, as well as other neuromuscular disorders, do not respond as well to repeated electrical stimulation compared to muscles in normal individuals.

What is the treatment?

Myasthenia gravis can be controlled though not cured. There are several therapies available to help reduce and improve muscle weakness. Medications: Medicines used to treat the disorder include agents such as neostigmine and pyridostigmine, which help improve neuromuscular transmission and increase muscle strength. Immunosuppressive drugs such as prednisone, cyclosporine, and azathioprine may also be used. These medications improve muscle strength by suppressing the production of abnormal antibodies. They must be used with careful medical followup because they may cause major side effects. Surgery: Thymectomy, the surgical removal of the thymus gland (which is abnormal in myasthenia gravis patients), improves symptoms in more than 50 percent of patients and may cure some individuals, possibly by re-balancing the immune system. Plasmapheresis: This is a procedure in which abnormal antibodies are removed from the blood. Blood is taken, passed through a filter that removes the specific antibodies and then returned to the body.A neurologist, along with the primary care physician, will determine which treatment option is best for each individual depending on the severity of the weakness, which muscles are affected, and the individual's age and other associated medical problems. Physical and occupational therapy may also be suggested.

What is the prognosis?

With treatment, the outlook for most patients with myasthenia gravis is bright. They will have significant improvement of their muscle weakness and they can expect to lead normal or nearly normal lives. Some cases of myasthenia gravis may go into remission temporarily and muscle weakness may disappear completely so that medications can be discontinued. In a few cases, the severe weakness of myasthenia gravis may cause a crisis (respiratory failure), which requires immediate emergency medical care.

What is the homecare treatment?

Guidelines for coping with myasthenia gravisAdjust your eating routine: Try to eat when you have good muscle strength, possibly an hour after taking your medication. Also, take your time eating and rest between bites. Try soft foods and avoid sticky foods. Use safety precautions at home: Install grab bars or railings in places where you may need support, such as when you're getting out of the tub. Keep the floors and halls in your house clear of clutter, cords and loose rugs.Wear an eye patch: Using an eye patch can relieve double vision if you suffer from this effect. Wear the patch while you read or watch television. Plan ahead: If you have to do a chore around the house or shopping, plan the activity to coincide with when your medication provides you peak energy level. Ask for help: Depending on your energy level, you may not be able to do everything you planned. Ask family members and friends to lend a hand. Manage stress: Because emotional stress can make myasthenia gravis worse, look for ways to reduce stress. These may include relaxation techniques such as biofeedback and meditation.Avoid excessive alcoholic drinks, tonic water and smoking.

DoctorNDTV Team