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MYASTHENIA GRAVIS

What is Myasthenia Gravis ?

Myasthenia gravis is the Latin name for serious muscle weakness. The weakness only occurs after the muscles are exercised and tired, and then improves with resting. There is therefore fatigue of muscles, made worse by use and towards the end of the day. Myasthenia often begins with weakness of the eye muscles, causing a droopy eyelid or double vision. The muscles of the mouth and throat may be affected, causing difficulty in swallowing and with prolonged speech. The weakness may extend to the neck and shoulder muscles. Weakness in the limbs may also occur.

How does Myasthenia Gravis occur ?

Muscles are controlled by nerves. The muscles move or contract when the nerve releases a particular chemical (neurotransmitter). This chemical acts on a special area of the muscle (the receptor site). In myasthenia gravis the body appears to produce an abnormal chemical called an antibody. Although most antibodies are generated to protect against external agents, in this case the antibody blocks the receptor site so that the normal neurotransmitter cannot do its job. The muscle therefore does not contract properly. In some cases, the problem may be due to a defect in the manufacture of the neurotransmitter.

Why does Myasthenia Gravis occur ?

The disease probably starts by the body producing a chemical (the antibody) to the special receptor site on the muscle. People with myasthenia gravis may have a more widespread tendency to produce abnormal antibodies against their own tissues. Accordingly, some people with this disorder make antibodies to their thyroid gland, with resulting thyroid malfunction.. Similarly, diabetes mellitus and rheumatoid arthritis (so-called auto-immune disorders) occurs rather more often in patients with myasthenia, or their relatives. Myasthenia itself only rarely affects members of the same family. The abnormal antibody is produced in cells called lymphocytes from the thymus gland. This gland lies in the lower neck or behind the breastbone. In about 10% of cases, a tumour of the thymus gland is present.

Treatment Involved for Myasthenia Gravis

Management firstly involves blood tests to look for the body's antibodies to the receptor site. This test is positive in most patients with myasthenia gravis. Electrical studies of affected muscles (electromyography) may demonstrate the problem. A very fine needle is inserted into the muscle and the response to contraction and stimulation of the muscle is recorded. Another helpful test involves injecting a drug into the bloodstream. The diagnosis of myasthenia is confirmed if the weakness subsequently improves within a minute or so. A CT scan of the chest may be done to detect any swelling of the thymus gland. ¨ Treatment in the first instance consists of tablets. The first group of drugs are called anticholinesterases. These stop the breakdown of the essential neuro-transmitter called acetylcholine. Examples are neostigmine or pyridostigmine. These drugs must be taken three or four times a day. The dose is increased gradually until symptoms improve. The second strategy is to suppress the body's production of abnormal antibodies. These agents are called immunosuppressant drugs. Examples include prednisolone (a cortisone-like drug) and azathioprine. In some cases, it will be recommended that the thymus gland is removed by doing an operation through the breastbone. As mentioned above, the thymus may actually contain a tumour. However, more often it is simply overactive and removal of the gland helps to suppress the condition. Sometimes the operation is done quite soon after diagnosis, at other times it is used if other treatments fail or if a tumour is shown to present in the scan. If weakness becomes progressively worse and affects breathing, urgent plasma exchange (a kind of blood washing treatment) is needed. Sometimes an intravenous drip containing plasma may be used.

During Treatment for Myasthenia Gravis

Anticholinesterase treatment should cause improvement of the muscle weakness or prolong the period before the muscle becomes tired. However, when prednisolone or other steroids are started, the myasthenia may actually become worse before it gets better. If you become exhausted and and are finding talking, breathing or swallowing difficult, you must be admitted to hospital as an emergency. The principal side effects of the anticholinesterases are excessive sweating and saliva production, together with abdominal cramps and diarrhoea. If given in too high a dosage, they can actually worsen the weakness. Steroid-type drugs may cause weight gain, fluid retention, high blood pressure and a tendency to diabetes. Azathioprine may suppress the body's own defence mechanism against infection. The doctor will check this with blood tests. Should a sore throat develop, or an infection which is not clearing, the doctor should be consulted immediately.

After Treatment for Myasthenia Gravis

Treatment must be continuous, not just when symptoms are troublesome. Increasing weakness or a different pattern of weakness must be reported to the doctor. In many cases, after a stormy few months, the condition is controlled and normal strength is restored. At this stage, the treatment can often be reduced or even stopped. However, at any stage, particularly following a cold or other infection, the myasthenia may recur and require more aggressive treatment.

If Myasthenia Gravis is Left Untreated

Quite a few cases may improve temporarily. However, in most people severe weakness can develop quite quickly. Not only movement, but breathing might be affected, and this could be fatal.

Effects on Family of Myasthenia Gravis

Myasthenia is not infectious and cannot be transmitted to family and friends. People in close contact need to know that if you suddenly become weaker or have difficulty talking or breathing, they should contact the doctor immediately. Some doctors may recommend that close relatives should be screened for other antibody-type disorders.