Treatment
There are no treatments that reliably cure myasthenia gravis. The aim of treatment is to control the muscle weakness and fatigability using the lowest possible doses of effective drugs. Other treatments including surgical removal of the thymus gland. This may promote remission or decrease the symptom severity in a large group of patients.
Anticholinesterases
The cornerstone of myasthenia gravis treatment is a class of drugs called anticholinesterases inhibitors, which relieve muscle weakness and fatigability. These drugs delay the breakdown of acetylcholine at nerve endings, thus increasing the amount acetylcholine available to act on muscle fibres. The most commonly prescribed medication is pyridostigmine; neostigmine is also used.
Anticholinesterases tend to have dose related side effects on other muscles in the body, since they are mimicking normal physiological actions. The troublesome effects include abdominal pain, diarrhoea and excess salivation. Other anticholinergic drugs such as propantheline and diphenoxylate are prescribed to counteract these problems.
Pyridostigmine is taken 3 or 4 times a day. The dose and its frequency of administration need to be tailored to the individual to achieve maximal improvement of muscle power with minimum side effects. Anticholinesterases are most useful in mild or early disease.
Corticosteroids and other immunosuppressant drugs
In more severe and progressive myasthenia, disease modifying immunosuppressant drugs are used. Corticosteroids, such prednisolone or prednisone, are given in gradually increasing doses over some weeks. Most people experience improvement over 6 – 12 months, and the dose can be subsequently reduced to the minimum amount that alleviates symptoms effectively.
Steroids are often used in combination with other immunosuppressant drugs to reduce the undesirable side effects of steroid medication. Other drugs prescribed include azothiaprine, ciclosporin, cyclophosphamide, methotrexate and mycophenolate mofetil. People taking these types of drugs need regular blood tests to detect any toxic effects.
Thymectomy
Thoracic surgery is carried out to remove the thymus gland if a tumour has been identified on scans. Most thymomas are benign, but a small number are malignant. Thymectomy is usually also advised as an initial treatment option in younger people (adolescence to age sixty), who have generalised disease. In some cases thymectomy induces a remission; in others control of symptoms is possible with lower doses of drugs. The beneficial effects of thymectomy may continue over some months and years following the operation
Hospital admission for myasthenic crisis
People with severe breathing difficulties and generalised paralysis require hospital admission for artificial ventilation in intensive care.
Plasmapharesis and immunoglobulin injection
These treatments are used in people with more severe disease, when the disease fails respond to drugs and in myasthenic crisis.
Plasmapharesis (plasma exchange) is a hospital-based procedure that involves exchanging the person’s plasma (a component of the blood) for that of plasma free of abnormal antibodies.
A course of intravenous immunoglobulins, given on a daily basis over five days, helps to improve symptoms.
Ocular devices
Various aids are available to treat the drooping eyelids and double vision caused by ocular myasthenia. Devices (‘crutches’) attached to spectacles and taping of eyelids can be used to correct drooping eyelids. Various types of special lenses can be prescribed to ameliorate double vision.
Complications of treatment – ‘cholinergic crises’
On some occasions excessive dosages of anticholinesterases drugs cause rapidly progressive muscle weakness with excessive sweating, salivation and diarrhoea. This is called a cholinergic crisis and requires hospital admission to stabilise treatment.
Amended June 2008
