Von willebrand's disease

稱之類血友病(凝血因子缺乏)
Inleiding
Blood is the red coloured fluid found in the body, it can be divided into two parts - blood cells and fluid (also called plasma). There are three types of blood cells - red blood cells (RBCs), white blood cells (WBCs), and platelets. RBCs give blood its red colour, and are responsible for caring oxygen to the tissues. WBCs consist of a number of different types of cells that are responsible for fighting infection, while platelets are essential in stopping bleeding by helping form blocks, called clots, at the site of bleeding.


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What is on Willebrands disease?
Von Willebrand's disease is a bleeding disorder that runs in families (i.e. an inherited disorder) and is characterised by excessive bleeding. It is the most common inherited bleeding disorder. The bleeding may follow trauma, or may occur spontaneously in those with the disorder.


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What causes von Willebrands disease?
The plasma contains proteins and other substances that have a variety of functions. A group of these proteins, called factors, are responsible for stopping bleeding at a site of injury. These factors are collectively called the clotting system. These factors, along with platelets, form a clot at the site of bleeding. They also prevent spontaneous bleeding from occurring.
Von Willebrand's disease is caused by a deficiency of one of these factors, called von Willebrand's factor. Von Willebrand's factor is a protein that helps platelets to stick to the blood vessel wall and to each other. Von Willebrand's factor also helps transport another factor, called factor VIII (factor "eight"). Hence, a deficiency of von Willebrand's factor may also be associated with decreased blood levels of factor VIII.


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What are the features of von Willebrands disease?
Von Willebrand's disease is equally common in men and women. The severity of symptoms is very variable between affected individuals. Some people will have severe and frequent bleeding, while others will have only mild bleeding. Von Willebrand's disease is characterized by excessive bleeding, either following trauma, or occurring spontaneously. Bleeding into the skin, giving rise to tiny pinpoint bleeds of purplish discolouration (petechiae), or larger areas of discolouration (ecchymoses) may be seen. Bleeding from the nose and gums, excessive menstrual bleeding, and bleeding into urine and stool, may also occur. Prolonged bleeding is also seen with surgery, and tooth extractions.


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How is von Willebrands disease diagnosed?
In patients with suspected von Willebrand's disease, blood tests (activated partial thromboplastin time (APTT), prothrombin time (PT), bleeding time, fibrinogen level) are done. Bleeding time will be prolonged (increased), while the other tests will be normal in von Willebrand's disease. If this is the case, blood tests for the presence, or absence, of specific factors are done. In cases where there is an associated decrease in factor VIII levels, partial thromboplastin time will be prolonged (increased).


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How is von Willebrands disease treated?
The treatment of von Willebrand's disease varies with the severity of the disease. Patients with mild von Willebrand's disease may be treated with medications such as desmopressin (DDAVP), which stimulates the body to release more clotting factors. Patients with severe bleeding are treated with transfusions of von Willebrand factor and/or factor VIII. Repeat transfusions may be required.


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What are the complications of von Willebrands disease?
Complications may be due to the disease itself, or may arise due to treatment. A person with von Willebrand's disease may develop bleeding while undergoing surgery, or after surgery, despite adequate precautions. While all blood products are carefully screened, there still remains a very small risk of transmission of infections. It is best to discuss this with your doctor.


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What can I do to help myself?
Most people with von Willebrand's disease live an active and productive life, with current treatment regimens. Transfusions may be helpful in preventing bleeding episodes. In case of cuts, put pressure on the wound with an ice pack.
Receiving vaccinations against blood-borne diseases (eg. Hepatitis B) is important. Preferably, a bracelet should be worn stating the condition, and the factor that is deficient. This may prove invaluable in an emergency.
Always avoid aspirin, as aspirin predisposes to bleeding.


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Referenties
Mackie, M.J., Ludlam, C.A. & Haynes, A.P. 1999, "Diseases of the blood", in Davidson's Principles and Practice of Medicine, eds C. Haslett, E.R.E. Chilvers, J.A.A. Hunter, & N.A. Boon, 18th edn, Churchill, Livingstone, London.

Von Willebrand's disease, 2001 [Online] Available: http://www.nlm.nih.gov/medlineplus/ency/article/000544.htm [2001, Aug. 01].