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General Clinical
Information
HHT is an hereditary
condition that affects the blood vessels in many parts of the body.
Blood is brought to tissues (e.g. muscles or the brain) by arteries and
then drains away from tissues by veins. Normally, a fine network
of blood vessels called capillaries connects the arteries to the veins.
In the case of HHT, the capillaries are lost in some areas, and instead
the artery connects straight to the vein. When these connections
are less than a few millimeters in size, we call them
telangiectasias. When they are larger, say one quarter to several inches in diameter, we call them arteriovenous malformations or AVM. In 80-90% of patients with HHT, the disease is due to a genetic mutation in the gene for either the endoglin protein or the ALK1 receptor - both of which are proteins involved in blood vessel formation and regulation. A third gene has recently been discovered in which HHT is associated with polyps in the colon.
Diagnosis
1. Recurrent and spontaneous nosebleeds.
Signs and symptoms of
HHT
• Chest
X-ray: A standard X-ray of the lungs to
look at the size of your heart and the condition of your lungs. This
test takes about 15 minutes and will not cause any discomfort.
• Shunt test: This test is to look for PAVM .
During this test you breathe pure oxygen for 15 minutes with a nose clip on, and then a small sample of arterial blood is collected from an artery in your wrist. The main risks include slight discomfort or bruising where the needle is inserted, and less commonly a local infection. • Pulmonary function tests (PFT): These are also know as breathing tests and are used to measure your lung function. You will be asked to breath into a tube to test your lung function and capacity. These tests may take up to 40 minutes and usually will not cause any discomfort, though they might leave some people a little out of breath. • Echocardiogram: This test uses sound waves (ultrasound) to measure the size of your heart chambers, estimate the pulmonary artery pressure, and look for the presence of PAVM. It is performed by a technician who rubs a microphone in the area of your left breast to look at and listen to your heart - it is similar to the ultrasound test that is used to check a pregnant woman. Technician will also inject a small amount of saline through an IV in your arm. This test may take up to 30 minutes. There is mild discomfort from inserting an IV line into your arm and some patients may feel mild discomfort where the microphone is rubbed.![]()
CT scan of the lungs: • Pulmonary angiogram:![]() This is a procedure that is performed to look for PAVM. The test basically involves inserting a catheter (thin rubber tube) through a large vein in either you leg or neck, and passing it up into the arteries of the lungs. This involves one or more injections of “X-ray dye” into the arteries to help us see AVM. Click here for a detailed discussion of this procedure and its risks. MRI of the brain: This test uses magnetic waves to look for AVM or evidence of stroke in your brain. The test involves laying down on a platform which then moves into a tunnel. It is not painful but some people who are claustrophobic (afraid of small places) may get nervous during this test. • Right heart catheterization: This is a procedure that is performed to evaluate the blood pressure in the right side of your heart and lungs. The test basically involves inserting a catheter (thin rubber tube) through a large vein in either you leg or neck, and passing it up into your heart to measure the blood pressure. Click here for a detailed discussion of this procedure and its risks. • Genetic testing: This is a blood test that allows us to determine if you or a relative has inherited the gene for HHT. If this test detects a gene for HHT in your family, it is 99% accurate in determining whether other relatives have or don’t have HHT. Unfortunately, it is able to detect the gene for HHT in only about 80% of families. In the other 20% of families, genetic testing will not be helpful. The process of genetic testing involves first testing someone in the family who definitely has HHT. The initial test for a family is fairly expensive, and so some families decide to pool money together to pay for this first test. If this first test is positive, other family members can be tested for about $200-300 each. If this test is negative, genetic testing will not be helpful for this family. Genetic testing can only be ordered through HHT centers or genetic counselors, and takes about 4-8 weeks for results to come back. Private insurance will often pay for genetic testing, but Medicare usually will not. If you are interested in genetic testing, please contact our center. |
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Copyright |
Department
of Medicine |
Medical College of
Georgia
March 21, 2006 | |