General Clinical Information About HHT

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

The four diagnostic criteria for HHT are listed below. A person has definite HHT if they meet at least three criteria, and possible HHT if they meet two. Persons with less than two criteria are unlikely to have HHT.

1. Recurrent and spontaneous nosebleeds.
2. Multiple telangiectasias on the skin and mucus membranes; most commonly seen on the face, chest, fingers, ears, lips, tongue, and inside the nose.
3. AVM or telangiectasias in the internal organs including: lung, brain, liver, intestines, stomach, spinal cord.
4. A direct relative who meets these same criteria for definite HHT.

Signs and Symptoms

About 90% of people with the gene for HHT will eventually develop signs or symptoms of HHT, almost always by the age of 40. However, just because a person reaches the age of 50 without symptoms of HHT does not mean that they are not affected. They may have subtle signs on physical exam and lab testing that only a doctor familiar with HHT might detect. The earliest symptom of HHT is nosebleeds in most patients, often developing in adolescence. Patients also start to develop small purple spots or telangiectasias on the face, mouth, and fingers in their twenties and thirties. Other common symptoms include shortness of breath, exercise intolerance, fatigue, migraine headaches, seizures, abdominal pain, leg swelling, and intestinal bleeding. See complications for more information on specific signs and symptoms.

Diagnostic Evaluation and Screening

The goals of testing are two: 1) determine whether you meet criteria for a diagnosis of HHT and 2) look for common complications of HHT like pulmonary AVM (PAVM) and cerebral AVM (CAVM). In general, we begin with less invasive and less risky tests to screen for various complications and move towards more invasive and risky tests if your signs and symptoms are highly suspicious for a particular complication. You may even find that some of these tests are repeated even though you have already had them done elsewhere. Reasons why some tests may be repeated are: the original tests may be too old; the old test may not be of high enough quality; or the old test may have been performed a little differently.

• 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: This is like a 3-dimensional X-ray of your lungs and helps us to look for PAVM. This test takes about 15 minutes and will not cause any discomfort. If “X-ray dye” is used, an IV will need to be started. In this case there may be mild discomfort from inserting an IV line into your arm; there is also a small risk of kidney problems from the X-ray dye.
• 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.