Understanding HHT
Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder that affects blood vessels. This handout will discuss HHT, the causes and signs of HHT, how doctors test for it and how doctors diagnose it.
What Is HHT?
HHT is a genetic disorder of the blood vessels. It is also called Osler-Weber-Rendu (OWR) syndrome. HHT is hereditary, meaning it is passed down through generations of families. People with HHT have arteriovenous malformations, also called AVMs, in certain parts of their bodies, like the brain, lungs or liver. Arteries and veins are usually connected by tiny blood vessels called capillaries. In people with HHT, though, the capillaries are missing. Instead, there is an abnormal direct connection between the arteries and veins, which results in the AVM. When an AVM is extremely small, it is called a telangiectasia. Telangiectasias can occur on the skin, inside the mouth or nose or in the intestines.
There is no cure for HHT right now, but people with HHT will do better if they are diagnosed early and correctly. Making a diagnosis can be a challenge, but at the HHT Center at Massachusetts General Hospital, doctors can offer people with HHT opportunities for better health.
What Causes HHT?
HHT is caused by an abnormal change in a person’s genes. The change can be found through genetic testing.
What Are the Signs of HHT?
The signs of HHT are slightly different in each person. HHT can sometimes look like symptoms of other disorders. Some common signs of HHT are:
- Frequent nosebleeds, usually starting in childhood and increasing with age
- Small, red dots on the face, hands or inside of the mouth or nose (see pictures on right)
- Anemia with low iron levels in the blood
- Blood in the stool (either as a fresh drop or dark stool)
How Do Doctors Diagnose HHT?
There are many ways for doctors to diagnose HHT. The most common ways are:
- By reviewing a person’s medical history and family history
- By doing a physical exam of the person, looking for telangiectasias on the person’s skin or in the mouth or nose
- By testing a person’s blood for the genes that cause HHT
- Telangiectasias on a person’s tongue (left) and hand (right). Telangiectasias look like small, red dots.
What Are the Testing Options to Diagnose HHT?
The most important tests for HHT begin with 1.) a doctor’s review of a person’s medical and family history and 2.) a physical exam of the person. If a doctor thinks a person has HHT based on these 2 tests, an HHT doctor will have the person get a contrast echocardiogram and as needed, a CAT scan of the lungs, as well as imaging of the brain. These tests, and other tests for HHT, are explained below:
Contrast Echocardiogram
An echocardiogram is an ultrasound that looks at the heart. For people with HHT, doctors recommend they get a contrast echocardiogram. A contrast echocardiogram is a special type of ultrasound that uses saline (special salt water) to look at the heart. For this test, a doctor injects a small amount of saline into a person’s vein, usually in the right arm. Doctors can tell if a person might have HHT by using the ultrasound machine to look at the location, size and number of the bubbles that appear in the heart.
CAT (or CT) Scan of the Lungs
For this test, a computer uses many X-ray images and creates pictures of person’s body part on a computer screen. This lets doctors look at a person’s blood vessels for signs of HHT.
MRI Scan of the Brain
This test uses a computer to create many images of a person’s brain on a computer screen. This lets doctors look at the blood vessels for signs of HHT. Unlike a CAT scan, an MRI scan does not use radiation.
Endoscopy or Colonoscopy
Both of these tests look at person’s “food tube,” which begins with the esophagus (throat), continues to the stomach and on to the intestines. For an endoscopy, a long tube with a small camera on one end is placed down a person’s throat while they are asleep. The camera takes pictures of the stomach to check the blood vessels for signs of HHT. For a colonoscopy, the tube is placed inside the person’s rectum while they are asleep. The camera takes pictures of the intestines to check the blood vessels for signs of HHT.
Genetic Testing
Doctors can test a person’s blood for the genes that cause HHT. A geneticist (a doctor who practices genetics) will order genetic testing and a doctor or genetic counselor will discuss the results with the person.
What Resources Are Available at the HHT Center?
The HHT Center at Massachusetts General Hospital is a resource that offers compassionate, family-centered and multidisciplinary care for people of all ages. At the HHT Center, some care services we provide are:
- Arranging evaluations with specialists at Massachusetts General Hospital and Massachusetts Eye and Ear Infirmary
- Working with a person’s current primary care doctor and local community resources
- Creating a “medical home,” team-based medical care that is focused on the person’s needs
- Performing genetic testing and counseling
- Arranging care with the appropriate specialists in people’s communities