Hereditary Hemorrhagic Telangiectasia (HHT)
With every beat of your heart, blood courses through your cardiovascular (circulatory) system—a complex, canal-like network of strong, flexible tubes such as arteries, capillaries, and veins.
When these vessels function normally, blood flows easily through them, transporting the entire body’s oxygen and nutrients while helping to maintain blood pressure and remove cellular waste. However, sometimes structural weaknesses or anomalies can present danger. This happens especially in people born with Hereditary Hemorrhagic Telangiectasia (HHT), a genetic disorder that affects the blood vessels.
Because this condition doesn’t cause any warning symptoms—and leaves people vulnerable to stroke and life-threatening infections—proper diagnosis, treatment, and monitoring is important.
People with this genetic condition have multiple malformed blood vessel connections that bypass capillaries, which normally connect arteries to veins. In the absence of capillaries, direct links between arteries and veins (called telangiectasia when small and arteriovenous malformations [AVM], when larger) occur.
These can allow clots and bacteria that would normally be filtered out by the capillaries to get into the lung, where they can cause stroke and serious infections such as brain abscess. Also, AVMs and telangiectasia can be weak and prone to burst open and bleed. Depending on where these artery-vein connections are located in the body, this can be a life-threatening emergency.
“Patients with suspected HHT, such was those with family members having this condition,” says Jeffrey Pollak, MD, interventional radiologist and medical director of the Yale Medicine HHT and Vascular Malformations Program, “should be screened for this condition and specific sites of involvement, especially since sudden life-altering events that might occur even in the absence of any preceding symptoms can potentially be prevented if HHT is known and treated in advance.”
At Yale Medicine’s HHT & Vascular Malformation Program, we are leaders in the diagnosis, treatment, and research of vascular malformations, whether they are caused by HHT or not. Our program’s multidisciplinary approach and principles of care have been adopted by HHT centers worldwide.
We continue to develop care guidelines for the diagnosis, treatment, and follow up of pulmonary and cerebral AVMs. We’re also leading the way in developing guidelines for managing patients with heart failure and other complications of HHT liver vascular malformations.
What is HHT?
HHT is a genetic disorder of the blood vessels that affects people of all ages and backgrounds. An estimated 50,000 to 100,000 Americans are affected by HHT, and most cases go undiagnosed. About 10 percent of people with HHT die prematurely or are disabled due to complications of their AVMs. Early diagnosis, treatment, and follow up can help people avoid these complications.
However, because most patients have few, if any, symptoms, many people are unaware of the condition until they experience serious complications. (See below for a list of signs that might suggest HHT.)
There are three main types of HHT:
- Type 1 is caused by mutations in the endoglin gene
- Type 2 is caused by mutations in the ACVRL1 (ALK1) gene
- HHT-juvenile polyposis syndrome is caused by mutations in the SMAD4 gene
All of these genes encode proteins that are involved in the proper development of blood vessels. Even though HHT runs in families, its effects can vary from one affected family member to the next.
For people with HHT, where in the body do arteriovenous malformations occur?
HHT can cause vascular malformations of the skin, gastrointestinal (GI) tract, and inside the nose (called telangiectasia). Larger arteriovenous malformations may be found in the brain, lung, or liver. Approximately, 50 percent of patients with HHT have an AVM of the brain, lung, or liver, or a combination of these.
It’s important to know that people may have vascular malformations unrelated to the genetic condition, HHT.
What are the symptoms of HHT?
Mild-to-moderate nosebleeds are the most common symptom of HHT, which usually begin around age 12. However, the age at which they begin, as well as their frequency and severity, vary.
Other serious symptoms include the following:
- Ischemic stroke, brain abscess, and transient ischemic attack (TIA) due to pulmonary arteriovenous malformations
- Gastrointestinal bleeding due to GI tract telangiectasia/AVM
- Hemorrhagic stroke and seizure due to cerebral arteriovenous malformation
Though rarer, some people with HHT have the following symptoms, due to liver vascular malformations:
- Heart failure
- Abdominal pain and abnormal liver function tests (biliary type)
- Fluid in the abdomen (ascites) and enlarged blood vessels in the esophagus (varices)
How is a diagnosis of HHT made?
A common sign of HHT is spontaneous and recurrent nosebleeds (mild or severe). Doctors also look for telangiectases on the hands, fingers, lips, and inside the mouth. Another consideration is if a close relative has HHT, or a pulmonary AVM, which is often a marker of HHT.
Diagnostic imaging tests (such as CT scans, MRIs or echocardiograms) are the best way to screen for AVMs within organ systems. Genetic testing is also recommended to look for gene mutations that cause the disorder. Once a family member is diagnosed, it’s recommended that other family members seek genetic counseling and screening.
How is HHT treated?
Treatments include local measures to control nosebleeds, embolization for significant-sized lung AVMs, and embolization, surgery, and stereotactic radiosurgery for brain AVMs. The location and size of the AVM determines what course of treatment is recommended. Even after treatment, patients should be monitored for the rest of their lives, as certain manifestations may worsen over time and some may not develop until later in life.
Here’s how the treatments work:
- Pulmonary Arteriovenous Malformations (PAVM): These occur in the lung. While they are a marker for HHT, not everyone with PAVMs has HHT. Treatment consists of transcatheter embolization, a nonsurgical procedure done under local anesthesia in adults and general anesthesia in children. The procedure involves routing a catheter through the blood vessels to the PAVM and inserting a blocking agent to stop the flow of blood to it. The procedure is performed by interventional radiologists, who are doctors specially trained in nonsurgical, image-guided therapies.
- Cerebral Arteriovenous Malformations (CAVM): These vascular malformations occur in the brain. Most CAVMs are not a result of HHT. All CAVMs are treated the same way, with embolization, surgery, stereotactic radiosurgery or a combination of these treatments.
- Epistaxis (nosebleeds): Ninety percent of people with HHT have nosebleeds, ranging from mild to severe. The majority can be treated with nasal lubricants and humidification, laser therapy, medications, or a combination of these treatments. A minority are more severe and resistant to such measures; these often respond to advanced medication that prevents blood vessel formation.
- Liver Arteriovenous Malformations: While most people with HHT have these malformations, only a relative few (less than 5 percent) have symptoms, which may include fatigue, shortness of breath, and leg swelling. Initial treatments are aimed at controlling these symptoms using medications such as diuretics (water pills) and others that control abnormal heart rhythms that may develop. In patients who do not respond favorably to this therapy, medications that prevent the formation of blood vessels and liver transplant should be considered.
- Gastrointestinal bleeding: About 20 percent of people with HHT develop gastrointestinal bleeding. It usually arises from telangiectases (small AVMs) in the stomach or small bowel (duodenum). Therapies include hormonal, anti-fibrinolytic, and anti-angiogenic medications, and the management of anemia.
Why is Yale Medicine’s HHT & Vascular Malformation Program unique?
“The HHT and Vascular Malformation Program is a model of success,” says Dr. Pollak. “Since its development at Yale School of Medicine in 1994, our center’s principles of care have been replicated by HHT centers worldwide.” Pollak leads the multidisciplinary care team, which helps care for patients with HHT and nongenetic vascular malformations.
“While there is no cure for HHT,” Dr. Pollak says, “together at Yale Medicine, we are working to prevent needless tragedies by diagnosing the disorder early and providing excellent treatment to patients and their families with continued monitoring.”