Hereditary hemorrhagic telangiectasia is a disorder that results in the development of multiple abnormalities in the blood vessels.

In the circulatory system, blood carrying oxygen from the lungs is normally pumped by the heart into the arteries at high pressure. The pressure allows the blood to make its way through the arteries to the smaller vessels (arterioles and capillaries) that supply oxygen to the body's tissues. By the time blood reaches the capillaries, the pressure is much lower. The blood then proceeds from the capillaries into veins, through which it eventually returns to the heart.

In hereditary hemorrhagic telangiectasia, some arterial vessels flow directly into veins rather than into the capillaries. These abnormalities are called arteriovenous malformations. When they occur in vessels near the surface of the skin, where they are visible as red markings, they are known as telangiectases (the singular is telangiectasia).

Without the normal buffer of the capillaries, the blood moves from the arteries at high pressure into the thinner walled, less elastic veins. The extra pressure tends to strain and enlarge these blood vessels, and may result in compression or irritation of adjacent tissues and frequent episodes of severe bleeding (hemorrhage). Nosebleeds are very common in people with hereditary hemorrhagic telangiectasia, and more serious problems may arise from hemorrhages in the brain, liver, lungs, or other organs.

There are several forms of hereditary hemorrhagic telangiectasia, distinguished mainly by their genetic cause but with some differences in patterns of signs and symptoms. People with type 1 tend to develop symptoms earlier than those with type 2, and are more likely to have blood vessel malformations in the lungs and brain. Type 2 and type 3 may be associated with a higher risk of liver involvement. Women are more likely than men to develop blood vessel malformations in the lungs with type 1, and are also at higher risk of liver involvement with both type 1 and type 2. Individuals with any form of hereditary hemorrhagic telangiectasia, however, can have any of these problems.

Juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome is a condition that involves both arteriovenous malformations and a tendency to develop growths (polyps) in the gastrointestinal tract. Hereditary hemorrhagic telangiectasia types 1, 2 and 3 do not appear to increase the likelihood of such polyps.

Nosebleeds are the most common sign of HHT, resulting from small abnormal blood vessels within the inside layer of the nose. Abnormal blood vessels in the skin can appear on the hands, fingertips, face, lips, lining of the mouth, and nose as delicate red or purplish spots that lighten briefly when touched. Bleeding within the stomach or intestines is another possible indicator of HHT that occurs because of abnormal blood vessels lining the digestive tract. Additional signs of HHT include abnormal artery-vein connections within the brain, lungs, and liver, which often do not display any warning signs before rupturing.

HHT is a genetic disorder. Each person with HHT has one gene that is altered (mutated), which causes HHT, as well as one normal gene. It takes only one mutant gene to cause HHT. When someone with HHT has children, each child has a 50% chance to receive the mutant gene from his/her parent, and therefore to have HHT, as well. Each child also has a 50% chance to receive the normal gene and not be affected with HHT. At least five different genes can cause HHT, three of which are known.

HHT can be diagnosed by performing genetic testing. Genetic testing can detect a gene mutation in about ¾ of families with signs of HHT, which if found can establish the diagnosis of HHT in individuals and families who are unsure about whether they have HHT. HHT can also be diagnosed by using clinical criteria (presence of signs and a history of signs in a parent, sibling, or child).

Although current treatment cannot stop telangiectasias or arteriovenous malformations (AVMs) from forming, many of the symptoms and complications associated with hereditary hemorrhagic telangiectasia (HHT) can be treated or prevented. Management of HHT includes checking for new or worsening AVMs and the treatment of complications such as nosebleeds, bleeding from the intestines or stomach, and anemia. Treatment of AVMs of the lung (pulmonary), brain (cerebral) and liver (hepatic) may also be recommended.

Reducing the number and severity of nosebleeds can help prevent anemia. Treatment of nosebleeds may include using a vaporizer to increase the moisture of room air and keeping the inside of nose moist using nasal lubricants or sprays. Laser therapy may be used to remove the abnormal blood vessels (laser ablation). Other treatment may include medication or hormone therapy, but the effectiveness and safety of these treatments has not been established. If the nosebleeds continue despite other treatment, skin from a different part of the body may be grafted to replace the thin lining of the nose (septal dermoplasty) in an effort to cover and protect the fragile telangiectases.

Bleeding in the intestine or stomach is usually only treated if oral iron supplements cannot keep iron levels high enough to avoid anemia. Treatment may include surgical removal of AVMs or laser therapy to destroy and close the AVMs. If severe bleeding with uncontrolled anemia develops, treatment of AVMs in the stomach or intestine may include medication or hormone therapy, but the effectiveness and safety of these treatments has not been established. In addition to oral iron supplements, anemia may be treated by intravenous (IV) iron therapy or, in more severe cases, red blood cell transfusions.

Treatment of AVMs of the lungs (pulmonary AVMs) is recommended if the person with HHT is having a hard time breathing (dyspnea), is unable to exercise without extreme fatigue (exercise intolerance), or has low blood oxygen levels (hypoxemia). Treatment of pulmonary AVMs may also be performed to prevent lung hemorrhage and the neurologic complications of brain abscesses and/or stroke. Treatment may include inserting a small inflated balloon or small metal coil in the artery that leads into the AVM in order to stop the blood flow through the AVM (embolotherapy) or surgical removal of the AVM. People with pulmonary AVMs are advised to take extra precautions to avoid serious complications. These recommendations include taking antibiotics before dental or surgical procedures, using special filters in IV lines to prevent even tiny air bubbles from entering the blood stream, avoiding blood thinners and non-steroidal anti-inflammatory drugs (such as aspirin, ibuprofin, and naproxen), and regular monitoring by a doctor familiar with HHT.

AVMs in the brain (cerebral AVMs) greater than 1.0 cm in diameter may be surgically removed. Alternative treatment includes inserting a small inflated balloon or glue-like substance to stop the blood flow through the artery involved in the AVM (embolotherapy) and/or using a narrow, focused beam of radiation to destroy the AVM (stereotactic radiosurgery).

AVMs in the liver (hepatic AVMs) are currently treated only if a person shows signs of heart failure or significant health problems related to the liver not working properly. Treatment might include standard heart failure medications, liver transplantation, or medications like bevacizumab.In addition, guidelines for people with HHT recommend annual evaluations for anemia and neurologic conditions and re-evaluation for pulmonary AVMs every one to two years during childhood and every five years thereafter. Blood tests to check for anemia may be recommended more often depending on the frequency and severity of nose bleeds or if an intestinal or stomach AVM is bleeding. Women with HHT considering pregnancy are screened and treated for pulmonary AVMs; if pulmonary AVMs are discovered during pregnancy, they are treated during the second trimester.