Hereditary hemorrhagic telangiectasia

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In medicine, hereditary hemorrhagic telangiectasia (also known as "Osler's disease," "Osler-Weber-Rendu disease"^[1]:844, and Osler-Weber-Rendu syndrome,^[2]) is an autosomal dominant genetic disorder that leads to vascular malformations.

[edit] Signs and symptoms

HHT is characterised by telangiectasia (small vascular malformations) on the skin and mucosal linings, epistaxis (nosebleeds), and arteriovenous malformations (AVMs) in various internal organs. Skin and mucosa telangiectasias are most remarkable on the tongue, hands/fingers, nose, lips, mouth/throat and conjunctiva.

The internal organs that can harbor AVMs often include the brain and lungs. In both, bleeding can seriously endanger life. Anemia may occur due to bleeding from digestive tract AVMs. High-output heart failure may develop in the presence of marked shunting arterial blood to the venous circulation, e.g. when AVMs are present in the liver. Cerebral vascular accidents can occur from embolization from vascular malformations of the pulmonary circulation.

[edit] Diagnosis

There are four diagnostic criteria, otherwise known as the Curacao criteria, named after the city where the meeting took place to formally define hereditary hemorrhagic telangiectasia.^[3] If three or four are met, a patient has definite HHT, while two gives a possible diagnosis:

1. Spontaneous recurrent epistaxis
2. Multiple teleangiectasias on typical locations (see above)
3. Proven visceral AVM (lung, liver, brain, spine)
4. First-degree family member with HHT

When HHT is suspected, physical examination focuses on inspecting the skin for teleangiectasias, which are usually located on the digits, pinna, and bridge of the nose. Telangiectasias can also be seen with high frequency on the tongue and palate. In addition, auscultation of the liver for presence of bruits, and heart for high-output cardiac failure should be performed. A detailed neurological examination could reveal prior evidence of a stroke.

Pulmonary AVMs can be anticipated by measuring oxygen levels, sampling arterial blood gas (ABG), and performing a 2D echocardiogram with bubble study. An X-ray or CT of the chest can show lesions; in addition, low oxygen tension (<96% or a 2% decrease upon standing) or low blood oxygen levels on ABG are required for a diagnosis. CT and MRI of the brain can demonstrate cerebral AVMs. Abdominal ultrasound with doppler study or CT can show AVMs of the liver. Upper endoscopy, enteroscopy or capsule endoscopy can show gastrointestinal involvement. Rarely, telangiectasias can be demonstrated in the large intestine by colonoscopy.

[edit] Genetics

Hereditary hemorrhagic telangiectasia has an autosomal dominant pattern of inheritance.

HHT is a genetic disorder by definition. It is inherited in an autosomal dominant manner.

Four forms have been described:

It is possible to test patients for the presence of mutations in endoglin, ALK-1 and SMAD4. When the mutation in an affected family member has been found it is possible to test other family members and identify those people not at risk for developing the disease.

[edit] Pathophysiology

The mechanism underlying the formation of vascular malformations is not completely understood, but signalling of transforming growth factor-β1 is most likely to be involved. Possibly, connective tissue is required to support and guide proliferating blood vessels during angiogenesis, and defects in TGF-β signalling adversely affect connective tissue and matrix production.

[edit] Treatment

There is no specific treatment for the condition, but complications can be addressed. Any patient undergoing dental work who has demonstrated pulmonary AVMs should have antibiotic prophylaxis. Anemia due to bleeding from digestive tract AVMs often necessitates repeated blood transfusions, intravenous iron therapy, and possible ablative therapy with cautery or argon plasma coagulation. Estrogen therapy is occasionally efficacious in chronic gastrointestinal blood loss. Interventional radiologists can ablate pulmonary AVMs with coil embolization. For severe nosebleeds, ENT physicians can cauterize bleeding vessels. Rarely, high output cardiac failure from hepatic AVMs necessitate liver transplantation.

[edit] Epidemiology

HHT occurs mainly in whites (1:5,000), more in certain areas of France, but much less in blacks (1 in 1 million). It is found in all continents throughout the world. It is also seen with increased frequency in Mormon families from Utah.^{[citation needed]}

However, HHT is not limited to, nor found predominantly in people of a particular ethnic background, as are some genetic disorders.^[6]

[edit] References

[edit] External links

• Online 'Mendelian Inheritance in Man' (OMIM) HHT1 -187300, 600376, 601101, 610655
• HHT.org
• Information about Hereditary Hemorrhagic Telangiectasia from Children's Hospital, Seattle.