Hereditary Haemorrhagic Telangiectasia and Pulmonary AVM
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Direct answer
Hereditary haemorrhagic telangiectasia is an autosomal dominant vascular dysplasia, most often caused by ENG or ACVRL1 mutations, with mucocutaneous telangiectasias and visceral arteriovenous malformations. The Curacao criteria need three of four features for a definite diagnosis: spontaneous epistaxis, multiple telangiectasias, visceral AVMs and a first-degree relative with the disease. Pulmonary AVMs cause right-to-left shunting, so every confirmed case is screened for them with contrast echocardiography.
What you must remember
- Curacao criteria: spontaneous recurrent epistaxis, mucocutaneous telangiectasias, visceral AVMs and a first-degree relative; three or more make the diagnosis definite.
- Genetics: ENG causes HHT1, ACVRL1 causes HHT2, and SMAD4 is linked with juvenile polyposis overlap, all with incomplete penetrance.
- Epistaxis: the commonest symptom, often causing iron deficiency anaemia that needs replacement.
- Pulmonary AVM: mostly in the lower lobes, causing hypoxaemia, platypnoea and orthodeoxia, with a right-to-left shunt.
- Paradoxical emboli: a pulmonary AVM allows venous clots or bacteria to bypass the lungs and cause stroke or brain abscess.
- Screening: transthoracic contrast echocardiography for pulmonary AVMs, with late bubble appearance after three to five cycles, and CT for confirmation.
- Treatment: transcatheter embolisation of the feeding artery is first line for pulmonary AVMs, and bevacizumab is used for refractory bleeding.
- Prophylaxis: antibiotics before procedures with bacteraemia risk are advised for patients with pulmonary AVMs.
Screening a suspected HHT patient, step by step
Diagnosis rests on clinical criteria, but the pulmonary and cerebral screening is what changes management. The steps below move from the bedside to the imaging that alters treatment.
- Count the criteria: check the four Curacao features and record the number that are present.
- Screen the lungs: perform contrast echocardiography, because early bubbles point to a cardiac shunt while late bubbles point to a pulmonary one.
- Confirm with CT: a CT chest defines the size and feeding artery of each pulmonary AVM before treatment is planned.
- Embolise the lesion: coils or occlusion devices are placed in the feeding artery, which is safer and more effective than surgery.
- Screen the brain: MRI of the brain looks for cerebral AVMs, since these carry a risk of haemorrhage and abscess.
- Protect against infection: antibiotic prophylaxis is given before dental and other bacteraemic procedures.
- Test family members: first-degree relatives are offered genetic testing and screening.
Where the exam tries to catch you
The stem usually describes breathlessness or a stroke without an obvious cause, and the trap is to miss the shunt.
- Trap: attributing hypoxaemia to lung disease when the chest is clear Correct: orthodeoxia and platypnoea point to a right-to-left shunt through a basal pulmonary AVM.
- Trap: taking any positive bubble study as proof of a pulmonary AVM Correct: early bubbles suggest an intracardiac shunt, while late bubbles after three to five cycles indicate an intrapulmonary shunt.
- Trap: choosing surgical resection first for a pulmonary AVM Correct: transcatheter embolisation is the first-line treatment.
- Trap: assuming antibiotic prophylaxis is needed only for valve disease Correct: pulmonary AVMs also cause paradoxical embolism, so prophylaxis is advised for these patients.
Frequently asked questions
How many Curacao criteria are needed for a definite HHT diagnosis?
Three or more of the four Curacao criteria make a definite diagnosis of hereditary haemorrhagic telangiectasia. Two criteria give a possible diagnosis, and fewer than two make it unlikely.
Which test screens for pulmonary arteriovenous malformations?
Transthoracic contrast echocardiography, a bubble study, is the screening test for pulmonary arteriovenous malformations. Late appearance of bubbles after three to five cardiac cycles points to an intrapulmonary shunt, and CT confirms the lesion.
What is the treatment of a symptomatic pulmonary AVM?
Transcatheter embolisation with coils or occlusion devices placed in the feeding artery is the treatment of a symptomatic pulmonary AVM. It is preferred over surgery because it is less invasive and effective for most lesions.
Why do patients with a pulmonary AVM need antibiotic prophylaxis?
A pulmonary AVM allows bacteria or clots to bypass the lungs, so they can reach the brain and cause abscess or stroke. Antibiotic prophylaxis before dental and other bacteraemic procedures lowers this risk.