Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disease affecting multiple organ systems. The Second International HHT Guidelines provide evidence-informed consensus guidelines... Description: Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disease with an estimated prevalence of 1 in 5000 that is characterized by the presence of vascular malformations (...

Hereditary haemorrhagic telangiectasia, inherited as an autosomal dominant trait, affects approximately 1 in 5000 people. The abnormal vascular structures in HHT result from mutations in genes (most commonly endoglin or ACVRL1) whose protein products influence TGF-ß superfamily signalling in vascular endothelial cells. The cellular mechanisms underlying the generation of HHT telangiectasia and arteriovenous malformations are being unravelled, with recent data focussing on a defective response to angiogenic stimuli in particular settings. For affected individuals, there is often substantial morbidity due to sustained and repeated haemorrhages from telangiectasia in the nose and gut. Particular haematological clinical challenges include the management of severe iron deficiency anaemia; handling the intricate balance of antiplatelet or anticoagulants for HHT patients in whom there are often compelling clinical reasons to use such agents; and evaluation of apparently attractive experimental therapies promoted in high profile publications when guidelines and reviews are quickly superseded. There is also a need for sound screening programmes for silent arteriovenous malformations. These occur commonly in the pulmonary, cerebral, and hepatic circulations, may haemorrhage, but predominantly result in more complex pathophysiology due to consequences of defective endothelium, or shunts that bypass specific capillary beds. This review will focus on the new evidence and concepts in this complex and fascinating condition, placing these in context for both clinicians and scientists, with a particular emphasis on haematological settings.

The autosomal-dominant trait hereditary haemorrhagic telangiectasia (HHT) affects 1 in 5–8000 people. Genes mutated in HHT (most commonly for endoglin or activin receptor-like kinase (ALK1)) encode proteins that modulate transforming growth factor (TGF)-β superfamily signalling in vascular endothelial cells; mutations lead to the development of fragile telangiectatic vessels and arteriovenous malformations. In this article, we review the underlying molecular, cellular and circulatory pathobiology; explore HHT clinical and genetic diagnostic strategies; present detailed considerations regarding screening for asymptomatic visceral involvement; and provide overviews of management strategies.

Background: Brain abscesses and ischaemic strokes complicate pulmonary arteriovenous malformations (PAVMs). At risk individuals are poorly recognised. Stroke/abscess risk factors have not been defined. Methods: A cohort study of 323 consecutive individuals with PAVMs (n = 219) and/or the commonly associated condition hereditary haemorrhagic telangiectasia (HHT, n = 305) was performed. Most of the 201 individuals with PAVMs and HHT had no respiratory symptoms, and were unaware they had HHT. Anderson–Gill models assessed constant and time dependent potential predictive variables for stroke/abscess, and rate reduction by PAVM embolisation. Results: 57 individuals with PAVMs and HHT experienced brain abscess or ischaemic stroke, usually prior to the diagnosis of underlying PAVMs/HHT. The primary determinants of stroke and abscess risks were unrelated to severity of PAVMs. Males had higher brain abscess rates (hazard ratio 3.61 (95% CI 1.58, 8.25), p = 0.0024); interventional histories and bacteriological isolates suggested dental sources. Once adjusted for gender, there was a marginal association between brain abscess and low oxygen saturation. For ischaemic stroke, there was no association with any marker of PAVM severity, or with conventional neurovascular risk factors. Surprisingly, low mean pulmonary artery pressure was strongly associated with ischaemic stroke (hazard ratio 0.89 (95% CI 0.83, 0.95) per mm Hg increase; p = 6.2×10⁻⁵). PAVM embolisation significantly reduced ischaemic stroke rate (p = 0.028); no strokes/abscesses occurred following obliteration of all angiographically visible PAVMs. The mean PAVM diagnosis–treatment interval was longer, however, when neurological risks were unrecognised. Conclusions: Ischaemic strokes and brain abscesses occur commonly in undiagnosed HHT patients with PAVMs. Risk reduction could be improved.

The classical patient with the vascular disorder hereditary haemorrhagic telangiectasia (HHT) has nose bleeds, dilated blood vessels over the lips and finger tips, and gastrointestinal bleeding in later life. However, this clinical scenario represents only one of the presentation patterns of HHT.1 , 2 It is now recognised that, in addition to microscopic mucocutaneous telangiectases derived from post capillary venules (fig 1A),3 HHT leads to the development of larger abnormal vascular structures at other sites. Arteriovenous malformations in the pulmonary, cerebral, and hepatic circulations account for some of the most devastating clinical complications of the disease.