Non-CAA angiopathies and their possible interactions with cerebral amyloid angiopathy.

Cerebral amyloid angiopathy (CAA) is one of the two most common cerebral arteriopathies seen in the brains of elderly patients. The other is arteriosclerosis (AS), historically considered a consequence of chronic hypertension and also described as lipohyalinosis (LH), a clinicopathologic association that is increasingly questioned. These and other less frequently encountered degeneralions of the cerebral microvasculature (CADASIL, Binswanger subcortical leukoencephalopathy) share the common feature of degeneration of the medial smooth muscle layer within arteriolar walls. This can be dramatic in CAA, in the course of which complete replacement of medial smooth muscle by fibrillar amyloid may occur. It is a less prominent feature of CADASIL and BSLE: in the latter condition, medial smooth muscle hyperplasia, possibly a response to some kind of injury, is a more dramatic finding. In some of these "angiomyopathies", fibrinoid necrosis of the arterial wall and microaneurvsm formation may lead to stroke, manifest as cerebral hemorrhage. With CADASIL and BSLE, ischemic brain injury is more common. In the case of CAA, upregulation of the Abeta-amyloid precursor protein occurs when arteriolar smooth muscle cells in culture are exposed to prolonged hypoxia, especially with reoxygenation. Injury to arteriolar smooth muscle cells may be one mechanism by which angiomyopathies progress and become symptomatic.