Brain biopsy specimens from five patients with Alzheimer's disease obtained in the course of a trial of intracerebroventricular bethanechol were studied by immunohistochemical (antibody to A4 peptide) and ultrastructural techniques, with particular emphasis on the microvessels. In some cases, numbers of A4-immunoreactive lesions (senile plaques) correlated well with numbers of plaques demonstrable by silver stains. Prominent A4-immunoreactive amyloid angiopathy was seen in one patient. The patient with severe cerebral amyloid angiopathy (CAA) showed extensive arteriolar deposition of amyloid filaments with apparent destruction of the media but remarkably intact endothelium. A cell of origin for amyloid filaments was not apparent, although close proximity to smooth muscle cell remnants in the arteriolar media suggested this as one possible cell of origin. Frequent vessels showed medial or adventitial collagen deposition, even when the amount of amyloid was minimal or negligible. Thus relatively severe CAA can exist in the absence of overt endothelial injury, although related studies on this tissue indicate definite abnormalities of the blood-brain barrier. Conversely, destruction of smooth muscle cells and collagen deposition in vessel walls may be the cellular correlates of arteriolar weakening that can lead to CAA-related brain hemorrhage.

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Fabry''s disease, a rare X-linked disorder of glycosphingolipid metabolism, can present as an insidious dementia in middle or later life. This genetic disorder produces a deficiency of α-galactosidase A which results in the deposition of glycosphingolipids in blood vessel walls in the brain as well as in the kidney, heart, peripheral nerves, and other organs. Among the cerebrovascular manifestations of this disorder is a vascular dementia from involvement of multiple small penetrating blood vessels. Fabry''s disease is a consideration in the work-up of an otherwise unexplained vascular dementia, particularly in males less than 65 years of age.

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