Cortical angiopathy in Alzheimer's disease: the formation of dystrophic perivascular neurites is related to the exudation of amyloid fibrils from the pathological vessels.

We studied the organization of dystrophic neurites around pathological vessels in Alzheimer cortex. Two techniques were used simultaneously on serial sections: thioflavine staining of amyloid substance and immunohistochemistry with immune sera against Paired Helical Filaments (anti-PHF) and native Tau proteins (anti-Tau). We observed different distributions of dystrophic neurites (immunolabelled with anti-PHF or anti-Tau) around thioflavine-stained angiopathic arterioles. The wall of the vessels with large diameter (greater than 100 microns) presented a congophilic angiopathy without neuropil reaction. In vessels with lesser diameter (less than 100 microns), dystrophic neurites constituted a discontinuous sleeve around vessels, always in close contact with amyloid substance outside the wall (dysphoric angiopathy). We observed structures similar to senile plaques around capillaries (diameter: 10-15 microns). The sleeve of dystrophic neurites with aggregated Tau proteins were always observed in the close vicinity of the amyloid substance which exuded from the pathological blood vessels. Thus, the exudation of these amyloid fibrils seems to induce the formation of dystrophic neurites (neuritic reaction).