Subpial Amyloid Plaques in the Cerebellum in a Case of Alzheimer's Disease

We studied the morphological and immunohistochemical characteristics of subpial amyloid plaques (SAPs), which were found particularly in the cerebellum of an Alzheimer''s disease (AD) patient, and compared them to the senile plaques (SPs) and amyloid angiopathy in AD cerebrum. The case presented herein exhibited a variety of amyloid deposition including SAPs and amyloid angiopathy. SAPs were visualized most intensely with antibodies to amyloid-β protein (Aβ), compared with the conventional staining methods including silver impregnation techniques. The most unique feature of the SAPs consisted in their morphology and location, which was between the pia mater and brain parenchyma, occasionally bulging outside the brain surface. Immuno-staining with monoclonal antibodies against the carboxyl termini of Aβ showed that SAPs were invariably positive for Aβ42/43, two-thirds of which were associated with Aβ40. Ultrastructurally SAPs appeared either fibrillar or amorphous and were separated originally from the brain parenchyma by sheets of glia limitans. The chronological relationships in the evolution of the SAPs are discussed with relevance to their morphology and location.