May be due to deposition of amyloid in the parenchyma of the brain which is toxic to neurons and oligodendroglia. An alternative hypothesis is that deposition of amyloid is a secondary effect. The amyloid deposition is thought to be due to an abnormality in the amyloid precursor protein. Alzheimer's disease is the most common senile dementia in patients greater than 65 years old. Alzheimer's disease is seen before 65 years of age and is called presenile dementia.
Most familial cases are presenile.
Since the 85 years of age and older group is increasing rapidly, Alzheimer' disease is becoming an important disease. Generally atrophied with large ventricles. Alzheimer's disease is characterized by the formation of round senile plaques often with an amyloid center in the neuropil of the cerebral cortex as well as neurofibrillary tangles within neurons. The diagnosis is made by counting the number of senile plaques per 20x field and the number of neurofibrillary tangles in the same area, using the Bielschowsky stain. Alzheimer's disease is a devastating disease causing loss of recent memory, followed by old memories and apraxias or inability to carry out a normal procedure such as dressing, eating etc.