Microscopically, cells in the affected regions contain neurofibrillary tangles (NFTs) with diffuse neuritic plaques that are filled with an abnormal amyloid protein called beta amyloid. These plaques and tangles are the two major characteristic neuropathologic abnormalities identified by Dr. Alois Alzheimer in 1906.

Neuritic (also called senile) plaques are chemical deposits consisting of degenerating neurons combined with beta amyloid. These deposits are extracellular. Neurofibrillary tangles (NFTs) are intracellular abnormalities which are formed from paired helical filaments (PHFs). These intracellular derangements interfere with cellular transport of nutrients and trophic (growth) factors, which has been postulated to contribute to cell death.

Imaging studies suggest that these microscopic changes appear several years before behavioral changes are seen and may be present when a patient has no evidence of dementia.