= diffuse gray matter disease with large loss of cells from cerebral cortex + other areas

◊Most common of dementing disorders in elderly!

Incidence: 10% of people >65 years of age; 50% of people >85 years of age

Histo: intraneuronal deposits of abnormally phosphorylated τ protein (neurofibrillary tangles) and extracellular β-amyloid (senile plaques)

• slowly progressive cognitive decline, memory impairment, adverse impact on activities of daily living (large overlap with other dementias of elderly)

Location: early neuronal loss + gliosis in mesiotemporal cortex

• “cracked walnut” appearance of brain atrophy = symmetrically enlarged sulci in high-convexity area
• focal atrophic change in medial temporal lobe (82% sensitive, 75% specific, 80% accurate):
  • volume loss of hippocampus + parahippocampal gyrus
  • enlargement of perihippocampal fissures
• smooth periventricular halo of hyperintensity (50%)

PET (axial images with 3D stereotactic surface projection):

• classic pattern of altered cortical metabolism:
  • hypometabolism in posterior cingulate gyrus, precuneus, posterior temporal + parietal lobes (earliest changes)
  • hypometabolism of prefrontal association cortices ± frontal lobe involvement
• sparing of sensorimotor cortex, visual cortex, anterior cingulate cortex, basal ganglia, thalamus, posterior fossa

Prognosis: 4^th leading cause of death in individuals >65 years