Stage

Typical Age of Onset

Brain Region Affected

Description of Damage

1. Preclinical AD (Silent stage)

~40-65 years (depending on risk factors, like APOE4)

- Amyloid deposits in neocortex
- Early tau in entorhinal cortex

- No visible atrophy
- Silent accumulation of Aβ plaques
- Early tau seeding in medial temporal lobe

2. Mild Cognitive Impairment (MCI) due to AD

~60-75 years

- Entorhinal cortex
- Hippocampus

- Tau pathology spreads
- Early hippocampal shrinkage
- Some amyloid in cortex

3. Mild AD (Early dementia)

~65-80 years

- Hippocampus (more severe)
- Temporal lobe (esp. lateral temporal)
- Parietal cortex begins

- Progressive atrophy
- Amyloid & tau spread

4. Moderate AD

~70-85 years

- Temporal-parietal cortex
- Frontal cortex involved

- Severe atrophy in memory, language, and attention areas

5. Severe AD (Late stage)

~75-90+ years

- Global cortical atrophy
- Frontal cortex, Occipital cortex, Motor cortex, Subcortical areas (like thalamus)

- Widespread brain shrinkage
- Severe synapse and neuron loss