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Preclinical stage. In the preclinical stage, the patient may appear normal on physical and mental status examination, but specific areas of the brain (e.g., entorhinal cortex, hippocampus) begin to be affected more than 10 years before symptomatic impairment.

Mild cognitive impairment. Definitive diagnosis is possible at this stage with memory loss, confusion, and difficulties in language and executive functions. Agnosia (loss of the ability to recognize objects, persons, sounds, shapes) and apraxia (inability to execute learned purposeful movements) are prominent. AD does not affect all memory capacities equally; episodic memory (older memories), semantic memory (learned fact), and implicit memory (the memory of the body on how to do things) are relatively less affected than newer facts or memories. Many patients experience vocabulary and fluency difficulties but continue to perform tasks independently.

Moderate. Progressive deterioration leading toward complete dependence marks the moderate stage of AD. Speech difficulties, urinary incontinence, incoordination in complex motor activities, inability to read or write, and worsening memory problems including loss of previously intact long-term memory become more evident. Behavioral changes are also observed with patient displaying increased irritability, labiality of emotions, and aggression especially toward caregivers. Approximately 30% show illusionary misidentifications and delusional disorder.

Advanced. In advanced-stage AD, the patient becomes completely dependent upon caregivers. Language is limited to small phrases or single words, eventually leading to complete loss of speech. Aggressiveness can still be present, although apathy and fatigue are much more common. Patients cannot perform the most simple of tasks without assistance, leading to eventual immobility. Death in most instances is caused by systemic infections like pneumonia or secondary to pressure sores.