Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.
Alzheimer disease dissolves recent memory first and remote memory last. The patient repeats questions, misplaces belongings, forgets conversations, and gets lost on familiar routes. Childhood events and old addresses persist. This dissociation is selective, not random. The hippocampus is required for forming new memories, and it is destroyed early. Old memories are distributed across the cortex, so they persist much longer.
Functional impairment: the diagnostic boundary
Cognitive symptoms alone do not define dementia. The impairment must interfere with the ability to function at work or in usual activities. Managing finances, cooking, dressing, and navigating familiar places fail. When decline is progressive and irreversible and daily activities fail, the boundary into dementia is crossed.
Mild cognitive impairment (MCI) sits on the border between normal ageing and disease. The patient notices forgetfulness. Appointments and names take longer. Driving, finances, and relationships continue without major errors. Daily activities remain largely intact. Amnestic MCI progresses to Alzheimer disease at roughly 10–15% per year in referral settings such as memory clinics. Rates run lower in unselected community cohorts. Not all MCI converts.
The sequence of affected domains
The disease reaches cortical regions in order. Each newly involved region adds its deficit:
- Memory. Recent memory fails first: repeated questions, lost belongings, forgotten conversations, wandering on familiar routes.
- Orientation. Time goes before space. Losing track of the season or year precedes losing track of the city. Birthplace outlasts current address.
- Language. Reduced spontaneous speech and word-finding pauses (anomia) with circumlocution narrow the vocabulary. In later stages, echolalia and perseveration replace meaningful speech.
- Visuospatial function. Parietal involvement brings failure to copy figures or navigate routes. It eventually brings failure to recognise faces or objects in plain view.
- Executive function. As the frontal lobes are reached, planning, judgment, and impulse control erode. Poor financial decisions, poor hygiene, and inability to sequence simple actions follow.
- Praxis. Purposeful movement fails late. The patient cannot dress or use common implements despite intact strength and sensation.
Primitive reflexes suppressed by the healthy adult cortex may re-emerge as cortical inhibition fails. Sucking, grasp, and palmomental responses belong to this group. They confirm cortical involvement but are not specific to Alzheimer disease. Motor strength, deep tendon reflexes, and plantar responses stay normal. This pattern marks a cortical degenerative disease rather than a vascular or subcortical one.
Behavioural and psychological symptoms
Behavioural change is a core manifestation. It is driven by neurotransmitter failure in specific circuits:
- Apathy is the most common change and often precedes formal diagnosis: lost initiative, withdrawn conversation, abandoned hobbies, emotional flatness. This is lost drive from frontal circuit failure, not depression in the usual sense.
- Agitation appears in moderate stages, with restlessness and sometimes aggression when the patient can neither understand nor communicate.
- Wandering is among the most dangerous symptoms. Spatial disorientation drives aimless walking. Getting lost outside the home often forces the end of independent living.
- Sleep disturbance is common through circadian disruption, including late-day worsening of confusion (sundowning).
- Depression may appear early, sometimes before cognitive symptoms dominate. This creates the pseudodementia pitfall: depression can produce reversible cognitive impairment. A useful contrast is that the depressed patient often answers “I don’t know” and appears distressed by the loss. The Alzheimer patient tries, fails or confabulates, and remains unaware of the deficit’s extent.
- Psychosis — delusions, often of theft, and hallucinations — appears late. Early prominent visual hallucinations point toward Lewy body dementia instead.
Clinical differentiation from other dementias
The onset pattern and the first symptom differentiate dementias at the bedside more reliably than any single test:
| Dementia | Onset pattern | First or distinguishing feature |
|---|---|---|
| Alzheimer disease | Insidious, slowly progressive over months to years | Recent memory loss; motor function preserved; no focal deficits |
| Vascular dementia | Stepwise: a visible drop with each vascular event, stable between | Focal neurological signs and stroke or vascular risk-factor history |
| Dementia with Lewy bodies | Fluctuating cognition, good days and bad days | Early well-formed visual hallucinations with rigidity and bradykinesia |
| Frontotemporal dementia | Insidious, typically younger onset (around 50–65 years) | Personality change first — disinhibition, lost empathy — with memory relatively preserved early |
Evidence anchors
- NICE. Dementia: assessment, management and support (NG97): https://www.nice.org.uk/guidance/ng97
- National Institute of Neurological Disorders and Stroke. Alzheimer’s disease: https://www.ninds.nih.gov/health-information/disorders/alzheimers-disease
- Alzheimer’s Association. Symptoms and stages: https://www.alz.org/alzheimers-dementia/symptoms