Alzheimer's disease: an animated, cited guide
This page needs JavaScript for its animations. The outline and key answers are below, and every claim in the full version carries a numbered citation.
Not medical advice. Alzheimer's Companion is an educational synthesis of published literature. It does not replace a clinician.
What is in it
- What Alzheimer's is Dementia versus Alzheimer's, who it affects, the numbers.
- The brain that forgets Where it starts and how it spreads, stage by stage.
- Amyloid, animated From one protein cut to a plaque, and the debate about it.
- Tau and the tangle How a scaffold protein turns into a tangle and spreads.
- Microglia and the lost synapse Inflammation, pruning, and the strongest link to memory loss.
- Genes and inheritance APOE, the dominant families, Down syndrome, and what a test means.
- Twenty years before symptoms The biomarker cascade, in order.
- Stages and symptoms From no symptoms to severe dementia, function by function.
- Diagnosis and biomarkers Criteria, scans, spinal fluid, blood tests and screening tools.
- The differential Delirium, vascular, Lewy body, frontotemporal and reversible causes.
- Cholinesterase inhibitors and memantine Inside the synapse, and what the benefit really is.
- Anti-amyloid antibodies over time Lecanemab and donanemab over 18 months, ARIA and the debate.
- Beyond memory Agitation, mood, psychosis and sleep, and the drug cautions.
- Lowering the risk The 14 modifiable risk factors and what trials show.
- Living with dementia and caregiving Planning, safety, caregivers and the end of life.
- Nursing care Assessment, giving the medicines, communication, documentation.
- Toward a cure The pipeline, prevention trials, and the evidence for each route.
- History and people From Auguste Deter in 1901 to the antibodies.
- Flashcards and mnemonics Flip cards by topic.
- Quiz Questions with explanations.
- Glossary Every term, searchable.
- Sources Every reference behind the app.
Common questions
What is the difference between dementia and Alzheimer's disease?
Dementia is a syndrome: cognitive problems severe enough to interfere with everyday tasks. Alzheimer's disease is its most common cause. The Alzheimer's Association estimates it accounts for 60 to 80 percent of dementia cases and the WHO gives 60 to 70 percent. Most people with Alzheimer's also have other brain changes, such as vascular disease, which is called mixed dementia.
How many people have Alzheimer's disease?
The WHO reports 57 million people living with dementia worldwide in 2021, with nearly 10 million new cases each year. In the United States an estimated 7.2 million people aged 65 and older were living with Alzheimer's dementia in 2025, about 1 in 9 people in that age group.
When do the brain changes of Alzheimer's begin?
Many years before symptoms. In families with dominantly inherited Alzheimer's, changes in amyloid in spinal fluid were detected about 25 years before expected symptom onset, amyloid on PET scans about 15 years before, and memory decline about 10 years before. Amyloid builds first, tau spreads later, and tau tracks symptoms more closely.
Is there a blood test for Alzheimer's disease?
Yes, as an aid to diagnosis rather than a screening test. In May 2025 the FDA cleared the first blood test, which measures the ratio of p-tau217 to amyloid beta 42, for adults 55 and older with symptoms of cognitive decline seen in specialised care. The Alzheimer's Association's 2025 guideline says tests need at least 90 percent sensitivity and 75 percent specificity to be used for triage, and that they do not replace a full clinical evaluation.
How well do lecanemab and donanemab work?
They remove amyloid plaques and slow decline modestly; they do not stop or reverse it. In the CLARITY AD trial, lecanemab slowed decline on the CDR-SB scale by 0.45 points over 18 months, a 27 percent slowing. In TRAILBLAZER-ALZ 2, donanemab slowed decline by 0.70 points over 76 weeks in the combined population. Both cause amyloid-related imaging abnormalities (ARIA), swelling or small bleeds seen on MRI, which are more common in people with two copies of APOE4. Whether the benefit is clinically meaningful is still debated.
Can Alzheimer's disease be prevented?
No intervention has been shown to prevent it, but risk can be lowered. The 2024 Lancet Commission estimated that 14 modifiable risk factors account for about 45 percent of dementia cases worldwide, including hearing loss, high LDL cholesterol, less education, high blood pressure, smoking, inactivity, social isolation and untreated vision loss. That figure is a modelled upper bound that assumes the factors are causes, and most prevention trials have shown small or no effects.
How long do people live after an Alzheimer's diagnosis?
It varies widely. The Alzheimer's Association reports that people aged 65 and older survive on average 4 to 8 years after diagnosis, and some live 20 years. Age at diagnosis matters: one study found median survival of 8.3 years when diagnosed at 65 and 3.4 years at 90. Pneumonia is the most commonly identified immediate cause of death.