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Most families learn what dementia is in the worst possible way: a parent gets a diagnosis, and suddenly there's a doctor in front of them using words like "Alzheimer's," "Lewy body," and "frontotemporal" as if they're interchangeable. They aren't.
This post is the one I wish someone had handed my family on day one. It's a plain-language guide to what dementia actually is, why Alzheimer's is one type of it (not a synonym for it), and how the major dementias differ in ways that matter for care, expectations, and treatment.
Dementia is not a single disease. It's a clinical category — a description of a pattern of symptoms that includes memory loss, difficulty with thinking and reasoning, and problems with daily function, severe enough to interfere with independent living.1
Many different diseases can cause dementia. The symptoms look similar at the surface, but the underlying biology, the rate of progression, and the practical care implications can be very different. Treating Alzheimer's and Lewy body dementia the same way is like treating a broken arm and a torn ligament the same way because both involve "the arm hurts."
Among older adults, the most common causes of dementia are:
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Alzheimer's is the most common and most studied form of dementia. It's caused by the buildup of two abnormal proteins in the brain: beta-amyloid plaques between neurons, and tau tangles inside them.1 These proteins damage and ultimately kill brain cells, starting in the regions responsible for memory (the hippocampus and surrounding entorhinal cortex) and gradually spreading outward.
What this means in practice: the earliest symptoms of Alzheimer's are almost always memory problems. Recent events fade. Repetitive questions become common. Names of familiar people slip. Over years, the disease spreads into language, judgment, spatial awareness, and eventually basic motor function.
Alzheimer's progresses slowly and predictably compared to most other dementias. The Reisberg Global Deterioration Scale describes seven recognizable stages of progression.
Vascular dementia is the second-most-common type, accounting for roughly 5–10% of cases.2 It's caused by reduced blood flow to parts of the brain — often the result of a major stroke, a series of small strokes (some so small the person didn't notice them), or chronic narrowing of small blood vessels in the brain.
The symptoms depend on which part of the brain lost blood flow, which is why vascular dementia can look very different from one person to the next. Some people have prominent memory problems; others have trouble with planning, organization, or attention; others have changes in mood or judgment. Progression can be stepwise — relatively stable, then a sudden decline after another stroke, then stable again — rather than the smooth slope you see in Alzheimer's.
One important practical implication: vascular dementia is the form of dementia most directly tied to cardiovascular risk factors. Blood pressure control, cholesterol management, smoking cessation, and diabetes management all matter — and they matter measurably, based on the latest evidence from large-scale prevention trials.
Lewy body dementia is the third-most-common dementia, and the one most often misdiagnosed in its early stages.3 The defining biology is the buildup of abnormal alpha-synuclein protein deposits — Lewy bodies — in brain cells. The same protein deposits cause Parkinson's disease.
LBD is actually an umbrella for two closely related conditions:
Several features distinguish LBD from Alzheimer's, and they matter for care:
Frontotemporal dementia is less common overall but is the most common dementia diagnosis in people under 60.4 Instead of starting with memory loss, FTD starts with changes in personality, behavior, judgment, or language — because it begins in the frontal and temporal lobes rather than the memory regions.
There are two main clinical patterns:
FTD progresses faster than Alzheimer's on average and often affects people in their 50s or early 60s. There is no FDA-approved treatment specifically for FTD; care is symptomatic and supportive.
Mixed dementia means more than one type is happening at once — most commonly Alzheimer's plus vascular changes. Brain autopsy studies suggest mixed pathology is actually the most common finding in people who died with dementia, especially those over 80.2 Many people who carry a single diagnostic label of "Alzheimer's" likely had vascular or Lewy body components contributing as well.
The practical implication for families: don't be surprised if a parent's symptoms don't fit one neat pattern. Real disease often doesn't.
TypeWhat causes itEarliest symptomsSpeed of progressionKey thing for caregiversAlzheimer'sAmyloid plaques and tau tanglesShort-term memory loss; word-findingSlow, gradual (years)Plan for a long arcVascularReduced blood flow; strokesVariable by region; planning, attention often affectedStepwise — sudden drops, then stableAggressively manage cardiovascular riskLewy bodyAlpha-synuclein depositsHallucinations, sleep disorder, fluctuating cognitionVariable, often faster than Alzheimer'sAntipsychotic sensitivity — flag the diagnosis everywhereFrontotemporalFrontal/temporal lobe degenerationPersonality and behavior changes; language lossFaster than Alzheimer'sOften diagnosed late; consider FTD if symptoms don't fit Alzheimer'sMixedMore than one of the aboveVariableVariableDon't expect a textbook progression
Many families leave the first appointment with the word "dementia" but no specific subtype. That's normal — accurate subtyping often takes additional testing — but it's worth asking the following questions explicitly:
Subtype matters because treatment, expectations, and risk vary. The same symptoms can point to different diseases, and the right care plan depends on knowing which one you're dealing with.
Dementia under age 65 is sometimes called younger-onset or early-onset dementia. The distribution of types is very different at younger ages: frontotemporal dementia is more common, autosomal-dominant Alzheimer's (driven by rare mutations in the APP, PSEN1, or PSEN2 genes) becomes more relevant, and unusual forms like Creutzfeldt-Jakob disease enter the differential. Genetic testing and a thorough neurological workup are especially important at younger ages.
If you have a family history that suggests a strong genetic pattern, talk to a genetic counselor about whether testing for APOE-4 and the rare deterministic genes is right for your family.
If you take only one thing from this post, take this: Alzheimer's is one type of dementia, not all of dementia. The differences between the types matter for what to expect, what to watch for, and what medications to avoid. If your parent's diagnosis is "dementia" without a subtype, ask the neurologist to be more specific — and don't be afraid to push for additional workup if the symptoms don't fit the most common pattern.
Knowing what disease you're actually dealing with is the foundation for everything else. From there, the next conversation is usually about what to expect over time — the stages of progression, and what each one tends to look like at home.
— King
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