For years, "dementia" was a single word for a single shape of loss. Forgetting. Slowing. The slow vanishing of someone you knew.
It is not one shape. It has never been one shape.
What it has been is a word large enough to absorb several different illnesses, each with its own pace, its own warnings, its own particular way of asking you to be present. The two most common are Alzheimer's disease and Lewy body dementia. Most families assume that whatever is happening to their person is the first one, because the first one is the one they know the name of. Often they are right. Sometimes they aren't, and the difference matters more than people realize.
This post is for the families currently living inside the question. It will not give you a diagnosis. It will, we hope, help you ask better questions of the people who can.
Two diseases that share a word
Alzheimer's disease and Lewy body dementia are both forms of dementia. Both involve abnormal protein deposits in the brain. Both are progressive. Both are, eventually, terminal.
That is where the similarity ends.
The proteins are different. The areas of the brain affected first are different. The earliest symptoms are different. And the medications used to treat the symptoms are sometimes the same and sometimes — importantly — incompatible. A drug that helps one dementia can severely harm someone with the other.
So when families say, "Mom has dementia," and stop there, they are answering only the first half of the question. The second half — which kind? — is the one that shapes everything that comes next.
What Alzheimer's tends to look like
This is the dementia most people picture, and for good reason: it is the most common.
Alzheimer's typically begins with memory. Short-term memory first. The same question asked twice, then three times. The errand forgotten on the way home. Names beginning to slide. Over time, language follows — words become harder to find, conversations become harder to follow. Then judgment, then orientation, then eventually the long-known faces.
The progression is usually gradual. Day to day, week to week, the change is small enough that families adapt without realizing they are adapting. Bad days happen, but they don't usually swing wildly. Hallucinations are unusual until late stages. Movement and gait remain relatively normal until the disease is advanced.
If you had to describe Alzheimer's in a single word, it would be fading.
What Lewy body dementia tends to look like
Lewy body dementia is older than its public name. Most families have never heard of it until a doctor uses the phrase carefully in a clinic room. Then they go home and learn that some of what they had been blaming on age, or on Alzheimer's, or on a strange medication reaction, was actually this all along.
What sets it apart, in our experience and in the careful observation of clinicians who know it well:
- Hallucinations early. Often visual, often vivid. People. Children. Animals in the corner. The hallucinations can be benign — a man in the chair, a dog under the table — or distressing. They may appear before significant memory issues do.
- Fluctuating cognition. Sharp on Tuesday morning, profoundly confused by Wednesday afternoon. Then sharp again. Families often describe a swing they can't predict and can't explain. This fluctuation is one of the most reliable signatures.
- Movement changes that resemble Parkinson's. Stiffness. A shuffling gait. A blank facial expression. Tremor sometimes, but the rigidity and slowing are more consistent.
- REM sleep behavior disorder. Acting out dreams — kicking, shouting, falling out of bed — sometimes years before any cognitive symptoms appear. Spouses often describe this long before anyone connects it to dementia.
- Severe sensitivity to antipsychotic medications. Many people with Lewy body dementia have profound, sometimes dangerous reactions to common antipsychotics prescribed for agitation or hallucinations. This alone is reason to know the diagnosis: a well-meaning prescription can make things much, much worse.
If you had to describe Lewy body dementia in a word, it would be fluctuating. Not a slow fade, but a turning of the tide that doesn't keep a clock.
If Alzheimer's is fading, Lewy body dementia is fluctuating — not a slow goodbye, but a tide that doesn't keep a clock.
Why the difference matters in care
It matters in three quiet, practical ways.
It matters for medication. The wrong antipsychotic, given to someone with Lewy body dementia for what looks like ordinary agitation, can produce severe rigidity, confusion, and sometimes dangerous adverse events. Knowing the diagnosis changes which drugs are off the table.
It matters for expectations. A family expecting a slow Alzheimer's-style fade and instead living with weekly fluctuations begins to feel they are doing something wrong, that they cannot read their loved one's needs. They are not doing anything wrong. They are tracking a different illness.
It matters for hallucinations. Hallucinations in someone with Lewy body dementia are usually not psychiatric in origin and usually do not respond to the medications a family might be offered first. The kind, evidence-aware response is often environmental — better lighting, fewer mirrors, gentle redirection — and sometimes a carefully chosen medication that respects the diagnosis.
And it matters for hope. Not the hope of cure, which neither illness offers. But the hope of being met. A family who understands that Wednesday is not a regression but a fluctuation, and that Thursday may bring back the person they thought was gone for good, lives a different week than a family who reads every bad day as the beginning of the end.
Naming as its own act of love
One of the things this work has taught us is that naming is not a small thing.
To name what is happening is to refuse to be alone inside it.
It is also to tell the truth in front of the person, in a way that is not a diminishment. Saying "you have Lewy body dementia" rather than "something is wrong" gives the person back their context. They are not failing. They are unwell, in a specific way that has been seen before and will be seen again, by people who understand it.
There is dignity in that. Not the dignity of choosing well. The dignity of being known clearly, without softening or evasion, by the people who love you.
We have watched families discover this, late. Sometimes very late. We have watched them grieve the years they spent assuming it was Alzheimer's, then having to learn this whole different set of patterns. The grief is real. It is also not a failure. The naming, when it comes, is still an act of love.
What to do if you are not sure
If you suspect your person's dementia might not be straightforward Alzheimer's — if their hallucinations have been vivid and early, if their cognition swings without explanation, if they have acted out dreams for years, if antipsychotics have made them worse rather than better — the next gentle step is a referral.
A geriatric specialist, a memory clinic, or a neurologist with training in dementia subtypes can usually distinguish Alzheimer's from Lewy body dementia with a careful clinical evaluation, sometimes supplemented by imaging or a sleep study. The process is not invasive. It will not change the eventual outcome, but it will change the kind of road you walk on the way there.
Bring notes. Bring specific examples. Patients with Lewy body dementia in particular often present sharply during the appointment itself — that is the fluctuation at work. Your observations from the rest of the week are the data the clinician needs.
The bottom line
Two diseases share a word. Alzheimer's typically fades, slowly, beginning with memory. Lewy body dementia typically fluctuates, beginning sometimes with hallucinations, with movement changes, with dreams acted out years in advance, with severe reactions to common medications. The treatments are sometimes the same and sometimes incompatible, and the family experience of each is shaped, more than people realize, by which one is actually present in the room. If you are not sure which one your person has, the next gentle step is a careful evaluation. Not because a name will save them. Because a name lets you and the people who love them stop guessing — and start being present to the actual thing that is happening, which is a quieter and more loving place to stand than the one full of unanswered questions.