Alzheimer’s vs. dementia: what’s the difference?

I avoided this post for awhile because existing online resources cover it pretty thoroughly: “What’s the difference between ‘Alzheimer’s disease’ and ‘dementia’?”

But I noticed that many folks, sometimes even highly knowledgeable people, use the terms “dementia” and “Alzheimer’s disease” interchangeably…incorrectly. So here are some quick definitions (just to be sure that you’re speaking the same language as your peers, care team, or staff).

Dementia is a cluster of signs and symptoms involving the loss of cognitive ability.

Symptoms of dementia can result from a number of different diseases; Alzheimer’s disease is one of many diseases that can cause dementia.

In addition to Alzheimer’s disease, other forms of dementia include:

vascular dementia (often resulting from a stroke)
frontotemporal dementia
dementia with Lewy bodies
Creutzfeldt-Jakob disease
Parkinson’s disease
Mild Cognitive Impairment*
and more…

This gets mixed-up for a number of reasons:

First of all, it seems that far more people know about Alzheimer’s disease than other forms of dementia. This is in-part because the bulk of diagnosed dementia is Alzheimer’s disease (50-70%, depending on your source). It makes sense that we’d mistakenly use “Alzheimer’s disease” and “dementia” to mean the same thing.
Clusters of symptoms suggesting any particular form of dementia tend to overlap. A lot. And an accurate diagnosis isn’t ensured without cutting into the brain.
Diagnoses based on “symptomatology” are, at best, statements that we should think of starting with “It’s highly probable that she has….” and not “She has…”
Some people exhibit two (or more!) types of dementia at the same time. As far as we know, no type of dementia protects against any other types.

All of this makes it really confusing: “Well, does my wife have Alzheimer’s or is it Lewy bodies?” is the type of question that can’t be answered with 100% accuracy. At least, not without a brain biopsy to determine if there are unusual accumulations of plaques and tangles or Lewy bodies (aka, balls of alpha-synuclein) in the nerves.

Instead, the symptoms and the patient’s history get close examination. For example, if the symptoms occur with hallucinations and Parkinson’s-like movement, it’s more likely Lewy bodies dementia.

That said, even if you can’t know with absolute certainty which disease you’re seeing the effects of, the symptoms can still correctly be called “dementia.” Dementia is, by definition, based on symptomatology.

It’s estimated that 5-8% of Americans over the age of 65 have some form of dementia. Of those, approximately 60% are thought to have Alzheimer’s disease.

If you only remember 3 things about the definitions of dementia vs Alzheimer’s disease:

Dementia is a group of symptoms. It is distinct from the natural process of aging.

Alzheimer’s disease is but one of many diseases that can cause the symptoms of dementia.

It’s possible for a person to have more than one disease that causes symptoms of dementia.

Additional Notes:

*Most of what we’re talking about on this site is “progressive dementia” in which symptoms of dementia worsen over time. However, you can also have “static dementia” (something that might follow major head trauma, for example), in which, after the initial loss, there is little additional decline.

*Mild Cognitive Impairment (MCI) is indicated when symptoms of dementia are present but don’t heavily impact daily life. Technically, MCI is not dementia. It could be described as “dementia-lite:” although some hallmark signs of dementia are present and may be noticeable to others, they don’t necessarily interfere with day-to-day living.

10-20% of adults aged 65+ have MCI. “It’s estimated that as many as 15 percent of these individuals progress from MCI to dementia each year. From this estimate, nearly half of all people who have visited a physician about MCI symptoms will develop dementia in three or four years.”(emphasis mine)

MCI is a risk factor for dementia.

*Delirium can have identical symptoms to dementia but is present for less time.

Generally, dementia symptoms must be present for at least 6 months for it to qualify as “dementia.” Anything shorter than that may be “delirium,” although delirium is most often measured in days and weeks.

About Dementia

from The Alzheimer’s Foundation of America

Dementia is a general term that describes a group of symptoms-such as loss of memory, judgment, language, complex motor skills, and other intellectual function-caused by the permanent damage or death of the brain’s nerve cells, or neurons.

One or more of several diseases, including Alzheimer’s disease, can cause dementia.

Alzheimer’s disease is the most common cause of dementia in persons over the age of 65. It represents about 60 percent of all dementias.

The other most common causes of dementia are vascular dementia, caused by stroke or blockage of blood supply, and dementia with Lewy bodies. Other types include alcohol dementia, caused by sustained use of alcohol; trauma dementia, caused by head injury; and a rare form of dementia, frontotemporal dementia.

The clinical symptoms and the progression of dementia vary, depending on the type of disease causing it, and the location and number of damaged brain cells. Some types progress slowly over years, while others may result in sudden loss of intellectual function.

Each type of dementia is characterized by different pathologic, or structural, changes in the brain, such as an accumulation of abnormal plaques and tangles in individuals with Alzheimer’s disease, and abnormal tau protein in individuals with frontotemporal dementia.

About dementia (definition)

from The Alzheimer’s Foundation of America

Additional Reading about Dementia

2011 Alzheimer’s Disease Facts and Figures from The Alzheimer’s Association, Alzheimer’s & Dementia, Volume 7, Issue 2. 2011.
About Alzheimer’s: Statistics from the Alzheimer’s Foundation of America
What is Vascular dementia? from The National Stroke Association
Frontotemporal dementia from the Family Caregiver Alliance
Dementia with Lewy bodies from Family Caregiver Alliance
Alzheimer’s Disease Fact Sheet from theUS Department of Health and Human Services: National Institutes of Health: National Institute on Aging
One in Seven Americans Age 71 and Older Has Some Type of Dementia, NIH-Funded Study Estimates from the US Department of Health and Human Services: National Institutes of Health News. October 2007.

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