Dementia vs Alzheimer's: What's the Difference?

It is one of the most common questions in a primary care office after a new diagnosis: "Does she have dementia, or Alzheimer's?" The two words are used interchangeably in everyday speech, including by clinicians when talking to families. They are not the same thing, and the distinction matters.

Here is the short version. Dementia is an umbrella term — a category — for a pattern of cognitive decline that interferes with daily life. Alzheimer's disease is the most common specific cause of dementia, but not the only one. A person with Alzheimer's disease has dementia. A person with dementia may or may not have Alzheimer's.

This article walks through the distinction, the other common causes of dementia, and why knowing which one someone has actually matters.

Dementia: the umbrella

"Dementia" describes a set of symptoms — memory loss, problems with thinking and reasoning, changes in personality or judgment — that are severe enough to interfere with daily life. It is a clinical syndrome, not a specific disease. Something causes it, and the cause is a specific underlying condition.

Think of it like "chest pain." Chest pain is a symptom category. It could be caused by a heart attack, or by reflux, or by a pulled muscle, or by anxiety. A clinician has to figure out what's causing the chest pain, because the treatment depends entirely on the cause.

Dementia works the same way. A person presenting with memory loss and confusion might have Alzheimer's disease, vascular dementia, Lewy body dementia, frontotemporal dementia, or one of several less common causes. Some of these respond differently to medications. Some progress differently. Some have specific risk factors or preventive measures that matter.

Alzheimer's disease: the most common cause

Alzheimer's disease accounts for roughly 60 to 80 percent of dementia cases worldwide. It is the reason most people have heard the word. When a family is told "Mom has dementia," they are most likely told later (or separately) that the cause is Alzheimer's disease.

Alzheimer's has a specific biological story. Two abnormal proteins accumulate in the brain: amyloid plaques (between neurons) and tau tangles (inside neurons). Over years, these disrupt neuronal function, particularly in the hippocampus and other areas involved in memory. The clinical picture that results is what most people associate with dementia: progressive memory loss, then language and judgment changes, then progressive loss of daily function.

Alzheimer's progresses over roughly 8 to 12 years on average, though individual variation is enormous. For more on what to expect, see our stages of dementia guide.

The other common causes of dementia

Vascular dementia (~10–20% of cases)

Caused by reduced blood flow to parts of the brain, often from small strokes or cumulative damage from high blood pressure, diabetes, and cardiovascular disease. Vascular dementia tends to progress stepwise — periods of stability punctuated by abrupt worsening — rather than smoothly. It often affects executive function (planning, sequencing) before memory.

Risk factors overlap heavily with heart disease: smoking, hypertension, diabetes, high cholesterol. Managing those reduces risk.

Lewy body dementia (~5–10%)

Caused by abnormal deposits of a protein called alpha-synuclein. Symptoms include:

• Visual hallucinations (often well-formed and unthreatening, like seeing children in the room)
• Fluctuating attention and cognition — very different from day to day, or hour to hour
• Parkinsonian features — tremor, shuffling gait, rigidity
• REM sleep behavior disorder — acting out dreams, years before other symptoms

Lewy body dementia is important to recognize because people with it are often dangerously sensitive to antipsychotic medications. The wrong prescription can cause severe side effects.

Frontotemporal dementia (~5–10% of younger-onset cases)

Often begins earlier — in the 50s and 60s rather than 70s and 80s. Unlike Alzheimer's, memory may be relatively preserved early. Instead, the first signs are usually changes in personality, judgment, or language: a restrained person becomes disinhibited, a gentle person becomes blunt, someone loses access to familiar words. Frontotemporal dementia can look more like a psychiatric condition than a memory condition at first.

Mixed dementia

Increasingly recognized. Many people, especially in their 80s and beyond, have two or more causes simultaneously — most commonly Alzheimer's plus vascular changes. The clinical picture blends the two.

Reversible causes that can look like dementia

Some conditions mimic dementia but respond to treatment. These are the reason a good workup always screens for them:

• Thyroid disease (especially hypothyroidism)
• Vitamin B12 deficiency
• Depression (sometimes called "pseudodementia" in older adults)
• Medication side effects (anticholinergics, sedatives, opioids, polypharmacy)
• Sleep apnea
• Normal pressure hydrocephalus (classic triad: gait problems, incontinence, cognitive changes — often reversible with shunt placement)
• Alcohol-related cognitive impairment
• Chronic infections affecting the brain

A formal cognitive evaluation almost always includes blood work to look for these. See what to do after a low clock drawing test score for what a typical workup looks like.

Why the distinction matters

If someone in your family has dementia, knowing which kind has real implications:

• Medication choice differs. Cholinesterase inhibitors (donepezil, rivastigmine) work for Alzheimer's and Lewy body dementia. Memantine is used in moderate-to-severe Alzheimer's. Vascular dementia management focuses on controlling vascular risk factors. Frontotemporal dementia has different medication considerations and sometimes responds to different psychiatric treatments.
• Prognosis and trajectory differ. Step-wise decline (vascular) versus smooth progression (Alzheimer's) versus highly variable day-to-day (Lewy body) versus personality-first (frontotemporal) means families plan differently.
• Safety considerations differ. Lewy body dementia's antipsychotic sensitivity is a specific, dangerous thing to know. Frontotemporal dementia's disinhibition raises different safety concerns (financial impulsivity, risky decisions) than Alzheimer's memory loss.
• Research and clinical trial eligibility differ. The new amyloid-targeting medications for Alzheimer's disease (for example, lecanemab) are specific to Alzheimer's; they don't work for other dementias.

How diagnosis works

A dementia diagnosis typically involves:

1. Clinical history from the patient and a close family member.
2. Cognitive testing — brief screens like the MMSE, MoCA, or clock drawing test first, then sometimes a longer neuropsychological battery.
3. Physical and neurological exam.
4. Blood work to rule out reversible causes.
5. Brain imaging — usually MRI — to look for strokes, tumors, hydrocephalus, or patterns suggestive of a specific dementia type.
6. Specialist evaluation with a neurologist or memory clinic for complex or younger cases.
7. Occasionally, advanced testing — amyloid PET imaging, cerebrospinal fluid biomarkers, or genetic testing — when it will change management.

A clinician puts these together and makes a clinical diagnosis. For many people, the answer is "probable Alzheimer's disease." For others, the picture points toward vascular, Lewy body, frontotemporal, or mixed dementia.

What to ask at the diagnosis appointment

• What type of dementia do you think this is? How confident are you?
• Could any reversible causes still be contributing?
• What do the medications you're prescribing do, and how will we know if they help?
• What should we watch for that would change the picture?
• Who is the right specialist to consult?

Bring a family member. Bring a notebook. Dementia diagnoses are often delivered when the patient is not in the best state to absorb details, and a second set of ears matters.

Related reading

• 10 Warning Signs of Alzheimer's Disease
• Stages of Dementia: A Family Guide
• MMSE vs Clock Drawing Test vs MoCA
• Mild Cognitive Impairment (MCI): Is It Dementia?

References

• Alzheimer's Association. 2024 Alzheimer's Disease Facts and Figures. alz.org.
• National Institute on Aging. Alzheimer's Disease and Related Dementias. nia.nih.gov.
• Livingston G, Huntley J, Sommerlad A, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. The Lancet. 2020;396(10248):413–446.

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Disclosure: Dr. Shimada is the founder of Tokei Health. This article is informational and is not a substitute for individual medical advice from your own clinician.