Dementia is not a disease. It’s an umbrella term describing a wide range of symptoms that affect memory, thinking, and the ability to perform everyday activities independently. Alzheimer’s disease is one specific brain disease that causes dementia, and it’s the most common one, contributing to 60–70% of all dementia cases. Think of it this way: dementia is like saying “cancer,” while Alzheimer’s is like saying “breast cancer.” One describes the broader category, the other names the specific condition.
Dementia as a Syndrome, Not a Diagnosis
When a doctor says someone “has dementia,” they’re describing what’s happening, not why. Dementia means a person has lost enough cognitive function to interfere with daily life. That could mean forgetting recent conversations, struggling to manage finances, getting lost in familiar places, or having difficulty following a recipe they’ve made dozens of times. These symptoms can stem from many different underlying diseases, each with its own cause, pattern, and outlook.
Some causes of dementia are even reversible. Vitamin B12 deficiency, for example, can cause rapidly progressive cognitive decline that looks very much like degenerative dementia but improves with treatment. Thyroid problems, certain infections, and immune-mediated conditions can also mimic dementia. This is one reason a thorough workup matters: not every case of cognitive decline is permanent.
What Makes Alzheimer’s Different
Alzheimer’s disease is a specific, progressive brain disease with identifiable biological changes. Two hallmark features set it apart. First, a protein fragment called beta-amyloid clumps into plaques between brain cells, disrupting their function. Second, a protein called tau, which normally helps support the internal structure of neurons, becomes chemically altered. The damaged tau detaches, sticks to other tau molecules, and forms tangles inside neurons that block the cell’s transport system and destroy communication between brain cells.
These two processes appear to feed each other. Abnormal tau builds up first in memory-related brain regions, while amyloid plaques accumulate between neurons. Once amyloid reaches a tipping point, tau spreads rapidly throughout the brain, accelerating damage. The result is a steady, gradual decline. Alzheimer’s typically starts with difficulty remembering new information and recent events, then expands over years to affect language, reasoning, orientation, and eventually basic physical functions like swallowing and walking.
Other Major Types of Dementia
Because Alzheimer’s accounts for roughly two-thirds of dementia cases, it gets the most attention. But the remaining third includes several distinct conditions, each with a different pattern of symptoms.
Vascular Dementia
Vascular dementia results from disrupted blood flow to the brain, often caused by blood clots, small strokes, or narrowed blood vessels. Symptoms include forgetting current or past events, misplacing items, trouble following instructions, poor judgment, and sometimes hallucinations or delusions. It’s typically diagnosed after age 65. Unlike Alzheimer’s gradual slide, vascular dementia sometimes progresses in noticeable steps, worsening suddenly after a stroke and then plateauing before the next event.
Lewy Body Dementia
Lewy body dementia involves abnormal protein deposits that affect the brain’s chemical messengers. It tends to look different from Alzheimer’s early on. Rather than memory loss being the first sign, people often experience trouble concentrating, visual hallucinations (seeing things that aren’t there), sleep disturbances like excessive daytime drowsiness or acting out dreams, and movement problems such as muscle rigidity, reduced facial expression, and loss of coordination. It’s typically diagnosed at age 50 or older. The fluctuating nature of alertness, where someone seems sharp one hour and confused the next, is a distinguishing feature.
Frontotemporal Dementia
Frontotemporal dementia strikes younger than most other types, with diagnosis typically between ages 45 and 64. It targets the brain’s frontal and temporal lobes, which govern personality, behavior, and language. Early symptoms often involve personality changes rather than memory loss: impulsive behavior, emotional flatness or inappropriately intense emotions, difficulty planning and organizing, or trouble producing or understanding speech. Some people also develop shaky hands and balance problems. Because it shows up earlier and looks nothing like the “forgetful grandparent” stereotype, it’s frequently misdiagnosed as a psychiatric condition.
How Doctors Tell Them Apart
Distinguishing Alzheimer’s from other dementias involves more than a memory test. Doctors typically start with a comprehensive clinical assessment that includes cognitive testing, a detailed medical history, and blood work to rule out reversible causes like vitamin deficiencies or thyroid dysfunction.
When Alzheimer’s is suspected but the diagnosis remains uncertain, brain imaging can help. PET scans can now visualize both of Alzheimer’s hallmark features directly. Amyloid PET imaging, which has been FDA-approved for over a decade, detects amyloid plaques in patients with cognitive impairment. Tau PET, approved in 2020, shows tau tangles and helps determine how advanced the disease is. These scans are most useful in early stages of cognitive decline, when symptoms alone aren’t enough to pin down a cause. They supplement rather than replace a full clinical evaluation, and they’re typically ordered by a dementia specialist when the picture is unclear.
Treatment Differences
The type of dementia matters for treatment. Because each form of dementia has a different underlying cause, what helps one type may not help another, and in some cases could make things worse.
For Alzheimer’s specifically, treatment has entered a new phase. Newer medications now target the disease’s biology directly by clearing amyloid plaques from the brain. One such treatment, donanemab (sold as Kisunla), was approved by the FDA for adults with mild cognitive impairment or mild-stage Alzheimer’s. In clinical trials, patients who received the drug showed significantly less decline in both cognitive function and daily living abilities over 76 weeks compared to those on a placebo. These treatments work best when started early, which makes accurate diagnosis especially important.
For vascular dementia, treatment focuses on managing the cardiovascular risk factors (high blood pressure, diabetes, high cholesterol) that caused the blood flow problems in the first place. Lewy body dementia requires particular caution because certain medications commonly used for behavioral symptoms in other dementias can cause severe reactions. Frontotemporal dementia has no disease-modifying treatment yet, so care centers on managing behavioral and language symptoms.
Why the Distinction Matters
People often use “dementia” and “Alzheimer’s” interchangeably, and in casual conversation the confusion is understandable. But the distinction has real consequences. It affects which treatments are appropriate, what symptoms to expect next, how quickly the disease will progress, and what kind of support will be most helpful. A person with Lewy body dementia needs a care plan built around fluctuating alertness and movement problems. A person with frontotemporal dementia may need behavioral support decades earlier than most people associate with cognitive decline. And a person whose “dementia” is actually caused by a B12 deficiency may recover fully with the right treatment.
If you or someone you care about has been told they have dementia, the most useful next step is finding out which kind. That specific diagnosis shapes everything that follows.