Yes, Alzheimer’s disease is a form of dementia. Dementia is an umbrella term for a range of neurological conditions that progressively damage the brain, and Alzheimer’s is the most common type, accounting for 60% to 80% of all dementia cases. The two terms are related but not interchangeable: every case of Alzheimer’s involves dementia, but not every case of dementia is caused by Alzheimer’s.
How Dementia and Alzheimer’s Are Related
Think of dementia as a category, not a single disease. It describes a group of symptoms, primarily declining memory and thinking skills, that become severe enough to interfere with daily life. Alzheimer’s is one specific disease that causes those symptoms. Other diseases cause dementia too, including vascular dementia (triggered by disrupted blood flow to the brain) and Lewy body dementia (caused by abnormal protein deposits that affect the brain’s chemical messengers).
This distinction matters because different types of dementia have different causes, different early warning signs, and increasingly different treatment options. A diagnosis of “dementia” tells you what’s happening. A diagnosis of “Alzheimer’s disease” tells you why.
What Happens in the Brain With Alzheimer’s
Alzheimer’s disease is characterized by two specific abnormalities in brain tissue: amyloid plaques and neurofibrillary tangles. Amyloid plaques are unusual clumps of a protein called beta amyloid that build up in the spaces between nerve cells. Neurofibrillary tangles form inside the neurons themselves, made up of a protein called tau that has become misshapen.
In a healthy brain, tau helps maintain the internal transport system that nerve cells rely on to move nutrients and signals. In Alzheimer’s, tau twists into tangled filaments, and that transport system collapses. Nerve cells lose the ability to communicate with each other and eventually die. Interestingly, researchers still don’t know for certain whether these plaques and tangles directly cause the damage or are byproducts of some other process that’s killing neurons.
How Alzheimer’s Progresses
Alzheimer’s generally moves through five stages, though the timeline varies significantly from person to person.
The process starts with a preclinical stage, where changes are already happening in the brain but no one, including the person affected, notices any symptoms. This phase can last years or even decades. It’s typically only detected in research settings through specialized testing.
Next comes mild cognitive impairment. Memory lapses become noticeable, and decision-making gets harder. At this point, the changes are real but not yet severe enough to disrupt everyday routines. Not everyone with mild cognitive impairment has Alzheimer’s, which is one reason accurate diagnosis matters.
Mild dementia is often when Alzheimer’s is formally diagnosed. Memory and thinking problems become obvious to family and doctors, and they start affecting daily functioning: repeating questions, wandering and getting lost, struggling with tasks that used to be routine.
In the moderate stage, symptoms deepen considerably. People may not recognize friends or family. Behavioral changes become more pronounced: suspicion of loved ones, seeing or hearing things that aren’t there, restlessness and agitation (particularly late in the day), and sometimes aggressive outbursts.
Severe dementia, the final stage, affects physical capabilities along with mental function. Muscles may become rigid, reflexes stop responding normally, and eventually a person loses the ability to sit up without support, swallow, or control bladder and bowel functions.
How Alzheimer’s Differs From Other Dementias
Because “dementia” covers several diseases, the symptom profiles can look quite different depending on the cause.
- Alzheimer’s disease typically starts with memory loss, particularly forgetting recent events and repeating questions. Personality changes and difficulty recognizing people come later.
- Lewy body dementia often presents differently. Early signs include visual hallucinations, difficulty concentrating, muscle rigidity, reduced facial expression, and significant sleep disturbances like insomnia or excessive daytime sleepiness. Movement problems can resemble Parkinson’s disease.
- Vascular dementia results from blood clots or other conditions that cut off blood flow in the brain. Symptoms overlap with Alzheimer’s (forgetting events, misplacing items, poor judgment) but the onset pattern is different. Vascular dementia sometimes worsens in noticeable steps after each vascular event rather than declining gradually.
These distinctions aren’t always clean. Some people have mixed dementia, where more than one type is present simultaneously.
How Alzheimer’s Is Diagnosed
Revised diagnostic criteria now define Alzheimer’s as a biological process that begins with measurable brain changes before symptoms ever appear. Doctors can look for specific biomarkers, essentially biological signatures of the disease, through brain imaging (PET scans) or by testing spinal fluid or blood for abnormal levels of amyloid and tau proteins.
A single abnormal result on what clinicians call a “Core 1” biomarker test, one that directly measures amyloid plaques or a specific form of tau, is sufficient to establish an Alzheimer’s diagnosis. Blood-based tests for a tau protein marker called p-tau217 are among the newer options that may make diagnosis more accessible than traditional spinal taps or PET scans.
That said, biomarker testing is currently recommended only for people who are already showing symptoms. For people with no cognitive issues, testing outside of research studies isn’t advised, partly because no approved treatments exist yet for that preclinical stage. Clinical judgment remains central to the diagnostic process. Biomarkers assist but don’t replace a thorough evaluation.
Risk Factors and Genetics
Age is the single biggest risk factor for Alzheimer’s, but genetics play a significant role too. The most important genetic risk factor is a variant of a gene called APOE4. About 25% of people carry one copy, and 2 to 3% carry two copies. APOE4 is the strongest known genetic risk factor for Alzheimer’s, though carrying it does not guarantee a person will develop the disease. The most common variant, APOE3, doesn’t appear to affect risk either way. A rarer form, APOE2, may actually provide some protection.
APOE4 status has become clinically relevant beyond just risk prediction. One of the newer FDA-approved treatments carries a boxed warning about brain swelling and small bleeds (called amyloid-related imaging abnormalities), and people who carry two copies of APOE4 face a substantially higher risk of these side effects. Genetic testing is now recommended before starting that class of medication.
Current Treatment Options
For decades, Alzheimer’s treatments could only manage symptoms. That changed with the approval of a new class of drugs that target the underlying disease. These medications are antibodies delivered through IV infusions that work by clearing amyloid plaques from the brain.
The most recently approved option, donanemab, is given as an infusion every four weeks. In clinical trials of over 1,700 patients, those receiving the drug showed a statistically significant slowing of cognitive and functional decline compared to placebo over about 18 months. The treatment is approved for people in the mild cognitive impairment or mild dementia stages, not for advanced disease.
These treatments don’t stop or reverse Alzheimer’s. They slow it down. And they come with real risks: brain swelling, small brain bleeds, infusion reactions, and in rare cases severe allergic responses. Regular brain MRIs are needed to monitor for side effects. Still, they represent the first therapies that address the biology of the disease rather than just its symptoms, which is a meaningful shift in how Alzheimer’s is treated.