Dementia is not a disease. It’s an umbrella term for a group of symptoms that affect memory, thinking, and the ability to carry out daily activities. Alzheimer’s disease is one specific disease that causes dementia, and it’s the most common one, accounting for an estimated 60 to 70% of all dementia cases. Think of it like the relationship between “cancer” and “lung cancer”: one is a broad category, the other is a specific diagnosis within it.
Dementia Is a Syndrome, Not a Diagnosis
When someone says a person “has dementia,” they’re describing a set of symptoms, not identifying the cause. Those symptoms generally include memory loss, difficulty reasoning, trouble with language, and changes in behavior severe enough to interfere with daily life. Many different diseases can produce these symptoms, and figuring out which one is responsible matters because the cause shapes the treatment, the progression, and what a family can expect.
The most common types of dementia beyond Alzheimer’s are vascular dementia, dementia with Lewy bodies, and frontotemporal dementia. Each has a different underlying cause, tends to affect different parts of the brain, and shows up differently in a person’s behavior and abilities.
What Makes Alzheimer’s Distinct
Alzheimer’s disease involves two specific types of damage in the brain. First, fragments of a protein called beta-amyloid clump together between nerve cells, forming plaques that disrupt how cells function. Second, another protein called tau, which normally helps support the internal structure of neurons, becomes chemically altered and forms tangles inside the cells. These tangles block the cell’s transport system, cutting off communication between neurons. As beta-amyloid plaques build up and reach a tipping point, tau spreads rapidly through the brain, and the disease accelerates.
This biological process begins years, sometimes decades, before symptoms appear. Updated diagnostic guidelines from 2024 now define Alzheimer’s as a biological disease rather than a clinical syndrome, meaning it can technically be identified through biomarkers (measurable signs of the disease in the brain or spinal fluid) even before a person shows any cognitive decline. In practice, that kind of testing is still mostly used in research settings, not routine clinical care.
How Symptoms Differ by Type
Alzheimer’s typically starts with difficulty forming new memories. Early signs include repeating questions, getting lost in familiar places, and wandering. As the disease progresses into its moderate stage, people may stop recognizing friends and family and begin showing impulsive behavior. In severe stages, the ability to communicate is largely or entirely lost.
Vascular dementia, caused by reduced blood flow to the brain (often from strokes, sometimes ones so small they go unnoticed), can look similar on the surface. People may forget current or past events, misplace items, or struggle to follow instructions. But vascular dementia is more likely to also involve physical symptoms like weakness on one side of the body, difficulty walking, or problems with bladder control. It’s also more common in people with risk factors for heart disease: high blood pressure, diabetes, elevated cholesterol, and smoking.
Dementia with Lewy bodies combines features of both Alzheimer’s and Parkinson’s disease. People may experience visual hallucinations or delusions early on, have episodes where their mental clarity fluctuates dramatically, and show a general slowing of movement. Vivid, sometimes violent dream-enactment during sleep is another hallmark.
Frontotemporal dementia stands apart from the others in a key way: it tends to strike younger. It’s most common in people under 65 and rare in those over 75. Rather than starting with memory loss, it often begins with changes in personality, behavior, or language. Someone might become socially inappropriate, lose empathy, or develop compulsive behaviors. Different genetic mutations (most commonly in genes called C9ORF72, MAPT, and GRN) drive many inherited cases of frontotemporal dementia, and some of these mutations can also cause symptoms that mimic Alzheimer’s, which complicates diagnosis.
How Alzheimer’s Progresses
Alzheimer’s develops slowly and worsens over years. Clinicians generally describe five stages: a preclinical phase with no symptoms (which can last years or decades), mild cognitive impairment, then mild, moderate, and severe dementia. On average, people live between 3 and 11 years after diagnosis, though some live 20 years or more. The rate of progression varies widely from person to person, and untreated vascular risk factors like high blood pressure can speed it up.
This gradual, predictable decline is one way Alzheimer’s differs from vascular dementia, which can worsen in sudden steps after each new stroke, or from Lewy body dementia, where cognitive abilities can swing dramatically from one day to the next.
Not All Cognitive Decline Is Permanent
One of the most important reasons to get a proper diagnosis rather than accepting “dementia” as a final answer is that some causes of dementia-like symptoms are treatable and even reversible. Depression can make people seem confused, withdrawn, and forgetful. Medication interactions, common in older adults taking multiple prescriptions, can cloud thinking. Poor nutrition, particularly deficiencies in vitamin B-12 and folate, can impair brain function. Thyroid disorders, certain infections like Lyme disease, and heart or lung conditions that starve the brain of oxygen can all produce symptoms that look like dementia but resolve once the underlying problem is treated.
Treatment Differences
Because Alzheimer’s has a specific biological mechanism, it’s the only form of dementia with disease-modifying treatments. The FDA has approved drugs that target and clear amyloid plaques from the brain. The most recent, donanemab (brand name Kisunla), was shown in clinical trials to significantly slow cognitive and functional decline over 76 weeks compared to a placebo. These treatments are approved for people in the early stages of the disease, specifically mild cognitive impairment or mild dementia, and they carry real risks, including temporary brain swelling and small spots of bleeding that require monitoring with brain scans.
For other types of dementia, treatment focuses on managing symptoms and addressing the underlying cause when possible. Vascular dementia, for instance, is managed largely by controlling stroke risk factors. Lewy body dementia requires careful medication choices because some drugs commonly used for behavioral symptoms can cause severe reactions in these patients. None of these other types currently have treatments that slow the disease process itself, which makes accurate diagnosis all the more critical for people with Alzheimer’s who might benefit from newer therapies.