There is no single definitive number, but the current diagnostic manual used by psychiatrists lists 12 distinct subtypes of dementia. Beyond those formal categories, researchers continue to identify new forms, and many people ultimately have more than one type at the same time. The reality is that dementia is not one disease but a broad umbrella covering dozens of conditions that damage the brain in different ways.
The Four Most Common Forms
The vast majority of dementia cases fall into four categories: Alzheimer’s disease, vascular dementia, Lewy body dementia, and frontotemporal dementia. Alzheimer’s alone accounts for an estimated 60 to 70 percent of all cases, making it by far the most prevalent. The remaining three each represent a smaller share, though exact percentages vary across studies.
These four forms differ not just in how common they are but in what goes wrong inside the brain, which symptoms appear first, and how quickly they progress.
Alzheimer’s Disease
In Alzheimer’s, two types of abnormal protein deposits accumulate in the brain. Sticky clumps called plaques build up between nerve cells, disrupting their function. At the same time, twisted fibers called tangles form inside neurons, blocking the internal transport system that moves nutrients through each cell. This combination gradually destroys the connections between neurons, starting in areas responsible for memory and spreading outward over years.
Short-term memory loss is typically the earliest and most recognizable symptom. Over time, problems with language, spatial awareness, reasoning, and eventually basic daily tasks follow. Alzheimer’s progresses slowly in most people, with the period from first symptoms to severe impairment spanning several years or longer.
Vascular Dementia
Vascular dementia results from damage to the brain’s blood supply. This can happen suddenly after a major stroke or develop gradually from years of small vessel disease, where tiny blood vessels deep in the brain narrow and restrict blood flow. Either way, parts of the brain are starved of oxygen, and the affected tissue dies.
Symptoms depend on which brain regions lose blood flow. Some people notice difficulty with planning and organizing before any memory problems appear, which is a key difference from Alzheimer’s. Because vascular dementia is driven by cardiovascular health, managing blood pressure, cholesterol, and diabetes can sometimes slow its progression.
Lewy Body Dementia
Lewy body dementia is caused by abnormal protein deposits that form inside nerve cells throughout the brain. It produces a distinctive cluster of symptoms that sets it apart from other forms. Visual hallucinations, often vivid and detailed, can be one of the earliest signs. People may see animals, shapes, or figures that aren’t there.
Another hallmark is REM sleep behavior disorder, where people physically act out their dreams by punching, kicking, or yelling during sleep. This can begin years before other cognitive symptoms appear. Attention and alertness tend to fluctuate dramatically from one day or even one hour to the next, which can be confusing for both the person and their family. Movement problems similar to Parkinson’s disease, such as stiffness and slow walking, are also common.
Frontotemporal Dementia
Frontotemporal dementia targets the front and side portions of the brain, regions that control personality, behavior, and language. It tends to strike earlier than other forms, often appearing between the ages of 45 and 65. In younger people with dementia, frontotemporal dementia is much more common than it is in older populations, where Alzheimer’s dominates.
Depending on which brain areas are affected first, initial symptoms may involve dramatic personality changes, loss of social awareness, or progressive difficulty finding words and forming sentences. Memory often remains relatively intact in the early stages, which can delay diagnosis because it doesn’t match most people’s idea of what dementia looks like.
Mixed Dementia Is Surprisingly Common
Many people don’t have just one type. Research from Alzheimer’s Disease Research Centers found that more than 50 percent of people with dementia had evidence of more than one cause when their brains were examined after death. A large study called the Rush Memory and Aging Project put the number even higher: among participants with at least one type of brain pathology, 78 percent had two or more types, and 58 percent had three or more.
The most common combination is Alzheimer’s disease alongside vascular damage, but any pairing is possible. Mixed dementia is difficult to diagnose during life because the symptoms of different types overlap. This is one reason why the same symptoms can look slightly different from person to person.
The Full List of Recognized Subtypes
The DSM-5-TR, the diagnostic manual used by clinicians, formally recognizes these subtypes of major neurocognitive disorder (the clinical term for dementia):
- Alzheimer’s disease
- Vascular dementia
- Lewy body dementia
- Frontotemporal dementia
- Parkinson’s disease dementia
- Traumatic brain injury
- HIV-related dementia
- Substance or medication-induced dementia
- Huntington’s disease
- Prion disease (including Creutzfeldt-Jakob disease)
- Dementia due to another medical condition
- Dementia due to multiple causes
That last category, “another medical condition,” is intentionally broad. It covers rarer causes like Huntington’s-adjacent genetic conditions and diseases that don’t fit neatly into the other boxes.
Rarer Forms Worth Knowing
Creutzfeldt-Jakob disease is caused by misfolded proteins called prions. It is extremely rare but progresses far more rapidly than other dementias, often causing severe decline within months rather than years. Most cases arise spontaneously, though a small fraction result from medical procedures that inadvertently transmit the prion.
Huntington’s disease is an inherited condition caused by a genetic mutation on chromosome 4. It typically appears in a person’s 30s or 40s and causes involuntary movements, difficulty walking, and speech problems alongside cognitive decline. Because it is genetic, a predictive test can identify carriers before symptoms begin.
A more recently defined form called LATE (limbic-predominant age-related TDP-43 encephalopathy) was formally described in 2019. It involves a different abnormal protein that accumulates in memory-related brain structures. Autopsy studies suggest that roughly 25 percent of older adults’ brains show enough of this pathology to cause noticeable cognitive problems. LATE closely mimics Alzheimer’s and was likely misdiagnosed as Alzheimer’s for decades before researchers identified it as distinct.
Conditions That Mimic Dementia but Are Treatable
Not everything that looks like dementia is permanent. Several reversible conditions can cause similar symptoms, which is why a thorough medical workup matters before any diagnosis is made.
Thyroid problems, both overactive and underactive, can interfere with thinking and memory. Vitamin deficiencies, particularly B12, produce cognitive symptoms that improve with supplementation. Normal pressure hydrocephalus, a condition where fluid accumulates in the brain’s cavities, causes a recognizable triad of memory problems, difficulty walking, and loss of bladder control. It can often be treated with a surgical procedure to drain the excess fluid.
Infections like Lyme disease, syphilis, and HIV can mimic dementia if they go untreated for long enough. Liver or kidney disease can allow toxic waste products to build up in the blood and dull mental function. Even a seemingly minor fall can cause a slow bleed inside the skull called a subdural hematoma, producing gradual cognitive decline that reverses once the blood is drained. Depression in older adults is another frequent mimic, sometimes called pseudodementia, where concentration and memory improve once the depression is treated.
Young-Onset Dementia Has a Different Profile
When dementia develops before age 65, the distribution of types shifts. Alzheimer’s still leads, affecting about one in three younger people with dementia, but frontotemporal dementia makes up a much larger share than it does in older populations. Rarer genetic and metabolic causes are also proportionally more common in younger people. Lewy body dementia, by contrast, is less common in this age group.
Diagnosis tends to take longer in younger people because neither patients nor doctors initially suspect dementia. Symptoms like personality changes, difficulty at work, or trouble with language are often attributed to stress, depression, or burnout before a neurological cause is considered.