Dementia is a general term for loss of memory and other mental abilities severe enough to interfere with daily life. It is caused by physical changes in the brain.

Alzheimer's disease is the most common type of dementia, accounting for 60 to 80 percent of cases. Other causes of dementia are discussed in this section.

Type of Dementia

Characteristics

Alzheimer's disease

Most common type of dementia; accounts for an estimated 60 to 80 percent of cases.

Symptoms: Difficulty remembering names and recent events is often an early clinical symptom; apathy and depression are also often early symptoms. Later symptoms include impaired judgment, disorientation, confusion, behavior changes and difficulty speaking, swallowing and walking.
New criteria and guidelines for diagnosing Alzheimer's were published in 2011 recommending that Alzheimer's disease be considered a disease with three stages, beginning well before the development of symptoms.

Brain changes: Hallmark abnormalities are deposits of the protein fragment beta-amyloid (plaques) and twisted strands of the protein tau (tangles) as well as evidence of nerve cell damage and death in the brain.

Learn more about Alzheimer's disease.

Vascular dementia

Previously known as multi-infarct or post-stroke dementia, vascular dementia is less common as a sole cause of dementia than is Alzheimer's disease.

Symptoms: Impaired judgment or ability to make plans is more likely to be the initial symptom, as opposed to the memory loss often associated with the initial symptoms of Alzheimer's. Occurs because of brain injuries such as microscopic bleeding and blood vessel blockage. The location of the brain injury determines how the individual's thinking and physical functioning are affected.

Brain changes: In the past, evidence for vascular dementia was used to exclude a diagnosis of Alzheimer's disease (and vice versa). That practice is no longer considered consistent with pathologic evidence, which shows that the brain changes of both types of dementia can be present simultaneously. When any two or more types of dementia are present at the same time, the individual is considered to have "mixed dementia" (see entry below).

Learn more about vascular dementia.

Dementia with Lewy bodies

Symptoms: People with dementia with Lewy bodies have some of the symptoms common in Alzheimer's, but are more likely than people with Alzheimer's to have initial or early symptoms such as sleep disturbances, well-formed visual hallucinations, and muscle rigidity or other parkinsonian movement features.

Brain changes: Lewy bodies are abnormal aggregations (or clumps) of the protein alpha-synuclein. When they develop in a part of the brain called the cortex, dementia can result. Alpha-synuclein also aggregates in the brains of people with Parkinson's disease, but the aggregates may appear in a pattern that is different from dementia with Lewy bodies.

The brain changes of dementia with Lewy bodies alone can cause dementia, or they can be present at the same time as the brain changes of Alzheimer's disease and/or vascular dementia, with each entity contributing to the development of dementia. When this happens, the individual is said to have "mixed dementia."

Learn more about dementia with Lewy bodies.

Mixed dementia

Recent studies suggest that mixed dementia is more common than previously thought.

Brain changes: Characterized by the hallmark abnormalities of Alzheimer's and another type of dementia —most commonly, vascular dementia, but also other types, such as dementia with Lewy bodies.

Learn more about mixed dementia.

Parkinson's disease

As Parkinson's disease progresses, it often results in a severe dementia similar to dementia with Lewy bodies or Alzheimer's.

Symptoms: Problems with movement are a common symptom early in the disease.

Brain changes: Alpha-synuclein aggregates are likely to begin in an area deep in the brain called the substantia nigra. The aggregates are thought to cause degeneration of the nerve cells that produce dopamine.

The incidence of Parkinson's disease is about one-tenth that of Alzheimer's disease.

Learn more about Parkinson's disease.

Frontotemporal lobar degeneration

Includes dementias such as behavioral variant FTLD (bvFTD), primary progressive aphasia, Pick's disease and progressive supranuclear palsy.

Symptoms: Typical symptoms include changes in personality and behavior and difficulty with language. Nerve cells in the front and side regions of the brain are especially affected. No distinguishing microscopic abnormality is linked to all cases.

Brain changes: The brain changes of bvFTD may be present at the same time as the brain changes of Alzheimer's, but people with bvFTD generally develop symptoms at a younger age (at about age 60) and survive for fewer years than those with Alzheimer's.

Learn more about frontotemporal dementia.

Creutzfeldt-Jakob disease

Variant Creutzfeldt-Jakob disease is believed to be caused by consumption of products from cattle affected by mad cow disease.

Symptoms: Rapidly fatal disorder that impairs memory and coordination and causes behavior changes.

Brain changes: Results from an infectious misfolded protein (prion) that causes other proteins throughout the brain to misfold and thus malfunction.

Learn more about Creutzfeldt-Jakob disease.

Normal pressure hydrocephalus

Symptoms: Symptoms include difficulty walking, memory loss and inability to control urination.

Brain changes: Caused by the buildup of fluid in the brain. Can sometimes be corrected with surgical installation of a shunt in the brain to drain excess fluid.

Learn more about normal pressure hydrocephalus.

Huntington's Disease

Wernicke-Korsakoff Syndrome