Dementia is not a specific disease. It’s an overall term that describes a wide range of symptoms associated with a decline in memory or other thinking skills severe enough to reduce a person’s ability to perform everyday activities. Alzheimer’s disease accounts for 60 to 80 percent of cases. Vascular dementia, which occurs after a stroke, is the second most common dementia type. But there are many other conditions that can cause symptoms of dementia, including some that are reversible, such as thyroid problems and vitamin deficiencies.
Dementia is often incorrectly referred to as “senility” or “senile dementia,” which reflects the formerly widespread but incorrect belief that serious mental decline is a normal part of aging.
Types of Dementia
Alzheimer’s disease
Most common type of dementia; accounts for an estimated 60 to 80 percent of cases.
Symptoms: Difficulty remembering recent conversations, names or events is often an early clinical symptom; apathy and depression are also often early symptoms. Later symptoms include impaired communication, poor judgment, disorientation, confusion, behavior changes and difficulty speaking, swallowing and walking.
Revised criteria and guidelines for diagnosing Alzheimer’s were published in 2011 recommending that Alzheimer’s be considered a slowly progressive brain disease that begins well before symptoms emerge.
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
back to top
Vascular dementia
Previously known as multi-infarct or post-stroke dementia, vascular dementia is less common as a sole cause of dementia than Alzheimer’s, accounting for about 10 percent of dementia cases.
Symptoms: Impaired judgment or ability to make decisions, plan or organize is more likely to be the initial symptom, as opposed to the memory loss often associated with the initial symptoms of Alzheimer’s. Occurs from blood vessel blockage or damage leading to infarcts (strokes) or bleeding in the brain. The location, number and size of the brain injury determines how the individual’s thinking and physical functioning are affected.
Brain changes: Brain imaging can often detect blood vessel problems implicated in vascular dementia. 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 several 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”.
back to top
Dementia with Lewy bodies (DLB)
Symptoms: People with dementia with Lewy bodies often have memory loss and thinking problems 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 slowness, gait imbalance 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 abnormality contributing to the development of dementia. When this happens, the individual is said to have “mixed dementia.”
back to top
Huntington’s Disease
Huntington’s disease is a progressive brain disorder caused by a single defective gene on chromosome 4.
Symptoms: Include abnormal involuntary movements, a severe decline in thinking and reasoning skills, and irritability, depression and other mood changes.
Brain changes: The gene defect causes abnormalities in a brain protein that, over time, lead to worsening symptoms.
back to top
Mixed Dementia
In mixed dementia abnormalities linked to more than one cause of dementia occur simultaneously in the brain. Recent studies suggest that mixed dementia is more common than previously thought.
Brain changes: Characterized by the hallmark abnormalities of more than one cause of dementia —most commonly, Alzheimer’s and vascular dementia, but also other types, such as dementia with Lewy bodies.
back to top
Parkinson’s disease
As Parkinson’s disease progresses, it often results in a progressive dementia similar to dementia with Lewy bodies or Alzheimer’s.
Symptoms: Problems with movement are common symptoms of the disease. If dementia develops, symptoms are often similar to dementia with Lewy bodies.
Brain changes: Alpha-synuclein clumps are likely to begin in an area deep in the brain called the substantia nigra. These clumps are thought to cause degeneration of the nerve cells that produce dopamine.
back to top
Frontotemporal dementia
Includes dementias such as behavioral variant FTD (bvFTD), primary progressive aphasia, Pick’s disease, corticobasal degeneration 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.
Brain changes: No distinguishing microscopic abnormality is linked to all cases. People with FTD generally develop symptoms at a younger age (at about age 60) and survive for fewer years than those with Alzheimer’s.
back to top
Creutzfeldt-Jakob disease
CJD is the most common human form of a group of rare, fatal brain disorders affecting people and certain other mammals. Variant CJD (“mad cow disease”) occurs in cattle, and has been transmitted to people under certain circumstances.
Symptoms: Rapidly fatal disorder that impairs memory and coordination and causes behavior changes.
Brain changes: Results from misfolded prion protein that causes a “domino effect” in which prion protein throughout the brain misfolds and thus malfunctions.
back to top
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.
back to top
Wernicke-Korsakoff Syndrome
Korsakoff syndrome is a chronic memory disorder caused by severe deficiency of thiamine (vitamin B-1). The most common cause is alcohol misuse.
Symptoms: Memory problems may be strikingly severe while other thinking and social skills seem relatively unaffected.
Brain changes: Thiamine helps brain cells produce energy from sugar. When thiamine levels fall too low, brain cells cannot generate enough energy to function properly.
back to top
To learn more about Dementia, visit http://www.alz.org/what-is-dementia.asp
