Dementia is a clinical syndrome of loss or decline in memory and other cognitive abilities. It is caused by various diseases and conditions that result in damaged brain cells.
Alzheimer’s disease is the most common cause of dementia.
This section provides information about the definition of dementia, the characteristics of specific types of dementia and the symptoms, risk factors for and treatment of Alzheimer’s disease.
Dementia: Definition and Specific Types
Dementia is a clinical syndrome of loss or decline in memory and other cognitive abilities. It is caused by various diseases and conditions that result in damaged brain cells. To be classified as dementia, the syndrome must meet the following criteria:
• It must include decline in memory and in at least one of the following cognitive abilities:
1. Ability to generate coherent speech and understand spoken or written language;
2. Ability to recognize or identify objects, assuming intact sensory function;
3. Ability to execute motor activities, assuming intact motor abilities, sensory function and comprehension
of the required task; and
4. Ability to think abstractly, make sound judgments and plan and carry out complex tasks.
• The decline in cognitive abilities must be severe enough to interfere with daily life.
Diff erent types of dementia have been associated with distinct symptom patterns and distinguishing microscopic brain abnormalities. Increasing evidence from long-term epidemiological observation and autopsy studies suggests that many people have microscopic brain abnormalities associated with more than one type of dementia. The symptoms of diff erent types of dementia also overlap and can be further complicated by coexisting medical
Table 1 provides information about the most common types of dementia.
Table 1: Common Types of Dementia and Their Typical Characteristics
Type of Dementia Characteristics
Alzheimer’s disease. Most common type of dementia; accounts for 60 to 80 percent of cases.
Difficulty remembering names and recent events is often an early clinical
symptom; later symptoms include impaired judgment, disorientation, confusion,
behavior changes and trouble speaking, swallowing and walking.
Hallmark abnormalities are deposits of the protein fragment beta-amyloid
(plaques) and twisted strands of the protein tau (tangles).
Vascular dementia. Considered the second-most-common type of dementia.
Impairment is caused by decreased blood fl ow to parts of the brain, often due
to a series of small strokes that block arteries.
Symptoms often overlap with those of Alzheimer’s, although memory may not
be as seriously aff ected.
Mixed dementia. Characterized by the presence of 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, frontotemporal dementia and
normal pressure hydrocephalus.
Dementia with Lewy bodies. Pattern of decline may be similar to Alzheimer’s, including problems with memory, judgment and behavior changes.
Alertness and severity of cognitive symptoms may fluctuate daily.
Visual hallucinations, muscle rigidity and tremors are common.
Hallmarks include Lewy bodies (abnormal deposits of the protein alphasynuclein)
that form inside nerve cells in the brain.
Parkinson’s disease. Many people who have Parkinson’s disease develop dementia in the later stages of the disease.
The hallmark abnormality is Lewy bodies (abnormal deposits of the protein
alpha-synuclein) that form inside nerve cells in the brain.
Frontotemporal dementia. Involves damage to brain cells, especially in the front and side regions
of the brain.
Typical symptoms include changes in personality and behavior and diffi culty
No distinguishing microscopic abnormality is linked to all cases.
Pick’s disease, characterized by “Pick’s bodies,” is one type of frontotemporal
Creutzfeldt-Jakob disease. Rapidly fatal disorder that impairs memory and coordination and causes behavior changes.
“Variant Creutzfeldt-Jakob disease” is believed to be caused by consumption of
products from cattle affected by “mad cow disease.”
Caused by the misfolding of prion protein throughout the brain.
Normal pressure hydrocephalus. Caused by the buildup of fl uid in the brain.
Symptoms include difficulty walking, memory loss and inability to control urine.
Can sometimes be corrected with surgical installation of a shunt in the brain to
drain excess fluid.
Mild cognitive impairment is a condition in which a person has problems with memory, language or another essential cognitive function that are severe enough to be noticeable to others and show up on tests, but not severe enough to interfere with daily life. Some people with mild cognitive impairment go on to develop dementia. For others, the symptoms of mild cognitive impairment do not progress to dementia, and some people who have mild cognitive impairment at one point in time later revert to normal cognitive status.
Bob De Marco
Alzheimer's Reading Room
Original content Bob DeMarco, the Alzheimer's Reading Room