According the Alzheimer's Association, dementia is characterized by the loss of, or decline in, memory and other cognitive abilities. Various diseases and conditions damage brain cells and can lead to dementia. Over 100 different types of dementia exist. The most common cause of dementia is Alzheimer's disease (AD).
Alzheimer's Disease
The Alzheimer's Association estimates that AD accounts for 60 to 80 percent of cases of dementia, and as many as 5.3 million Americans have AD. Research suggests that the risk of developing AD is largely genetic and beyond a person's control, but environmental and lifestyle factors have also been implicated in causing AD. According to the National Institutes of Health (NIH), AD causes development of amyloid plaques and neurofibrillary tangles, which cause nerve cells to die. Brains with advanced AD shrink intensely from brain cell loss, causing dementia.
Vascular Dementia
Damaged cerebral arteries cause vascular dementia. Thickening of the inside lining of the cerebral arteries interrupts the supply of blood to the brain. The brain depends on its blood supply more than any other organ in the body. High blood pressure, heart problems, high cholesterol and diabetes can all cause the linings of the arteries to thicken.
Mixed Dementia
According to the Alzheimer's Association, mixed dementia is a condition in which Alzheimer's disease and vascular dementia are present simultaneously. However, mixed dementia can also described as Alzheimer's coexisting with other forms of dementia.
Dementia with Lewy Bodies
Dementia with Lewy bodies accounts for approximately 4 percent of all cases of dementia in older people. Lewy bodies are abnormal deposits of the protein alpha-synuclein found inside nerve cells in the brain. Their presence in the brain disrupts the brain's normal functioning, interrupting the action of important chemical messengers, including acetylcholine and dopamine. Researchers have yet to understand fully why Lewy bodies occur in the brain, and how they cause damage. Dementia with Lewy bodies is a form of dementia that shares characteristics with both AD and Parkinson's diseases.
Other Less Common Causes of Dementia
Many people who have Parkinson's disease, a condition that usually involves movement problems, also develop dementia in the later stages of the disease. Lewy bodies associated with Parkinson's disease cause dementia.
Frontotemporal dementia (FTD) describes a group of diseases characterized by degeneration of nerve cells--especially those in the frontal and temporal lobes of the brain. The cause of FTD is unknown, but some cases are due to a genetic mutation. Frontotemporal dementia occurs far less frequently than other conditions such as AD. It is more likely to affect younger people, especially those under the age of 65, and it is slightly more common in men.
Creutzfeldt-Jakob disease is disease that rapidly kills its host. Research shows that the proteins called "prions" misfold throughout the brain, causing memory, coordination and behavioral problems. Prions become infectious agents that attack the central nervous system and then invade the brain.
Normal pressure hydrocephalus causes dementia by allowing fluid buildup in the brain. Symptoms include difficulty walking, memory loss and inability to control urination. It can sometimes be corrected by surgically draining excess fluid.
