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By MayoClinic.com

Dementia is a neurological disorder that affects your ability to think, speak, reason, remember and move. While Alzheimer's disease is the most common cause of dementia, many other conditions also cause these symptoms. Some of these disorders get worse with time and cannot be cured. Other types can be treated and reversed.

The three most common forms of dementia are Alzheimer's disease, vascular dementia and Lewy body dementia. Sometimes, a person can have more than one of these problems at the same time.

Alzheimer's disease: Most common cause

Alzheimer's disease involves a loss of nerve cells in the areas of the brain vital to memory and other mental functions. This loss is associated with the development of abnormal clumps and tangles of protein in brain cells.

The first sign of Alzheimer's disease is usually forgetfulness. As the disease progresses, it affects language, reasoning and understanding. Eventually, people with Alzheimer's lose the ability to care for themselves.

The precise cause of Alzheimer's disease is unknown, but risk increases with age. Ten percent of the population over the age of 65 has Alzheimer's, while nearly half of the population over 85 has the disease.

Vascular dementia: Frequently follows stroke

Another common form of dementia, vascular dementia occurs when arteries feeding the brain become narrowed or blocked. The onset of symptoms usually is abrupt, frequently occurring after a stroke.

However, some forms of vascular dementia progress slowly, making them difficult to distinguish from Alzheimer's disease. Some people have Alzheimer's and vascular dementia at the same time.

Vascular dementia often causes problems with thinking, language, walking, bladder control and vision. Preventing additional strokes by treating underlying diseases, such as high blood pressure, may halt the progression of vascular dementia.

Lewy body dementia: Has Alzheimer's-like and Parkinson's-like features

In this form of dementia, abnormal round structures - Lewy bodies - develop within cells of the midbrain, beneath the cerebral hemispheres. Lewy body dementia shares characteristics with both Alzheimer's disease and Parkinson's disease. Like Alzheimer's disease, it causes confusion and impaired memory and judgment. And it often produces two distinctive physical signs typical of Parkinson's disease - a shuffling gait and flexed posture. Lewy body dementia can also cause hallucinations.

Lewy bodies contain a protein associated with Parkinson's disease, and Lewy bodies often are found in the brains of people who have Parkinson's disease or Alzheimer's disease. This suggests that the three ailments are related, or that Lewy body dementia and Alzheimer's or Parkinson's disease sometimes co-exist in the same person. Some people with Lewy body dementia have experienced dramatic improvements in symptoms when treated with Alzheimer's or Parkinson's medications.

Other disorders linked to dementia

Several less common brain disorders also can result in dementia.

• Frontotemporal dementia. Because it affects the lobes of the brain that are responsible for judgment and social behavior, frontotemporal dementia can result in impolite and socially inappropriate behavior. Symptoms of this form of dementia usually appear between the ages of 40 and 65. The disease seems to run in families.

• Huntington's disease. Symptoms of this hereditary disorder typically begin between the ages of 30 and 50, starting with mild personality changes. As the disorder progresses, a person with Huntington's develops involuntary jerky movements, muscle weakness and clumsiness. Dementia commonly develops in the later stages of the disease.

• Parkinson's disease. People with Parkinson's disease may experience stiffness of limbs, shaking at rest (tremor), speech impairment and a shuffling gait. Some people with Parkinson's develop dementia late in the disease.

• Creutzfeldt-Jakob disease. This extremely rare and fatal brain disorder belongs to a family of human and animal diseases known as the transmissible spongiform encephalopathies. A new variety of Creutzfeldt-Jakob disease has emerged - particularly in Great Britain. It's believed to be linked to the human consumption of beef from cattle with mad cow disease (bovine spongiform encephalopathy).

Some causes are treatable

Many other conditions, some reversible, can cause dementia or dementia-like symptoms.

• Reactions to medications. Some medications have side effects that mimic the symptoms of dementia. A single medicine may trigger such a reaction in an older person or in someone whose liver fails to eliminate the drug properly. Interactions among two or more drugs may lead to reversible symptoms of dementia as well.

• Metabolic abnormalities. Decreased thyroid function (hypothyroidism) can result in apathy, depression or dementia. Hypoglycemia, a condition in which there isn't enough sugar in the bloodstream, can cause confusion or personality changes. Pernicious anemia - an impaired ability to absorb vitamin B-12 - also can cause personality changes.

• Nutritional deficiencies. Chronic alcoholism can result in deficiencies of thiamin (vitamin B-1), which can seriously impair mental abilities. Severe deficiency of vitamin B-6 may lead to pellagra, a neurological illness with features of dementia. Dehydration also can cause confusion that may resemble dementia.

• Emotional problems. The confusion, apathy and forgetfulness associated with depression are sometimes mistaken for dementia, particularly in older individuals.

• Infections. Meningitis and encephalitis, which are infections of the brain or the membrane that covers it, can cause confusion, memory loss or sudden dementia. Untreated syphilis can damage the brain and cause dementia. People in the advanced stages of AIDS also may develop a form of dementia.

Seek evaluation and treatment

Dementia isn't always due to Alzheimer's. Before you conclude that a loved one's memory loss and confusion stem from an irreversible disease process, get a thorough medical evaluation. Even if the evaluation uncovers no underlying condition that, with treatment, can reverse dementia, options may be available for easing its symptoms. Knowing the likely cause of dementia, however, is the essential first step toward managing it.

content by: Mayo Clinic

download pdf of the Dementia White Paper from the Mayo Clinic