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Causes

By Mayo Clinic staff

Dementia has many causes. Some dementias such as Alzheimer's disease occur on their own, not as a result of another disease. Much is still unknown about how some diseases may be linked to dementia.

Dementias can be classified in a variety of ways and are often grouped by what they have in common, such as what part of the brain is affected, or whether they worsen over time (progressive dementias). Some dementias, such as those caused by a reaction to medications or an infection, are reversible with treatment.

Progressive dementias
Types of dementias that worsen over time include:

  • Alzheimer's disease. Alzheimer's disease is the most common cause of dementia in people age 65 and older. Symptoms usually appear after age 60, but early-onset forms of the disease can occur, usually as the result of a defective gene. Although in most cases the exact cause of Alzheimer's disease isn't known, two types of brain cell (neuron) damage are common. These include plaques and tangles. Plaques are clumps of a normally harmless protein called beta-amyloid, and tangles are fibrous tangles made up of an abnormal protein called tau protein. Alzheimer's disease usually progresses slowly, over seven to 10 years, causing a gradual decline in cognitive abilities. Eventually, the affected areas of the brain don't work properly, including those parts involving memory, movement, language, judgment, behavior and abstract thinking.
  • Lewy body dementia. Dementia with Lewy bodies affects approximately 20 percent of people with dementia, making it one of the most common types of dementia. Lewy body dementia becomes more common with age. Lewy bodies are abnormal clumps of protein that have been found in the brains of people with Lewy body dementia, Alzheimer's disease and Parkinson's disease. The symptoms of this dementia are similar to Alzheimer's disease, but its unique features often include fluctuations between confusion and clear thinking (lucidity), visual hallucinations, and Parkinson's signs such as tremor and rigidity. People with Lewy body dementia often have a condition called REM sleep behavior disorder that involves acting out dreams, including thrashing or kicking during sleep.
  • Vascular dementia. The second most common dementia after Alzheimer's disease is a result of damage to your brain caused by problems with the arteries serving your brain or heart. Symptoms begin suddenly, often after a stroke, and may occur in people with high blood pressure, or who have had previous strokes or heart attacks. Vascular dementia may also be caused by infection of a heart valve (endocarditis) or a buildup of amyloid protein in the brain's blood vessels (amyloid angiopathy) that sometimes causes "bleeding" (hemorrhagic) strokes.

Several types of vascular dementia exist and vary in their causes and symptoms. Some types affect only one side of the body, and some cause memory loss, confusion and mood changes. In some forms, symptoms may progressively worsen, while in others, they may be temporary. In general, vascular dementia is more common with age. Often this dementia coexists with Alzheimer's disease.

  • Frontotemporal dementia. This less common cause of dementia tends to occur at a younger age than does Alzheimer's disease, generally between the ages of 40 and 70. This is a group of diseases characterized by the degeneration of nerve cells in the frontal and temporal lobes of the brain — the areas generally associated with personality, behavior and language. Signs and symptoms of frontotemporal dementia can include socially inappropriate behaviors, loss of mental flexibility, language problems, and difficulty with thinking and concentration. As with others dementias, the cause isn't known, although in some cases this dementia is related to certain genetic mutations. But many people with frontotemporal dementia have no family history of the disease. One form of this condition is called Pick's disease. Pick's disease affects parts of the brain that contain fibrous tangles made up of the abnormal protein called tau protein. Pick's disease causes progressive dementia.

Other disorders linked to dementia

  • Huntington's disease. This inherited disease causes certain nerve cells in your brain and spinal cord to waste away. Signs and symptoms typically appear during your 30s or 40s. They may include mild personality changes at first — irritability, anxiety and depression — and progress to severe dementia. Huntington's disease also causes difficulty with walking and movement, weakness and clumsiness.
  • Dementia pugilistica. This condition, also called chronic traumatic encephalopathy or boxer's dementia, is caused by repetitive head trauma, such as experienced by boxers. Depending on the part of the brain injured, it can cause dementia signs and symptoms such as memory problems, poor coordination and impaired speech, as well as tremors, slow movement and muscle stiffness (parkinsonism). Symptoms may not appear until many years after the actual trauma. A single traumatic head injury can cause post-traumatic dementia, which is much like dementia pugilistica, but may include long-term memory problems.
  • HIV-associated dementia. Infection with the human immunodeficiency virus (HIV), which causes AIDS, leads to widespread destruction of brain matter and results in impaired memory, apathy, social withdrawal and difficulty concentrating. Often, problems with movement also develop.
  • Creutzfeldt-Jakob disease. This rare, fatal brain disorder most often occurs sporadically in people with no known risk factors. However, a few cases are hereditary or caused by exposure to diseased brain or nervous system tissue. Signs and symptoms usually appear around age 60 and initially include problems with coordination, personality changes, and impaired memory, judgment, thinking and vision. Mental impairment becomes severe as the illness progresses, and it often leads to blindness. Pneumonia and other infections also are common.
  • Secondary dementias. Sometimes, people with other disorders that primarily affect movement, for example, Parkinson's disease, may eventually develop symptoms of dementia. The relationship between these disorders and dementia isn't completely understood.

Dementia causes that can be reversed
Some causes of dementia or dementia-like symptoms can be reversed. Your doctor can identify, treat and sometimes cure these causes:

  • Infections and immune disorders. Dementia can result from fever or other side effects of your body's attempt to fight off an infection. Examples of such infections include brain infections like meningitis and encephalitis, untreated syphilis, Lyme disease, and conditions that cause a completely compromised immune system, such as leukemia. Conditions such as multiple sclerosis that arise from the body's immune system attacking nerve cells also can cause dementia.
  • Metabolic problems and endocrine abnormalities. These include thyroid problems, too little sugar in the bloodstream (hypoglycemia), too little or too much sodium or calcium, and an impaired ability to absorb vitamin B-12.
  • Nutritional deficiencies. Symptoms can occur as a result of dehydration, not having enough thiamin (vitamin B-1) — a condition common in people with chronic alcoholism — and deficiencies in vitamins B-6 and B-12. Bananas, lentils, spinach, fortified breakfast cereals, salmon, pork, chicken, whole-wheat bread, milk and eggs are all good sources of these B vitamins.
  • Reactions to medications. Dementia may occur as a reaction to a single medication or because of an interaction of several drugs.
  • Subdural hematomas. These are caused by bleeding between the brain's surface and its outer covering.
  • Poisoning. Dementia symptoms can occur as a result of exposure to heavy metals, such as lead or manganese, and other poisons, such as pesticides. People who have abused alcohol and recreational drugs also sometimes display symptoms. In all of these instances, symptoms may go away after treatment or after exposure to the substance has ended.
  • Brain tumors. It's rare, but dementia can be the result of damage caused by a brain tumor.
  • Anoxia. This condition, also called hypoxia, occurs when not enough oxygen gets to organ tissue. Causes include heart attack, severe asthma, carbon monoxide poisoning, strangulation, high-altitude exposure or an overdose of anesthetic. Recovery depends on the severity of the oxygen deprivation. Symptoms may occur during recovery.
  • Heart and lung problems. Your brain can't survive without oxygen. Symptoms may occur in people with chronic lung problems or a heart condition that deprives the brain of the oxygen it needs.
Risk factors Symptoms
References
  1. Dementia: Hope through research. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/dementias/detail_dementia.htm#1318919213. Accessed Jan. 25, 2010.
  2. Dementia. Alzheimer's Association. http://www.alz.org/alzheimers_disease_dementia.asp. Accessed Jan. 25, 2011.
  3. Alternative treatments. Alzheimer's Association. http://www.alz.org/alzheimers_disease_alternative_treatments.asp. Accessed Jan. 25, 2011.
  4. A guide to dementia diagnosis and treatment. The American Geriatrics Society. http://www.americangeriatrics.org/press/listservs/december_10_2010427672/id:1442 Accessed Jan. 25, 2011.
  5. NIH State-of-the-science conference statement on preventing Alzheimer's disease and cognitive decline. National Institutes of Health. http://consensus.nih.gov/2010/docs/alz/alz_stmt.pdf. Accessed Jan. 7, 2011.
  6. Ritchie K, et al. Designing prevention programmes to reduce incidence of dementia: Prospective cohort study of modifiable risk factors. British Medical Journal. 2010;341:c3885.
  7. Rusanen M, et al. Heavy smoking in midlife and long-term risk of Alzheimer disease and vascular dementia. Archives of Internal Medicine. In press. Accessed Jan. 25, 2011.
  8. Siedlecki KL, et al. Comparison of patient and caregiver reports of patient activity participation and its relationship to mental health in patients with Alzheimer's disease. Journal of Gerontology: Psychological Services. 2009;64B:687.
  9. Scarmeas N, et al. Physical activity, diet, and risk of Alzheimer's disease. Journal of the American Medical Association. 2009;302:627.
DS01131 April 16, 2011

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