Dementia involves damage of nerve cells in the brain, which may occur in several areas of the brain. Dementia may affect people differently, depending on the area of the brain affected.

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. In people age 65 and older, Alzheimer's disease is the most common cause of dementia. People generally may develop symptoms after age 60, but some people may have early-onset forms of the disease, often as the result of a defective gene.

    Although in most cases the exact cause of Alzheimer's disease isn't known, plaques and tangles are often found in the brains of people with Alzheimer's. Plaques are clumps of a protein called beta-amyloid, and tangles are fibrous tangles made up of tau protein.

    Certain genetic factors also may make it more likely that people will develop Alzheimer's.

    Alzheimer's disease usually progresses slowly over seven to 10 years. Your cognitive abilities slowly decline. Eventually, the affected areas of your brain don't work properly, including parts of your brain that control memory, language, judgment and spatial abilities.

  • Lewy body dementia. Lewy body dementia affects approximately 10 to 22 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.

    Lewy body dementia symptoms are similar to symptoms of Alzheimer's disease. Its unique features include fluctuations between confusion and clear thinking (lucidity), visual hallucinations, and tremor and rigidity (parkinsonism).

    People with Lewy body dementia often have a condition called rapid eye movement (REM) sleep behavior disorder that involves acting out dreams.

  • Vascular dementia. Vascular dementia, the second most common type of dementia, occurs as a result of brain damage due to reduced or blocked blood flow in blood vessels leading to your brain.

    Blood vessel problems may be caused by stroke, infection of a heart valve (endocarditis) or other blood vessel (vascular) conditions.

    Symptoms usually start suddenly and often occur in people with high blood pressure or people who have had strokes or heart attacks in the past.

    Several different types of vascular dementia exist, and the types have different causes and symptoms. Alzheimer's disease and other dementias also may be present at the same time as this dementia.

  • 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 65.

    This is a group of diseases characterized by the breakdown (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 inappropriate behaviors, language problems, difficulty with thinking and concentration, and movement problems.

    As with other dementias, the cause isn't known, although in some cases this dementia is related to certain genetic mutations.

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 usually appear during your 30s or 40s. People may experience personality changes, such as irritability or anxiety. The condition causes a severe decline in thinking (cognitive) skills over time. Huntington's disease also causes weakness and difficulty with walking and movement.

  • Traumatic brain injury. This condition is caused by repetitive head trauma, such as experienced by boxers, football players or soldiers.

    Depending on the part of the brain injured, this condition can cause dementia signs and symptoms such as uncoordinated movement and impaired speech, as well as slow movement, tremors and rigidity (parkinsonism). Symptoms may not appear until many years after the actual trauma.

    A person who has experienced a single traumatic head injury could develop a similar condition called post-traumatic dementia, which may cause symptoms such as long-term memory problems.

  • HIV-associated dementia. Infection with the human immunodeficiency virus (HIV), which causes AIDS, destroys brain matter and may cause memory problems, withdrawal from social situations, concentration problems or movement problems.
  • Creutzfeldt-Jakob disease. This rare brain disorder usually occurs in people without risk factors. This condition may be due to an abnormal form of a protein. Creutzfeldt-Jakob disease sometimes may be inherited or caused by exposure to diseased brain or nervous system tissue.

    Signs and symptoms of this fatal condition usually appear around age 60 and initially include problems with coordination, memory, thinking and vision. Symptoms worsen over time and may include the inability to move or talk, blindness, or infections.

  • Secondary dementias. People with movement disorders and other conditions may develop dementia. For example, many people with Parkinson's disease eventually develop dementia symptoms (Parkinson's disease 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 may identify and treat 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. People may develop dementia or thinking difficulties if they have brain infections like meningitis and encephalitis, untreated syphilis, Lyme disease, or 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. People with thyroid problems, too little sugar in the bloodstream (hypoglycemia), too low or too high amounts of sodium or calcium, or an impaired ability to absorb vitamin B-12 may develop dementia or other personality changes.
  • Nutritional deficiencies. Dementia symptoms can occur as a result of not drinking enough liquids (dehydration); not having enough thiamine (vitamin B-1), a condition common in people with chronic alcoholism; and not having enough vitamins B-6 and B-12 in your diet.
  • Reactions to medications. Dementia may occur as a reaction to a single medication or because of an interaction of several medications.
  • Subdural hematomas. Subdural hematomas are caused by bleeding between the surface of the brain and the covering over the brain. They can cause symptoms similar to dementia.
  • Poisoning. Dementia symptoms can occur as a result of exposure to heavy metals, such as lead, and other poisons, such as pesticides.

    Dementia symptoms also may occur in some people who have abused alcohol or recreational drugs. Symptoms may disappear after treatment, but in some cases symptoms may still be present after treatment.

  • Brain tumors. Dementia rarely can result from damage caused by a brain tumor.
  • Anoxia. This condition, also called hypoxia, occurs when organ tissues aren't getting enough oxygen. Anoxia may occur due to severe asthma, heart attack, carbon monoxide poisoning or other causes.

    If you've experienced a severe lack of oxygen, recovery may take longer. Symptoms, such as memory problems or confusion, may occur during recovery.

  • Heart and lung problems. Your brain can't survive without oxygen. Dementia symptoms may occur in people with chronic lung problems or a heart condition that deprives the brain of the oxygen it needs.
  • Normal-pressure hydrocephalus. Sometimes people have normal-pressure hydrocephalus, a condition caused by enlarged ventricles in the brain. This condition can cause walking problems, urinary difficulty and memory loss. Shunt surgery, which delivers cerebrospinal fluid from the head to the abdomen or heart, may help these symptoms.
Apr. 16, 2013