Dementia Overview (cont.)
Dementia: Irreversible Causes
Dementia has many different causes, some of which are difficult to tell apart. Many medical conditions can cause dementia symptoms, especially in older people.
- The causes of dementia include various diseases and infections, strokes, head injuries, drugs, and nutritional deficiencies.
- All dementias reflect dysfunction in the cerebral cortex, the part of the brain that controls perception, memory, thoughts, language, and consciousness. Some disease processes damage the cortex directly; others disrupt subcortical areas of the brain that normally regulate the function of the cortex.
- When the underlying process does not permanently damage the cortical tissue, the dementia may sometimes be stopped or reversed.
- In classifying dementias, medical professionals may either separate the causes into cortical or subcortical dementias or into reversible and irreversible dementias.
The main irreversible causes of dementia are described here. These damage brain cells in both cortical and subcortical areas. Treatment focuses on slowing progress of the underlying condition and relieving symptoms.
- Alzheimer's disease: This is the most common cause of dementia, accounting for about half of all cases. Alzheimer's disease is at least partly hereditary in that it tends to run in families. (Just because a relative has Alzheimer's disease, however, does not mean that another family member will have the disease.) In this disease, abnormal protein deposits in the brain destroy cells in the areas of the brain that control memory and mental functions. People with Alzheimer's disease also have lower-than-normal levels of brain chemicals called neurotransmitters that control important brain functions. Alzheimer's disease is not reversible, and no known cure exists. However, certain medications can slow its progress.
- Vascular dementia: This is the second most common cause of dementia, accounting for as many as 40% of cases. This dementia is caused by atherosclerosis, or "hardening of the arteries," in the brain. Deposits of fats, dead cells, and other debris form on the inside of arteries, partially (or completely) blocking blood flow. These blockages cause multiple strokes, or interruptions of blood flow, to the brain. Because this interruption of blood flow is also called "infarction," this type of dementia is sometimes called multi-infarct dementia. One subtype whose origin is not well understood is Binswanger disease. Vascular dementia is related to high blood pressure, high cholesterol, heart disease, diabetes, and related conditions. Treating those conditions can slow the progress of vascular dementia, but functions do not come back once they are lost.
- Parkinson's disease: People with this disease typically have limb stiffness (which causes them to shuffle when they walk), speech problems, and tremor (shaking at rest). Dementia may develop late in the disease, but not everyone with Parkinson's disease has dementia. Reasoning, memory, speech, and judgment are most likely to be affected.
- Lewy body dementia: This is caused by abnormal microscopic deposits of protein, called Lewy bodies, which destroy nerve cells. These deposits can cause symptoms typical of Parkinson's disease, such as tremor and muscle rigidity, as well as dementia similar to that of Alzheimer's disease. Lewy body dementia affects thinking, attention, and concentration more than memory and language. Like Alzheimer's disease, Lewy body dementia is not reversible and has no known cure. The drugs used to treat Alzheimer's disease also benefit some people with Lewy body disease.
- Huntington's disease: This inherited disease causes wasting of certain types of brain cells that control movement as well as thinking. Dementia is common and occurs in the late stages of the disease. Personality changes are typical. Reasoning, memory, speech, and judgment may also be affected.
- Creutzfeldt-Jakob disease: This rare disease occurs most often in young and middle-aged adults. Infectious agents called prions invade and kill brain cells, leading to behavior changes and memory loss. The disease progresses rapidly and is fatal.
- Pick disease (frontotemporal dementia): This is another rare disorder that damages cells in the frontal part of the brain. Behavior and personality changes usually precede memory loss and language problems.
- Parkinson's disease and Huntington's disease begin in subcortical areas. They cause the subcortical type of dementia.
- Multiple sclerosis: In this condition, brain and spinal cord cells are damaged by an autoimmune process. Dementia can result in some people.
- Untreated brain infections (for example, HIV, Lyme disease) damage brain cells by forming lesions and trigger inflammatory responses that damage or kill brain cells.
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