Dementia 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, or brain tissue. Some disease processes damage the cortex directly; others disrupt subcortical areas 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 cortical or subcortical dementias or divide 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 disease: This is the most common cause of dementia, accounting for about half of all cases. Alzheimer disease is at least partly hereditary in that it tends to run in families. (Just because a relative has Alzheimer 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 disease also have lower-than-normal levels of brain chemicals called neurotransmitters that control important brain functions. Alzheimer 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 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 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 disease, such as tremor and muscle rigidity, as well as dementia similar to that of Alzheimer disease. Lewy body dementia affects thinking, attention, and concentration more than memory and language. Like Alzheimer disease, Lewy body dementia is not reversible and has no known cure. The drugs used to treat Alzheimer disease also benefit some people with Lewy body disease.  
  
  
• Huntington 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 front part of the brain. Behavior and personality changes usually precede memory loss and language problems.  
  
  
• Parkinson disease and Huntington disease begin in subcortical areas. They cause the subcortical type of dementia.

The dementia in these conditions may be reversible or partially reversible, even if the underlying disease or damage is not.

• Head injury: This refers to brain damage from accidents, such as motor vehicle wrecks and falls; from assaults, such as gunshot wounds or beatings; or from activities such as boxing without protective gear. The resulting damage of brain cells can lead to dementia. 
  
  
• Infections: Infections of brain structures, such as meningitis and encephalitis, are primary causes of dementia. Other infections, such as HIV/AIDS and syphilis, can affect the brain in later stages. In all cases, inflammation in the brain damages cells.  
  
  
• Normal pressure hydrocephalus: The brain floats in a clear fluid called cerebrospinal fluid. This fluid also fills internal spaces in the brain called cerebral ventricles. If too much fluid collects outside the brain, it causes hydrocephalus. This condition raises the fluid pressure inside the skull and compresses brain tissue from outside. It may cause severe damage and death. If fluid builds up in the ventricles, the fluid pressure remains normal ("normal pressure hydrocephalus"), but brain tissue is compressed from within. 
  
  
• Simple hydrocephalus: Simple hydrocephalus may cause typical dementia symptoms or lead to coma. In normal pressure hydrocephalus, people have trouble walking and become incontinent (unable to control urination) at the same time they start to lose mental functions, such as memory. If normal pressure hydrocephalus is diagnosed early, the internal fluid pressure may be lowerable by putting in a shunt. This can stop the dementia, the gait problems, and the incontinence from getting worse.
  
  
• Brain tumors: Tumors can cause dementia symptoms in a number of ways. A tumor can press on structures such as the hypothalamus or pituitary gland, which control hormone secretion. They can also press directly on brain cells, damaging them. Treating the tumor, either medically or surgically, can reverse the symptoms in some cases. 
  
  
• Toxic exposure: People who work around solvents or heavy metal dust and fumes (lead especially) without adequate protective equipment may develop dementia from the damage these substances can cause to brain cells. Some exposures can be treated, and avoiding further exposure can prevent further damage. 
  
  
• Metabolic disorders: Diseases of the liver, pancreas or kidneys can lead to dementia by disrupting the balances of salts and other chemicals in the blood. Often, these changes occur rapidly and affect the person's level of consciousness. This is called delirium. Although the person with delirium, like the person with dementia, cannot think well or remember, treatment of the underlying disease may fully reverse the condition. If the underlying disease persists, however, brain cells may die, and the person will have dementia. 
  
  
• Hormone disorders: Disorders of hormone-secreting and hormone-regulating organs such as the thyroid gland, the parathyroid glands, the pituitary gland, or the adrenal glands can lead to hormone imbalances, which can cause dementia if not corrected. 
  
  
• Poor oxygenation (hypoxia): People who do not have enough oxygen in their blood may develop dementia because the blood brings oxygen to the brain cells, and brains cells need oxygen to live. The most common causes of hypoxia are lung diseases such as emphysema or pneumonia. These limit oxygen intake or transfer of oxygen from the airways of the lungs to the blood. Cigarette smoking is a frequent cause of emphysema. It can worsen hypoxic brain damage by damaging the lungs and also by increasing the levels of carobon monoxide in the blood. Heart disease leading to congestive heart failure may also lower the amount of oxygen in the blood. Sudden, severe hypoxia may also cause brain damage and symptoms of dementia. Sudden hypoxia may occur if someone is comatose or has to be resuscitated.
  
  
• Drug reactions, overuse, or abuse: Some drugs can cause temporary problems with memory and concentration as side effects in elderly people. Misuse of prescription drugs over time, whether intentional or accidental, can cause dementia. The most common culprits are sleeping pills and tranquilizers. Other drugs that cause dry mouth, constipation, and sedation ("anticholinergic side effects") may cause dementia or dementia symptoms. Illegal drugs, especially cocaine (which affects circulation and may cause small strokes) and heroin (which is very anticholinergic) may also cause dementia, especially in high doses, if taken for long periods, or in older people. The withdrawal of the drug usually reverses the symptoms.  
  
  
• Nutritional deficiencies: Deficiencies of certain nutrients, especially B vitamins, can cause dementia if not corrected. 
  
  
• Chronic alcoholism: Dementia in people with chronic alcoholism is believed to result from other complications such as liver disease and nutritional deficiencies.