Dementia involves damage of nerve cells in the brain, which can occur in several areas of the brain. Dementia affects people differently, depending on the area of the brain affected.
Dementias are often grouped by what they have in common, such as the part of the brain that's affected or whether they worsen over time (progressive dementias). Some dementias, such as those caused by a reaction to medications or vitamin deficiencies, might improve with treatment.
Types of dementias that progress and aren't reversible include:
Alzheimer's disease. In people age 65 and older, Alzheimer's disease is the most common cause of dementia.
Although the 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 might make it more likely that people will develop Alzheimer's.
- Vascular dementia. This second most common type of dementia occurs as a result of damage to the vessels that supply blood to your brain. Blood vessel problems can be caused by stroke or other blood vessel conditions.
- Lewy body dementia. 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. This is one of the more common types of progressive dementia.
Frontotemporal dementia. 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.
As with other dementias, the cause isn't known.
- Mixed dementia. Autopsy studies of the brains of people 80 and older who had dementia indicate that many had a combination of Alzheimer's disease, vascular dementia and Lewy body dementia. Studies are ongoing to determine how having mixed dementia affects symptoms and treatments.
Other disorders linked to dementia
- Huntington's disease. Caused by a genetic mutation, this disease causes certain nerve cells in your brain and spinal cord to waste away. Signs and symptoms, including a severe decline in thinking (cognitive) skills usually appear around age 30 or 40.
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 that's injured, this condition can cause dementia signs and symptoms, such as depression, explosiveness, memory loss, uncoordinated movement and impaired speech, as well as slow movement, tremors and rigidity (parkinsonism). Symptoms might not appear until years after the trauma.
Creutzfeldt-Jakob disease. This rare brain disorder usually occurs in people without known risk factors. This condition might be due to an abnormal form of a protein. Creutzfeldt-Jakob disease can 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.
- Parkinson's disease. Many people with Parkinson's disease eventually develop dementia symptoms (Parkinson's disease dementia).
Dementia-like conditions that can be reversed
Some causes of dementia or dementia-like symptoms can be reversed with treatment. They include:
- Infections and immune disorders. Dementia-like symptoms can result from fever or other side effects of your body's attempt to fight off an infection. Conditions such as multiple sclerosis that result from the body's immune system attacking nerve cells also can cause dementia.
- Metabolic problems and endocrine abnormalities. People with thyroid problems, low blood sugar (hypoglycemia), too little or too much sodium or calcium, or an impaired ability to absorb vitamin B-12 can develop dementia-like symptoms or other personality changes.
- Nutritional deficiencies. Not drinking enough liquids (dehydration); not getting enough thiamin (vitamin B-1), which is common in people with chronic alcoholism; and not getting enough vitamins B-6 and B-12 in your diet can cause dementia-like symptoms.
- Reactions to medications. A reaction to a medication or an interaction of several medications can cause dementia-like symptoms.
- Subdural hematomas. Bleeding between the surface of the brain and the covering over the brain, which is common in the elderly after a fall, can cause symptoms similar to dementia.
- Poisoning. Exposure to heavy metals, such as lead, and other poisons, such as pesticides, as well as alcohol abuse or recreational drug use can lead to symptoms of dementia. Symptoms might resolve with treatment.
- Brain tumors. Rarely, dementia 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 can occur due to severe asthma, heart attack, carbon monoxide poisoning or other causes.
- Normal-pressure hydrocephalus. This condition, which is caused by enlarged ventricles in the brain, can cause walking problems, urinary difficulty and memory loss.