Dementia is caused by damage to or changes in the brain. Alzheimer's disease is the most common cause. Stroke is the second most common cause of dementia. Dementia caused by stroke is called vascular dementia.
Some causes of dementia can be reversed with treatment, but most cannot.
Causes that cannot be reversed
Common causes of dementia that cannot be reversed are:
- Parkinson's disease. Dementia is common in people with this condition.
- Dementia with Lewy bodies. It can cause short-term memory loss.
- Frontotemporal dementia, a group of diseases that includes Pick's disease.
- Severe head injury that caused a loss of consciousness.
- Vascular dementia that may occur in people who have a stroke, long-term high blood pressure, or severe hardening of the arteries (atherosclerosis).
Less common causes of dementia that cannot be reversed include:
- Huntington's disease.
- Leukoencephalopathies, which are diseases that affect the deeper, white-matter brain tissue.
- Creutzfeldt-Jakob disease, a rare and fatal condition that destroys brain tissue.
- Brain injuries from accidents or boxing.
- Some cases of multiple sclerosis (MS) or amyotrophic lateral sclerosis (ALS).
- Multiple-system atrophy (a group of degenerative brain diseases affecting speech, movement, and autonomic functions).
- Infections such as late-stage syphilis. Antibiotics can effectively treat syphilis at any stage, but they cannot reverse the brain damage already done.
Causes that may be reversible
When dementia is caused by certain treatable problems, the treatment may also help the dementia. These treatable problems include:
- Underactive thyroid gland (hypothyroidism).
- Vitamin B12 deficiency.
- Heavy-metal poisoning, such as from lead.
- Side effects of medicines or drug interactions.
- Some brain tumors.
- Normal-pressure hydrocephalus.
- Some cases of chronic alcoholism.
- Some cases of encephalitis.
Some disorders that cause dementia can run in families. Doctors often suspect an inherited cause if someone younger than 50 has symptoms of dementia. For more information, see the topic Alzheimer's Disease.