What causes dementia?

Dementia, a term for a decline in memory and cognitive function so severe that it interferes with a person's normal activities and relationships, can be caused by a variety of diseases and conditions. All forms of dementia result from the death of nerve cells and/or the loss of communication among these cells. Alzheimer's disease is the most common cause of dementia, accounting for 50 to 60 percent of all cases. Among the estimated 50 or more other causes of dementia are:

- Vascular dementia, which is caused by brain damage from cerebrovascular or cardiovascular problems such as strokes, heart problems, and genetic diseases.

- Lewy body dementia, a progressive dementia linked to the abnormal protein present in Parkinson's disease.

- Frontotemporal dementia, in which nerve cells in the frontal and temporal lobes of the brain deteriorate. Its prevalence among people with a family history of dementia suggests a strong genetic factor in the disease.

- HIV-associated dementia, which occurs in people with HIV. The drugs used to treat AIDS can delay onset of the disease and reduce symptoms.

- Huntington's disease, a hereditary disorder caused by a faulty gene, which causes degeneration in many regions of the brain and spinal cord.

- Dementia pugilistica, which results from repeated head trauma. Dementia symptoms can appear many years after the trauma ends.

- Corticobasal degeneration, a progressive disorder linked to the accumulation of an abnormal protein the brain.

- Secondary dementias, dementia that occurs in patients with disorders that primarily affect movement—Parkinson's disease, multiple sclerosis, motor neuron diseases such as amyotrophic lateral sclerosis (Lou Gehrig's disease), olivopontocerebellar atrophy, Wilson's disease, and normal pressure hydrocephalus.

Dementia is caused by damage to or changes in the brain. After Alzheimer's disease, stroke is the 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.
• HIV/AIDS.

Inherited dementia - Some disorders that cause dementia can run in families. Doctors often suspect an inherited cause if someone younger than 50 has symptoms of dementia.

More than 50 conditions can mimic or cause dementia. Alzheimer's disease is by far the most common intractable condition. But other causes of irreversible dementia include blood vessel disease (vascular dementia), other degenerative disorders (frontotemporal lobar degeneration, Parkinson's disease, Huntington's disease), slow-growing brain tumors, or infections of the central nervous system (Creutzfeldt-Jakob disease, acquired immune deficiency syndrome [AIDS] dementia, neurosyphilis).