Causes of dementia

Types of dementia

There are different diseases that can cause dementia. Many of these diseases are associated with an abnormal build-up of proteins in the brain.

This build-up causes nerve cells to function less well and ultimately die. As the nerve cells die, different areas of the brain shrink.

Diseases that can cause dementia include:

• Alzheimer’s disease
• vascular dementia
• Lewy bodies
• frontotemporal dementia
• mixed dementia

Causes of Alzheimer's disease

Alzheimer's disease is the most common type of dementia.

It is thought to be caused by the abnormal build-up of two proteins called amyloid and tau.

Deposits of amyloid, called plaques, build up around brain cells. Deposits of tau form tangles within brain cells.

As brain cells become affected in Alzheimer's, there's also a decrease in chemical messengers (called neurotransmitters) involved in sending messages, or signals, between brain cells.

Levels of one neurotransmitter, acetylcholine, are particularly low in the brains of people with Alzheimer's disease.

Medicines like donepezil increase levels of acetylcholine and improve brain function and symptoms.

These treatments are not cure for Alzheimer's disease, but they do help improve symptoms.

• Treatments for dementia

The symptoms that people develop depend on the areas of the brain that have been affected by the disease.

The hippocampus is often affected early on in Alzheimer's disease.

This area of the brain is responsible for storing new memories. That's why memory problems are one of the earliest symptoms in Alzheimer's.

Unusual forms of Alzheimer's disease can start with problems with vision or with language.

• Alzheimer's disease

Causes of vascular dementia

Vascular dementia is caused by reduced blood flow to the brain, which damages and eventually kills brain cells.

This can happen because of:

• narrowing and blockage of the small blood vessels inside the brain
• a single stroke, where the blood supply to part of the brain is suddenly cut off
• lots of mini strokes that cause tiny but widespread damage to the brain

Not everyone who has a stroke will go on to develop vascular dementia.

• Vascular dementia

Causes of dementia with Lewy bodies

Lewy bodies are tiny clumps of a protein called alpha-synuclein that can develop inside brain cells.

These clumps damage the way the cells work and communicate with each other, and the brain cells eventually die.

Dementia with Lewy bodies is closely related to Parkinson's disease and often has some of the same symptoms, including difficulty with movement and a higher risk of falls.

• Dementia with Lewy bodies

Causes of frontotemporal dementia

This type of dementia is more common in younger people. It's most often diagnosed between the ages of 45 and 65.

It's caused by an abnormal clumping of proteins, including tau, at the front and sides of the brain.

The clumping of these proteins damages nerve cells in the frontal and temporal lobes, causing brain cells to die. This leads to shrinking of these areas of the brain.

• Frontotemporal dementia

Causes of mixed dementia

Mixed dementia is a combination of more than one type of dementia.

Vascular dementia and Alzheimer's disease is the most common type of mixed dementia, but other combinations are possible.

Rarer causes of dementia

There are many rarer diseases and conditions that can lead to dementia, or dementia-like symptoms.

They include:

• Huntington's disease
• corticobasal degeneration
• progressive supranuclear palsy
• normal pressure hydrocephalus

Mild cognitive impairment

Mild cognitive impairment (MCI) is not a cause of dementia.

It's a term used to describe minor memory and thinking problems, such as:

• memory loss (amnesia)
• difficulty concentrating
• problems with planning and reasoning

These symptoms are not severe enough to cause problems in everyday life.

MCI can be caused by an underlying illness, such as:

• depression
• anxiety
• thyroid problems

If the underlying illness is treated or managed, symptoms of MCI often disappear and cause no further problems.

But in some cases, people with MCI are at increased risk of going on to develop dementia, which is usually caused by Alzheimer's disease.