Dementia with Lewy bodies

What is dementia with Lewy bodies?

Dementia with Lewy bodies (DLB) is a type of dementia that shares symptoms with both Alzheimer's disease and Parkinson's disease. It may account for 10-15 per cent of all cases of dementia. DLB can be diagnosed wrongly and is often mistaken for Alzheimer's disease. This section describes the symptoms of DLB and how it is diagnosed, as well as the treatment and support available.

DLB is sometimes known by other names. These include Lewy body dementia, Lewy body variant of Alzheimer's disease, diffuse Lewy body disease and cortical Lewy body disease. All these terms refer to the same condition.

Lewy bodies

Lewy bodies are named after the German doctor who first identified them. They are tiny deposits of a protein (alpha-synuclein) that appear in nerve cells in the brain. Researchers don't have a full understanding of why Lewy bodies appear, or exactly how they contribute to dementia. However, this is linked to two factors:

  • low levels of important chemicals (mainly acetylcholine and dopamine) that carry messages between nerve cells
  • a loss of connections between nerve cells, which then die.

Lewy bodies are the cause of DLB and Parkinson's disease. They are two of several diseases caused by Lewy bodies that affect the brain and nervous system and get worse over time. These are sometimes called Lewy body disorders. 

The way someone is affected by DLB will depend partly on where the Lewy bodies are in the brain: 

  • Lewy bodies at the base of the brain are closely linked to problems with movement (motor symptoms). These are the main feature of Parkinson's disease.
  • Lewy bodies in the outer layers of the brain are linked to problems with mental abilities (cognitive symptoms), which is a feature of DLB.

People with a Lewy body disorder can have problems with movement and changes in mental abilities at the same time. About one-third of people diagnosed with Parkinson's disease eventually develop dementia (Parkinson's disease dementia). Where Parkinson's disease dementia does develop, it is generally a long time - sometimes 10 years or so - after Parkinson's disease has first been diagnosed.

Who is affected?

DLB accounts for around 4 per cent of all recorded dementia, but there is good evidence that the condition is not always diagnosed correctly. Based on studies of brain tissue after death, scientists think DLB may account for as much as 10-15 per cent of all dementia.

DLB appears to affect men and women equally. As with Alzheimer's disease and vascular dementia, DLB becomes more common over the age of 65. However, it can also affect people under 65.

Other than age, there are few risk factors (such as medical conditions or lifestyle choices) that are known to increase a person's chances of developing DLB. Most people who develop DLB have no clear family history of the condition. A few families seem to have genetic mutations that are linked to inherited Lewy body disease, but these are very rare. For more on this see factsheet 405, Genetics of dementia.