Dementia with Lewy bodies (DLB)

Information provided by the Alzheimers Society

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 factsheet 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.

Similarly, at least two-thirds of people with DLB develop movement problems at some point. The symptoms of DLB and Parkinson's disease dementia become more similar as the conditions progress. Together they are referred to as Lewy body dementias.

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.


As with most types of dementia, the first symptoms of DLB may affect someone only slightly, but gradually they get worse and cause problems with daily living. Everyone is different, but a person with DLB will usually have some of the symptoms of Alzheimer's disease and some of the symptoms of Parkinson's disease. They will also have some symptoms which are unique to DLB. These are covered in the sections below.

Problems with mental abilities

Problems with attention and alertness are very common in DLB. An important feature of the condition is that these problems may switch between being bad and then better - or the other way round - over the course of the day, by the hour or even a few minutes. Someone with DLB may stare into space for a long time or have periods when their speech is disorganised.

People may also have difficulties judging distances and seeing objects in three dimensions. It is common to struggle with planning, organising and decision-making. Some people also experience depression. Day-to-day memory is often affected in people with DLB, but usually less in the early stages than in early Alzheimer's disease.

Hallucinations and delusions

Visual hallucinations (seeing things that are not there) occur frequently in people with DLB, often in the early stages of the condition. They can happen daily. Visual hallucinations are often of people or animals, and are detailed and convincing to the person with dementia. They can last several minutes and may be distressing. (Someone may also have visual misperceptions, such as mistaking a shadow or a coat on a hanger for a person.) Auditory hallucinations - hearing sounds that are not real, such as knocking or footsteps - can happen but are less common.

Hallucinations and visual misperceptions partly explain why most people with DLB have delusions (persistently thinking things that are not true) at some stage. Some common delusions held by people with DLB are believing that someone is out to get them, that there are strangers living in the house, or that a spouse is having an affair or has been replaced by an identical imposter. The person's relatives and carers may find these delusions very distressing.

Visual hallucinations are also a common reason for a person with DLB to stop driving, because it is no longer safe for them to be on the road. For more on this sensitive issue see factsheet 439, Driving and dementia.

Movement problems

Up to two-thirds of people with DLB have movement difficulties when the condition is diagnosed, and this number increases as DLB progresses. These symptoms are similar to those of Parkinson's disease, and include slow and stiff (rigid) movement with a blank facial expression.

The person's posture may be stooped and their walk may be shuffling. They may also have difficulty with their balance, and their limbs may sometimes tremble.

Movement problems are one reason why a person with DLB is particularly prone to falls.

Sleep disturbance

Sleep disturbance is another common symptom of DLB and may start years before the diagnosis. Someone with DLB may fall asleep very easily during the day, but have restless, disturbed nights. In the most common night-time sleep problem, the person has violent movements (eg yelling, hitting out) as they try to act out nightmares. This is called rapid eye movement sleep behaviour disorder and is found in different Lewy body disorders such as DLB and Parkinson's disease. For bed partners it can be very distressing or even physically harmful.

Other symptoms

Some people with DLB lose their sense of smell, become constipated or have urinary incontinence (passing urine when they don't intend to). They may also faint or have unexplained episodes when they lose consciousness for a few minutes.

Later stages

DLB is a progressive condition. Over time, symptoms increase and get worse. This is generally over a period of several years.

As the disease progresses, problems with day-to-day memory and other mental abilities become more similar to those of middle- or later-stage Alzheimer's disease. People can also develop behaviours that challenge (eg agitation, restlessness, shouting out).

Worsening movement problems mean that walking gets slower and less steady. As a result, falls become more common. In the later stages of DLB, many people have problems with speech and swallowing, leading to chest infections or risk of choking.

Eventually, someone with DLB is likely to need a large amount of nursing care. How quickly the condition progresses and the life expectancy of a person with DLB vary a lot. On average someone might live for about six to 12 years after the first symptoms, similar to a person with Alzheimer's disease.