What causes Lewy body dementia?
Lewy body dementia (LBD), which is an umbrella term to describe the 2 types of Lewy body dementias detailed below, is caused by deposits of an abnormal protein called Lewy bodies that build up inside nerve cells in the brain. The protein is called alpha-synuclein and the protein clumps damage the way nerve cells work and communicate.
In the healthy brain, a protein associated with alpha-synuclein plays a number of important roles in neurons (nerve cells) in the brain, especially at synapses, where brain cells communicate with each other. In LBD, alpha-synuclein forms into clumps inside neurons throughout the brain. This process may cause neurons to work less effectively and, eventually, to die. The activities of brain chemicals important to brain function are also affected. The result is widespread damage to certain parts of the brain and a decline in abilities affected by those brain regions.
The two types of Lewy body dementias are –
- Dementia with Lewy bodies – in which cognitive (thinking) symptoms appear within a year of movement problems.
- Parkinson’s disease dementia – in which cognitive symptoms develop more than a year after the onset of movement problems.
About one third of people diagnosed with Parkinson’s disease eventually develop dementia (Parkinson’s disease dementia). Similarly, at least two thirds of people with dementia with Lewy bodies develop movement problems at some point.
The main difference between the two Lewy body dementias, which essentially share the same array of symptoms, is how the disease starts i.e. whether the movement or cognitive problems occur first as detailed above.
The other main differences are:
- In dementia with Lewy bodies, tremor does not occur early, and is less severe than in Parkinson’s.
- In dementia with Lewy bodies, problems with the autonomic nervous system are more prominent than in Parkinson’s disease dementia.
- In Parkinson’s disease dementia psychiatric symptoms (e.g., hallucinations, delusions) appear to be less frequent and/or less severe than in dementia with Lewy bodies.
- Dementia with Lewy bodies may progress more quickly than Parkinson’s disease dementia.
Lewy body dementia symptoms fall into five categories:
- Dementia is a primary symptom of Lewy body dementia i.e. a decline in the cognitive (thinking) abilities that interferes with everyday life.
- Changes or “fluctuations” in cognition (awareness and concentration). The person will swing from a state of alertness to appearing drowsy and/or confused, as well as reduced attention span.
- Recurrent visual hallucinations, such as seeing shapes, colours, people, or animals that aren’t there or conversing with deceased loved ones.
- More trouble with complex mental activities, such as multitasking, problem solving, and analytical thinking.
- Problems with visual and spatial perception, such as judging and navigating distances.
Note: Unlike other types of dementia, memory problems may not be evident at first but often arise
as the disease progresses.
People with Lewy body dementia also experience motor problems (the part of the nervous system involved with movement) and experience symptoms similar to Parkinson’s including:
- Slow movement / shuffling walk / stiff limbs / tremors and shaking / balance problems / difficulty swallowing / weak voice.
They also experience fluctuations in autonomic processes (the part of the nervous system that regulates bodily functions) including:
- Blood pressure / body temperature / urinary difficulties / constipation / dizziness / frequent falls and fainting / impaired sense of smell / runny nose.
Sleep problems include:
- REM sleep behaviour disorder – a disorder where you physically move limbs and talk while sleeping.
- Excessive daytime sleeping.
Behaviour & mood
Changes in behaviour and mood (psychiatric disturbances) often occur with Lewy body dementia including:
- Depression / apathy / anxiety / agitation / delusions / paranoia.
The average life expectancy for people with DLB after the onset of symptoms is 5 to 8 years.