Lewy body diseases are a group of conditions caused by deposits of an abnormal protein called Lewy bodies (named after Friedrich H Lewy, the doctor who first identified them) inside brain cells.
There are 3 types of Lewy body diseases:
Parkinson disease – The main symptoms of Parkinson’s are tremor, rigidity and slowness of movement.
Dementia with Lewy bodies – Symptoms include changes in thinking and reasoning, fluctuating cognition, balance problems and muscle rigidity, visual hallucinations, delusions, trouble interpreting visual information, sleep disorders, malfunctions of the autonomic nervous system and memory loss (but less prominent than in Alzheimer’s).
Parkinson’s disease dementia – Symptoms include changes in memory, concentration and judgement, trouble interpreting visual information, muffled speech, visual hallucinations, delusions, depression and sleep disturbances.
Together dementia with Lewy bodies and Parkinson’s disease dementia are referred to as Lewy body dementias.
Whether dementia with Lewy bodies or Parkinson’s disease dementia is diagnosed will depend on when the cognitive impairment appears relative to the Parkinson’s disease symptoms.
The diagnosis is dementia with Lewy bodies when:
- Dementia symptoms develop first.
- When both dementia symptoms and movement symptoms are present at the time of diagnosis.
- When dementia symptoms appear within one year after movement symptoms.
The diagnosis is Parkinson’s disease dementia when a person is originally diagnosed with Parkinson’s and dementia symptoms don’t appear until a year or more.
- About one third of people diagnosed with Parkinson’s disease eventually develop dementia (Parkinson’s disease dementia). The average time from onset of Parkinson’s to developing dementia is about 10 years.
- Similarly, at least two thirds of people with dementia with Lewy bodies develop movement problems at some point.
- Someone aged 50-60 with Lewy bodies in their brain, is more likely to develop Parkinson’s disease.
- Whereas someone aged 70-80 is more likely to develop dementia with Lewy bodies.
A significant difference between Parkinson’s disease and dementia with Lewy bodies is the location of the Lewy bodies in the brain. In Parkinson’s they are found mainly in the substantia nigra which is in the mid-brain, whereas in dementia with Lewy bodies they are more widely distributed throughout the cerebral cortex.