Dementia is a slowly progressive brain disorder marked by the loss of ability to think, reason and remember. In Lewy body dementia, abnormal round structures — called Lewy bodies — develop in regions of your brain involved in thinking and movement.

Lewy body dementia shares characteristics with both Alzheimer's disease and Parkinson's disease. Like Alzheimer's, it causes confusion. It may also cause distinctive physical signs typical of Parkinson's — rigid muscles, slowed movement and tremors. Lewy body dementia also cause hallucinations.