Dementia with Lewy bodies is a progressive disease that causes hallucinations, decline in mental abilities, rigid muscles, slow movement and tremors. With symptoms similar to Alzheimer’s disease and Parkinson’s disease, a correct diagnosis can be difficult. A new study shows that a lack of shrinkage in the area of the brain called the hippocampus may be a sign that people with thinking and memory problems may develop dementia with Lewy bodies rather than Alzheimer’s disease.