Dementia with Lewy bodies typically involves cognitive symptoms, such as difficulty paying attention and solving problems, in its early phases, while Parkinson's disease with dementia usually begins with movement-related symptoms, such as tremors and stiff muscles, according to the National Institute on Aging. Both conditions are forms of Lewy body dementia.
The main difference between the two types of Lewy body dementia is the timing of the cognitive symptoms, notes the UCSF Memory and Aging Center. Patients who begin to exhibit cognitive decline following the presentation of a motor disorder receive a diagnosis of Parkinson's disease with dementia, or PDD, while doctors assign a diagnosis of dementia with Lewy bodies, or DLB, when the cognitive issues appear before or at the same time as the movement problems.
Examples of motor symptoms include poor coordination, smaller handwriting than normal and declining posture, explains the National Institute on Aging. Cognitive problems may include disorganized thoughts, memory loss or difficulty with executive functioning. In both forms of Lewy body dementia, rapid eye movement-related sleep disorders sometimes develop years before the cognitive and motor symptoms occur, but the sleeping problems often go undiagnosed. As many as 80 percent of patients with a Lewy body dementia disorder experience visual hallucinations, and the hallucinations often begin early in the disease progression.