Department: Ask the Experts
Q What is the difference between Lewy body dementia and other dementias, such as Alzheimer's disease?
A Lewy body dementia (LBD) is characterized by dementia plus two or more of the following features: parkinsonism; recurrent fully formed visual hallucinations; fluctuations in cognition and/or arousal; and REM sleep behavior disorder (RBD).
The parkinsonian features include less facial animation, a stooped posture and shuffling gait, and slowness of movement. Tremor, an unintentional to-and-fro movement, may also be present. The hallucinations can involve vivid visions of people or animals, often with the same imagery/perceptions from day to day. Cognitive problems are usually notable in judgment, problem solving, complex decision-making, and multitasking, as well as in visuospatial functions (required for activities such as driving). Memory may or may not be impaired.
Sleep disorders may cause problems with cognition and arousal as well as excessive daytime sleepiness. RBD refers to the tendency for people to “act out their dreams.” During normal REM sleep, our brains are active but most of the muscles in our bodies are still. But in RBD, the muscles are abnormally active, and injuries such as bruising, pulled hair, and even fractured bones can occur. The dreams often have a nightmare quality, with the person being chased or attacked.
These features contrast with other common dementia syndromes. In Alzheimer's disease, forgetting the details of recent events and upcoming appointments is the prominent early feature. Parkinsonism and hallucinations occur late in the disease if at all, and RBD is extremely rare. Frontotemporal dementia is manifested by marked changes in personality and behavior and/or language, whereas memory and visuospatial functioning tend to be minimally affected. Parkinsonism and visual hallucinations are uncommon in frontotemporal dementia, and RBD is also rare.