Improvement in sundowning in dementia with Lewy bodies after treatment with donepezil.

Sundowning, manifested as a recurring increase in restlessness and agitation in the evening, is described in a 71-year-old man with clinically diagnosed dementia with Lewy bodies. An objective measure of activity using the activity electronic monitoring technique indicated a marked increase in activity level during the evening compared to earlier in the day. After treatment with donepezil, a cholinesterase inhibitor, ratings of behavioural symptoms improved. In addition, there was a marked reduction in evening activity and an increase in daytime activity. Cognition and parkinsonism also improved. Possible explanations for this finding are discussed.