Responses to donepezil in Alzheimer's disease and Parkinson's disease

Alzheimer's disease is the most common cause of dementia, but Parkinson's disease also shows dementia in the later stages. Donepezil is a cholinesterase inhibitor used for the treatment of Alzheimer's disease. Variable responses to this drug suggest that Alzheimer's disease is clinically heterogeneous. In the clinical trial of tacrine, a first developed cholinesterase inhibitor, three cases markedly improved and, several years later, they were pathologically confirmed as dementia with Lewy bodies (DLB). In recent years, another cholinesterase inhibitor, rivastigmine, has also been reported to be effective for patients with DLB by a placebo-controlled, double-blind, multi-center study. Parkinson's disease with dementia, which is known to fulfill the pathological criteria of DLB, also shows a favorable response to donepezil. In some cases, not only does cognitive function improve, but also parkinsonism. Both DLB and Parkinson's disease with dementia show characteristic CBF patterns: While the parietal and temporal lobes are involved in Alzheimer's disease, the occipital lobe is additionally affected in these diseases. Alzheimer's disease and Parkinson's disease have been considered discrete disease entities. However, viewed from the aspects of response to donepezil treatment and CBF patterns, both diseases overlapped. A brain SPECT may be a useful tool to detect such treatable conditions.