EDITOR--Donnellan et al report on four patients with Parkinson's disease in whom prescription of oxybutynin was associated with worsening cognitive function. Cognitive impairment in Parkinson's disease is common. It has been suggested that when a progressive decline in cognitive function in Parkinson's disease is accompanied by visual hallucinations and fluctuating cognition a secondary diagnosis of dementia with Lewy bodies is made. Dementia with Lewy bodies may present with neuropsychiatric features in the absence of parkinsonism and, indeed, is probably the second most common form of dementia in old age, only Alzheimer's disease being more common.
Previous case series of patients with dementia with Lewy bodies have shown exacerbations of confusion with orphenadrine (one case), little or no effect on confusion with benzhexol, and no effect on fluctuating confusion of withdrawing anticholinergic drugs in a 70 year old woman with visual hallucinations. A prospective study of dementia with Lewy bodies showed no link between anticholinergic drugs and visual hallucinations.
Oxybutynin is commonly prescribed in elderly people, especially in the population with dementia. It is likely to cause confusion not only in Parkinson's disease but also in dementia with Lewy bodies and Alzheimer's disease. A pronounced cholinergic deficit is found in cognitive impairment associated with all three of these diseases. In dementia with Lewy bodies the extent of cholinergic deficit is correlated with both cognitive dysfunction and hallucinosis. Treatments of cognitive impairment in Alzheimer's disease by cholinesterase inhibitors are now licensed, and trials of cholinesterase inhibitors in both Parkinson's disease and dementia with Lewy bodies are under way. The possible interaction of oxybutynin with cholinesterase inhibitors such as donepezil should be considered.
Although the authors give insufficient clinical information in this series for a diagnosis of dementia with Lewy bodies to be made, it is a diagnosis that should be considered in elderly patients with concomitant parkinsonism and cognitive impairment.
We have no conflict of interest in writing these opinions.
Jan Grace Clinical research associate Department of Old Age Psychiatry, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE
I G McKeith Professor of old age psychiatry Institute for the Health of the Elderly, University of Newcastle, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE
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