As someone with a keen research interest both in dementia with Lewy bodies and Parkinson's disease dementia, one of the most common questions I encounter after a presentation has now become something of a classic: “Are dementia with Lewy bodies and Parkinson's disease dementia the same condition?” Having spent the last thirty minutes or so finely discussing subtle details of similarity and difference between the two, I am always somewhat at a loss to know how to answer this global and important question succinctly and I usually end up with a rather unsatisfactory “yes and no.” Since this seems to be something of a burning and recurring issue, it is very fitting that this subject is being aired as part of the International Psychogeriatrics “For Debate” series and I am absolutely delighted that a group of such distinguished experts in the field has agreed to take part.
Previous debates have tackled issues such as the use of antipsychotic drugs in dementia (Ames et al., 2005), whether mild cognitive impairment is a useful entity (Ames et al., 2006), the usefulness of electroconvulsive therapy (ECT) for depression (Ganguli et al., 2007), the use of neuroimaging in cases of suspected dementia (O'Brien et al., 2007), the influence of the pharmaceutical industry on prescribing (Ames et al., 2007), and whether cholinesterase inhibitors are really as effective as we think (Ames et al., 2008). These are very informative pieces on controversial and highly topical subjects and if you have missed any then I highly commend them to you. I think the current debate more than matches these previous epics and we look forward to further debates on controversial topics in our field as part of this series.
When I became interested in this area just over a decade ago, my first impressions were that these were indeed two very different entities. Cognitive impairment as a part of Parkinson's disease was rooted in patients with profound movement disorder under the care of neurologists, whilst dementia with Lewy bodies was a condition often misdiagnosed as Alzheimer's disease, with patients having mild parkinsonism, and under the care of old age psychiatrists. However, we have learnt much in the past decade about both disorders and the boundaries between the two certainly have grown closer. We might indeed now have a common language, even a common currency in terms of assessment instruments applicable to both, and common treatments as well, but whether we wish to dispense with border control is, as we will see from the articles below, an entirely different matter.
Drs Revuelta and Lipper, from one side of the Atlantic, are the splitters who argue that, despite similarities, these disorders are best viewed as distinct entities. Across the pond, Drs Aarsland, Londos and Ballard prefer to view them more as a single disorder. We are fortunate indeed to have not only seasoned debaters but cutting-edge scientists on both sides, providing articles that not only debate the issues but provide state-of-the-art reviews of the latest science underpinning our understanding of both dementia with Lewy bodies and Parkinson's disease dementia.
Finally, Ian McKeith provides a typically masterful and comprehensive commentary, summarizing both positions and providing a very helpful historical perspective on the debate, as well as emphasizing the clinical relevance of the terms and so reminding us that this is far from just an academic debate. I am certainly much better informed about the issue having had the pleasure to commission and edit these pieces – and next time I am asked the question “Are they the same disorder?” I can improve on my previous answer by using material from this debate. Perhaps best of all, rather than “yes and no” I can use the far more erudite phrase of Ian McKeith that “I agree with them both.”
