Classification of the dementias

Sir—Karen Ritchie and Simon Lovestone (Nov 30, p 1759) courageously emphasise that nosological boundaries within the dementias are being reassessed because of new information about genetic and neurochemical mechanisms. They point out that the relations between Alzheimer’s disease and vascular disease, and among the varieties of dementia that include parkinsonism as a clinical feature and Lewy bodies as a pathological feature, are less clear than we had previously thought. What the authors do not describe in this review, however, is that dimensionality should serve as an important feature of our nosological classification of dementia, rather than mere reshuffling of categories. Dysfunction of neurons and resulting cognitive impairment occurs in varying degrees. The term mild cognitive impairment (MCI) is the latest attempt to label part of the continuum of agerelated cognitive dysfunction. Terms such as benign senile forgetfulness and ageing-associated memory impairment (AAMI) were earlier efforts, although AAMI itself is undergoing somewhat of a revival. Yet these terms remind us of a long history of labelling parts of a continuum, and of the fact that distinctions between different categories are often arbitrary. Alterations in cholinergic markers are one such biological marker that changes with age. How responsive patients with MCI will be to cholinesterase inhibitors remains to be seen in several ongoing randomised controlled studies. In a small study we have used sensitive performance measures (occupationspecific activities of daily living) to show that, in flight simulators, healthy, cognitively intact, 50-year-old pilots might respond positively to donepezil. In our rush to create new categories of disease, and to determine what medications they respond to, we must not forget that such efforts have profound implications for patients with memory concerns. The term MCI might be useful in research to identify people who could benefit from preventative treatments, but it is a troublesome label when used in clinical practice. Does it mean that someone does not have Alzheimer’s disease; does have Alzheimer’s disease; or will or might get Alzheimer’s disease? In our efforts to develop more effective treatments and “medicalise” age-related cognitive changes, perhaps we need to revisit our nosological categories with regard to the fuzziness of the boundaries and fuzziness of our thinking. The assertion that Alzheimer’s disease is not normal ageing is more a political than a scientific statement. If we recognise that we all fall on some part of the developmental continuum, would we address the issues of agerelated cognitive changes in different ways? Would we prevent the terror of the label of Alzheimer’s disease? Would we focus on the positive aspects of cognitive ageing? We would be wise to do so, because the likelihood of biological fixes for all causes of agerelated cognitive decline seems remote despite the power of current medical research approaches. Peter J Whitehouse