Summary

Only a minority of Lewy body dementia brains lack concomitant Alzheimer disease pathology, but the percentages of combined Lewy body disease and Alzheimer disease versus pure Lewy body disease vary depending upon what neuropathological criteria are employed to make a diagnosis of Alzheimer disease. Using criteria from the Consortium to Establish a Registry for Alzheimer Disease, nearly 90% of all Lewy body dementia brains have definite or probable Alzheimer disease. Such Lewy body variants of Alzheimer disease also show medial temporal lobe neurofibrillary pathology intermediate in severity between that seen in pure Alzheimer disease and that encountered in elderly nondemented controls or pure Lewy body disease patients. Like Alzheimer disease, but unlike pure Lewy body disease, Lewy body variants of Alzheimer disease have an increased apolipoprotein ∈4 allelic frequency. If myriads of neocortical neurofibrillary tangles are deemed requisite for a diagnosis of Alzheimer disease, the percentage of mixed Alzheimer disease and Lewy body disease falls from 89% of all Lewy body dementia brains to 32%. Even in the absence of concomitant Alzheimer disease pathology, nosologic uncertainty persists in Lewy body disease since no established neuropathologic criteria can reliably distinguish pure Parkinson's disease from so-called diffuse Lewy body disease.

Introduction

‘When I use a word’, Humpty Dumpty said in a rather scornful tone ‘It means just what I choose it to mean – neither more nor less.’ ‘The question is,’ said Alice, ‘Whether you can make words mean so many different things.’ ‘The question,’ said Humpty Dumpty, ‘Is which is to be master – that's all.’