Résumé
To specify the existing relationship between Parkinson's disease dementia (PDD) and Lewy body dementia (LBD), it is necessary to retrace the natural history of an histopathological lesion, which, although being non-specific, is essential for a precise diagnosis, the Lewy body. The occurrence of Lewy bodies in Parkinson's disease, as in the other two types of dementia, unveils a potential continuum between these affections, which could be reunited under the term of alpha-synucleinopathy. However, defining the modalities of various types of alpha-synucleinopathy has not been historically based on the notion of a continuum. Thus, their nosological framework remains imprecise and controversial. Nevertheless, the LBD and PDD clinical, radiological and neuropathological expressions reveal many similarities. Their clinical distinction could then seem quite arbitrary. Furthermore, some studies underline the relationships between the various "proteinopathies" described in the degenerative dementias (Lewy body dementia, Parkinson's disease dementia and Alzheimer's disease). Finally, the role played by associated vascular lesions needs to be specified. It becomes essential to better define the boundaries of these cerebral neurodegenerative diseases. The perspective of common physiopathological mechanisms and certain vulnerability profiles could lead to new therapeutic pathways.