Dementia with Lewy bodies.

The presence of a high number of Lewy bodies--the morphological marker of Parkinson's disease--in the cerebral cortex of some cases of dementia has been frequently observed in association to Alzheimer type lesions (mainly senile plaques) and changes in the substantia nigra, that may be held responsible for the frequently associated symptoms of parkinsonism. The term "dementia with Lewy body" (DLB) has recently been suggested by a consensus conference and indicates that the pathogenetic mechanism of the dementia remains poorly understood. Marked fluctuations of alertness and of the cognitive performances, moderate parkinsonism and episodes of visual hallucinations may lead to suspect this diagnosis in cases of dementia. Unexplained falls, syncopes, delirium or alterations of consciousness may also be observed, and the patients may then be admitted in departments of internal medicine or geriatrics. The Lewy body is an intraneuronal spherical inclusion, present in Parkinson's disease. It is observed in the brainstem (substantia nigra, locus coeruleus, dorsal nucleus of the Xth nerve) and in the nucleus basalis of Meynert. The cortical Lewy bodies have a different aspect, but retain their antigenic characteristics: they are, in particular, stained by the antiubiquitin antibodies. Recently, they were found to be also labeled by antisynuclein antibodies. A mutation of the synuclein gene was recently identified in cases of familial Parkinson's disease. Clinically as well as pathologically, DLB may thus be difficult to distinguish from Alzheimer's disease on the one hand, and from Parkinson's disease, on the other. That diagnosis, however, is associated with a poor prognosis and should lead to specific therapeutic measures.