Dementia and Parkinson's Disease — Pathhological and Neurochemical Considerations

The prevalence of dementia in Parkinson's disease is greater than that expected in an age-matched population. While the pathology of Parkinson's disease itself may cause cognitive deficits, this seems unlikely to be responsible for the excess prevalence of dementia. Coincidental Alzheimer's disease certainly occurs, but again does not appear to account for the excess of dementia. However, coincident subclinical degrees of Alzheimer change may combine with similar biochemical and neuronal loss due to Parkinson's disease to cause a deficit sufficient to lead to dementia. Such superimposition of the pathological and biochemical changes of the two diseases could account for a wide spectrum of clinical presentations of the “parkingsonian dement” or the “demented parkinsonian”.