Relationship between Alzheimers disease and Parkinsons Disease
Is there any relationship between Alzheimers disease (AD) and Parkinsons Disease (PD)?
Currently available data do not support the existence of a common etiology for AD and PD.
However, approximately 20% of patients with PD have troublesome dementia. AD accounts for an unknown proportion of these cases.
Unlike AD, the pattern of dementia in PD is characterized by lack of cortical signs, such as aphasia and apraxia, and the presence of forgetfulness, bradyphrenia, and depression. In a longitudinal study clinical features that differentiated dementia in PD were cognitive fluctuations, auditory/visual hallucinations, sleep disturbance, and depression.
The different patterns suggest that different mechanisms are responsible for cognitive dysfunction in the two diseases, and pathologic studies support this distinction.
PD is characterized by relative sparing of the cortex and by neuronal loss in the SN and other subcortical structures, such as the locus ceruleus. Lewy bodies are found in the remaining cells.
On the other hand, the cerebral cortex is primarily involved in AD; neurofibrillary tangles and deposits of amyloid are the most important lesions.
However, a recent study shows that over 50% of patients with AD display parkinsonism and myoclonus during the course of the disease.