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While dementia in Parkinson's disease (PD) is well described, PD features in Alzheimer's disease (AD) are being increasingly recognized. In 20 neuropathologically confirmed AD brains, 11 cases (55%) showed PD changes (Lewy body formation, neuronal loss, and gliosis of pigmented nuclei), with no significant difference in age or symptom duration between those cases with and without PD pathology. A history of rigidity in the absence of neuroleptic medication was noted in 80% of those with PD pathology but only 14% of those without PD pathology. Tremor was not observed in either group. This suggests that extrapyramidal signs, especially rigidity, noted in many AD patients are related to coexistent PD pathology.
Ditter et al. (1987) studied this question.