Parkinson's and Alzheimer's diseases: Focus on mild cognitive impairment

The mild cognitive impairment (MCI) concept was developed to identify the earliest stages of cognitive impairment. MCI and, more specifically, amnestic MCI were initially proposed as transitional states that ultimately progress to full blown Alzheimer's disease (AD). However, MCI subjects do not uniformly progress to dementia (either AD or another) and may revert back to normal cognitive state. The MCI as concept has been borrowed from AD to other neurodegenerative diseases, particularly Parkinson's disease (PD). However the operational definition of MCI may not adequately convey the intended concept. Additional modifications to the concept and its operationalization are needed in order to better identify patients with incipient cognitive impairment and to guide clinical and research practices.Patients with PD have a very high likelihood of developing dementia, insidiously over many years. Cognitive impairment may start even before other symptoms.No constellation of cognitive symptoms in an otherwise healthy individual will herald development of AD or indeed will progress to dementia, including PD-dementia, in high likelihood.At present, identification of subtle cognitive dysfunction even in a person with diagnosed PD does not benefit the patient and should be avoided, except for research purposes.