Alzheimer disease biomarkers and insights into mild cognitive impairment.

Persons with mild cognitive impairment (MCI) have overt changes in thinking and memory, but they are still largely independent in daily affairs. They have a far higher rate of developing dementia (progressing to a more debilitating state of cognitive impairment) than cognitively normal persons, but at the individual patient level, prognosis is variable. Sometimes persons with MCI do not worsen and a few even revert back to cognitive normality.(1,2) The variable prognosis in MCI is one reason why the term "MCI" has caught on: not only does it denote a sense of severity at the mildest level, it also conveys uncertainty of prognosis. Identification of the subset of patients with MCI at highest risk to progress to more severe cognitive impairment is a very important goal for research and future clinical care. Quantitating the degree of cognitive impairment by traditional history-taking, brief mental status testing, and more detailed neuropsychological assessment are necessary and informative first steps. However, knowledge of cognitive and functional status in MCI still leaves much uncertainty regarding the ability to predict worsening.