Mild Cognitive Impairment
Mild Cognitive Impairment is a term used to describe an abnormal cognitive state in which memory ("Amnestic MCI") or non-memory cognitive functions ("Atypical MCI") are affected. Having MCI means that there has been a decline in memory or thinking abilities beyond what is considered normal for someone's age, but the decline is isolated and not diagnostically indicative of AD or another form of dementia. Someone with Amnestic MCI has difficulty remembering, but experiences no significant difficulty in other areas of thinking, and no serious decline in daily activities. Conversely, someone with Atypical MCI usually has normal memory functions, but experiences problems in a non-memory related ability (i.e., attention, concentration, processing speed, language, perceptual ability, problem solving, reasoning, etc.) or has a more subtle memory change. In both types of MCI, the decline is not sufficiently severe to cause disruption in day to day functioning.
One conceptualization of MCI is that it is a stage of cognitive functioning between normal aging and dementia. Alternatively, it has been proposed that Amnestic MCI actually represents very early AD. It is suspected that everyone who develops AD will first experience MCI for some period of time. However, researchers do not know if everyone who develops MCI will eventually develop AD. Longitudinal studies are currently underway to answer this question, and drug trials are underway to determine if a diagnosis of AD can be delayed or avoided for those already experiencing MCI.
For those persons with MCI who do later develop AD, it is important to know that the rate at which someone passes through the MCI stage to AD varies from person to person. Clinical observation of patients with carefully documented Amnestic MCI suggests that 10-15% per year will eventually go on to develop AD.
MCI is a concept that is still evolving and is not yet a clinical diagnosis. However, the concept reflects the growing interests of researchers and clinicians in identifying non age-related changes in memory and cognition that may predict AD or other dementias.
According to guidelines published by the American Academy of Neurology, persons with MCI are considered to be "at risk" for developing dementia, and should therefore receive ongoing clinical monitoring post-evaluation (see Petersen, R.C. et al., Practice Parameter: Early detection of dementia: Mild cognitive impairment, Neurology, 2001; 56:1133-1142; Peterson, R.C., Doody, R., Kurz, A., et al., Current concepts in mild cognitive impairment, Archives of Neurology, 2001; 58:1985-1992).