Mild cognitive impairment (MCI) is a diagnosis that reflects an intermediate stage of cognitive impairment that is often, but not always, a transitional phase from cognitive changes in normal aging to those typically found in dementia, especially dementia due to Alzheimer's disease (Alzheimer's dementia). MCI may include both memory and non-memory neurocognitive impairments. About 50 percent of people diagnosed with MCI have Alzheimer's disease and go on to develop Alzheimer's dementia within five years. MCI can also serve as an early indicator for other types of dementia, although MCI may also remain stable or remit. Many definitions of MCI exist. A common feature of many of these is that MCI involves cognitive impairments that are measurable but that are not significant enough to interfere with instrumental activities of daily living. The DSM-5 introduces the concept of mild neurocognitive disorder (mNCD), which is designed to be largely equivalent to MCI. The International Classification of Diseases (ICD-11) refers to MCI as "Mild Neurocognitive Disorder (MND)". It is controversial whether MCI should be used as a diagnosis. The definition of MCI continues to evolve. Academic discussion revolves around whether MCI should be classified or diagnosed algorithmically or clinically, the reliability of clinical judgment, stability of the diagnosis over time, and the utility or predictivity of biomarkers. Differences in the definition and implementation of the MCI construct can explain some discrepancies between research studies.
Classification MCI can present with a variety of symptoms, but is divided generally into two types. Amnestic MCI (aMCI) is mild cognitive impairment with memory loss as the predominant symptom; aMCI is frequently seen as a prodromal stage of Alzheimer's disease. Studies suggest that these individuals tend to progress to probable Alzheimer's disease at a rate of approximately 10% to 15% per year. It is possible that being diagnosed with cognitive decline may serve as an indicator of MCI. Nonamnestic MCI (naMCI) is mild cognitive impairment in which impairments in domains other than memory (for example, language, visuospatial, executive) are more prominent. It may be further divided as nonamnestic single- or multiple-domain MCI, and these individuals are believed to be more likely to convert to other dementias (for example, dementia with Lewy bodies).
Causes Mild cognitive impairment (MCI) may be caused due to alteration in the brain triggered during early stages of Alzheimer's disease, to other causes, or to a combination of causes. Brain damage, brain injury, delirium and prolonged substance abuse can cause MCI. HIV-associated neurocognitive disorder can cause MCI. Risk factors of both dementia and MCI are the same, and include: aging, genetics, and cardiovascular disease. There is a significant association between mild cognitive impairment (MCI) and hearing impairment, although most cases of MCI are not due to hearing impairment. Hearing loss in individuals with MCI may contribute to further cognitive decline; however, this relationship may also reflect shared neuropathological processes involving cortical regions responsible for auditory function.
Diagnosis The first step in the diagnosis is screening. Montreal Cognitive Assessment (MoCA) is one of the screening tools that may guide a detailed evaluation. The diagnosis of MCI requires clinical judgement, possibly including clinical observation, neuroimaging, blood tests and neuropsychological testing. MCI may be diagnosed differently by different clinicians using different definitions or criteria, but generally including:
Evidence of modest cognitive decline from a previous level of performance in one or more cognitive domains, based on either: concern about cognitive decline from the individual, a knowledgeable informant, or a clinician, or modest impairment in cognitive performance documented by standardized neuropsychological testing. The cognitive deficits do not interfere with capacity for independence in everyday activities. However, greater effort, compensatory strategies, or accommodation may be required for complex tasks.
Neuropathology Magnetic resonance imaging can observe deterioration, including progressive loss of gray matter in the brain, from MCI to full-blown Alzheimer dementia. A technique known as PiB PET imaging is used to show the sites and shapes of beta amyloid deposits in living subjects using a 11C tracer that binds selectively to such deposits. Individuals with MCI may have increased oxidative damage in their nuclear and mitochondrial brain DNA.
Treatment
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