Mild cognitive impairment
Encyclopedia
Mild cognitive impairment (MCI, also known as incipient dementia, or isolated memory impairment) is a brain-function syndrome
involving the onset and evolution of cognitive impairments beyond those expected based on the age and education of the individual, but which are not significant enough to interfere with their daily activities. It is often found to be a transitional stage between normal aging and dementia
. Although MCI can present with a variety of symptoms, when memory loss is the predominant symptom it is termed "amnestic MCI" and 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.
Additionally, when individuals have impairments in domains other than memory it is classified as non-amnestic single- or multiple-domain MCI and these individuals are believed to be more likely to convert to other dementias (e.g. dementia with Lewy bodies
). However, some instances of MCI may simply remain stable over time or even remit. Causation of the syndrome in and of itself remains unknown, as therefore do prevention and treatment.
, blood test
s and neuropsychological test
ing are best in order to rule out an alternate diagnosis. A similar assessment is usually given for diagnosis of Alzheimer's disease.
MCI is diagnosed when there is:
in the neocortex
and frequent neurofibrillary tangle
s in the medial temporal lobe
.
There is emerging evidence that magnetic resonance imaging
can observe deterioration, including progressive loss of gray matter in the brain, from mild cognitive impairment to full-blown Alzheimer disease. A technique known as PiB
PET
imaging is used to clearly show the sites and shapes of beta amyloid deposits in living subjects using a tracer
that binds selectively to such deposits. Such tools may help greatly in assisting clinical research for therapies.
state to clinical Alzheimer’s disease, treatments proposed for Alzheimer’s disease, such as antioxidant
s and cholinesterase inhibitors
, may be useful. However, several potential treatments are still under investigations. Two drugs used to treat Alzheimer's disease have been assessed for their ability to treat MCI or prevent progression to full Alzheimer's disease. Rivastigmine
failed to stop or slow progression to Alzheimer's disease or on cognitive function for individuals with mild cognitive impairment, and donepezil
showed only minor, short-term benefits and was associated with significant side effects
.
In a two-year randomized trial of 168 people with MCI given either high-dose vitamins or placebo, vitamins cut the rate of brain shrinkage by up to half. The vitamins were the three B vitamins folic acid
, vitamin B6
, and vitamin B12
, which inhibit production of the amino acid
homocysteine
. High blood levels of homocysteine are associated with increased risk of dementia and cardiovascular disease.
Syndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
involving the onset and evolution of cognitive impairments beyond those expected based on the age and education of the individual, but which are not significant enough to interfere with their daily activities. It is often found to be a transitional stage between normal aging and dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
. Although MCI can present with a variety of symptoms, when memory loss is the predominant symptom it is termed "amnestic MCI" and is frequently seen as a prodromal stage of Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
. Studies suggest that these individuals tend to progress to probable Alzheimer’s disease at a rate of approximately 10% to 15% per year.
Additionally, when individuals have impairments in domains other than memory it is classified as non-amnestic single- or multiple-domain MCI and these individuals are believed to be more likely to convert to other dementias (e.g. dementia with Lewy bodies
Dementia with Lewy bodies
Dementia with Lewy bodies , also known under a variety of other names including Lewy body dementia, diffuse Lewy body disease, cortical Lewy body disease, and senile dementia of Lewy type, is a type of dementia closely allied to both Alzheimers and Parkinson's Diseases...
). However, some instances of MCI may simply remain stable over time or even remit. Causation of the syndrome in and of itself remains unknown, as therefore do prevention and treatment.
Diagnosis
The diagnosis of MCI requires considerable clinical judgement, and as such a comprehensive clinical assessment including clinical observation, neuroimagingNeuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
, blood test
Blood test
A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a needle, or via fingerprick....
s and neuropsychological test
Neuropsychological test
Neuropsychological tests are specifically designed tasks used to measure a psychological function known to be linked to a particular brain structure or pathway. Tests are used for research into brain function and in a clinical setting for the diagnosis of deficits. They usually involve the...
ing are best in order to rule out an alternate diagnosis. A similar assessment is usually given for diagnosis of Alzheimer's disease.
MCI is diagnosed when there is:
- Evidence of memory impairment
- Preservation of general cognitive and functional abilities
- Absence of diagnosed dementia
Neuropathology
There is evidence suggesting that while amnestic MCI patients may not meet neuropathologic criteria for Alzheimer's disease, patients may be in a transitional stage of evolving Alzheimer's disease; patients in this hypothesized transitional stage demonstrated diffuse amyloidAmyloid
Amyloids are insoluble fibrous protein aggregates sharing specific structural traits. Abnormal accumulation of amyloid in organs may lead to amyloidosis, and may play a role in various neurodegenerative diseases.-Definition:...
in the neocortex
Neocortex
The neocortex , also called the neopallium and isocortex , is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI...
and frequent neurofibrillary tangle
Neurofibrillary tangle
Neurofibrillary Tangles are aggregates of hyperphosphorylated tau protein that are most commonly known as a primary marker of Alzheimer's Disease. Their presence is also found in numerous other diseases known as Tauopathies...
s in the medial temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
.
There is emerging evidence that magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
can observe deterioration, including progressive loss of gray matter in the brain, from mild cognitive impairment to full-blown Alzheimer disease. A technique known as PiB
Pittsburgh compound B
Pittsburgh compound B is a fluorescent analog of thioflavin T, which can be used in positron emission tomography scans to image beta-amyloid plaques in neuronal tissue...
PET
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
imaging is used to clearly show the sites and shapes of beta amyloid deposits in living subjects using a tracer
Radioactive tracer
A radioactive tracer, also called a radioactive label, is a substance containing a radioisotope that is used to measure the speed of chemical processes and to track the movement of a substance through a natural system such as a cell or tissue...
that binds selectively to such deposits. Such tools may help greatly in assisting clinical research for therapies.
Treatment
There is no proven treatment or therapy for mild cognitive impairment. As MCI may represent a prodromalProdrome
In medicine, a prodrome is an early symptom that might indicate the start of a disease before specific symptoms occur. It is derived from the Greek word prodromos or precursor...
state to clinical Alzheimer’s disease, treatments proposed for Alzheimer’s disease, such as antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
s and cholinesterase inhibitors
Acetylcholinesterase inhibitor
An acetylcholinesterase inhibitor or anti-cholinesterase is a chemical that inhibits the cholinesterase enzyme from breaking down acetylcholine, increasing both the level and duration of action of the neurotransmitter acetylcholine.- Uses :Acetylcholinesterase inhibitors:* Occur naturally as...
, may be useful. However, several potential treatments are still under investigations. Two drugs used to treat Alzheimer's disease have been assessed for their ability to treat MCI or prevent progression to full Alzheimer's disease. Rivastigmine
Rivastigmine
Rivastigmine is a parasympathomimetic or cholinergic agent for the treatment of mild to moderate dementia of the Alzheimer’s type and dementia due to Parkinson's disease. The drug can be administered orally or via a transdermal patch; the latter form reduces the prevalence of side effects, which...
failed to stop or slow progression to Alzheimer's disease or on cognitive function for individuals with mild cognitive impairment, and donepezil
Donepezil
Donepezil, marketed under the trade name Aricept by its developer Eisai and partner Pfizer, is a centrally acting reversible acetylcholinesterase inhibitor. Its main therapeutic use is in the palliative treatment of mild to moderate Alzheimer's disease. Common side effects include...
showed only minor, short-term benefits and was associated with significant side effects
Adverse drug reaction
An adverse drug reaction is an expression that describes harm associated with the use of given medications at a normal dosage. ADRs may occur following a single dose or prolonged administration of a drug or result from the combination of two or more drugs...
.
In a two-year randomized trial of 168 people with MCI given either high-dose vitamins or placebo, vitamins cut the rate of brain shrinkage by up to half. The vitamins were the three B vitamins folic acid
Folic acid
Folic acid and folate , as well as pteroyl-L-glutamic acid, pteroyl-L-glutamate, and pteroylmonoglutamic acid are forms of the water-soluble vitamin B9...
, vitamin B6
Vitamin B6
Vitamin B6 is a water-soluble vitamin and is part of the vitamin B complex group. Several forms of the vitamin are known, but pyridoxal phosphate is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation...
, and vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
, which inhibit production of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
homocysteine
Homocysteine
Homocysteine is a non-protein amino acid with the formula HSCH2CH2CHCO2H. It is a homologue of the amino acid cysteine, differing by an additional methylene group. It is biosynthesized from methionine by the removal of its terminal Cε methyl group...
. High blood levels of homocysteine are associated with increased risk of dementia and cardiovascular disease.
External links
- MCI information from the UCSF Memory and Aging Center
- Mild cognitive impairment Alzheimer's Society fact sheet
- Topic Sheet on Mild Cognitive Impairment