The term cognition describes the human brain's ability to learn, think, and process information. For a normal daily life to be possible, cognitive functions must be intact. Impairment of cognitive functions results in difficulties in coping with both complex and everyday activities, such as daily planning, meeting the demands of work life, managing finances, preparing food, keeping order, socializing, or cultivating interests. Impaired cognitive functions also lead to an increased sensitivity to stress.
There are several disorders and medical procedures that show cognitive impairment as an important - though not always identified - manifestation, such as affective disorders, schizophrenia, abuse, neurological motor disorders, MS, traumatic brain injury, cancer, infections, vascular disease (ischemic heart disorder, heart failure, hypertension, diabetes mellitus, stroke, small vessel disease), coronary by-pass surgery, and other major surgical procedures. Multimorbidity relatively often result in disabling cognitive impairment. Also increasingly acknowledged are cognitive effects and side effects of pharmaceutical treatments, not just of psychopharmacological drugs, but also for instance cytostatic drugs. The groups of disorders in which cognitive dysfunction constitutes the core symptomatology are developmental disorders, ADHD (attention deficit hyperactivity disorder)/autism spectrum disorders, Alzheimers disease, and cerebrovascular disease.
Dementia, stroke, and neuropsychiatric disorders account for up to 50% of the medically caused disability in low and middle income countries. The percentage is most likely higher in high income countries, due to the relatively larger share of elderly in these coutries. What unites these diseases is the fact that they impair cognition. This is obvious in the case of dementia and neuropsychiatric disorders, but it also applies to stroke, which usually consists of minor stroke, in which cognitive impairment predominates over motor symptoms.
The cognitive disorders are delirium, dementia, and amnestic disorders. Table 8- 1 lists the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, classification of cognitive disorders.
Delirium is a reversible state of global cortical dysfunction characterized by alterations in attention and cognition and produced by a definable precipitant.
Delirium is categorized by its etiology (see Table 8-1) as due to general medical conditions, substance-related, or multifactorial in origin.
Delirium is a syndrome with many causes. Most frequently, delirium is the result of a general medical condition; substance intoxication and withdrawal also are common causes. Structural central nervous system lesions can also lead to delirium. Table 8-2 lists common general medical and substance-related causes of delirium. Delirium is often multifactorial and may be produced by a combination of minor illnesses and minor metabolic derangements (e.g., mild anemia, mild hyponatremia, mild hypoxia, and urinary tract infection, especially in an elderly person).
Alzheimers disease and cerebrovascular disease are the quantitatively most important causes of cognitive impairment in adults. These, and other similar disorders, such as Lewy body disease and frontotemporal dementia, are the main focus of the research group.
A common and serious mental disorder characterized by loss of contact with reality (psychosis), hallucinations (false perceptions), delusions (false beliefs), abnormal thinking
What is Frontotemporal Dementia?
Frontotemporal dementia (FTD) is a group of related conditions resulting from the progressive degeneration of the temporal and frontal lobes of the brain. These areas of the brain play a significant role in decision-making, behavioral control, emotion and language.
Dementia is characterized by the presence of memory impairment in the presence of other cognitive defects. Dementia is categorized according to its etiology (see Table 8-1). It can arise as a result of a specific disease, for example Alzheimer's disease or HIV infection; a general medical condition; or a substance-related condition; or it can have multiple etiologies. The definitive cause may not be determined until autopsy.
Generally, the etiology of dementia is brain neuronal loss that may be due to neuronal degeneration or to cell death secondary to trauma, infarction, hypoxia, infection, or hydrocephalus. Table 8-1 lists the major discrete illnesses known to produce dementia. In addition, there are a large number of general medical, substance-related, and multifactorial causes of dementia.
The prevalence of dementia of all types is about 2% to 4% after age 65, increasing with age to a prevalence of about 20% after age 85. Specific epidemiologic factors relating to disease-specific causes of dementia are listed in Table 8-4.
Amnestic disorders are isolated disturbances of memory without impairment of other cognitive functions. They may be due to a general medical condition or substance related.
Amnestic disorders are caused by general medical conditions or substance use. Common general medical conditions include head trauma, hypoxia, herpes simplex encephalitis, and posterior cerebral artery infarction. Amnestic disorders often are associated with damage of the mammillary bodies, fornix, and hippocampus. Bilateral damage to these structures produces the most severe deficits. Amnestic disorders due to substance-related causes may be due to substance abuse, prescribed or over-the- counter medications, or accidental exposure to toxins. Alcohol abuse is a leading cause of substance- related amnestic disorder. Persistent alcohol use may lead to thiamine deficiency and induce Wernicke- Korsakoff's syndrome. If properly treated, the acute symptoms of ataxia, abnormal eye movements, and confusion may resolve, leaving a residual disorder called Korsakoff's psychosis induced persistent amnestic disorder).
Cognitive disorders can be caused by all sorts of brain problems, including tumors, strokes, closed-head injuries, infections, exposure to neurotoxins (i.e., substances that are toxic to the brain), genetic factors, and disease. The specific type of cognitive disorder someone develops depends on the part of the brain that is affected. For instance, a tumor that grows in the brain's speech centers will result in problems with communication. Similarly, an infection in the brain's motor centers will cause problems with movement.
Tumors are masses of cells that grow and infiltrate the body. These masses of cells can be either benign (i.e., they will stop growing once they are removed via surgery) or malignant (i.e., they are difficult to remove and will continue to grow and spread). Both benign and malignant tumors in the brain can cause impaired cognitive functioning, depending on their size and location.
Even the most skilled surgeon cannot remove a benign tumor without causing some damage to surrounding brain areas. As a result, someone who has had a benign tumor removed may still experience residual weakness or numbness, for example. Individuals with malignant tumors will experience cognitive problems as the cell mass presses on and destroys healthy tissue in the brain and spinal cord, blocks the fluid that flows around and through the brain, and/or causes swelling due to accumulation of fluid. Malignant tumors are often lethal.
Strokes - disruptions in the blood supply to the brain - are one of the most common causes of brain damage. Strokes are caused by blockages to blood vessels (ischemic strokes), or when a blood vessel bursts (a hemorrhagic stroke). The risk factors for stroke include age, family history, heart disease, uncontrolled diabetes, high blood pressure, and smoking. Common cognitive effects of stroke include impaired memory, language difficulties, and paralysis, but depend on the part of the brain that is affected. For more information about stroke, please see our related topic center.
Closed head injuries are blows to the head that do not penetrate the skull (e.g., when someone hits his or her head during a car accident). Concussions (when the brain bounces against the skull), hematomas (brain bruises or bleeding), and traumatic brain injuries all all types of closed head injuries. Again, the severity and type of cognitive impairment caused by closed head injuries depends on the portion of the brain that is injured. More information about traumatic brain injuries can be found at the end of this article, by clicking here .
Infections can also cause cognitive disorders. Both bacteria and viruses (e.g., the virus that causes rabies) can disrupt brain functioning. One of the most common forms of brain infection is meningitis, an inflammation of the meninges, the protective covering that surrounds the brain and the central nervous system. Meningitis can cause deafness, other forms of cognitive impairment, and in severe cases, death.
Repeated and/or significant exposure to toxic chemicals (neurotoxins) such as metals (e.g., lead, mercury), drugs (e.g., cocaine, alcohol), or other substances (e.g., paint, glue, etc.) can cause cognitive impairment. The type of cognitive impairment created by neurotoxins depends on the type of toxin, the degree of exposure (how much of the substance was taken in, and for how long), and when the exposure occurred (whether the person affected was an infant, child, or adult). Typically, young children exposed to neurotoxins are more likely to develop cognitive disorders (because their brains are experiencing more rapid development) than adults.
Some individuals who develop cognitive impairment have inherited a problem in their genetic makeup. For instance, individuals with Down syndrome have an extra 21st chromosome. People with this syndrome often have mental retardation (intellectual functioning that is significantly below average, combined with an impaired ability to adapt to the demands of everyday functioning).
What is mild cognitive impairment (MCI)?
In contrast to Alzheimer's disease (AD) where other cognitive skills are affected, mild cognitive impairment (MCI) is defined by deficits in memory that do not significantly impact daily functioning. Memory problems may be minimal to mild and hardly noticeable to the individual. Writing reminders and taking notes allow a person to compensate for memory difficulties. Unlike AD where cognitive abilities gradually decline, the memory deficits in MCI may remain stable for years. However, some individuals with MCI develop cognitive deficits and functional impairment consistent with AD. Whether MCI is a disorder distinct from AD or a very early phase of AD is a topic of continuing investigation.
The diagnosis of MCI relies on the fact that the individual is able to perform all their usual activities successfully, without more assistance from others than they previously needed.
Signs & symptoms of mild cognitive impairment (MCI)
Typically, memory complaints include trouble remembering the names of people they met recently, trouble remembering the flow of a conversation and an increased tendency to misplace things or similar problems. In many cases, the individual will be quite aware of these difficulties and will compensate with increased reliance on notes and calendars. These problems are similar, but less severe, than the neuropsychological findings associated with Alzheimer's disease. In some cases, the patient may have mild difficulties with daily activities, such as performing hobbies.
The medical evaluation should include a thorough exploration of the memory complaints, including what type of information is being forgotten and when, the duration of the problem, and whether other cognitive complaints are occurring (problems with organization, planning, visuospatial abilities, etc.). The physician should be aware of the patient's medical history, the medications taken, etc. As subjective memory complaints can be associated with depression, screening for depressive symptoms is always warranted. Depending on the results of this evaluation, further testing may necessary, including blood-work and brain imaging. This evaluation is similar to that given to individuals with more severe memory problems, and is directed towards better defining the problem and looking for medical conditions that might have an effect on the brain (infections, nutritional deficiencies, autoimmune disorders, medication side effects, etc.). The medical history usually requires the participation of a knowledgeable informant.
Additional assessment could include neuropsychological testing to document objectively any memory deficit and to assess its severity. Although normal performance on neuropsychological testing does not guarantee that the individual will not develop dementia, the current data indicate that normal results are relatively reassuring, at least for the next few years.
Progression of mild cognitive impairment (MCI)
Certain features are associated with a higher likelihood of progression from MCI to Alzheimer's. These include confirmation of memory difficulties by a knowledgeable informant (such as a spouse, child or close friend), poor performance on objective memory testing, and any changes in the ability to perform daily tasks, such as hobbies or finances, handling emergencies or attending to one's personal hygiene.
Treatment of mild cognitive impairment (MCI)
There is currently no specific treatment for MCI. As new medical interventions for Alzheimer's disease are developed, these are likely to be tried on patients with MCI as well. If data from such trials indicates a beneficial effect in slowing cognitive decline, the importance of recognizing MCI and identifying it early will increase. However, it is important to remember some drugs may impair memory, especially in older adults. Examples are Valium®, Ativan®, Benadryl®, Tylenol PM®, Advil PM® (both contain Benadryl®), Cogentin® and many others. A very careful assessment of medications is essential when considering a diagnosis of MCI.
A general recommendation for individuals concerned about their memory would be to discuss these concerns with their significant other (friend, spouse, child, etc.), as well as their physician. Bringing the outside informant to the physician appointment is often very helpful in the evaluation process.