Dementia

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Dementia
Classification and external resources
ICD-10 F00-F07
ICD-9 290-294
DiseasesDB 29283
MedlinePlus 000739
MeSH D003704

Dementia is a broad category of brain diseases that includes any disease that causes loss of cognitive ability (the ability to think and reason clearly) that is severe enough to affect a person's daily functioning. It must also be a worsening of functioning compared to how the person was previously.[1] The most common form of dementia is Alzheimer's disease (75%).[1] Other common forms of dementia include: Lewy body dementia, vascular dementia, frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration, normal pressure hydrocephalus and Creutzfeldt–Jakob disease.

Dementia is a disease that becomes more common with age. While only 3% of people between the ages of 65–74 have dementia, 47% of people over the age of 85 have some form of dementia.[1] Therefore, as more people are living longer, dementia is becoming more common.

In DSM-5 the decision was taken to rename the dementias as neurocognitive disorders, with various degrees of severity.

Signs and symptoms[edit]

Dementia can affect any area of the brain's ability to think and reason clearly. The most common affected areas include: memory, visual-spatial, language, attention, and executive function (problem solving). It reduces the ability to learn, reason, retain or recall past experience and there is also loss of patterns of thoughts, feelings and activities. Additional mental and behavioral problems often affect people who have dementia, and may influence quality of life, caregivers, and the need for institutionalization. As dementia worsens individuals may neglect themselves and may become disinhibited and may become incontinent. Behaviour may be disorganized, restless or inappropriate. Some people become restless or wander about by day and sometimes at night. When people with dementia are put in circumstances beyond their abilities, there may be a sudden change to tears or anger (a "catastrophic reaction").[2] A common symptom of dementia is for dementia sufferers to deny that relatives, even relatives in their immediate family, are their own relatives.

Depression affects 20–30% of people who have dementia, and about 20% have anxiety.[3] Psychosis (often delusions of persecution) and agitation/aggression also often accompany dementia. Each of these must be assessed and treated independently of the underlying dementia.[4]

It is possible for a patient to exhibit two or more dementing processes at the same time, as none of the known types of dementia protects against the others. Indeed, about 10% of people with dementia have what is known as mixed dementia, which may be a combination of Alzheimer's disease and multi-infarct dementia.[5][6]

Causes[edit]

Fixed cognitive impairment[edit]

Various types of brain injury may cause irreversible but fixed cognitive impairment. Traumatic brain injury may cause generalized damage to the white matter of the brain (diffuse axonal injury), or more localized damage (as also may neurosurgery). A temporary reduction in the brain's supply of blood or oxygen may lead to hypoxic-ischemic injury. Strokes (ischemic stroke, or intracerebral, subarachnoid, subdural or extradural hemorrhage) or infections (meningitis and/or encephalitis) affecting the brain, prolonged epileptic seizures and acute hydrocephalus may also have long-term effects on cognition. Excessive alcohol use may cause alcohol dementia, Wernicke's encephalopathy and/or Korsakoff's psychosis.

Slowly progressive[edit]

Dementia that begins gradually and worsens progressively over several years is usually caused by neurodegenerative disease—that is, by conditions that affect only or primarily the neurons of the brain and cause gradual but irreversible loss of function of these cells. Less commonly, a non-degenerative condition may have secondary effects on brain cells, which may or may not be reversible if the condition is treated.

Causes of dementia depend on the age at which symptoms begin. In the elderly population (usually defined in this context as over 65 years of age), a large majority of dementia cases are caused by Alzheimer's disease, vascular dementia, or both. Dementia with Lewy bodies is another commonly exhibited form, which again may occur alongside either or both of the other causes.[7][8][9] Hypothyroidism sometimes causes slowly progressive cognitive impairment as the main symptom, and this may be fully reversible with treatment. Normal pressure hydrocephalus, though relatively rare, is important to recognize since treatment may prevent progression and improve other symptoms of the condition. However, significant cognitive improvement is unusual.

Dementia is much less common under 65 years of age. Alzheimer's disease is still the most frequent cause, but inherited forms of the disease account for a higher proportion of cases in this age group. Frontotemporal lobar degeneration and Huntington's disease account for most of the remaining cases.[10] Vascular dementia also occurs, but this in turn may be due to underlying conditions (including antiphospholipid syndrome, CADASIL, MELAS, homocystinuria, moyamoya and Binswanger's disease). People who receive frequent head trauma, such as boxers or football players, are at risk of chronic traumatic encephalopathy[11] (also called dementia pugilistica in boxers).

In young adults (up to 40 years of age) who were previously of normal intelligence, it is very rare to develop dementia without other features of neurological disease, or without features of disease elsewhere in the body. Most cases of progressive cognitive disturbance in this age group are caused by psychiatric illness, alcohol or other drugs, or metabolic disturbance. However, certain genetic disorders can cause true neurodegenerative dementia at this age. These include familial Alzheimer's disease, SCA17 (dominant inheritance); adrenoleukodystrophy (X-linked); Gaucher's disease type 3, metachromatic leukodystrophy, Niemann-Pick disease type C, pantothenate kinase-associated neurodegeneration, Tay-Sachs disease and Wilson's disease (all recessive). Wilson's disease is particularly important since cognition can improve with treatment.

At all ages, a substantial proportion of patients who complain of memory difficulty or other cognitive symptoms have depression rather than a neurodegenerative disease. Vitamin deficiencies and chronic infections may also occur at any age; they usually cause other symptoms before dementia occurs, but occasionally mimic degenerative dementia. These include deficiencies of vitamin B12, folate or niacin, and infective causes including cryptococcal meningitis, HIV, Lyme disease, progressive multifocal leukoencephalopathy, subacute sclerosing panencephalitis, syphilis and Whipple's disease.

Rapidly progressive[edit]

Creutzfeldt-Jakob disease typically causes a dementia that worsens over weeks to months, being caused by prions. The common causes of slowly progressive dementia also sometimes present with rapid progression: Alzheimer's disease, dementia with Lewy bodies, frontotemporal lobar degeneration (including corticobasal degeneration and progressive supranuclear palsy).

On the other hand, encephalopathy or delirium may develop relatively slowly and resemble dementia. Possible causes include brain infection (viral encephalitis, subacute sclerosing panencephalitis, Whipple's disease) or inflammation (limbic encephalitis, Hashimoto's encephalopathy, cerebral vasculitis); tumors such as lymphoma or glioma; drug toxicity (e.g. anticonvulsant drugs); metabolic causes such as liver failure or kidney failure; and chronic subdural hematoma.

Other conditions[edit]

There are many other medical and neurological conditions in which dementia only occurs late in the illness. For example, a proportion of patients with Parkinson's disease develop dementia, though widely varying figures are quoted for this proportion.[citation needed] When dementia occurs in Parkinson's disease, the underlying cause may be dementia with Lewy bodies or Alzheimer's disease, or both.[12] Cognitive impairment also occurs in the Parkinson-plus syndromes of progressive supranuclear palsy and corticobasal degeneration (and the same underlying pathology may cause the clinical syndromes of frontotemporal lobar degeneration). Chronic inflammatory conditions of the brain may affect cognition in the long term, including Behçet's disease, multiple sclerosis, sarcoidosis, Sjögren's syndrome and systemic lupus erythematosus. Although the acute porphyrias may cause episodes of confusion and psychiatric disturbance, dementia is a rare feature of these rare diseases.

Aside from those mentioned above, inherited conditions that can cause dementia (alongside other symptoms) include:[13]

Diagnosis[edit]

There are many specific types and causes of dementia, often showing slightly different symptoms. However, the symptom overlap is such that usually it is impossible to diagnose the type of dementia by symptomatology alone. Diagnosis may be aided by brain scanning techniques. In some cases certainty cannot be attained except with brain biopsy during life, or at autopsy. Proper differential diagnosis between the types of dementia (cortical and subcortical) requires referral to a specialist.[citation needed] In those who are getting older general screening for cognitive impairment using cognitive testing or early diagnosis of dementia has not been shown to improve outcomes.[14]

Normally, symptoms must be present for at least six months to support a diagnosis.[15] Cognitive dysfunction of shorter duration is called delirium. Delirium can be easily confused with dementia due to similar symptoms. Delirium is characterized by a sudden onset, fluctuating course, a short duration (often lasting from hours to weeks), and is primarily related to a somatic (or medical) disturbance. In comparison, dementia has typically an insidious onset (except in the cases of a stroke or trauma), slow decline of mental functioning, as well as a longer duration (from months to years).[16]

Some mental illnesses, including depression and psychosis, may produce symptoms that must be differentiated from both delirium and dementia.[17]

Cognitive testing[edit]

Sensitivity and specificity of common tests for dementia
Test Sensitivity Specificity Reference
MMSE 71%–92% 56%–96% [18]
3MS 83%–93.5% 85%–90% [19]
AMTS 73%–100% 71%–100% [19]

There exist some brief tests (5–15 minutes) that have reasonable reliability to screen cognitive status. While many tests have been studied,[20][21][22] presently the mini mental state examination (MMSE) is the best studied and most commonly used, albeit some may emerge as better alternatives. Other examples include the abbreviated mental test score (AMTS), the, Modified Mini-Mental State Examination (3MS),[23] the Cognitive Abilities Screening Instrument (CASI),[24] the Trail-making test,[25] and the clock drawing test.[26]

Another approach to screening for dementia is to ask an informant (relative or other supporter) to fill out a questionnaire about the person's everyday cognitive functioning. Informant questionnaires provide complementary information to brief cognitive tests. Probably the best known questionnaire of this sort is the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE).[27] On the other hand the General Practitioner Assessment Of Cognition combines both, a patient assessment and an informant interview. It was specifically designed for the use in the primary care setting.

Clinical neuropsychologists provide diagnostic consultation following administration of a full battery of cognitive testing, often lasting several hours, to determine functional patterns of decline associated with varying types of dementia. Tests of memory, executive function, processing speed, attention, and language skills are relevant, as well as tests of emotional and psychological adjustment. These tests assist with ruling out other etiologies and determining relative cognitive decline over time or from estimates of prior cognitive abilities.

Laboratory tests[edit]

Routine blood tests are also usually performed to rule out treatable causes. These tests include vitamin B12, folic acid, thyroid-stimulating hormone (TSH), C-reactive protein, full blood count, electrolytes, calcium, renal function, and liver enzymes. Abnormalities may suggest vitamin deficiency, infection or other problems that commonly cause confusion or disorientation in the elderly. The problem is complicated by the fact that these cause confusion more often in persons who have early dementia, so that "reversal" of such problems may ultimately only be temporary.[citation needed]

Testing for alcohol and other known dementia-inducing drugs may be indicated.

Imaging[edit]

A CT scan or magnetic resonance imaging (MRI scan) is commonly performed, although these tests do not pick up diffuse metabolic changes associated with dementia in a person that shows no gross neurological problems (such as paralysis or weakness) on neurological exam. CT or MRI may suggest normal pressure hydrocephalus, a potentially reversible cause of dementia, and can yield information relevant to other types of dementia, such as infarction (stroke) that would point at a vascular type of dementia.

The functional neuroimaging modalities of SPECT and PET are more useful in assessing long-standing cognitive dysfunction, since they have shown similar ability to diagnose dementia as a clinical exam and cognitive testing.[28] The ability of SPECT to differentiate the vascular cause (i.e., multi-infarct dementia) from Alzheimer's disease dementias, appears superior to differentiation by clinical exam.[29]

Recent research has established the value of PET imaging using carbon-11 Pittsburgh Compound B as a radiotracer (PIB-PET) in predictive diagnosis of various kinds of dementia, in particular Alzheimer's disease. Studies from Australia have found PIB-PET 86% accurate in predicting which patients with mild cognitive impairment would develop Alzheimer's disease within two years. In another study, carried out using 66 patients seen at the University of Michigan, PET studies using either PIB or another radiotracer, carbon-11 dihydrotetrabenazine (DTBZ), led to more accurate diagnosis for more than one-fourth of patients with mild cognitive impairment or mild dementia.[30]

Prevention[edit]

Many prevention measures have been proposed, including both lifestyle changes and medication although none has been reliably shown to be effective.

Management[edit]

Except for the treatable types listed above, there is no cure. Cholinesterase inhibitors are often used early in the disease course; however, benefit is slight. Cognitive and behavioral interventions may also be appropriate. Educating and providing emotional support to the caregiver is of importance as well. Exercise programs are beneficial with respect to activities of daily living and potentially improve dementia.[31]

Cognitive therapies for dementia[edit]

Cognitive therapies which are considered as a treatment for dementia include aromatherapy with slight evidence,[32] massage with unclear evidence,[33] music therapy with unclear evidence,[34] tentative evidence for reminiscence therapy,[35] some benefit for cognitive reframing for caretakers,[36] unclear evidence for validation therapy,[37] and tentative evidence for mental exercise.[38] Adult daycare centers as well as special care units in nursing homes often provide specialized care for dementia patients. Adult daycare centers offer supervision, recreation, meals, and limited health care to participants, as well as providing respite for caregivers. In addition, home care can provide one-on-one support and care in the home allowing for more individualized attention that is needed as the disease progresses. Psychiatric nurses can make a distinctive contribution to people's mental health.[39]

Since dementia impairs normal communication due to changes in receptive and expressive language, as well as the ability to plan and problem solve, agitated behaviour is often a form of communication for the person with dementia and actively searching for a potential cause, such as pain, physical illness, or overstimulation can be helpful in reducing agitation.[40] Additionally, using an "ABC analysis of behaviour" can be a useful tool for understanding behavior in people with dementia. It involves looking at the antecedents (A), behavior (B), and consequences (C) associated with an event to help define the problem and prevent further incidents that may arise if the person's needs are misunderstood.[41]

Medications[edit]

Currently, no medications have been shown to prevent or cure dementia.[42] Medications are used to treat the behavioural and cognitive symptoms and have no effect on the underlying pathophysiology.[43]

Antipsychotic drugs should be used to treat dementia only if non-drug therapies have failed to be effective and the patient's actions threaten themselves or others.[44] Aggressive behavior changes are sometimes the result of other solvable problems, that could make treatment with antipsychotics unnecessary.[44] Because people with dementia can be aggressive, resistant to their treatment, and otherwise disruptive, sometimes antipsychotic drugs are considered as a therapy in response.[44] These drugs have risky adverse effects, including increasing the patient's chance of stroke and death.[44] Generally stopping antipsychotics for people with dementia does not cause problems, even in those who have been on them a long time.[45]

Acetylcholinesterase inhibitors, such as donepezil, may be useful for Alzheimer disease and other similar diseases causing dementia such as Parkinsons or vascular dementia.[43] The quality of the evidence however is poor.[46] No difference has been shown between the agents in this family.[47] In a minority of people side effects include bradycardia and syncope.[48]

N-methyl-D-aspartate (NMDA) receptor blockers such as memantine may be of benefit but the evidence is less conclusive than for AChEIs.[49] Due to their differing mechanisms of action memantine and acetylcholinesterase inhibitors can be used in combination however the benefit is slight.[50][51]

Antidepressant drugs: Depression is frequently associated with dementia and generally worsens the degree of cognitive and behavioral impairment. Antidepressants effectively treat the cognitive and behavioral symptoms of depression in patients with Alzheimer's disease,[52] but evidence for their use in other forms of dementia is weak.[53]

It is recommended that benzodiazepines such as diazepam be avoided in dementia due to the risks of increased cognitive impairment and falls.[54] There is little evidence for the effectiveness in this population.[55]

There is no solid evidence that folate or vitamin B12 improves outcomes in those with cognitive problems.[56]

Pain[edit]

As people age, they experience more health problems, and most health problems associated with aging carry a substantial burden of pain; so, between 25% and 50% of older adults experience persistent pain. Seniors with dementia experience the same prevalence of conditions likely to cause pain as seniors without dementia.[57] Pain is often overlooked in older adults and, when screened for, often poorly assessed, especially among those with dementia since they become incapable of informing others that they're in pain.[57][58] Beyond the issue of humane care, unrelieved pain has functional implications. Persistent pain can lead to decreased ambulation, depressed mood, sleep disturbances, impaired appetite and exacerbation of cognitive impairment,[58] and pain-related interference with activity is a factor contributing to falls in the elderly.[57][59]

Although persistent pain in the person with dementia is difficult to communicate, diagnose and treat, failure to address persistent pain has profound functional, psychosocial and quality of life implications for this vulnerable population. Health professionals often lack the skills and usually lack the time needed to recognize, accurately assess and adequately monitor pain in people with dementia.[57][60] Family members and friends can make a valuable contribution to the care of a person with dementia by learning to recognize and assess their pain. Educational resources (such as the Understand Pain and Dementia tutorial) and observational assessment tools are available.[57][61][62]

Responding to difficulty eating[edit]

Persons with dementia may have difficulty eating. Whenever it is available as an option, the recommended response to eating problems is having a caretaker do assisted feeding for the patient.[63] A secondary option for patients who cannot swallow effectively is to consider gastrostomy feeding tube placement as a way to give nutrition. However, in bringing patient comfort and keeping functional status while lowering risk of aspiration pneumonia and death, assistance with oral feeding is at least as good as tube feeding.[63] Tube-feeding is associated with agitation, increased use of physical and chemical restraints and worsening pressure ulcers.

Benefits of this procedure in those with advanced dementia has not been shown.[64] The risks of using tube feeding include agitation, the person pulling out the tube or otherwise being physically or chemically immobilized to prevent them from doing this, or getting pressure ulcers.[63] There is about a 1% fatality rate directly related to the procedure[65] with a 3% major complication rate.[66]

Society and culture[edit]

Many countries consider the care of people living with dementia to be a national priority, and invest in resources and education to better inform health and social service workers, unpaid caregivers, relatives and members of the wider community. Several countries have national plans or strategies.[67] In these national plans, there is recognition that people can live well with dementia for a number of years, as long as there is the right support and timely access to a diagnosis. David Cameron has described dementia as being a "national crisis", affecting 800,000 people in the United Kingdom.[68]

In the United States, Florida's Baker Act allows law-enforcement authorities and the judiciary to force mental evaluation for those suspected of having developed dementia or other mental incapacities.[citation needed] In the United Kingdom, as with all mental disorders, where a person with dementia could potentially be a danger to themselves or others, they can be detained under the Mental Health Act 1983 for the purposes of assessment, care and treatment. This is a last resort, and usually avoided if the patient has family or friends who can ensure care.

Driving with dementia could lead to severe injury or even death to self and others. Doctors should advise appropriate testing on when to quit driving.[69] The United Kingdom DVLA (Driving & Vehicle Licensing Agency) states that people with dementia who specifically have poor short term memory, disorientation, lack of insight or judgment are not fit to drive, and in these instances the DVLA must be informed so that the driving licence can be revoked. They do, however, acknowledge low-severity cases and those with an early diagnosis, and those drivers may be permitted to drive pending medical reports.

There are many support networks available to those who have a diagnosis of dementia, and their families and caregivers. There are also charitable organisations which aim to raise awareness and campaign for the rights of people living with dementia.

Epidemiology[edit]

Disability-adjusted life year for Alzheimer and other dementias per 100,000 inhabitants in 2002.
  <100
  100-120
  120-140
  140-160
  160-180
  180-200
  200-220
  220-240
  240-260
  260-280
  280–300
  >300

The number of cases of dementia worldwide in 2010 was estimated at 35.6 million.[70] Rates increase significantly with age, with dementia affecting 5% of the population older than 65 and 20–40% of those older than 85.[71] Around two thirds of individuals with dementia live in low and middle income countries, where the sharpest increases in numbers are predicted.[72] Rates are slightly higher in women than men at ages 65 and greater.[71]

History[edit]

Until the end of the 19th century, dementia was a much broader clinical concept. It included mental illness and any type of psychosocial incapacity, including conditions that could be reversed.[73] Dementia at this time simply referred to anyone who had lost the ability to reason, and was applied equally to psychosis of mental illness, "organic" diseases like syphilis that destroy the brain, and to the dementia associated with old age, which was attributed to "hardening of the arteries."

Dementia has been referred to in medical texts since antiquity. One of the earliest known accounts was by the 7th century BC physician and mathematician Pythagoras, who divided the human lifespan into six distinct phases, beginning respectively at birth and progressing through the ages of 7, 21, 49, 63, and 81. The last two he described as the "senium", a period of mental and physical decay, and of the final phase being where "the scene of mortal existence closes after a great length of time that very fortunately, few of the human species arrive at, where the mind is reduced to the imbecility of the first epoch of infancy" In 550 BC, the Athenian statesman and poet Solon argued that the terms of a man's will might be invalidated if he exhibited loss of judgement due to advanced age.

Aristotle and Plato both spoke of the mental decay of advanced age, but apparently simply viewed it as an inevitable process that affected all old men and which nothing could be done to prevent. The latter stated that the elderly were unsuited for any position of responsibility because "There is not much acumen of the mind that once carried them in their youth, those characteristics one would call judgement, imagination, power of reasoning, and memory. They see them gradually blunted by deterioration and can hardly fulfill their function."

For comparison, the Roman statesman Cicero held a view much more in line with modern-day medical wisdom that loss of mental function was not inevitable in the elderly and "affected only those old men who were weak-willed". He spoke of how those who remained mentally active and eager to learn new things could stave off dementia. However, Cicero's views on aging, although progressive, were largely ignored in a world that would be dominated by Aristotle's medical writings for centuries. Subsequent physicians during the time of Roman Empire such as Galen and Celsus simply repeated the beliefs of Aristotle while adding few new contributions to medical knowledge.

Byzantine physicians sometimes wrote of dementia, and it is recorded that at least seven emperors whose lifespans exceeded the age of 70 displayed signs of cognitive decline. In Constantinople, there existed special hospitals to house those diagnosed with dementia or insanity, but these naturally did not apply to the emperors who were above the law and whose health conditions could not be publicly acknowledged.

Otherwise, little is recorded about senile dementia in Western medical texts for nearly 1700 years. One of the few references to it was the 13th century friar Roger Bacon, who viewed old age as divine punishment for original sin. Although he repeated existing Aristotelian beliefs that dementia was inevitable after a long enough lifespan, he did make the extremely progressive assertion that the brain was the center of memory and thought rather than the heart.

Poets, playwrights, and other writers however made frequent allusions to the loss of mental function in old age. Shakespeare notably mentions it in some of his plays including Hamlet and King Lear.

Dementia in the elderly was called senile dementia or senility, and viewed as a normal and somewhat inevitable aspect of growing old, rather than as being caused by any specific diseases. At the same time, in 1907, a specific organic dementing process of early onset, called Alzheimer's disease, had been described. This was associated with particular microscopic changes in the brain, but was seen as a rare disease of middle age.

Much like other diseases associated with aging, dementia was rare before the 20th century, although by no means unknown, due to the fact that it is most prevalent in people over 80, and such lifespans were uncommon in preindustrial times. Conversely, syphilitic dementia was widespread in the developed world until largely being eradicated by the use of penicillin after WWII.

By the period of 1913–20, schizophrenia had been well-defined in a way similar to today, and also the term dementia praecox had been used to suggest the development of senile-type dementia at a younger age. Eventually the two terms fused, so that until 1952 physicians used the terms dementia praecox (precocious dementia) and schizophrenia interchangeably. The term precocious dementia for a mental illness suggested that a type of mental illness like schizophrenia (including paranoia and decreased cognitive capacity) could be expected to arrive normally in all persons with greater age (see paraphrenia). After about 1920, the beginning use of dementia for what we now understand as schizophrenia and senile dementia helped limit the word's meaning to "permanent, irreversible mental deterioration." This began the change to the more recognizable use of the term today.

In 1976, neurologist Robert Katzmann suggested a link between senile dementia and Alzheimer's disease.[74] Katzmann suggested that much of the senile dementia occurring (by definition) after the age of 65, was pathologically identical with Alzheimer's disease occurring before age 65 and therefore should not be treated differently. He noted that the fact that "senile dementia" was not considered a disease, but rather part of aging, was keeping millions of aged patients experiencing what otherwise was identical with Alzheimer's disease from being diagnosed as having a disease process, rather than simply considered as aging normally.[75] Katzmann thus suggested that Alzheimer's disease, if taken to occur over age 65, is actually common, not rare, and was the 4th or 5th leading cause of death, even though rarely reported on death certificates in 1976.

This suggestion opened the view that dementia is never normal, and must always be the result of a particular disease process, and is not part of the normal healthy aging process, per se. The ensuing debate led for a time to the proposed disease diagnosis of "senile dementia of the Alzheimer's type" (SDAT) in persons over the age of 65, with "Alzheimer's disease" diagnosed in persons younger than 65 who had the same pathology. Eventually, however, it was agreed that the age limit was artificial, and that Alzheimer's disease was the appropriate term for persons with the particular brain pathology seen in this disease, regardless of the age of the person with the diagnosis. A helpful finding was that although the incidence of Alzheimer's disease increased with age (from 5–10% of 75-year-olds to as many as 40–50% of 90-year-olds), there was no age at which all persons developed it, so it was not an inevitable consequence of aging, no matter how great an age a person attained. Evidence of this is shown by numerous documented supercentenarians (people living to 110+) that experienced no serious cognitive impairment.

Also, after 1952, mental illnesses like schizophrenia were removed from the category of organic brain syndromes, and thus (by definition) removed from possible causes of "dementing illnesses" (dementias). At the same, however, the traditional cause of senile dementia– "hardening of the arteries" – now returned as a set of dementias of vascular cause (small strokes). These were now termed multi-infarct dementias or vascular dementias.

In the 21st century, a number of other types of dementia have been differentiated from Alzheimer's disease and vascular dementias (these two being the most common types). This differentiation is on the basis of pathological examination of brain tissues, symptomatology, and by different patterns of brain metabolic activity in nuclear medical imaging tests such as SPECT and PETscans of the brain. The various forms of dementia have differing prognoses (expected outcome of illness), and also differing sets of epidemologic risk factors. The causal etiology of many of them, including Alzheimer's disease, remains unknown, although many theories exist such as accumulation of protein plaques as part of normal aging, inflammation, inadequate blood sugar, and traumatic brain injury.

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