Merck Manual

Please confirm that you are a health care professional

Loading

Alzheimer Disease

(Alzheimer's Disease)

By

Juebin Huang

, MD, PhD, Memory Impairment and Neurodegenerative Dementia (MIND) Center, University of Mississippi Medical Center

Last full review/revision Dec 2019| Content last modified Dec 2019
Click here for Patient Education
Topic Resources

Alzheimer disease causes progressive cognitive deterioration and is characterized by beta-amyloid deposits and neurofibrillary tangles in the cerebral cortex and subcortical gray matter. Diagnosis is clinical; laboratory and imaging tests are usually done to look for specific findings that suggest Alzheimer disease and to identify other treatable causes of dementia. Treatment is supportive. Cholinesterase inhibitors can sometimes temporarily improve cognitive function.

Alzheimer disease, a neurocognitive disorder, is the most common cause of dementia; it accounts for 60 to 80% of dementias in older people. In the US, an estimated 10% of people ≥ 65 have Alzheimer disease. The percentage of people with Alzheimer disease increases with age (1):

  • Age 65 to 74: 3%

  • Age 75 to 84: 17%

  • Age ≥ 85: 32%

The disease is twice as common among women as among men, partly because women have a longer life expectancy. Prevalence in industrialized countries is expected to increase as the proportion of older people increases.

General reference

Etiology

Most cases of Alzheimer disease are sporadic, with late onset ( 65 years) and unclear etiology. Risk of developing the disease is best predicted by age. However, about 5 to 15% of cases are familial; half of these cases have an early (presenile) onset (< 65 years) and are typically related to specific genetic mutations.

At least 5 distinct genetic loci, located on chromosomes 1, 12, 14, 19, and 21, influence initiation and progression of Alzheimer disease.

Mutations in genes for the amyloid precursor protein, presenilin I, and presenilin II may lead to autosomal dominant forms of Alzheimer disease, typically with presenile onset. In affected patients, the processing of amyloid precursor protein is altered, leading to deposition and fibrillar aggregation of beta-amyloid; beta-amyloid is the main component of senile plaques, which consist of degenerated axonal or dendritic processes, astrocytes, and glial cells around an amyloid core. Beta-amyloid may also alter kinase and phosphatase activities in ways that eventually lead to hyperphosphorylation of tau and formation of neurofibrillary tangles.

Other genetic determinants include the apolipoprotein (apo) E (epsilon) alleles. Apo E proteins influence beta-amyloid deposition, cytoskeletal integrity, and efficiency of neuronal repair. Risk of Alzheimer disease is substantially increased in people with 2 epsilon-4 alleles and may be decreased in those who have the epsilon-2 allele. For people with 2 epsilon-4 alleles, risk of developing Alzheimer disease by age 75 is about 10 to 30 times that for people without the allele.

The relationship of other factors (eg, low hormone levels, metal exposure) and Alzheimer disease is under study, but no definite causal links have been established.

Pathophysiology

The 2 pathologic hallmarks of Alzheimer disease are

  • Extracellular beta-amyloid deposits (in senile plaques)

  • Intracellular neurofibrillary tangles (paired helical filaments)

The beta-amyloid deposition and neurofibrillary tangles lead to loss of synapses and neurons, which results in gross atrophy of the affected areas of the brain, typically starting at the mesial temporal lobe.

The mechanism by which beta-amyloid peptide and neurofibrillary tangles cause such damage is incompletely understood. There are several theories.

The amyloid hypothesis posits that progressive accumulation of beta-amyloid in the brain triggers a complex cascade of events ending in neuronal cell death, loss of neuronal synapses, and progressive neurotransmitter deficits; all of these effects contribute to the clinical symptoms of dementia.

Prion mechanisms have been identified in Alzheimer disease. In prion diseases, a normal cell-surface brain protein called prion protein becomes misfolded into a pathogenic form termed a prion. The prion then causes other prion proteins to misfold similarly, resulting in a marked increase in the abnormal proteins, which leads to brain damage. In Alzheimer disease, it is thought that the beta-amyloid in cerebral amyloid deposits and tau in neurofibrillary tangles have prion-like, self-replicating properties.

Symptoms and Signs

Patients with Alzheimer disease have symptoms and signs of dementia.

The most common first manifestation of Alzheimer disease is

  • Loss of short-term memory (eg, asking repetitive questions, frequently misplacing objects or forgetting appointments)

Other cognitive deficits tend to involve multiple functions, including the following:

  • Impaired reasoning, difficulty handling complex tasks, and poor judgment (eg, being unable to manage bank account, making poor financial decisions)

  • Language dysfunction (eg, difficulty thinking of common words, errors speaking and/or writing)

  • Visuospatial dysfunction (eg, inability to recognize faces or common objects)

Alzheimer disease progresses gradually but may plateau for periods of time.

Behavior disorders (eg, wandering, agitation, yelling, persecutory ideation) are common.

Diagnosis

  • Similar to that of other dementias

  • Formal mental status examination

  • History and physical examination

  • Laboratory testing

  • Neuroimaging

Generally, diagnosis of Alzheimer disease is similar to the diagnosis of other dementias. However, despite clinical and specific laboratory and imaging characteristics, definitive diagnosis of Alzheimer disease can only be confirmed by histologic evaluation of brain tissue.

Evaluation includes a thorough history and standard neurologic examination. Clinical criteria are 85% accurate in establishing the diagnosis and differentiating Alzheimer disease from other forms of dementia, such as vascular dementia and dementia with Lewy bodies.

Traditional diagnostic criteria for Alzheimer disease include all of the following:

  • Dementia established clinically and documented by a formal mental status examination

  • Deficits in 2 areas of cognition

  • Gradual onset (ie, over months to years, rather than days or weeks) and progressive worsening of memory and other cognitive functions

  • No disturbance of consciousness

  • Onset after age 40, most often after age 65

  • No systemic or brain disorders (eg, tumor, stroke) that could account for the progressive deficits in memory and cognition

However, deviations from these criteria do not exclude a diagnosis of Alzheimer disease, particularly because patients may have mixed dementia.

The most recent (2011) National Institute on Aging–Alzheimer's Association diagnostic guidelines (1, 2) also include biomarkers for the pathophysiologic process of Alzheimer disease:

  • A low level of beta-amyloid in cerebrospinal fluid (CSF)

  • Beta-amyloid deposits in the brain detected by positron emission tomography (PET) imaging using radioactive tracer that binds specifically to beta-amyloid plaques (eg, Pittsburgh compound B [PiB], florbetapir)

Other biomarkers indicate downstream neuronal degeneration or injury:

  • Elevated levels of tau protein in CSF

  • Decreased cerebral metabolism in the temporoparietal cortex measured using PET with fluorine-18 (18F)–labeled deoxyglucose (fluorodeoxyglucose, or FDG)

  • Local atrophy in the medial, basal, and lateral temporal lobes and the medial parietal cortex, detected by MRI

These findings increase the probability that dementia is due to Alzheimer disease. However, the guidelines (1, 2) do not advocate routine use of these biomarkers for diagnosis because standardization and availability are limited at this time. Also, they do not recommend routine testing for the apo epsilon-4 allele.

Laboratory tests (eg, thyroid-stimulating hormone, vitamin B12 levels) and neuroimaging (MRI or CT) are done to check for other, treatable causes of dementia and disorders that can worsen symptoms. If clinical findings suggest another underlying disorder (eg, HIV, syphilis), tests for those disorders are indicated.

Differential diagnosis

Distinguishing Alzheimer disease from other dementias is difficult. Assessment tools (eg, Hachinski Ischemic Score—see table Modified Hachinski Ischemic Score) can help distinguish vascular dementia from Alzheimer disease. Fluctuations in cognition, parkinsonian symptoms, well-formed visual hallucinations, and relative preservation of short-term memory suggest dementia with Lewy bodies rather than Alzheimer disease (see table Differences Between Alzheimer Disease and Dementia With Lewy Bodies).

Patients with Alzheimer disease are often better-groomed and neater than patients with other dementias.

Table
icon

Modified Hachinski Ischemic Score

Feature

Points*

Abrupt onset of symptoms

2

Stepwise deterioration (eg, decline-stability-decline)

1

Fluctuating course

2

Nocturnal confusion

1

Personality relatively preserved

1

Depression

1

Somatic complaints (eg, body aches, chest pain)

1

Emotional lability

1

History or presence of hypertension

1

History of stroke

2

Evidence of coexisting atherosclerosis (eg, PAD, MI)

1

Focal neurologic symptoms (eg, hemiparesis, homonymous hemianopia, aphasia)

2

Focal neurologic signs (eg, unilateral weakness, sensory loss, asymmetric reflexes, Babinski sign)

2

* Total score is determined:

  • < 4 suggests primary dementia (eg, Alzheimer disease).

  • 4–7 is indeterminate.

  • > 7 suggests vascular dementia.

MI = myocardial infarction; PAD = peripheral arterial disease.

Table
icon

Differences Between Alzheimer Disease and Dementia with Lewy Bodies

Feature

Alzheimer Disease

Dementia with Lewy Bodies

Pathology

Senile plaques, neurofibrillary tangles, and beta-amyloid deposits in the cerebral cortex and subcortical gray matter

Lewy bodies in neurons of the cortex

Epidemiology

Affects twice as many women

Affects twice as many men

Inheritance

Familial in 5–15% cases

Rarely familial

Day-to-day fluctuation

Some

Prominent

Short-term memory

Lost early in the disease

Less affected

Deficits in alertness and attention more than in memory acquisition

Parkinsonian symptoms

Very rare, occurring late in the disease

Normal gait

Prominent, obvious early in the disease

Axial rigidity and unstable gait

Autonomic dysfunction

Rare

Common

Hallucinations

Occur in about 20% of patients, usually when disease is moderately advanced

Occur in about 80%, usually when disease is early

Most commonly, visual

Adverse effects with antipsychotics

Common

Possible worsening of symptoms of dementia

Common

Acute worsening of extrapyramidal symptoms, which may be severe or life threatening

Diagnosis references

  • 1. Jack CR Jr, Albert MS, Knopman DS, et al: Introduction to the recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease. Alzheimers Dement 7 (3):257–262, 2011. doi: 10.1016/j.jalz.2011.03.004.

  • 2. McKhann GM, Knopman DS, Chertkow H, et al: The diagnosis of dementia due to Alzheimer's disease: Recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease. Alzheimers Dement 7 (3):263–269, 2011. doi: 10.1016/j.jalz.2011.03.005.

Prognosis

Although progression rate varies in patients with Alzheimer disease, cognitive decline is inevitable. Average survival from time of diagnosis is 7 years, although this figure is debated. Average survival from the time patients can no longer walk is about 6 months.

Treatment

  • Safety and support measures

  • Possibly cholinesterase inhibitors and memantine

Safety and supportive measures for Alzheimer disease are the same as those for all dementias. For example, the environment should be bright, cheerful, and familiar, and it should be designed to reinforce orientation (eg, placement of large clocks and calendars in the room). Measures to ensure patient safety (eg, signal monitoring systems for patients who wander) should be implemented.

Providing help for caregivers, who may experience substantial stress, is also important. Nurses and social workers can teach caregivers how to best meet the patient’s needs. Health care practitioners should watch for early symptoms of caregiver stress and burnout and, when needed, suggest support services.

Drugs to treat Alzheimer disease

Cholinesterase inhibitors modestly improve cognitive function and memory in some patients. Four are available. Generally, donepezil, rivastigmine, and galantamine are equally effective, but tacrine is rarely used because of its hepatotoxicity.

Donepezil is a first-line drug because it has once-a-day dosing and is well-tolerated. The recommended dose is 5 mg orally once a day for 4 to 6 weeks, then increased to 10 mg once a day. Donepezil 23 mg once a day may be more effective than the traditional 10 mg once-a-day-dose for moderate to severe Alzheimer disease. Treatment should be continued if functional improvement is apparent after several months, but otherwise it should be stopped. The most common adverse effects are gastrointestinal (eg, nausea, diarrhea). Rarely, dizziness and cardiac arrhythmias occur. Adverse effects can be minimized by increasing the dose gradually (see table Drugs for Alzheimer Disease).

Memantine, an N-methyl-d-aspartate (NMDA) receptor antagonist, appears to improve cognition and functional capacity of patients with moderate to severe Alzheimer disease. The dose is 5 mg orally once a day, which is increased to 10 mg orally twice a day over about 4 weeks. For patients with renal insufficiency, the dose should be reduced or the drug should be avoided. Memantine can be used with a cholinesterase inhibitor.

Efficacy of high-dose vitamin E (1000 IU orally once or twice a day), selegiline, nonsteroidal anti-inflammatory drugs (NSAIDs), Ginkgo biloba extracts, and statins is unclear. Estrogen therapy does not appear useful in prevention or treatment and may be harmful. Clinical trials with investigational drugs that target beta-amyloid peptide accumulation and clearance have not been successful although some studies are still ongoing.

Table
icon

Drugs for Alzheimer Disease

Drug Name

Starting Dose

Maximum Dose

Comments

Donepezil

5 mg orally once a day

23 mg once a day (for moderate to severe Alzheimer disease)

Generally well-tolerated but can cause nausea or diarrhea

Galantamine

4 mg orally twice a day

Extended-release: 8 mg once a day in the am

12 mg twice a day

Extended-release: 24 mg once a day in the am

Possibly more beneficial for behavioral symptoms than other drugs

Modulates nicotinic receptors and appears to stimulate release of acetylcholine and enhances its effect

Memantine

5 mg orally twice a day

10 mg twice a day

Used in patients with moderate to severe Alzheimer disease

Rivastigmine

Liquid or capsule: 1.5 mg twice a day

Patch: 4.6 mg/24 hours

Liquid or capsule: 6 mg twice a day

Patch: 13.3 mg/24 hours

Available in liquid solution and a patch

End-of-life issues

Because insight and judgment deteriorate in patients with dementia, appointment of a family member, guardian, or lawyer to oversee finances may be necessary. Early in dementia, before the patient is incapacitated, the patient’s wishes about care should be clarified, and financial and legal arrangements (eg, durable power of attorney, durable power of attorney for health care) should be made. When these documents are signed, the patient’s capacity should be evaluated, and evaluation results recorded. Decisions about artificial feeding and treatment of acute disorders are best made before the need develops.

In advanced dementia, palliative measures may be more appropriate than highly aggressive interventions or hospital care.

Prevention

Preliminary, observational evidence suggests that risk of Alzheimer disease may be decreased by the following:

  • Continuing to do challenging mental activities (eg, learning new skills, doing crossword puzzles) well into old age

  • Exercising

  • Controlling hypertension

  • Lowering cholesterol levels

  • Consuming a diet rich in omega-3 fatty acids and low in saturated fats

  • Drinking alcohol in modest amounts

However, there is no convincing evidence that people who do not drink alcohol should start drinking to prevent Alzheimer disease. Once dementia develops, abstaining from alcohol is usually recommended because alcohol can worsen dementia symptoms.

Key Points

  • Although genetic factors can be involved, most cases of Alzheimer disease are sporadic, with risk predicted best by patient age.

  • Differentiating Alzheimer disease from other causes of dementia (eg, vascular dementia, dementia with Lewy bodies) can be difficult but is often best done using clinical criteria, which are 85% accurate in establishing the diagnosis.

  • Treat Alzheimer disease similarly to other dementias.

More Information

Drugs Mentioned In This Article

Drug Name Select Trade
EXELON
RAZADYNE
ELDEPRYL
NAMENDA
ARICEPT
Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Also of Interest

Videos

View All
Overview of Delirium
Video
Overview of Delirium
3D Models
View All
Brain Vasculature
3D Model
Brain Vasculature

SOCIAL MEDIA

TOP