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Alzheimer's disease

Description

An in-depth report on the causes, diagnosis, and treatment of Alzheimer's disease.

Diagnosis

A definitive test to diagnose Alzheimer's disease, even in patients showing signs of dementia, has not yet been developed. A number of expert groups have developed criteria to help diagnose Alzheimer's disease and rule out other disorders. A diagnosis often involves answering questions about the patient:

• Do psychologic tests indicate dementia?
• Does the patient have deficits in two or more areas of mental functioning (such as language, motor skills, and perceptions)?
• Has memory and mental functions gotten progressively worse?
• Is consciousness disturbed? (It is not in Alzheimer's disease.)
• Is the patient over age 40?
• Are other medical or physical conditions present that could account for the same symptoms?
• Are daily activity impaired or has the behavior changed?
• Is there a family history of Alzheimer's disease?
• Are there other symptoms, such as depression, insomnia, incontinence, delusions, hallucinations, dramatic verbal, emotional or physical outbursts, sexual disorders, and weight loss?

Other steps involved in making a decision include laboratory tests (EEG and possibly tests to rule out other diseases) and psychological testing to determine the presence of dementia.

Ruling out Conditions of Normal Aging that Can Cause Alzheimer's-like Symptoms

Although some memory impairment occurs in many people as they age, only some of these people develop Alzheimer's disease. Many similar symptoms can occur in healthy older individuals from other conditions associated with aging:

• Fatigue
• Grief or depression
• Illness
• Vision or hearing loss
• The use of alcohol or certain medications
• Simply the burden of too many details to remember at once

Ruling Out Other Causes Memory Loss or Dementia

The first step in diagnosing Alzheimer's disease is to rule out other conditions that might cause memory loss or dementia. There are a number of causes for dementia in the elderly besides Alzheimer's disease:

• Vascular dementia (abnormalities in the vessels that carry blood to the brain)
• Lewy bodies variant (LBV), also called dementia with Lewy bodies
• Parkinson's disease
• Frontotemporal dementia

Experts believe that 60% of cases of dementia are due to Alzheimer's, 15% to vascular injuries, and the rest are a mixture of the two or caused by other factors.

Vascular Dementia. Vascular dementia is primarily caused by either multi-infarct dementia (multiple small strokes) or Binswanger's disease (which affects tiny arteries in the midbrain). One major analysis suggested that patients with vascular dementia have better long term verbal memory than patients with Alzheimer's disease, but poorer executive function (less ability to integrate and organize).

Lewy Bodies Variant. Lewy bodies are abnormalities found in the brains of patients with both Parkinson's disease and Alzheimer's. They can also be present in the absence of either disease; in such cases, the condition is called Lewy bodies variant (LBV). In all cases, the presence of Lewy bodies is highly associated with dementia. LBV was defined in 1997 and some experts believe it may be responsible for about 20% of people who have been diagnosed with Alzheimer's. They can be difficult to distinguish. Compared to Alzheimer's disease patients, those with LBV may be more likely to have hallucinations and delusions early on, to walk with a stoop (similar to Parkinson's disease), to have more fluctuating attention problems, and to perform better than Alzheimer's disease patients on verbal recall but less well with organizing objects.

Parkinson's Disease. Dementia is about six times more common in the elderly Parkinson patient than in the average older adult. It is most likely to occur in older patients who have had major depression. Unlike in Alzheimer's, language is not usually affected in Parkinson's related dementia. Visual hallucinations occur in about a third of people on long-term medications.

Frontotemporal Dementia (FTD). Once considered rare, FTD is now considered to be the second most common cause of early-onset dementia. People who develop this condition tend to be in their mid-fifties although it can develop later on. It results in greater behavioral impairment (apathy, reduced empathy, poor self-care, unrestrained behavior) than with Alzheimer's disease. It may also be marked by speech problems and early incontinence. Brain imaging scans can help diagnose this problem.

Other Conditions that Cause Similar Symptoms. Some elderly people have a condition called mild cognitive impairment, which involves more severe memory loss than normal but no other symptoms of Alzheimer's. A number of conditions, including many medications, can produce symptoms similar to Alzheimer's:

• Severe depression
• Drug abuse
• Thyroid disease
• Severe vitamin B12 deficiency
• Blood clots
• Hydrocephalus (excessive accumulation of spinal fluid in the brain).
• Syphilis
• Huntington's disease
• Creutzfeldt-Jakob disease
• Brain tumors

It is important that the doctor recognize any treatable conditions that might be causing symptoms or worsening existing dementia caused by Alzheimer's or vascular abnormalities.

Psychological Testing

A number of psychologic tests are used or being developed to assess difficulties in attention, perception, and memory and problem-solving, social, and language skills. Experts are researching specific tests that may help identify early on people with mild memory impairment who are at high risk for Alzheimer's disease.

• Two commonly used tests that are very useful in identifying individuals who may be at risk for Alzheimer's are the Mini-Mental State Exam (MMSE) and the Mattis Dementia Rating Scale. Still, these tests have limitations.
• A clock drawing test is also a good test for Alzheimer's disease. The patient is given a piece of paper with a circle on it and is first asked to write the numbers in the face of a clock and then to show "10 minutes after 11." The score is based on spacing between the numbers and the positions of the hands.

Electroencephalography

Electroencephalography (EEG) traces brain-wave activity; in some patients with Alzheimer's disease this test reveals "slow waves." Although other diseases may evidence similar abnormalities, EEG data helps distinguish a potential patient with Alzheimer's disease from patient with severe depression, whose brain waves are normal.

Imaging Tests

Imaging tests include magnetic resonance imaging (MRI), positron-emission tomography (PET), and single photon emission computed tomography (SPECT). These tests are sometimes used to rule out other disorders such as multi-infarct dementia, stroke, blood clots, and tumors. Research is being conducted to determine if these tests can help to confirm a diagnosis of Alzheimer's disease and improve understanding of disease progression.

In 2005, the National Institute of Aging, in collaboration with industry partners, launched the $60 million Alzheimer's Disease Neuroimaging Initiative (ADNI). This landmark 5-year clinical trial, which will be conducted at 50 sites throughout the United States and Canada, will investigate whether neuroimaging techniques, such as MRI and PET scans, can be combined with biomarkers and neuropsychological tests to measure the progression of AD and mild cognitive impairment. In 2004, the U.S. Medicare system expanded insurance coverage of PET scans for eligible beneficiaries who meet specific diagnostic criteria for both Alzheimer's disease and fronto-temporal dementia. Medicare also covers the costs for patients enrolled in its agency-approved imaging clinical trials.

Research continues on Pittsburgh compound B, a tracer molecule used in PET brain scans to highlight beta-amyloid protein deposits. Results from this research may help to define potential drug targets and aid in the development of new Alzheimer's drugs.

Investigative Tests.

Blood Tests. Blood tests are currently used to check for anemia and other disorders that can produce dementia symptoms. Investigators are researching serum biomarkers, such as the iron transport protein p97, that might help detect the presence of Alzheimer's disease.

Cerebrospinal Fluid Test. Scientists are developing new nanotechnology screening methods that may eventually be used to identify Alzheimer's disease while it is still in its earliest stages and before plaque deposits accumulate. In 2005, a research team announced it had used a bio-barcode assay to detect tiny amounts of a protein called amyloid-beta-derived diffusable ligand (ADDL) in cerebrospinal fluid. ADDLs may be involved in cognitive decline and are a potential biomarker for early stage Alzheimer's disease. Tests for other proteins are also being developed.

Odor Test. Investigators are also using the impairment of smell in Alzheimer's disease to develop tests that require patients to distinguish between odors.

Determining Severity after a Diagnosis Has Been Made

Once a diagnosis has been made, some experts observe that certain factors at the time of diagnosis indicate a higher risk for a more rapid decline:

• Older age
• Being male
• The presence of high blood pressure
• Signs of loss of motor control and coordination
• Tremor
• Social withdrawal
• Loss of appetite and severe weight loss
• Accompanying sensory problems, such as hearing loss and a decline in reading ability
• General physical debility

• Review Date: 5/22/2006
• Reviewed By: Harvey Simon, M.D., Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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