There is no a single test for diagnosing Alzheimer's disease. Your doctor can only diagnose probable Alzheimer's disease after a thorough medical, psychiatric, and neurological evaluation, to rule out all other possible causes of dementia. Alzheimer's disease cannot be positively diagnosed until after death, when the brain can be closely examined for certain microscopic changes caused by the disease. However, through thorough testing and a "process of elimination," doctors today can diagnose probable Alzheimer's with almost 90 percent accuracy. Diagnosing Alzheimer's often entails:
- Taking a detailed medical history
- Performing general and neurological examinations
- Giving specific tests that measure cognitive skills
- Performing certain blood studies
- Analyzing images of the brain
This section has more on:
- Why dementia should be evaluated by a doctor
- What your doctor may well do first
- Tests your doctor might recommend
An early and accurate diagnosis of the cause of dementia is important for the following reasons:
- To identify any treatable condition and initiate treatment as appropriate
- To rule out Alzheimer's disease and so ease the patient's and his or her family's concern
- To identify Alzheimer's disease at the earliest possible stage, which gives the patient and family time to plan for the future needs and care of the patient
Alzheimer's disease is the single most common form of dementia, but a number of other causes are also known, some of which may be at least partially reversible. Evaluation for dementia includes a search for alternative causes—chemical or metabolic disorders such as hypothyroidism or vitamin B12 deficiency, effects of chemical substances including tranquilizers and alcohol, depression, and structural processes such as tumors, strokes, or enlargement of the ventricles (fluid sacs) within the brain.
In addition, some Alzheimer's disease symptoms—such as incontinence and depression—can be effectively treated. Therefore, it is very important to diagnose the cause of the dementia early and correctly.
The following diagnostic tools may be used to help make a diagnosis of Alzheimer's disease:
Patient history: A patient history helps the doctor assess an individual's past and current health situation. It also helps the doctor evaluate any medical problems, develop a plan of treatment, and monitor the patient's health over time. During this evaluation, the doctor asks the patient a series of questions. A thorough patient history includes:
- Patient's identifying information
- Chief complaint
- History of current illness
- Past medical history
- Current health status
- Psychosocial history (marital status, living conditions, employment, sexual history, significant life events)
- Mental status
- Family history (including any illnesses that seem to run in the family)
- Review of symptoms
Physical exam: The physical examination is part of the patient care process. The exam enables the doctor to assess the overall physical condition of the patient. If the patient has a medical complaint, the physical exam provides the doctor with more information about the problem, which helps the doctor determine an appropriate plan of treatment. The physical exam includes an evaluation of the following:
- Vital signs (temperature, blood pressure, pulse)
- Height and weight
- Head, eyes, ears, nose
- Chest, including lungs and heart
- Bones and muscles
- Rectal/genital area
- Chest X-ray (may be used by the doctor to help rule out other disorders that may be causing symptoms similar to those of Alzheimer's disease)
Your doctor may order these tests to help diagnose Alzheimer's disease, to understand the disease, or to rule out other disorders that cause symptoms similar to those of Alzheimer's disease.
Laboratory tests: When a doctor is diagnosing a disorder, he or she often orders laboratory tests on certain fluids and tissue samples from the body. These tests can help identify problems and diseases. There are hundreds of laboratory tests available to help a doctor make a diagnosis. The most common are blood tests and urinalysis. Blood tests involve a series of tests routinely done on blood to look for abnormalities associated with various diseases and disorders. A number of studies are generally recommended, including blood count, test of kidney and liver function, serum electrolytes, thyroid screen, vitamin B12 level, and sometimes a serologic test for syphilis. Blood tests also may be used to look for the presence of a specific gene that has been identified as a risk factor for Alzheimer's disease. (Genetic testing for Alzheimer's disease occurring after age 60 is not generally recommended.) A urinalysis is a test in which a urine sample is evaluated to detect abnormalities, such as improper levels of sugar or protein. This test may be used by the doctor to help rule out other disorders that may be causing symptoms similar to those of Alzheimer's disease.
Neuropsychological testing: This studies the relationship between the brain and behavior. It is used when the patient is having serious problems with short- and long-term memory, attention and concentration, word and name association, language understanding, and other symptoms that persist or worsen over time. These tests help in the diagnosis and treatment of conditions that affect thinking, emotion, and behavior. These include Alzheimer's disease, various psychiatric problems (depression, anxiety disorders), medication-related conditions, substance abuse, strokes, and tumors. Neuropsychological tests accompany a comprehensive interview with the patient and may include tests to assess attention, memory, language, ability to do arithmetic, the ability to plan and reason, and the ability to modify behavior, as well as assessments of personality and emotional stability. Neuropsychological testing also can help the doctor and family better understand the impact of a disorder on a patient's everyday functioning.
Electrocardiogram (ECG or EKG): A recording of the heart's electrical activity. This activity is registered as a graph or series of wavy lines on a moving strip of paper. This gives the doctor important information about the heart. For example, it can show the heart's rate and rhythm. It also can help show decreased blood flow, enlargement of the heart, or the presence of damage due to a current or past heart attack. EKGs are non-invasive, quick, safe, and painless, and they are routinely done if a heart condition is suspected. This test may be used by the doctor to help rule out other disorders that may be causing symptoms similar to those of Alzheimer's disease.
This section also discusses:
- Brain imaging for diagnosing Alzheimer's disease
- Brain imaging for diagnosing and monitoring the progression of Alzheimer's disease
These tests help a doctor rule out strokes, tumors, or other brain abnormalities that could cause the symptoms.
Computed tomography (CT or CAT) scan: a technique in which multiple X-rays of the body are taken from different angles in a very short period. These images are fed into a computer, which creates a series of cross-sectional "slices" of the body. Contrast material (such as barium) can be given to help distinguish organs from muscle and other tissue. CT imaging creates the images by measuring how quickly the body and organs absorb the X-rays. CT scans often can reveal certain changes that are characteristic of Alzheimer's disease in its later stages. These changes include a reduction in the size of the brain (atrophy), widened indentations in the tissues, and enlargement of the fluid-filled chambers called cerebral ventricles.
Magnetic resonance imaging (MRI): a test that produces very clear pictures, or images, of the human body without using X-rays. Instead, MRI uses a large magnet, radio waves, and a computer to produce these images. The MRI is a very sensitive test that is very helpful for imaging "soft tissues," such as organs. MRI is beneficial in ruling out other causes of dementia, such as tumors or strokes. It also may help to show the physical and functional changes in the brain that are associated with Alzheimer's disease.
Electroencephalography (EEG): a medical imaging technique that measures brain function by analyzing the electrical activity generated by the brain. This activity is measured through special electrodes applied to the scalp. EEG is a completely noninvasive procedure—meaning that nothing is inserted into the body. EEG can be used repeatedly in adults and children with virtually no risks or limitations and is helpful in the diagnosis of brain disorders. Because the EEG procedure is noninvasive and painless, it often is used to study various brain processes, such as perception, memory, attention, language, and emotion, and is most helpful in identifying disorders that can mimic Alzheimer's disease.
In addition, the following tests also may be done to help diagnose and monitor the progression of Alzheimer's disease:
Positron emission tomography (PET) scan: an imaging scan that measures the level of functional activity of the brain by measuring its use of glucose. PET scanning is a noninvasive, three-dimensional imaging technique that can show how the heart, brain, or other internal organs are functioning, unlike X-ray, CT, or MRI, which show only body structure. PET can provide information to pinpoint and evaluate diseases of the brain. PET imaging can show the region of the brain that is causing a patient to have seizures and is useful in evaluating degenerative brain diseases such as Alzheimer's. PET scans can show the difference in brain activity between a normal brain and one affected by Alzheimer's disease; they can also help differentiate Alzheimer's disease from other forms of dementia.
SPECT scans: a procedure that measures blood flow in different areas of the brain. SPECT is a noninvasive technique for creating very clear, three-dimensional pictures of a major organ, such as the brain or heart. SPECT scans use radionuclide imaging—a technique that involves the injection of a very small amount of a radioactive substance called a tracer. Energy from the tracer in the body is detected by a special camera, which then takes the pictures. SPECT can map blood flow in certain regions of the brain and is useful in evaluating specific brain functions. This may reveal abnormalities that are characteristic of Alzheimer's disease.
Magnetic resonance spectroscopy imaging (MRSI): a test that allows the doctor to observe certain substances throughout the brain without the use of radioactive materials. MRSI is a noninvasive imaging technique that is used to study metabolic changes in brain tumors, strokes, seizure disorders, Alzheimer's disease, depression, and other diseases affecting the brain. It also has been used to study the metabolism of other organs. MRSI can be done as part of a routine MRI, but they are different tests. An MRI creates an image, and an MRSI creates a graph of the types and quantity of chemicals in the brain or other organs.
Last reviewed on 10/21/2008
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