Alzheimer’s Disease: Overview of Diagnostic Tests
What tests are used to diagnose Alzheimer’s disease?
With thorough testing and a "process of elimination," doctors today can diagnose probable Alzheimer’s disease with almost 90% accuracy. Alzheimer’s disease cannot be definitely diagnosed until after death, when the brain can be closely examined for certain microscopic changes caused by the disease.
The following diagnostic tools might be used to help make a diagnosis of Alzheimer’s disease:
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:
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 examination of the following:
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. Blood tests also might be used to look for the presence of a specific gene that has been identified as a risk factor for Alzheimer’s disease. 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 might be used by the doctor to help rule out other disorders that might be causing symptoms similar to those of Alzheimer’s disease.
Lumbar puncture/spinal tap
A lumbar puncture, also called a spinal tap, is a procedure in which the fluid surrounding the spinal cord (called the cerebrospinal fluid or CSF) is withdrawn through a needle and examined in a laboratory. Testing the CSF can help your doctor diagnose disorders of the central nervous system (including multiple sclerosis) that may involve the brain, spinal cord, or their coverings (meninges).
Computed tomography (CT) scan
A computed tomography (CT) scan is a technique in which multiple X-rays of the body are taken from different angles in a very short period of time. These images are then fed into a computer, which creates a series of cross-sectional "slices" of the body. Contrast material can be given to help differentiate abnormal areas of the brain. 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)
Magnetic resonance imaging (MRI) is 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 might help to show the physical and functional changes in the brain that are associated with Alzheimer’s disease.
Electroencephalography (EEG) is 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 non-invasive procedure—meaning that nothing is inserted into the body. EEGs 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 non-invasive 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.
Electrocardiogram (ECG or EKG)
An electrocardiogram (EKG or ECG) is 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 are routinely done if a heart condition is suspected. This test might be used by the doctor to help rule out other disorders that might be causing symptoms similar to those of Alzheimer’s disease.
Neuropsychological testing 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 might include tests to assess attention, memory, language, 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.
In addition, the following tests also might be done to help diagnose and monitor the progression of Alzheimer’s disease:
Positron emission tomography (PET) scan
PET scanning is a three-dimensional imaging technique, utilizing the injection of a radioactive tracer that allows a doctor to examine the heart, brain, or other internal organs. PET scans can also show how the organs are functioning; unlike X-ray, CT, or MRI, which show only body structure. PET is particularly useful for the detection of cancer and coronary artery disease, and 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, Huntington's, and Parkinson's. PET scans can show the difference in brain activity between a normal brain and one affected by Alzheimer’s disease. It can also help differentiate Alzheimer's disease from other forms of dementia. Amyloid imaging is a special type of PET scanning which shows deposits of amyloid, a protein, in the brain.
Single photon emission computed tomography (SPECT) scan
SPECT is a non-invasive 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 might reveal abnormalities that are characteristic of Alzheimer's disease. Dopamine transporter SPECT is a special type of SPECT used in Parkinson’s disease and Lewy body dementia.
Magnetic resonance spectroscopy imaging (MRSI)
MRSI is a test that allows the doctor to observe certain substances throughout the brain without the use of radioactive materials. MRSI is a non-invasive 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.
National Institute on Aging: Alzheimer’s Disease Education and Referral Center. Diagnosis. www.nia.nih.gov/Alzheimers/AlzheimersInformation/Diagnosis/ Accessed 8/22/2011
Alzheimer’s Association. Diagnosing Alzheimer’s www.alz.org/alzheimers_disease_diagnosis.asp Accessed 8/22/2011
Alzheimer’s Foundation of America. About Alzheimer’s: Diagnosis www.alzfdn.org/AboutAlzheimers/diagnosis.html Accessed 8/22/2011
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