Determining whether or not someone has Alzheimer's disease (AD) is not an exact science. However, several tests can help ensure an accurate diagnosis. These include brain imaging, genetic testing, and neuropsychological testing. The tests can also help rule out other possible conditions and diseases. Here is a review of all three:
Types of Brain Imaging
MRI (Magnetic Resonance Imaging)
MRIs take multiple images of the brain using powerful magnets and radio waves. It can help detect cysts, tumors, bleeding, swelling, developmental and structural abnormalities, infections, inflammatory conditions, or problems with the blood vessels.
It is a pain-free, noninvasive procedure, and takes more than an hour. You lie down on a table that slides into the MRI machine. You may be given a contrast dye (usually injected into your arm) to enhance the images. You sometimes wear a hospital gown. You will have to remove all metallic objects, such as jewelry, eyeglasses, watches, hairpins, and zippers. In terms of preparation, you may be asked to fast (not eat or drink anything) for four to six hours prior to the MRI.
Three Important Caveats:
1) If you are uncomfortable in small spaces—or have claustrophobia—be sure to let the doctor know ahead of time. He or she can prescribe medication to help you relax, and/or recommend an "open" MRI, which isn't as visually confining as the standard MRI machine.
2) If you have a cardiac pacemaker, be sure to tell your doctor. People with cardiac pacemakers cannot, under most circumstances, have an MRI and should not enter an MRI area.
3) You may not be able to have an MRI if you have any of the following metallic objects in your body:
- brain aneurysm clips
- certain types of artificial heart valves
- heart defibrillator or pacemaker
- inner ear (cochlear) implants
- recently placed artificial joints
- certain types of vascular stents
CT (Computed Tomography) Scan
A CT scan uses x-ray technology to create multiple images of the brain. It helps detect conditions, such as bleeding in the brain, inflammation, skull fractures, blood clots, strokes, brain tumors, enlarged brain cavities, and other signs of disease.
A CT also is a pain-free and noninvasive test that last a few minutes. Like the MRI, you need only lie down on a table that slides into the CT machine. You have to lie still during the procedure and may have to hold your breath for short periods of time. You may be given a contrast dye (usually injected into your arm) to enhance the images. You may be asked to wear a hospital gown, and remove all metallic objects because x-rays have difficulty passing through metal. In terms of preparation, you may be asked to fast (not eat or drink anything) for four to six hours beforehand.
PET (Positron Emission Tomography) Scan
Unlike MRI and CT scans, which reveal the structure of the brain, a PET scan is an imaging test that can also provide information on how the brain and its tissues function—right down to the cellular level. It's used to detect changes in glucose metabolism, oxygen metabolism, and blood flow, all of which can reveal abnormalities of brain function.
Again, just like the MRI and CT scan, you need only lie down on a table that slides into the PET machine. About an hour prior to the PET, a small amount of radioactive material (called a tracer) is injected into a vein in your arm, or you will inhale it. You may be asked to perform various mental tasks, such as reading or naming letters, as this diagnostic tool allows the doctor to see levels of brain activity. Being required to fast for four to six hours prior to the test is not unusual. This test takes between 30 minutes and two hours, on average.
Research studies have shown that, in some people, amyloid plaque buildup can be detected with PET scan technology even before symptoms are evident. However, it's still unknown if these plaques are risk factors for AD, the result of the disease, or some combination thereof. Thus, using PET scans as an early detection diagnostic tool is still being developed and isn't ready for use by general practice clinicians.
Important Note: If you have diabetes, be sure to share that information with your doctor. Blood sugar or insulin levels may affect the PET scan test results.
Genetic Testing (Blood Tests)
Researchers now know of 10 genes believed to be associated with AD. The most notable is the gene apolipoprotein E (APOE). While genetic blood tests are available, they do not provide a definitive diagnosis. Additionally, having "AD genes" only increases your risk of developing AD; it doesn't mean you have it. And there are people with the "AD genes" who never develop AD. Any genetic testing results that may be obtained independent of medical council should be discussed in context of an individual patient's history and interpreted by a doctor.
Learn more about genetics and AD.
Studies of families with a history of early onset AD have identified defects in three different genes: APP (on chromosome 21), PSEN-1 (on chromosome 14) and PSEN-2 (on chromosome 1). People with mutations on one or more of these genes tend to develop early onset AD—all of which can be detected with a specialized genetic blood test. However, there are people who suffer from early onset AD who don't have mutations in any of these genes.
Additionally, prenatal diagnosis for pregnancies at increased risk for the PSEN1 mutation is possible through amniocentesis. However, this test is unlikely to be performed unless a family member has been diagnosed with the genetic mutation. The presence of a mutation does not guarantee an individual will develop Alzheimer's disease.
The most commonly used neuropsychological test is the Mini-Mental State Exam (MMSE). During the MMSE, you are asked questions and given instructions designed to evaluate your basic mental status. For example, you may be asked today's date and when is your birthday. You may also be asked to repeat a list of words or phrases and to count backwards from 100 by sevens. No advanced preparation is needed for this test.