Tests and diagnosis
By Mayo Clinic staff
There’s no specific test today that confirms you have Alzheimer’s disease. Your doctor will make a judgment about whether Alzheimer’s is the most likely cause of your symptoms based on the information you provide and results of various tests that can help clarify the diagnosis.
Doctors can nearly always determine whether you have dementia, and they can accurately identify whether your dementia is due to Alzheimer’s disease about 90 percent of the time. Alzheimer’s disease can be diagnosed with complete accuracy only after death, when microscopic examination of the brain reveals the characteristic plaques and tangles.
To help distinguish Alzheimer’s disease from other causes of memory loss, doctors now typically rely on the following types of tests.
Physical and neurological exam
Your doctor will perform a physical exam, and is likely to check your overall neurological health by testing your:
• Muscle tone and strength
• Ability to get up from a chair and walk across the room
• Sense of touch and sight
Blood tests may help your doctor rule out other potential causes of memory loss and confusion, such as thyroid disorders or vitamin deficiencies.
Mental status testing
Your doctor may conduct a brief mental status test to assess your memory and other thinking skills. Short forms of mental status testing can be done in about 10 minutes. Commonly used tests include the following tasks and questions:
• Draw a clock face with the hands showing a time specified by the examiner.
• Name today’s date and your location.
• Copy a design, such as two intersecting pentagons.
• Follow a three-step command.
• Remember a list of three words spoken to you by the examiner.
• Follow a written instruction.
• Write down a complete sentence.
• Count backward from 100 by sevens.
Your doctor may recommend a more extensive assessment of your thinking and memory. Longer forms of neuropsychological testing, which can take several hours to complete, may provide additional details about your mental function compared with others’ of a similar age and education level. This type of testing may be especially helpful if your doctor thinks you may have a very early stage of Alzheimer’s disease or another dementia. These tests may also help identify patterns of change associated with different types of dementia.
Images of the brain are now used chiefly to pinpoint visible abnormalities related to conditions other than Alzheimer’s disease — such as strokes, trauma or tumors — that may cause cognitive change. New imaging applications — currently used primarily in major medical centers or in clinical trials — may enable doctors to detect specific brain changes caused by Alzheimer’s.
Brain-imaging technologies include:
• Computerized tomography (CT). For a CT scan, you’ll lie on a narrow table that slides into a small chamber. X-rays pass through your body from various angles, and a computer uses this information to create cross-sectional images, or slices, of your brain. This test is painless and takes about 20 minutes. It’s currently used chiefly to rule out tumors, strokes and head injuries.
• Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to produce detailed images of your brain. You lie on a narrow table that slides into a tube-shaped MRI machine, which makes loud banging noises while it produces images. The entire procedure can take an hour or more. MRIs are painless, but some people feel claustrophobic inside the machine and are disturbed by the noise. MRIs are currently used primarily to rule out other conditions that may account for cognitive symptoms. In the future, they may be used to measure the volume of your brain tissue and whether shrinkage in brain regions implicated in Alzheimer’s disease has occurred.
• Positron emission tomography (PET). During a PET scan, you’ll be injected in a vein with a low-level radioactive tracer. You’ll lie on a table while an overhead scanner tracks the tracer’s flow through your brain. The tracer may be a special form of glucose (sugar) that shows overall activity in various brain regions. This can show which parts of your brain aren’t functioning well. New PET techniques may be able to detect your brain level of plaques — one hallmark abnormality linked to Alzheimer’s.
Future diagnostic tools
Researchers are working with doctors to develop new diagnostic tools to help clinch the diagnosis of Alzheimer’s. Another important goal is to detect the disease before it causes the symptoms targeted by current diagnostic techniques — at the stage when Alzheimer’s may be most treatable as new drugs are discovered. New tools under investigation include:
• Additional approaches to brain imaging
• Measuring levels of key proteins or protein patterns in blood or spinal fluid
• More-sensitive mental status tests
Reprinted with permission of Mayo Foundation for Medical Education and Research. All rights reserved.
Getting to Know Alzheimer’s: 12 Things You Must Know
What is Alzheimer’s? Part 1: Definition
How Can I Tell if it is Alzheimer’s? Part 2: Symptoms
How Does Alzheimer’s Affect the Brain? Part 3: Causes
How do You Get Alzheimer’s? Part 4: Risk Factors
What Other Risks Does Alzheimer’s Pose? Part 5: Complications
What Should I Know Before I See My Doctor About Alzheimer’s? Part 6: Preparing for your appointment