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Diagnosis of Alzheimer's Disease - Imaging Procedures and Psychological Evaluation

Carrie Steckl, Ph.D., edited by Natalie Staats Reiss, Ph.D.

Imaging procedures

These are a group of non-invasive (i.e., no surgery is required) tests that provide information about the shape, size, and health of brain structures, as well as how well the brain functions during activities. A CT scan (computerized tomography), and/or a MRI (magnetic resonance imaging) scan are used to look for brain tumors, blood clots, strokes, normal pressure hydrocephalus, or other abnormalities that might account for Alzheimer's-like symptoms. A PET scan (positron emission tomography), or SPECT scan (single photon emission computed tomography) can show more detailed information which doctors can use to confirm a diagnosis of AD. Each procedure is either done in a hospital or a clinic that specializes in imaging.

A CT scan produces a clear, two-dimensional image of the brain, and is used to detect brain tumors, blood clots, strokes, or damage due to head injury. CT scans are painless, but they may be frightening to people who are claustrophobic (afraid of small, enclosed spaces). The 20-minute procedure involves lying on a special table that is inserted into a chamber where the pictures are taken.

An MRI uses computer-generated radio waves and a strong magnetic field to produce a detailed image of the brain. MRIs are helpful in diagnosing tumors, infections, inflammation, and damage due to head injury. Similar to the CT procedure, an MRI requires the patient to lie on a table that is slid into a tube that houses the equipment which takes the images. Again, people who are uncomfortable in small, enclosed spaces, or who are obese may be uneasy with this procedure. Also, because of the strong magnetic field involved, individuals with medical implants such as pacemakers should avoid this procedure. MRIs take up to an hour to complete and produce both two-dimensional and three-dimensional images.

A PET scan provides both two- and three-dimensional pictures of brain activity by measuring radioactive isotopes (elements that attach to chemicals that flow through the brain) that are injected into the bloodstream. PET scans are used to detect tumors and damaged tissue, measure metabolism (chemical reactions that are the basis of brain function), and view blood flow in the brain. PET scans are often used as a follow-up to CT scans or MRIs in order to better understand what is happening in a certain part of the brain. After the isotope is injected into the bloodstream, the patient lies still while overhead sensors register the isotope's activity. The collected information is processed by a computer and displayed on a monitor or film. The length of time to complete a PET scan varies depending on the reason for the test (that is, what conditions are being evaluated).

A SPECT scan integrates two technologies: CT scan and an injection of a radioactive material or tracer (similar to a PET scan procedure) to view how blood flows through arteries and veins in the brain. Two-dimensional or three-dimensional pictures can be produced that show areas of the brain that have reduced blood flow (areas of injury). The test differs from a PET scan because the chemical stays in your blood stream (rather than being absorbed by surrounding tissues). SPECT scans are cheaper and more readily available than PET scans.

Psychological/Psychiatric Evaluation

This is a collection of procedures that are used to obtain detailed information about past and current mood, thinking, or behavioral problems. The person with suspected Alzheimer's symptoms and the primary caregiver should be interviewed separately in order to gain a complete picture of what is going on. This "double interview" technique is particularly important when a person's memory for past and present information is impaired, because he or she may inadvertently provide inaccurate information during the interview. This evaluation should include an assessment for anxiety and depression, which can create Alzheimer's-like symptoms in older people, as well as occur concurrently with Alzheimer's or another form of dementia. Depression, in particular, can result in a reversible set of symptoms collectively known as pseudodementia (described in more detail below).

The following tests may be used in a psychological/psychiatric evaluation:

The Geriatric Depression Scale (GDS) - The GDS is a screening instrument used to detect depression among older adults. Clinicians may use it to help determine whether someone is depressed (and doesn't have AD), or if depression coexists with Alzheimer's or another form of dementia. Results from the GDS are interpreted in the context of the other information collected about the person. For example, people with depression often complains about memory problems and is upset about them, while individuals with dementia will often deny memory problems or minimize their importance. Also, depressed people are less likely to exhibit large mood swings, remaining "down in the dumps" most of the time (except when they have bipolar disorder, a shift in moods from extreme highs to extreme lows). On the other hand, people with dementia usually show a range of emotions, and sometimes respond with an inappropriate emotion (e.g., laughing while others are sad). If a mood disorder such as depression is detected, it can be treated alongside other disorders, such as Alzheimer's. Generally speaking, high scores on the GDS suggest that people are experiencing depressive symptoms.

Mental status exam - Mental status exams assess memory, concentration, and other cognitive skills. The most frequently used mental status exam is called the Mini-Mental State Exam (MMSE), a research-based set of questions that results in a score representing a person's general level of cognitive functioning.

The MMSE is generally a reliable and valid indicator of cognitive impairment that can correctly distinguish between individuals with dementia, individuals with pseudodementia due to depression, and individuals with depression and no cognitive impairment. However, the test must be used with caution in certain groups of people. For example, highly educated people frequently score high on the MMSE, even if they have Alzheimer's Disease. Similarly, people with less than an eighth grade education or whose first language is not English often score poorly on the MMSE, even though they may not have cognitive impairment.

The MMSE takes only 5 - 10 minutes to administer and taps five areas of cognitive functioning: Orientation (the current year, the season, date, day, month, state, county, town, location); Short-term memory/retention (the ability to repeat the names of three common objects, e.g., apple, table, penny); Attention/calculation (counting backwards from 100 by 7s, or spelling the word "world" backwards); Memory/recall (the ability to repeat the three objects named during the short term task); Language (the ability to name common objects, repeat a simple sentence, follow a three-step spoken command, and follow a printed direction); and Visuospatial skills (the ability to copy a simple geometric design).

The maximum score on the MMSE is 30. In general, scores of 24 or more are considered within the "normal" range of cognitive functioning; scores between 20 and 23 are suggestive of mild cognitive impairment or possible early-stage Alzheimer's Disease; scores between 10 and 19 are associated with middle-stage Alzheimer's; and a score of 9 or less is considered consistent with severe or late-stage Alzheimer's Disease.

Although the MMSE is a useful screening tool, test results should not be the only information used to make a diagnosis. In other words, a person's MMSE score can indicate a need for concern, and additional testing and follow-up.