Diagnosis of Alzheimer's Disease

A detailed history of the symptoms and how they evolved is crucial to arriving at a correct diagnosis. There are a number of different late-life illnesses that cause dementia.

Often, one of the best clues to an individual's illness is the nature of the earliest changes observed by the family. It is very important for a knowledgeable family member to accompany the patient in order to provide this critical information.

It is also important to obtain information about any other medical problems that may be present, current medications used and whether there is a family history of a similar problem with memory and thinking. Both a physical and a neurologic exam are necessary to look for conditions that could produce a dementia syndrome (a condition of deteriorated mentality) or worsen the expression of Alzheimer's disease.

In addition, a "mental status" assessment should be done to determine the memory, language and other cognitive abilities of the patient.

Laboratory Studies
Other than identifying the presence of one of the gene mutations know to cause Alzheimer's disease, there are no laboratory tests that can be used to diagnosis Alzheimer's disease with complete certainty.

However, as we learn more, Alzheimer's disease is moving from a diagnosis of exclusion; (a diagnosis made in the presence of an appropriate clinical picture and in the absence of an alternative explanation) to a "diagnosis of inclusion" (a diagnosis made in the presence of both an appropriate clinical picture and specific disease related abnormalities on selected laboratory tests).

Some of these tests are only available at centers that specialize in the evaluation of patients with memory loss and dementia.

Blood Studies
Most physicians obtain a complete set of routine blood studies. This may include those needed to assess thyroid function and other conditions deemed relevant by the evaluating physician.

Spinal Fluid
The spinal fluid of many patients with Alzheimer's disease contains altered levels of two proteins; both suggest the presence of Alzheimer's disease. However, not all patients have these changes and patients with other neurologic problems that may mimic Alzheimer's disease can also have alterations in these two proteins. Therefore, using the existence of these two altered proteins to diagnose Alzheimer's disease may be limited to those centers that have experience in interpreting the results.

X-rays and Oher Imaging Studies
Computed Tomography (CT scans) and Magnetic Resonance Imaging (MRI scans) provide pictures of brain structure and one or the other is routinely used in the evaluation of a patient with symptoms of dementia. They are very good at identifying conditions such as strokes, subdural hematomas and tumors that alter brain anatomy. However, the changes in brain anatomy produced by Alzheimer's disease are often difficult to distinguish from normal age-related changes. Therefore, specialty centers have recently begun to modify the way these studies are done and the techniques used to evaluate the images so they can obtain specific quantitative information about the areas of the brain most affected by Alzheimer's disease.

Single Positron Computed Tomography (SPECT) scans provide information about blood flow in the brain and are used as an indirect measure of brain cell health. The clinician looks for patterns of decreased blood flow that match the areas of the brain known most often to be affected by Alzheimer's disease. Because this is an indirect measure of brain function and because other dementing illnesses can alter blood flow, the test often is not diagnostically definitive. Nevertheless, it may provide information that is very useful to the physician.

Positron Emission Tomography (PET) scans provide a direct indication of the health of brain cells. PET scans are not widely available and many clinicians regard them as a research tool when used in the evaluation of patients with dementia.