Diagnosing Alzheimer's Disease
According to the National Alzheimer's Association, there is currently no single diagnostic test that can detect if a person has Alzheimer's disease (AD). However, new diagnostic tools and criteria make it possible for a physician to make a positive clinical diagnosis of AD with an accuracy of 85-90%.
The diagnostic process generally takes more than one day and will involve the primary care physician and possibly other specialty physicians, such as a psychiatrist or neurologist. Here are the steps to diagnosing Alzheimer's disease:
- A complete medical history -- includes patient's current mental or physical conditions, prescription drug intake, and family history of health problems.
- A mental status evaluation -- assesses a person's sense of time and space, and his or her ability to remember, understand, talk, and do simple calculations. The person may be asked, "What year is it?" "Who is the president of the United States?" The person may also be asked to complete mental exercises, such as writing a sentence or spelling a word backwards.
- A physical examination -- includes evaluation of a person's nutritional status, blood pressure, and pulse. These tests are done to rule out other potential causes of dementia, such as cardiac, respiratory, liver, kidney, or thyroid disease, and atherosclerosis.
- A neurological examination -- tests the nervous system (brain and spinal cord) for evidence of other neurological disorders, such as stroke, Parkinson's disease, brain tumor, or hydrocephalus (excess fluid in the brain), that may cause dementia-like symptoms.* In this part of the exam, physicians evaluate coordination, muscle tone and strength, eye movement, speech, and sensory abilities.
- Laboratory tests - a variety of laboratory tests may be ordered to rule out other disorders that may be causing dementia. Blood and urine tests are used to check for anemia, infections, diabetes, kidney and liver disorders, nutritional deficiencies, and abnormally high or low levels of thyroid hormone. Brain imaging techniques, such as a CT scan or MRI, may be ordered to rule out the presence of tumors, stroke, blood clots, or other factors that may be causing memory and thinking problems.
- Psychiatric, psychological, and other evaluations - designed to rule out the presence of other illnesses such as depression, which might cause symptoms similar to those seen in AD. These evaluations test memory, reasoning, writing, vision-motor coordination, the ability to express ideas, and generally provide more in-depth information than the mental status evaluation alone.
There is no one or combination of diagnostic tests that will conclusively result in a diagnosis of AD. The tests will, however, help rule out other possible causes of the dementia-like symptoms. Once testing is completed, the diagnosing physician will review the results of the examinations, laboratory tests, and other consultations to arrive at a diagnosis. If all test results appear to be consistent with Alzheimer's disease, the clinical diagnosis is generally "probable Alzheimer's disease," or "dementia of the Alzheimer type." If the symptoms are not typical, but no other cause is found, the diagnosis may be "possible Alzheimer's disease." A definitive diagnosis of AD can only be obtained upon autopsy of the brain at death.
*Dementias are a variety of syndromes involving loss of cognitive or intellectual functioning such as thinking, remembering and reasoning, so severe that it interferes with an individual's daily functioning. Changes in personality and behavior, and motor impairment are also associated with various dementias.