Diagnosis of Alzheimer's Disease
The diagnosis of Alzheimer's disease involves taking a detailed history of symptoms and ruling out other treatable medical and psychological conditions that cause loss of cognitive function (dementia), such as the following:
- Head trauma
- Infection (e.g., HIV, syphilis)
- Intoxication or withdrawal from medication, poison, or substance of abuse
- Kidney disease
- Liver disease
- Neurodegenerative diseases (e.g., Creutzfeldt-Jakob, Huntington's)
- Seizures (epilepsy)
- Thiamine or vitamin B deficiency
- Thyroid disease
Normal effects of aging must be ruled out as well.
A mental status examination reviews systems of higher mental function. This involves asking questions to evaluate mental functions and making observations of the patient's behavior, appearance, and attitude. Questions are designed to assess orientation, memory, attention and concentration, insight and judgment, general intellectual functions (e.g., calculation; common knowledge, such as What is the capital of the United States?; identifying similarities and differences between words).
Slowly progressive loss of memory and orientation, normal lab test results, and brain imaging scans that show atrophy of the cerebral cortex and hippocampus indicate a diagnosis of Alzheimer's disease.
Diagnostic Tests for Alzheimer's Disease
Routine blood, serum, and plasma analyses can identify the presence of most diseases mentioned. Brain imaging studies are capable of identifying the presence of tumor, head trauma, and neurological conditions.
Magnetic resonance imaging (MRI) , computed tomography (CT), or positive emission tomography (PET) scans show diffuse atrophy of the cerebral cortex and hippocampus in Alzheimer's disease. Neuroimaging may be normal early in the disease.
In April 2012, the U.S. Food and Drug Administration (FDA) approved Florbetapir F 18 Injection (Amyvid) for use with PET imaging in adults being evaluated for Alzheimer's disease. In October 2013, the second drugFlutemetamol F 18 Injection (Vizamyl)was approved for this purpose. These drugs produce images that estimate neuritic plaque density of a certain protein that forms in people with cognitive disorders like Alzheimer's.
If these tests are negative, it indicates no or few amyloid plaques, reducing the likelihood that Alzheimer's disease is present. A positive test, indicated by moderate to frequent plaques, can be consistent with Alzheimer's, other types of cognitive impairment, or normal cognition; the tests are not definitive for Alzheimer's disease.
Amyvid and Vizamyl are radioactive drugs that are administered via intravenous injection. Side effects include headache, muscle and bone pain, nausea, fatigue, increased blood pressure, and others.