Alzheimer’s disease is a clinical diagnosis. At this point in time, there is no definitive test to prove that a living patient has Alzheimer’s disease. The disease is usually diagnosed clinically when the physician evaluates the patient’s symptoms and rules out other neurological disorders.
Alzheimer’s disease can only be suspected. It cannot be confirmed until an autopsy is performed. When an autopsy of the brain is performed, and the tissue is examined under the microscope, characteristic plaques and tangles can be observed. These are the classic hallmark signs of Alzheimer’s disease. At this point, a definitive diagnosis can be noted.
Lumbar Puncture
The physician may recommend a lumbar puncture as part of the workup for diagnosis of Alzheimer’s disease. If there are elevated levels of tau and phosphorylated tau within the cerebrospinal fluid, then it is suggestive of Alzheimer’s disease. Amyloid in the CSF is low in suspected Alzheimer’s patients.
Imaging
Imaging studies can be important in the diagnosis process, ecause other medical conditions that may mimic the same signs/symptoms as Alzheimer’s disease must be ruled out before a diagnosis of Alzheimer’s can be made. A specific study called the FDG-PET, with or without amyloid imaging, can be useful for early diagnosis of dementia.
Scans and images are often used to rule out other conditions. These include a Computerized Tomography (CT) scan or a Magnetic Resonance Image (MRI) of the brain. Each test has advantages and disadvantages.
Some of the possible findings on a scan that can lead to memory or cognitive impairment include subdural hemorrhage (bleeding around the brain), tumors, normal pressure hydrocephalus, stroke or even a focused area of loss of brain tissue, which would suggest a diagnosis like frontotemporal dementia.
A CT Scan is done very quickly and is ideal for people who are unable to lie still very long or who have metallic implants, such as certain pacemakers or defibrillators. MRI takes a lot longer and can last up to an hour. MRI can be a claustrophobic experience; and older adults, in particular, may find it too uncomfortable to lie flat for almost an hour.
A medical provider is the ideal person to guide the decision regarding the best test to be done for an individual patient, depending on the individual’s examination findings.
It is important to remember that neither CT scan, nor MRI scans are able to diagnose Alzheimer’s Disease. Rather, they are used to ensure that there are no other causes, and sometimes helpful when there is loss of brain tissue, particularly in the hippocampus. However, the hippocampus shrinks with age, so interpreting findings can be very difficult.
Other types of scans are not used routinely. However, when the diagnosis is in question, the FDG-PET scan can help distinguish Alzheimer’s Disease from other types of dementia, particularly frontotemporal dementia. SPECT scans can also be used, but interpretation can be challenging. In each of these scans, there is low metabolism or low blood flow in specific parts of the brain.
There are newer agents called amyloid PET tracers, developed to help measure how much amyloid a person has. Currently, these are not recommended for the diagnosis of Alzheimer’s Disease. Furthermore, these tracers are not covered by most insurance plans.
Mental Status Exam
There are many tools used to help with the diagnosis, including the Mini Mental Status Examination ™, the Montreal Cognitive Assessment, also known as the MOCA, and more recently the SLUMS or St Louis University Mental Status test. The MOCA and SLUMS can be downloaded and are freely available online. These tests all provide some standardized questions and answers which most people should be able to answer. Of course, there are limitations to every evaluation: if patients are unable to read or write due to being illiterate, blind, deaf or have some other impairment, then the evaluation is very difficult to administer.
Despite the possible barriers, each of these tests have been validated for use in cognitive assessments, and there are cut-off scores that are associated with mild, moderate and severe dementia. These tests are not specific for Alzheimer’s Disease, but rather for dementia.
Neuropsychological testing is a more in-depth test that can be used to evaluate people with memory or other problems. This is particularly helpful to try to establish a baseline for the particular person. A repeat test a year or more later, can guide possible treatment changes. This can also guide recommendations regarding driving and supervision for financial and other tasks.
Blood Work
In addition to memory testing, it is always important to remember that there are other causes for memory loss. Some of these include thyroid disease, syphilis, vitamin B12 deficiency, and human immunodeficiency virus (HIV). These are tested using blood work, and are routinely checked for people with memory loss.
Considering Genes
There is a genetic risk to developing Alzheimer’s disease. Some families carry a specific gene that increases the likelihood that others will develop the disease. It is important to understand that carrying the gene does not mean that the disease will develop with 100% certainty. Testing for the gene is most often limited to very special situations, and not done routinely.
Early-onset Alzheimer’s Disease refers to those people who are diagnosed with Alzheimer’s Disease before the age of 65. While this is rare, it can be caused by a genetic abnormality. The cause is due to mutations in genes that are responsible for the production or breakdown of amyloid.
People who have Down’s Syndrome have a much higher risk for developing Alzheimer’s Disease. Alzheimer’s Disease develops at a much earlier age in such patients, not uncommonly in their twenties and thirties.
Brain Changes in Alzheimer’s Disease
Although the first description of the abnormal findings in the brain by Dr. Alzheimer was more than a century ago, we continue to see the changes that he first reported. This includes plaques and tangles (tau protein). While these changes are microscopic, the brain becomes smaller and shrinks in people with Alzheimer’s disease, such that the normal brain is much larger than the brain of a person with Alzheimer’s disease.
Microscope
The ultimate test that confirms the diagnosis of Alzheimer’s Disease is looking at the brain under the microscope. Since most patients still need their brains, this is only done after death should the family and patient wish to have confirmation of the diagnosis or donate their brain to further the study of this terrible condition. Most medical schools offer a brain bank or can connect patients to a brain bank, should this be of interest. This should be planned of time, so that arrangements can be made well ahead of time.
