Alzheimer’s Disease Diagnosis Not Precise
By Richard C. Senelick, M.D. via Huffington Post
Alzheimer’s disease (AD), the most common form of dementia, is defined by progressive memory loss and the loss of other intellectual abilities that are serious enough to interfere with daily life. It is a common problem, and your chance of developing AD doubles every five years after the age of 65. Inside your brain, a protein called amyloid beta peptide accumulates around the nerve cells inside your brain — as early as 10 or 20 years before you have symptoms — and causes them to malfunction and die.
A great deal of research is directed toward identifying the amyloid protein in the brain and toward treatments to both prevent its deposition and remove amyloid that has already been deposited in the brain. This is important, because when the day arrives that we have effective methods to both prevent and treat Alzheimer’s disease, we will want to be able to identify, as early as possible, which individuals are going to develop AD.
As we age, memory loss is common and our concerns over developing Alzheimer’s disease (AD) are right up there with cancer. It may seem like we are desperate for a test to identify Alzheimer’s disease. A recent study, for example, claimed the distance from which you could smell peanut butter was a predictor of Alzheimer’s disease. They didn’t specify crunchy vs. smooth! The website “23 and Me” offers to not only tell you who your ancestors were, but for $99 they will also test your DNA and tell you if you are at risk for Alzheimer’s disease.
In addition, the FDA recently approved Vizamyl, a second radioactive diagnostic drug for “use with positron emission tomography (PET) imaging of the brain in adults being evaluated for Alzheimer’s disease and dementia.” The question is whether these tests are ready for “prime time” and use by physicians and the general public. CMS (The Centers for Medicare and Medicaid) has already denied payment (that is, access) to the first PET radioactive compound, Amyvid, on the basis that PET scans for Alzheimer’s disease will only be approved in a research setting and do not currently improve health outcomes. They may be right.
Who would want to be tested for Alzheimer’s disease? There is the woman whose mother and father both died of Alzheimer’s disease and who wants to know if she is at a high risk to develop the disease. A 65-year-old man may be worried about whether his memory loss is just a part of normal aging or whether he has early Alzheimer’s disease. He would like an answer so he can better plan his future. Do the current tests provide accurate information to assist these two individuals and their physicians to make intelligent predictions?
The PET Scan
A PET scan is different than an MRI scan. A radioactive “tracer” is injected in a vein, and, depending on the tracer, the scan looks at different ways in which the brain works. It may look at how the brain consumes oxygen or glucose, or how blood flows to the different parts of the brain. When testing for Alzheimer’s disease, the PET scan uses a tracer (Amyvid, Vizamyl) that identifies amyloid in the brain. The radioactive material attaches to the amyloid and the PET scanner produces elegant, full-color pictures of the brain. But, what does it mean if you have amyloid in your brain? Does it mean that you already have or that you will get Alzheimer’s disease?
The problem is that PET scans in older people routinely find amyloid protein in 30-40 percent of cognitively intact older people. Even if you already have mild cognitive impairment (MCI) there is only a 60 percent chance that you will have amyloid in your brain, and even if you do, that does not guarantee that you will go on to get Alzheimer’s disease. The good news — a negative scan means that there are few or no amyloid deposits in your brain and the likelihood of cognitive impairment is low. That is of course good news, but again doesn’t guarantee that you will not develop AD. The problem is that if you are cognitively normal, but still test positive for amyloid in your brain, we do not know how to accurately determine your risk of developing Alzheimer’s disease. The scan may provide you with information that will cause you to worry unnecessarily. It is for these reasons that CMS has restricted routine reimbursement for research studies. An amyloid PET scan alone just doesn’t help either of our two anxious patients.
Genetic Causes Some Cases
What about genetic testing? Should you order a kit online and send a swab that not only tells you how many of your relatives came from Scotland, but claims to tell you your risk of getting dementia? The role of genetics in AD is complicated and involves the new and exciting field of epigenetics. In brief, epigenetics is the analysis of how factors in the environment, like food, chemicals, or where you spent your childhood may interact with our genes to cause a disease. Two people may have the same gene, but only one, because of this interaction, may go on to develop a disease like Alzheimer’s.
There are different genes that are associated with the risk of developing AD. Some (PSEN1, PSEN2, APP) are associated with early-onset AD, before the age of 65 years, while the more common form of late onset AD is associated with the APOE4 gene. This is the gene that commercial companies most commonly test. The problem is, if you do test positive for the APOE4 gene, you may be more likely to get AD, but no one can tell you how much more likely or if you will get the disease. The results of the testing can be confusing and do not really supply you with any useful information on how to plan your future. Genetic testing will get there, but it isn’t there yet. Although there are healthcare professionals would argue that testing is at a point where it can help confirm AD, I believe that testing for Alzheimer’s has not reached a point where it should be routinely used by the average practicing physician or their patients. You are just as likely to get information that will confuse or worry you rather than help you make an intelligent decision about your future. We need to continue to perform research on testing because it will be every important when we have drugs that capable of preventing or modifying the course of AD.
So, what can you do if you are worried about your cognitive abilities or chances of developing AD? There are numerous articles, books, and blog posts that claim to have the answers on how to prevent or improve cognitive decline. For reasons noted in the post by Carol Steinberg, the president of the Alzheimer’s Foundation of America, it is important to know if you have AD, but scans and genetic testing ahead of your diagnosis are still not the answer. The jury is still out on all these approaches and we are still awaiting a medication or approach that will modify the course of Alzheimer’s disease. I can already hear the outcry from those who support one approach or another, but I await the science to support their claims.
What we do know is that, “if it is good for the heart, then it is good for the brain.” Follow a healthy diet, exercise, control your cholesterol and blood pressure, don’t smoke, and stay cognitively and socially involved with your environment. Alzheimer’s is still a clinical diagnosis and not one that can be made solely on the basis of scans and genetic testing. The tests supply useful information to the informed physician. For now, seek out the help of a neurologist who is interested in dementia. He should be able to rule out other causes of cognitive decline like depression, medications, sleep and vascular causes, while guiding you through the maze of potential. With all this information in hand, together you can plot a course of action. Alzheimer’s disease is not a diagnosis that is made all at once, but instead is more likely to become apparent over time.