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This is the second post in a series on Alzheimer’s disease, the most common cause of memory loss and dementia. Part 1 discussed its pathology and stages.
In special circumstances a lumbar puncture can help to confirm Alzheimer’s disease.
Analyzing the levels of beta-amyloid and tau in the spinal fluid can help to confirm that Alzheimer’s is present when the disease is strongly suspected but there is something unusual, such as the individual being younger than age 65. Other things that may make the situation unusual would include early changes in movement or behavior. We don’t use this test routinely both because it is not needed in the majority of individuals when the diagnosis is straightforward, and because the test provides the right answer about 85 to 90% of the time but can be inconclusive or misleading the other 10 to 15% of the time.
A lumbar puncture—more commonly known as a spinal tap—may sound frightening, but it is actually a very safe and simple test that is less painful for most people than having an IV (intravenous line or catheter) placed. If your doctor suggests this test, your loved one would begin by either sitting or lying down on their side with their back to the doctor, and curling into a little ball by bringing their shoulders down and their knees up. The doctor would find the right spot, clean the area well, give them some numbing medicine (like in the dentist’s office), insert a very thin needle, and take a small amount of spinal fluid out.
Amyloid PET scans can confirm Alzheimer’s disease but are not paid for by Medicare or other insurance.
A PET scan is like an ‘inside-out’ X-ray. With an X-ray, the radiation beams go from the transmitter, through your body, and collect on a film or X-ray detector. With an amyloid PET scan, the radiation built into a tiny molecule that is engineered to stick to amyloid plaques. The molecule is injected through an IV in the arm and if there are any amyloid plaques in the brain it will stick to them. The radiation of the molecule sticking to the plaques is then detected on the X-ray detector.
Amyloid PET scans can correctly identify when the plaques of Alzheimer’s disease are present 90 to 95% of the time. Most often, however, the diagnosis of Alzheimer’s is clear and these scans are not needed. As with the lumbar puncture, when circumstances are unusual, they can be helpful. Currently, amyloid PET scans are not paid for by Medicare or other health insurance; if that changes it is likely that these scans will be more widely used in the future.
You may be wondering whether amyloid PET scans would be useful in individuals who are worried about their memory but are not showing any symptoms of memory problems. At present, there are no treatments for individuals who are asymptomatic. For this reason, we do not order amyloid PET scans for individuals without memory problems.
Key Question: My loved one has dementia and we can afford to get one of those amyloid PET scans. Should we just have the doctor order one and not bother with the rest of the evaluation?
A: No. Even if the scan suggests Alzheimer’s disease there could still be many other treatable factors impairing their memory (such as a thyroid disorder, vitamin deficiency, or medication side effect) that can only be identified during the regular evaluation.
© Andrew E. Budson, MD, 2019, all rights reserved.
LinkedIn Image Credit: David Pereiras/Shutterstock
References
Budson AE, O’Connor MK. Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It, New York: Oxford University Press, 2017.
Budson AE, Solomon PR. Memory Loss, Alzheimer’s Disease, & Dementia: A Practical Guide for Clinicians, 2nd Edition, Philadelphia: Elsevier Inc., 2016.
