The imaging technology known as a PET scan may have promise as a diagnostic tool for Alzheimer’s disease.
In 2005, Medicare decided to cover the cost of a positron emission tomography (PET) scan for the diagnosis of Alzheimer’s disease. A PET scan is a unique imaging test that records organ and tissue function at a cellular level. This allows many health problems to be diagnosed earlier than would be the case with regular x-rays or magnetic resonance imaging (MRI).
An early diagnosis of some conditions often can mean a better outcome. This new Medicare coverage suggests PET scans might be used more widely for the diagnosis of Alzheimer’s disease in the future. Who needs this scan? And what does this mean for the future of Alzheimer’s disease treatment?
PET Scans for Diagnosis of Alzheimer’s Disease
Johns Hopkins psychiatrist Peter V. Rabins, M.D., M.P.H., stresses that a clinical evaluation can diagnose Alzheimer’s disease in the vast majority of cases. For now, Medicare has decided to cover a PET scan for Alzheimer’s disease diagnosis only in one very particular circumstance—when, after a thorough clinical evaluation, the cause of dementia is still uncertain. Dr. Rabins explains, “By this point, the doctor has already ruled out other potential causes of dementia, such as depression, a reaction to a medication, or alcohol abuse, and thoroughly assessed memory, problem-solving skills, and abstract thinking.”
Ways to put PET scan technology to work for Alzheimer’s disease are still being investigated. For instance, it is still unclear whether a PET scan can diagnose Alzheimer’s disease any earlier than a clinical evaluation—in other words, before symptoms begin. Used to confirm an uncertain diagnosis, though, a PET scan can be a useful tool.
Dr. Rabins observes, “An accurate diagnosis is the only way to ensure that people with Alzheimer’s disease receive appropriate treatment with the medications approved to prolong their quality of life and independence.” Furthermore, Dr. Rabins believes that “for people suffering from dementia, having a definitive diagnosis not only leads to better medical treatment for the patient, but also allows the patient and his or her family to make care-giving decisions with the understanding that Alzheimer’s disease worsens over time.”
If a PET scan is warranted, a major limitation is the cost, which ranges from $1,500 to $3,000. Many private insurance companies don’t cover this cost for Alzheimer’s disease diagnosis so the patient and family will need to weigh whether the additional information that a PET scan may provide is worth this cost.
The Procedure: Getting a PET Scan
First, patients are injected with tiny particles of a radioactive substance that are attached to glucose, the body’s primary source of fuel. This permits an assessment of the ability of cells to metabolize, or work. Patients lie very still on an examination table and are then moved into the center of the PET scanner.
The scanner records emissions given off by the radioactive particles as they are absorbed by tissues and organs that use glucose for energy. These emissions appear on screen as color images that indicate how well organs and tissues are functioning. For example, regions of reduced brain activity in patients with Alzheimer’s disease absorb less glucose and therefore produce fewer emissions. The scan lasts about 45 minutes and is not painful. The radioactive substance is harmless and gets flushed through the body in about a day.
When Is a PET Scan Useful For a Diagnosis of Alzheimer’s Disease?
Certainly, a PET scan is not necessary for anyone without symptoms of Alzheimer’s disease (memory loss, confusion, disorientation, difficulty performing routine activities like eating and bathing, and difficulty recognizing familiar people) and would not add any information if the clinician believes the diagnosis is highly likely. But in the future, improved PET scan methods may detect disease before it significantly impairs functioning or may identify which medications or other therapies are likely to benefit an individual.
“We are on the verge of discovering ways to modify the risk of developing Alzheimer’s disease with diet changes, mental and physical activity, and medical treatments. Knowing when we should recommend these approaches will help us ensure that those who can benefit will,” Dr. Rabins adds.
PET scanning techniques continue to improve and there is a good chance that someday a PET scanner will be able to predict who is at risk for Alzheimer’s disease even before symptoms start, much like a blood cholesterol test can determine who is at risk for coronary heart disease or stroke.
“If someday we can prevent anyone from developing this Alzheimer’s disease,” Dr. Rabins hopes, “then knowing who is at risk will be very important.” Right now, though, a PET scan is only needed in the rarest of circumstances for people with symptoms of dementia.
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Posted in Memory on June 10, 2008
