For nearly a century, Alzheimer's
destructive path in the brain could be seen only by directly examining the
tissue during an autopsy after the patient died. Consequently, a diagnosis of
Alzheimer's disease has been, and continues to be, based on results from a
comprehensive evaluation that typically includes a medical history, a mental
status evaluation, a clinical examination and laboratory tests.
Last year, the U.S. Food and Drug
Administration (FDA) approved a new radioactive dye (Florbetapir F 18 Injection,
Amyvid) that, when used during positron emission tomography (PET), enables
doctors to spot telltale signs of Alzheimer's while the patient is still alive.
But spotting signs of Alzheimer's disease and making an accurate diagnosis are
two different things. And while the Amyvid scan is a major step forward,
researchers have yet to find the Holy Grail. In the meantime, here are answers
to questions you may have about this important tool.
How is the test performed and what does it reveal?
Amyvid is a radioactive dye that is
injected into a vein prior to a PET scan. From there, the dye travels through
the bloodstream and into the brain, where it binds to amyloid plaques. These
plaques are abnormal clumps of brain cells mixed with beta-amyloid protein - a
type of protein that forms in some people, including individuals with
Alzheimer's disease. The PET scanner produces three-dimensional images of the
brain that show how much plaque is present and where it is located. The results
of the scan are graded as positive or negative.
Should everyone suspected of having Alzheimer's have a scan?
No. While Amyvid is approved for use
in adults who are being evaluated for Alzheimer's disease and other causes of
cognitive decline, most of the time, the doctor can make an accurate diagnosis
without the additional information provided by the scan. The test is likely to
be most useful in difficult cases, such as in younger patients with dementia or
in patients with dementia that is rapidly progressing.
A word of caution
A number of Alzheimer's disease
experts have expressed concern that disreputable companies may begin offering
Amyvid scans (or scans using other agents that may gain FDA approval in the
future). Be wary of any providers claiming that they can diagnose Alzheimer's
or predict one's risk of developing it or determine a person's prognosis based
on scan results. Also, be sure that the radiologist who interprets the findings
has successfully completed the Amyvid reader training program developed by the
product's manufacturer, Avid Radiopharmaceuticals.
(Source: John Hopkins Health Alerts, 27 May 2013)
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