Alzheimer's, Dementia & Mental Health
Study Says Early Alzheimer’s Disease Detected by
Imaging Test Predicts Full Disease
Did not predict those that developed dementia not
caused by Alzheimer's disease
Dec.
14, 2009 - A new study of senior citizens appears to confirm that “early
Alzheimer's disease” detected by a compound that binds to brain plaques
is likely to progress into regular Alzheimer's disease with dementia,
according to a report in the December issue of Archives of Neurology,
one of the JAMA/Archives journals.
"The concept of preclinical Alzheimer's disease
holds that the Alzheimer's pathologic process operates for many years
before producing a clinically detectable impairment," the authors write
as background information in the article.
"A key corollary of this concept is that
preclinical Alzheimer's disease is not benign and will eventually
produce sufficient synaptic and neuronal damage to cause cognitive
decline and other symptoms of Alzheimer's disease."
Support for the existence of preclinical
Alzheimer's disease comes from autopsies of cognitively normal older
adults, many of whom have the brain plaques, tangles and deposits of a
substance known as beta-amyloid that are characteristics of Alzheimer's
disease.
Preclinical Alzheimer's disease can be detected by
screening an individual's cerebrospinal fluid for biomarkers of the
condition.
In addition, imaging with positron emission
tomography (PET) using a compound known as Pittsburgh Compound B (PiB),
which binds to beta-amyloid, can detect deposits of the substance in
living patients.
John C. Morris, M.D., and colleagues at Washington
University, St. Louis, assessed 159 older adults (average age 71.5) who
had undergone PET scans using PiB and did not have symptoms of dementia.
These patients were followed for between 0.8 and
5.5 years after having the scan and underwent between two and six
assessments for dementia during that timeframe.
A total of 23 participants progressed to clinically
detectable dementia during follow-up, and nine were diagnosed with
dementia of the Alzheimer type.
These diagnoses were made by specialist clinicians
who diagnosed the condition at an earlier stage than typically occurs
and corroborated the diagnosis by declines in multiple cognitive domains
as well as a loss of volume in certain areas of the brain.
The PiB imaging identified individuals who would
develop Alzheimer's disease-related dementia - those in whom the
compound bound to more beta-amyloid plaques were more likely to develop
this condition. However, it did not predict which individuals would
develop dementia not caused by Alzheimer's disease.
"Many more individuals, studied for longer
intervals and ideally through autopsy, will be needed to confirm or
refute our observations," the authors write.
"Nonetheless, this study provides support for the
premise that preclinical Alzheimer's disease, detected either by the
cerebrospinal fluid signature for Alzheimer's disease or here by
elevated PiB retention, predicts symptomatic Alzheimer's disease."
Editor's Note: This study was supported by grants
from the National Institute on Aging, an anonymous foundation and the
Charles and Joanne Knight Alzheimer's Research Initiative.
