January 27, 2010
An imaging agent called Pittsburgh compound B may allow doctors to detect Alzheimer's at very early stages, before memory loss and other symptoms become evident, a new study suggests. An early test for Alzheimer's is important because it would allow doctors to identify those at high risk for the disease and develop new medications that might stop the disease from progressing.
The agent, a radioactive substance developed by researchers at the University of Pittsburgh, has been extensively studied in recent years as a possible early marker for Alzheimer's. Researchers now believe that Alzheimer's causes brain damage for many years, and even decades, before symptoms like memory loss emerge. Autopsies have confirmed that many seniors have the hallmark plaques and tangles of Alzheimer's in their brains, even though they may be relatively symptom free.
"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 wrote 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."
In the current study, researchers at Washington University in St. Louis looked at the brains of 159 seniors, most in their early 70s, who were mentally sharp. All were given injections of Pittsburgh compound B, which enters the bloodstream and attaches to the brain, followed by specialized PET brain scans.
During a follow-up period of from one to five years, Alzheimer's specialists determined that 23 had developed symptoms suggestive of early Alzheimer's or other forms of dementia. They found that those who had the most brain plaques highlighted by Pittsburgh compound B while still symptom-free were most likely to progress to Alzheimer's.
In addition to imaging agents like Pittsburgh compound B, doctors are also looking for other early markers of Alzheimer's disease. Some look at chemicals in the cerebrospinal fluid, which bathes the brain and spinal chord, for proteins that may be an Alzheimer's "fingerprint." In another recent study, doctors identified a hormone called leptin, made by fat cells, that may be an early marker for Alzheimer's.
Currently, Alzheimer's disease can be diagnosed with certainty only on autopsy, when doctors examine the brain. The development of a test that could diagnose the disease earlier would be valuable because doctors might be able to develop drugs to slow progression of the disease, at a time when brain damage has not yet reached a sufficient level to cause cognitive impairment. Current drugs to treat Alzheimer's may ease symptoms for a time but do not stop the disease's downward progression.
An early diagnostic test would also help researchers to monitor patients who are taking various medications, including experimental drugs. If brain scans showed that deposits of beta-amyloid plaque in the brain were not growing or were receding, it might be a signal that a new Alzheimer's drug was working.
John C. Morris; Catherine M. Roe; Elizabeth A. Grant; et al: "Pittsburgh Compound B Imaging and Prediction of Progression From Cognitive Normality to Symptomatic Alzheimer Disease." Archives of Neurology, Vol. 66, No. 12, December 2009, pages 1469-1475.