Imaging Detects Alzheimer’s Before Onset of Cognitive Decline

PET imaging combined with specific imaging agents detects beta amyloid in the brain, showing its presence may precede mild cognitive decline, allowing for earlier diagnosis of Alzheimer’s disease, said authors of several studies presented at the Society of Nuclear Medicine’s 2012 Annual Meeting, in Miami Beach, Fla.

"Diagnosis of Alzheimer's disease can now be made when the patient first presents symptoms and still has largely preserved mental function," said Christopher Rowe, MD, a lead investigator for the Australian Imaging, Biomarkers and Lifestyle study of aging and professor of nuclear medicine at Austin Hospital in Melbourne, Australia. "Previously there was an average delay of three years between consulting a doctor over memory concerns and the diagnosis of Alzheimer's, as the diagnosis required the presence of dementia."

In one study of 45 patients, researchers found that patients with high levels of F-18 florbetaben binding during imaging and atrophy of the hippocampus had an 80 percent chance of developing Alzheimer’s disease over the following two years.

A second reported study looked at 194 healthy subjects, along with 92 people with mild cognitive impairment and 70 people with Alzheimer’s disease. Using a different imaging agent, C-11 PiB, with PET to gauge amyloid burden in the brain, the researchers found that widespread amyloid plaque build-up preceded cognitive impairment, and those with extensive amyloid burden had a higher risk of cognitive decline.

Another similar study looked at 137 adults, ages 30 to 89, who had normal cognitive function. They underwent PET with F-18 florbetapir for researchers to explore how amyloid build-up affects connections in specific areas of the brain involved in cognition. It was found that those with an increased amyloid burden in these networks, namely the default mode and salience networks, were prone to impaired cognitive impairment.

Finally, in a fourth reported study, PET imaging agent C-11 PiB was assessed for its ability to detect amyloid plaque in comparison with the imaging agent 18-F fluorodeoxyglucose (F-18 FDG), which acts like glucose, to map out the metabolic functioning of the brain.
The researchers found that C-11 PiB amyloid imaging was superior in evaluating amyloid patterns in the brain than was F-18 FDG imaging.

“We are using state-of-the-art, noninvasive PET and MRI technologies to look at some of the earliest developments of Alzheimer’s disease onset in the brains of normal middle-aged people,” said Guofan Xu, MD, PhD, lead author of the fourth study. “With this we can evaluate whether pathological changes associated with Alzheimer’s disease are happening many years before the onset of significant clinical symptoms.”