Clinical assessment combined with a new single-photon emission computed tomography (SPECT) technique can boost diagnostic certainty for difficult cases of Alzheimer’s disease from 90 percent to almost 100 percent, according to an article in the May issue of the Journal of Nuclear Medicine.

The new technique looks for reduced blood flow in the posterior cingulated gyrus, a characteristic sign of Alzheimer’s disease that can distinguish it from the frontotemporal diseases, which are the second-leading cause of dementia in the elderly.

“This is the first publication using the posterior cingulate to rule out frontotemporal disease,” said Frederick Bonte, MD, the study’s lead author. “If the blood flow is significantly reduced to that structure, you have identified Alzheimer’s, and you have simultaneously excluded the frontotemporal dementias.

“The dementing diseases are becoming a very important socio-economic problem, in addition to being a group of scientific problems of incredible difficulty. The prospects are quite hopeful now that effective treatments for Alzheimer’s disease ? and possibly a cure ? will emerge in the not-too-distant future. This makes it even more important to find out who really has Alzheimer’s disease and is, therefore, eligible for treatment and who has one of the other dementing diseases, for whom these new treatments would be ineffective.”

In the current study, the new technique was used to measure blood flow in the posterior cingulate cortex of 60 people aged 54 to 92 years. Of the 60 people, 20 were possible Alzheimer’s disease patients, 20 were suspected of having frontotemporal disease, and the remaining 20 were normal volunteers without evidence of dementia.

Of the 20 people suspected of having Alzheimer’s, 16 exhibited significant blood-flow reductions in the posterior cingulate cortex. Of the 20 patients suspected of having frontotemporal disease, only 1 showed signs of reduced blood flow in the region. That patient was later re-evaluated and diagnosed with Alzheimer’s disease.

Dr. Linda Hynan, a coauthor of the paper, said that the study findings show that patients with poor blood flow in the posterior cingulate cortex are 16 times more likely to have Alzheimer’s disease than one of the frontotemporal dementias.
Evidence of shrinkage in brain structures such as the hippocampus and parietal cortex is also central to diagnosing Alzheimer’s. This shrinkage, or atrophy, can be seen on a standard magnetic resonance imaging. Still, autopsy remains the definitive diagnostic tool for Alzheimer’s disease.