Research Reveals PET Effectively Identifies Dementia

In a new report of imaging studies covering more than 10 years, scientists revealed that a positron emission tomography (PET) imaging technique safely and effectively identifies dementia, including the most typical and debilitating form affecting older individuals, Alzheimer’s disease.

The study’s findings were published in the January 2012 issue of the Journal of Nuclear Medicine. Researchers reviewed many PET studies to assess a molecular imaging technique that combines PET, which provides functional images of biologic mechanisms, with an injected biomarker called 18F-FDG to target major areas of metabolic decrease in the brain indicating dementia. Having physiologic evidence of neurodegenerative disease by imaging patients with PET could provide clinicians with the data they need to make more accurate diagnoses earlier than ever before.

“The new data support the role of 18F-FDG PET as an effective addition to other diagnostic methods used to assess patients with symptoms of dementia,” commented Nicolaas Bohnen, MD, PhD, lead author of the study and professor of radiology and neurology at the University of Michigan (Ann Arbor, MI, USA). “The review also identified new literature showing the benefit of this imaging technique for not only helping to diagnose dementia but also for improving physician confidence when diagnosing a patient with dementia. This process can be difficult for physicians, especially when evaluating younger patients or those who have subtle signs of disease.”

Dementia is not a specific disease but a pattern of symptoms characterized by a loss of cognitive ability. These disorders can be caused by injury or progressive disease affecting regions of the brain that regulate attention, memory, language, and mobility. Whereas Alzheimer’s is most typically associated with progressive memory impairment, dementia with Lewy bodies, another form of the disease, can be associated with symptoms of Parkinson’s and prominent hallucinations, while another disorder, called frontotemporal dementia, can be seen in patients showing abnormal personality changes and problems in communicating and relating. Physicians can use FDG-PET with high accuracy to not only help diagnose dementia but also differentiate between the individual disorders. The role molecular imaging plays in the diagnosis of dementia has expanded enough that the official principles physicians use to diagnose patients now includes evidence from molecular imaging studies.

“For the first time, imaging biomarkers of Alzheimer’s disease are included in the newly revised clinical diagnostic criteria for the disease,” said Dr. Bohnen. “This is a major shift in disease definition, as previously an Alzheimer’s diagnosis was based mainly on a process of evaluating patients to exclude possible trauma, hemorrhage, tumor, or metabolic disorder. Now it is becoming a process of inclusion based on biomarker evidence from molecular imaging.”

The PET biomarker 18F-FDG comprises a radionuclide combined with fluorodeoxyglucose (FDG), which mimics glucose in the body. Cells metabolize FDG as fuel, and the variation in this uptake by cells throughout the body can then be imaged to identify a range of abnormalities. In the instance of dementia, marked reductions in the metabolism of different lobes of the cerebral cortex can confirm a disorder. Physicians can differentiate Alzheimer’s disease from other dementias, depending on the specific cortices affected.

This study, according to the investigators, represents the newest and most significant evidence of FDG-PET’s effectiveness for the assessment of patients with suspected dementia. The goal of the study was to replace earlier retrospective reviews that were performed as the technique was just emerging and that suggested methodologic improvements. The new review includes studies with better methodology, including validation of diagnoses with autopsy, more expansive recruitment of subjects, and use of multicenter studies. After reviewing 11 studies that occurred since the year 2000 and that met more stringent study review standards, researchers concluded that 18F-FDG is very effective for detecting the presence and type of dementia.

“Using 18F-FDG PET in the evaluation of patients with dementia can improve diagnostic accuracy and lead to earlier treatment and better patient care,” said Dr. Bohnen. “The earlier we make a diagnosis, the more we can alleviate uncertainty and suffering for patients and their families."

The biomarker 18F-FDG is among a range of imaging agents being studied for its effectiveness in Alzheimer’s imaging. As dementia treatments become available for clinical use, PET should play a significant role in not only the diagnosis of these diseases, but also the assessment and monitoring of future therapies.

According to the World Health Organization (Geneva, Switzerland), an estimated 18 million people worldwide are currently living with Alzheimer disease. That number is projected to nearly double by 2025.

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