PET with 11C-labeled Pittsburgh Compound-B (PIB) is a powerful tool in examining the relationship between amyloid deposits, clinical symptoms and structural and functional brain changes in the normal aging and Alzheimer's disease, according to a survey in a special issue of Behavioral Neurology, released in December 2009.
PIB binds specifically to fibrillar beta-amyloid deposits, and is a sensitive marker for amyloid deposits in cognitively normal older individuals and patients with mild cognitive impairment and Alzheimer's disease, according to the authors Gil D. Rabinovici, MD, assistant clinical professor in the department of neurology at the University of California, San Francisco and William J. Jagust, MD, professor and chair, department of neurology at the University of California, Berkeley.
The investigators surveyed more than 100 studies and complemented the PIB-PET investigations by using MRI or FDG-PET.
"Our survey of PIB-PET studies, which looked cross-sectionally and longitudinally at people with normal cognitive performance, mild cognitive impairment and full-fledged Alzheimer's disease, showed that amyloid deposits can be detected in a significant proportion of cognitively normal older adults, and that their presence is associated with Alzheimer's-like brain atrophy and changes in brain activity," said Rabinovici.
The study also suggested that amyloid-based therapies most likely work very early in the disease process. "Amyloid deposits appear to reach a plateau early in the disease course, when patients experience very mild symptoms or no symptoms at all. By the time patients have developed the symptoms of Alzheimer's disease, clinical decline and brain changes are occurring independently of further amyloid accumulation," said Rabinovici.
However, Rabinovici "strongly discourages" uses of the technology in cognitively normal individuals until effective and safe anti-amyloid therapies are available and the benefit of preventive treatment is demonstrated in clinical trials.
In the future, “amyloid imaging is likely to supplement clinical evaluation in selecting patients for anti-amyloid therapies, while MRI and FDG-PET may be more appropriate markers of clinical progression”, concluded the authors.