PET and MR show promise in diagnosing Alzheimer disease.

New research shows that positron emission tomography (PET) and magnetic resonance (MR) can provide earlier diagnosis of Alzheimer disease and distinguish it from other types of dementia.

Mild cognitive impairment is a memory disorder that is a strong early predictor of Alzheimer disease.

Some people with mild cognitive impairment progress to Alzheimer disease while others do not. Being able to distinguish the 2 could help provide earlier Alzheimer diagnosis. Such a diagnosis is important because there are medications available that may help treat Alzheimer symptoms provided they are administered early enough.

Researchers from the University of Pittsburgh recently discovered that when they used PET with a new tracer known as Pittsburgh Compound B (PIB), they were able to detect abnormal clumps of protein in the brain called amyloid plaques that accumulate in the brains of Alzheimer patients.

In a new study, the same researchers used PET with PIB to image the brains of 5 people with mild cognitive impairment. They found that the subjects fell into 2 distinct groups. One group had evidence of amyloid distribution similar to that of cognitively normal control subjects, while the other group's amyloid distribution was indistinguishable from that of Alzheimer patients.

"Amyloid imaging with PET may become useful for predicting which people with mild cognitive impairment will progress to Alzheimer in the near future," said William E. Klunk, M.D., Ph.D., and colleagues at the University of Pittsburgh in Pittsburgh. "The technology also might help to determine the effectiveness of anti-amyloid therapies in people with mild cognitive impairment and Alzheimer disease."

Dr. Klunk suggested that levels of amyloid in the brain could play a role in the development of Alzheimer disease. The researchers will attempt to replicate these results in a much larger study.

Another new PET tracer is enabling researchers to see for the first time accumulations of the abnormal protein tau in the brains of people with a rare form of dementia. The tracer, known as FDDNP, accumulates in both amyloid plaques and the tangles of abnormal tan protein in the brains of Alzheimer patients.

In the study, researchers used this new compound to map the tangles also found in frontotemporal dementia, a fare disorder with symptoms similar to Alzheimer. The researchers compared PET scans of patients with frontotemporal dementia and Alzheimer disease and found very different distributions of tan protein.

"We believe this is the first time tau accumulation has been visualized in living patients," said Gary Small, M.D., of the University of California in Los Angeles. "The new technique may help us better differentiate between Alzheimer disease and other forms of dementia, leading to more effective treatments."

The researchers hope the technique also can help monitor the effectiveness of drugs to clear abnormal proteins such as tau from the brain.

Like PET, MR has shown promise at detecting brain abnormalities in people with Alzheimer disease. A study currently underway is using MR to identify brain changes in people who complain of cognitive deficits but do not meet the criteria for a diagnosis of mild cognitive impairment or Alzheimer disease.

In the study, researchers are tracking the cognitive abilities of 90 older adults as they age. At the outset of the study, 30 of the participants reported no significant declines in memory or other mental functions, while another 30 had cognitive deficits that warranted a diagnosis of mild cognitive impairment. The remaining 30 participants, known as the cognitive complaint group, had perceived deficits in memory and other mental functions that did not reach the threshold for mild cognitive impairment diagnosis and could not be explained by depression or other health problems. The researchers are using repeat MR scans to track changes among the 3 groups in gray matter and brain activity during memory task performance. However, even in the baseline study, researchers noted a surprising parallel between the cognitive complaint and mild cognitive impairment groups.

"The pattern of reduction of gray matter and brain activity in the older adults who complained of cognitive deficits was almost identical to that seen in patients with mild cognitive impairment, suggesting that many of these people may be in the earliest stages of Alzheimer disease," said Andrew J. Saykin, Psy.D., of Dartmouth Medical School in Lebanon, NH. "Early detection will be essential as new preventative and treatment strategies become available."

Researchers presented their findings in June at the 9th International Conference on Alzheimer Disease and Related Disorders in Philadelphia.

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