PET scans spot signs of early Alzheimer's

Scientists in Finland say a type of imaging technique known as positron emission tomography (PET) scanning may be a useful and non-invasive way of diagnosing the early stages of Alzheimer’s disease.

The team from the University of Kuopio say a PET scan may allow doctors to determine whether a person has "plaques" in the brain that are an indication of Alzheimer's disease.

The disease-related plaques are made of beta-amyloid and along with other compounds are considered signs of the development of Alzheimer’s disease.

Currently, the only reliable way to assess the presence of these compounds in the brain is through analyzing brain tissue samples obtained during life or after death.

The scientists say this presents a major obstacle in the consideration of clinical drug trials for early Alzheimer’s.

For the study Dr. Ville Leinonen and colleagues studied 10 patients without severe dementia who had undergone a biopsy of their frontal cortex because of a suspected abnormal increase of cerebrospinal fluid in the brain.

Cognitive impairment is a symptom of both Alzheimer’s disease and normal-pressure hydrocephalus, and 22 percent to 42 percent of patients with symptoms of normal-pressure hydrocephalus have brain lesions characteristic of Alzheimer’s disease.

By examining this brain tissue, the researchers determined that six of the people had Alzheimer's disease-related plaques in their brain and four had no such brain changes.

A 90-minute PET scan following an injection of a chemical "marker" known as carbon 11-labeled Pittsburgh Compound B, helped to pinpoint the brain plaques, accurately revealing in 9 of the 10 people who had the plaques and who did not.

The researchers say while it was not 100 percent correct, the correlation was very good.

Dr. Leinonen says at the time of the study none of the 10 people had developed severe dementia but says larger studies are now needed to verify that PET scans can become a common diagnostic tool.

The researchers say the study supports the use of PET scans to check for beta-amyloid deposits in the brain which may lead to mild cognitive impairment, Alzheimer’s disease or normal-pressure hydrocephalus.

They say PET scans which are commonly used to detect cancer, cardiac problems, and brain abnormalities, could also be useful in monitoring the effects of drugs in trials which target the early amyloid accumulation.

The researchers say large and prospective studies are now needed required to verify whether PET scans could become a tool in diagnosing Alzheimer’s disease.

Experts say worldwide an estimated 26 million people have Alzheimer's, this number can be expected to reach 106 million by 2050.

The study will be published in the October 2008 print issue of Archives of Neurology, one of the JAMA/Archives journals.