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PET scans have high error rate in the diagnosis of non-alzheimer's dementia.

Interpreting a type of brain scan called positron emission tomography (PET) is reliable for diagnosing Alzheimer's disease (AD), but the modality is prone to error when diagnosing another common form of degenerative dementia, according to researchers at University of Texas in Dallas.

"Doctors seem to have a Alzheimer's-centric approach to PET scans," said Dr. Kyle Womack, Assistant Professor of Neurology and Neurotherapeutics and Psychiatry and lead study author.

"If they see the classic changes associated with Alzheimer's, they stop. Unfortunately, PET scans are used primarily when other examinations cannot tell dementias apart, so it is vital that they are effective. Our results show that if clinicians pay more attention to certain areas of the brain when reading these scans, their interpretations improve."

The study tested physicians' ability to distinguish between AD and frontotemporal lobar degeneration (FTLD), the third most common cause of degenerative dementia, using a three-dimensional imaging technique called fludeoxyglucose F18 (FDG-PET) scanning.

In a PET scan, patients are given a solution of sugar tagged with a radioactive tracer. When the sugar reaches the brain, it congregates in metabolically active areas that "light up" on scans. In degenerative dementias, various areas of the brain suffer nerve death and show less activity.

The study involved 31 patients with AD and 14 patients with FTLD. The patients had undergone PET scans before their deaths, and their diagnoses were confirmed by autopsy.

The PET scans were examined by 12 raters, 10 neurologists, and two psychiatrists, none of whom were informed of any details of the patients' cases. All of the raters were correct in interpreting 87 percent of the AD scans but were correct for only 50 percent of the FTLD scans. In one case of FTLD, 11 of the 12 raters missed the diagnosis.

The clinical symptoms of people with FTPD often lead physicians to misdiagnose the condition as AD or a psychiatric disorder such as late-onset bipolar disorder, Dr. Womack said. that the Centers for Medicaid and Medicare recently approved PET scans as a way to distinguish FTPD from AD, so that reliable interpretation is critical, he said.

"Clinicians will have to be careful to take the entire pattern of the brain scan into account," Dr. Womack added.

(Source: Archives of Neurology, November 8, 2010.)
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Publication:Nutrition Health Review
Date:Dec 22, 2010
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