Report from SNM: PET imaging of brain chemistry bolsters characterization of dementias

Imaging scientists achieved a major breakthrough when they proved it was possible to predict the onset of Alzheimer's disease using PET scans of neurochemical activity. University of Michigan researchers are going for the next neuroimaging milestone by showing that the same technique can also aid in the differential diagnosis of dementia.

"Our preliminary results clearly indicate that molecular imaging technologies such as PET scans can help diagnose a patient's specific type of dementia," said principal investigator Dr. Kirk A. Frey, codirector of the Movement Disorders Clinic at the University of Michigan. < 

Frey and colleagues enrolled 66 patients with mild cognitive impairment or mild dementia who underwent a standard neurological assessment and structural imaging of the brain. Based on test results, three experts diagnosed these patients with Alzheimer's disease, frontotemporal dementia, or dementia with Lewy bodies.

Patients also underwent molecular imaging with carbon-11 Pittsburgh Compound B (PIB) to measure amyloid plaque deposits and carbon-11 dihydrotetrabenazine (DTBZ) PET to determine dopamine receptor integrity.

The investigators found both PIB- and DTBZ-PET led to a revised, more accurate diagnosis of dementia in at least one of every four patients. Results were reported at the 2009 SNM meeting in Toronto.

Researchers diagnosed patients with frontotemporal dementia if their PIB- and DTBZ-PET scans were normal. Patients with significant striatum defects on DTBZ-PET were diagnosed as having dementia with Lewy bodies. An Alzheimer's diagnosis, on the other hand, was handed down to patients with normal DTBZ-PET but increased frontal cortical binding on PIB-PET.

PET provided images of important disease indicators that other examinations missed. Examples included amyloid plaques, a common indicator of Alzheimer's disease, and damage to dopamine nerves, which is often observed in Lewy body dementia.

The study will track patients for another two years to confirm the accuracy of their diagnoses.

The standard clinical assessment cannot accurately identify the underlying causes of early-stage dementia nor can it differentiate among dementia types that share similar symptoms. But according to Frey, neurochemical PET can spot the presence of amyloid plaques or damaged dopamine nerves, disease signals that characterize Alzheimer's disease or Lewy body dementia.

An early, accurate diagnosis is essential for selecting appropriate therapies to treat early-stage disease, said Dr. Peter Conti, director of nuclear medicine at the University of Southern California. More than five million people are diagnosed with dementia each year. Identifying the underlying causes of different types of dementia may one day enable more targeted, individualized therapies and treatments, he said.

"This is critical for providing the best possible care," Frey said. "PET's ability to pinpoint neurological underpinnings of different forms of dementia could lead to new, more targeted drugs and therapies."