Research shows PET scans helpful in early diagnosis of Alzheimer's

Researchers at the University of California, Berkeley (UC Berkeley) have used positron emission tomography (PET) scans to detect the deposition in human brains of a protein linked to Alzheimer's disease.

In what could be a key advance in the early diagnosis and staging of Alzheimer's disease, the study on 53 adults indicates that PET scans can track the progressive stages of the neurodegenerative disorder in cognitively normal adults. The research was recently published in the Neuron journal.

Of the subjects, five were young adults aged 20-26, 33 were aged 64-90 but cognitively healthy, and 15 were aged 53-77 who had been diagnosed with probable Alzheimer's dementia.

The Alzheimer's-linked protein, known as tau, has emerged as a major player over the past decade. It is a microtubule protein important in maintaining the structure of neurons. When it gets tangled and twisted, its ability to support synaptic connections becomes impaired. Another protein, beta amyloid, also plays a role.

While symptoms exist that signal Alzheimer's disease, a definitive diagnosis has been possible only through an examination of the brain after the patient has died.

"Our study is the first to show the staging (of the disease) in people who are not only alive, but who have no signs of cognitive impairment," said William Jagust, the principal investigator of the study and a professor at UC Berkeley's School of Public Health.

Through PET scans, the researchers confirmed that with advancing age, tau accumulates in the brain's medial temporal lobe, home to the hippocampus and the memory center.

By asking the subjects to recall a list of words viewed 20 minutes earlier, the researchers revealed that higher levels of tau in the medial temporal lobe was associated with greater declines in episodic memory, the type of memory used to code new information.

While higher levels of tau were linked to more problems with episodic memory, it was when tau spread outside the medial temporal lobe to other parts of the brain, such as the neocortex, that the researchers saw more serious declines in global cognitive function.

They further discovered that tau's spread was connected to the presence of beta amyloid plaques, which once were considered the primary culprit in Alzheimer's disease.

"Amyloid may somehow facilitate the spread of tau, or tau may initiate the deposition of amyloid," said Jagust. "We don't know. We can't answer that at this point."

"All I can say is that when amyloid starts to show up, we start to see tau in other parts of the brain, and that is when real problems begin. We think that may be the beginning of symptomatic Alzheimer's disease," he said.

The researchers said they believe that with PET scans, tau imaging could become an important tool in helping develop therapeutic approaches that target the correct protein, either amyloid or tau, depending on the disease stage.

"This opens the door to the use of PET scans as a diagnostic and staging tool," said Jagust. Endi