New PET Scan Detects Tau Tangles, Additional Changes in Brains of Alzheimer’s Patients

A new study reports that positron emission tomography (PET) scanning using a new imaging agent called flortaucipir F18 accurately shows the density and distribution of tau protein deposits in the brains of people living with Alzheimer’s. Tau protein makes up the neurofibrillary tangles that, along with amyloid plaques, are the primary markers are Alzheimer’s disease.

The study also found that flortaucipir F18 PET accurately detects so-called neuropathological changes in the brain — a combination of tau neurofibrillary tangles and amyloid plaques — that together are the criteria for a definitive diagnosis of Alzheimer’s disease on autopsy. The study, published in the April 27, 2020 issue of JAMA Neurology, was funded by Avid Radiopharmaceuticals, a subsidiary of Eli Lilly, which holds the flortaucipir F18 patent. Study authors include Avid scientists and independent experts from across the United States.

“This study has two very important implications,” according to Howard Fillit, MD, Founding Executive Director and Chief Science Office at the Alzheimer’s Drug Discovery Foundation (ADDF). “First, it supports the use of this tau PET scan to confirm an Alzheimer’s diagnosis, which can influence how healthcare providers and caregivers approach and plan for patient care. Second, and very importantly, this scan can help identify, enroll and track the progress of the right patients in clinical trials testing anti-tau therapies.”

PET scans to detect amyloid protein are already available in the United States, but this is the first study to validate a PET scan to detect tau protein. The first amyloid PET approved for use in the United States, Amyvid™ in 2012, received critical seed funding from ADDF.

The current study, conducted at 27 centers in the United States and one in Australia, enrolled 156 people with cognitive status ranging from normal through dementia, including patients with Alzheimer’s and non-Alzheimer’s diagnoses. All participants had a terminal illness, were over age 50 and had a short life expectancy. Seventy-three patients died within nine months of their PET scan, and 64 had a valid study autopsy. The average time between PET scans and autopsies to confirm their accuracy was just 2.6 months, meaning there was very little time for the protein deposits in the brain to change.

A limitation of this study is that it looked at an older population (the average age was 82.5 years) and those who had Alzheimer’s tended to be in the later stages of the disease. Dr. Fillit says this study was a crucial first step in validating the effectiveness of the new tau PET scan, but that additional studies are needed to determine whether the scan is useful in identifying patients in the early stages of the disease, perhaps even before symptoms begin.

“Early diagnosis is crucial for patient care decisions and planning,” said Dr. Fillit, “but it’s also essential so we can include asymptomatic and early stage patients in clinical trials, when they are more likely to benefit from treatment.”