PET imaging for tau pathology has won regulatory approval in the US for assisting the diagnosis of Alzheimer’s disease.
The Food and Drug Administration (FDA) has approved a radioactive diagnostic agent flortaucipir F18 (Tauvid, Eli Lilly) intravenous injection for use with PET imaging of the brain to estimate the density and distribution of aggregated tau neurofibrillary tangles (NFTs) in adult patients with cognitive impairment who are being evaluated for Alzheimer’s disease.
The approval is based on recent studies – which included Australian centres – showing that the PET imaging with flortaucipir F18 has a high sensitivity and moderate to high specificity, and is able to identify the underlying presence of NFTs at the B3 level, consistent with a neuropathological diagnosis of Alzheimer’s disease.
“While there are FDA approved imaging drugs for amyloid pathology, this is the first drug approved for imaging tau pathology, one of the two neuropathological hallmarks of Alzheimer’s disease, and represents a major advance for patients with cognitive impairment being evaluated for the condition,” said Dr Charles Ganley, director of Office of Specialty Medicine in FDA’s Center for Drug Evaluation and Research.
The FDA approval is based on a study evaluating 156 patients with Alzheimer’s Disease, published in JAMA Neurology, which concluded that “in appropriate clinical cases of adults who have undergone adequate neurological assessment and have been evaluated for AD or other causes of cognitive decline, PET imaging with [18F]flortaucipir may help in establishing a diagnosis of AD.”
The study was conducted at 27 sites in the US and also at the Florey Institute of Neuroscience and Mental Health, Melbourne, under the supervision of Professor Colin Master.
In 64 of the patients who died within nine months of the brain scan, evaluators’ reading of the PET scan was compared to post-mortem readings from independent pathologists who evaluated the density and distribution of NFTs in the same brain.
The study showed evaluators reading the PET images had a high probability of correctly evaluating patients with tau pathology and had an average-to-high probability of correctly evaluating patients without tau pathology.
However an accompanying commentary cautioned that the study did not yet support the use of tau pathology imaging in early detection of Alzheimers disease because it did not show detection of early neuropathological changes as measured by the Braak staging scheme.
“These results are discouraging for selecting individuals with primary age-related tauopathy or those with intermediate levels of tau pathology who may be in the early stages of AD,” it said.