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Tau positron emission tomography prognostic in Alzheimer’s disease

Rod Tucker
1 July, 2021  

Tau positron emission tomography is of prognostic value in predicting cognitive changes over time in those with Alzheimer’s disease

A confirmed diagnosis of Alzheimer’s disease is important for care and treatment planning for both patients and their families. Accurately predicting the rate of cognitive decline in affected patients is a current challenge and while the presence of neurofibrillary tangles of the protein tau are a recognised feature of those with Alzheimer’s disease, real-time visualisation of tau may be of value in the prediction of future cognitive decline. The use of tau positron emission tomography (PET) tracers such as flortaucipir-18 (18-F) have been used to study tau pathology in neurodegenerative disorders and have potential as diagnostic markers. However, many studies have included small numbers of patients and focused on the early stages of Alzheimer’s disease. In a prospective study, a team from the Clinical Memory Research Unit, Lund University, Sweden, sought to examine the prognostic value of tau tracers in a large group of patients. More specifically, the team compared patients with Alzheimer’s disease dementia, mild cognitive impairment or normal cognition and then compared tau PET with other established magnetic resonance imaging and amyloid PET markers for predicting future cognitive change. This multi-centre study recruited patients from a range of existing clinics in several countries although only included those who had Alzheimer’s disease dementia and who were positive for amyloid-beta on PET scans. All patients underwent tau PET and a variety of neuropsychological tests including the Mini-Mental State Examination (MMSE), which is a diagnostic screening tool that measures a variety of cognitive abilities such as memory, attention, language and motor skills. Patients were required to have at least two MMSE recorded measurements at least 12 months apart.

Findings
There were a total of 1432 participants included with a mean age of 71.2 years (47.5% female). As might be expected, those with Alzheimer’s dementia had worse baseline MMSE scores and the greatest annual decline in MMSE scores when recorded an average of 22.7 months later. From the tau positron emission tomography scans, greater uptake of 18-F was strongly associated with annual changes in MMSE scores and this association was more significant than with amyloid PET scanning. Overall, the authors reported that baseline tau PET was able to predict changes in MMSE over time across the Alzheimer’s disease clinical spectrum. Furthermore, they suggested that tau PET is best suited to the prognostic processes, especially in the preclinical (i.e., before a clinical diagnosis but evidence of amyloidosis on PET imaging) and prodromal phase, which is characterised by mild cognitive impairment.

Citation
Ossenkoppele R et al. Accuracy of Tau Positron Emission Tomography as a Prognostic Marker in Preclinical and Prodromal Alzheimer Disease. A Head-to-Head Comparison Against Amyloid Positron Emission Tomography and Magnetic Resonance Imaging. JAMA Neurol 2021