Amyloid PETs are commonly negative in suspected Alzheimer’s disease with an increase in CSF phosphorylated-tau protein concentration but an Aβ42 concentration in the very high range: a prospective study
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Atypical cerebrospinal fluid (CSF) patterns, involving an increase in the concentration of phosphorylated-tau (P-tau) proteins but normal amyloid-β concentration, are not uncommon in patients with mild neurocognitive disorders and suspected Alzheimer’s disease (AD). In these conditions, however, AD diagnosis may be ruled out in the absence of any amyloid deposition at positron-emission tomography (PET). This pilot cross-sectional study was aimed to determine whether this negativity of amyloid PET can be predicted by CSF profiles in such patients.
Twenty-five patients (73 [68–80] years, 10 women) with mild neurocognitive disorders, suspected AD and an increase in the CSF concentration of P-tau proteins but normal Aβ42 concentration and Aβ42/Aβ40 ratio were prospectively included and referred to a 18F-florbetaben PET. The latter was considered as definitively negative with the conjunction of both visual (brain amyloid plaque load score) and quantified (standard uptake value ratios) criteria. Predictors of a negative PET were searched among current CSF biomarkers (Aß42, Aß40, T-tau, P-tau, Aß42/Aß40, Aß42/p-tau).
Amyloid PET was negative in 15 patients (60%) with a CSF Aß42 concentration being the sole independent predictor of this negativity. The criterion of an Aß42 concentration in the very high range (> 843 pg/mL), observed in 60% (15/25) of the study patients, was associated with a negative amyloid PET in 93% (14/15) of cases.
In mild neurocognitive disorders patients with suspected AD and showing an increase in CSF P-tau protein level, amyloid PETs are commonly negative, when Aß42 concentration is in the very high range. In such case, AD diagnosis based on biomarkers can be ruled out with reasonable certainty, without the need for additional CSF second-line assays or results from amyloid PET.
KeywordsAlzheimer’s disease CSF biomarkers Aß42 Amyloid PET Quantitative analysis
The authors thank Pierre Pothier for critical review of the manuscript.
This work was carried out thanks to the support of the Nancyclotep Imaging Platform and Nancy University Hospital.
Compliance with ethical standards
Conflicts of interest
The authors declare that they have no conflict of interest.
The study was approved by the French ethics committee CPP Est III on September 15th, 2015, as well as received the authorization from the national competent authority (ANSM) on September 18th 2015, and adhered to the Declaration of Helsinki.
All patients provided written informed consent for participation in the study. All patients provided written informed consent for publication.
Availability of data and materials
All data generated or analyzed during this study are included in this published article and its supplementary information files.
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