Diagnostic Accuracy of a Combined Analysis of Cerebrospinal Fluid t-PrP, t-tau, p-tau, and Aβ42 in the Differential Diagnosis of Creutzfeldt-Jakob Disease from Alzheimer's Disease with Emphasis on Atypical Disease Variants

Abstract

According to recent studies, the determination of cerebrospinal fluid (CSF) total tau (t-tau)/phosphorylated tau (p-tau) ratio and total prion protein (t-PrP) levels significantly improves the accuracy of the diagnosis of Alzheimer's disease (AD) in atypical cases with clinical or laboratory features mimicking Creutzfeldt-Jakob disease (CJD). However, this has neither been validated nor tested in series including atypical CJD variants. Furthermore, the added diagnostic value of amyloid-β (Aβ)42 remains unclear. To address these issues, we measured t-PrP, 14-3-3, t-tau, p-tau, and Aβ42 CSF levels in 45 typical and 44 atypical/rapidly progressive AD patients, 54 typical and 54 atypical CJD patients, and 33 controls. CJD patients showed significantly lower CSF t-PrP levels than controls and AD patients. Furthermore, atypical CJD was associated with lower t-PrP levels in comparison to typical CJD. T-tau, 14-3-3, or t-PrP alone yielded, respectively, 80.6, 63.0, and 73.0% sensitivity and 75.3, 92.1, and 75% specificity in distinguishing AD from CJD. On receiver operating characteristic (ROC) curve analyses of biomarker combinations, the (t-tau×Aβ42)/(p-tau×t-PrP) ratio achieved the best accuracy, with 98.1% sensitivity and 97.7% specificity overall, and 96.2% sensitivity and 95.5% specificity for the "atypical" disease groups. Our results show that the combined analysis of CSF t-PrP, t-tau, p-tau, and Aβ42 is clinically useful in the differential diagnosis between CJD and AD. Furthermore, the finding of reduced CSF t-PrP levels in CJD patients suggest that, likewise Aβ42 in AD, CSF t-PrP levels reflect the extent of PrPc conversion into abnormal PrP (PrPSc) and the burden of PrPSc deposition in CJD.

Keywords: Alzheimer’s disease; Creutzfeldt-Jakob disease; amyloid-β; biomarker; cerebrospinal fluid; prion protein; tau protein.

Fig.1

Boxplots illustrate levels of the CSF total prion protein (t-PrP) in control, Alzheimer’s disease (AD), and Creutzfeldt-Jakob disease (CJD) populations. Central horizontal lines indicate median values. Boxes illustrate the ranges between lower and upper quartiles. Error bars represent the full ranges of data, excluding outliers, which are displayed separately as single dots.

Fig.2

Receiver operating characteristics (ROC) curves illustrate sensitivity and specificity of various cerebrospinal fluid biomarker combinations. Area under the ROC curve is reported as area under the curve (AUC). The corresponding AUC values are also listed in Table 4.