Abstract
Importance Early and accurate in vivo diagnosis of Creutzfeldt-Jakob disease (CJD) is necessary for quickly distinguishing treatable from untreatable rapidly progressive dementias and for future therapeutic trials. This early diagnosis is becoming possible using the real-time quaking-induced conversion (RT-QuIC) seeding assay, which detects minute amounts of the disease-specific pathologic prion protein in cerebrospinal fluid (CSF) or olfactory mucosa (OM) samples.
Objective To develop an algorithm for accurate and early diagnosis of CJD by using the RT-QuIC assay on CSF samples, OM samples, or both.
Design, Setting, and Participants In this case-control study, samples of CSF and OM were collected from 86 patients with a clinical diagnosis of probable (n = 51), possible (n = 24), or suspected (n = 11) CJD and 104 negative control samples (54 CSF and 50 OM). The CSF and OM samples were analyzed using conventional RT-QuIC. The CSF samples underwent further testing using improved RT-QuIC conditions. In addition, the diagnostic performance of a novel, easy-to-use, gentle flocked swab for sampling of OM was evaluated. Data were collected from January 1 to June 30, 2015.
Main Outcome and Measures Correlations between RT-QuIC results and the final diagnosis of recruited patients.
Results Among the 86 patients (37 men [43%] and 49 women [57%]; mean [SD] age, 65.7 [11.5] years) included for analysis, all 61 patients with sporadic CJD had positive RT-QuIC findings using OM or CSF samples or both for an overall RT-QuIC diagnostic sensitivity of 100% (95% CI, 93%-100%). All patients with a final diagnosis of non–prion disease (71 CSF and 67 OM samples) had negative RT-QuIC findings for 100% specificity (95% CI, 94%-100%). Of 8 symptomatic patients with various mutations causing CJD or Gerstmann-Sträussler-Scheinker syndrome, 6 had positive and 2 had negative RT-QuIC findings for a sensitivity of 75% (95% CI, 36%-96%).
Conclusions and Relevance A proposed diagnostic algorithm for sporadic CJD combines CSF and OM RT-QuIC testing to provide virtually 100% diagnostic sensitivity and specificity in the clinical phase of the disease.
Introduction
Sporadic Creutzfeldt-Jakob disease (CJD) is the most common form of human transmissible spongiform encephalopathy or prion disease. Genetic CJD, Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia also belong to this group of fatal neurodegenerative disorders. Criteria for the diagnosis of probable sporadic CJD include the following: the presence of dementia; at least 2 clinical signs among visual disturbances, ataxia, extrapyramidal or pyramidal signs, myoclonus, and akinetic mutism; and the presence of periodic sharp and slow wave complexes in the electroencephalogram, a positive test result for 14-3-3 protein in the cerebrospinal fluid (CSF), or bilateral high-signal abnormalities in the caudate and/or putamen at diffusion-weighted imaging or fluid-attenuated inversion recovery sequences of magnetic resonance imaging of the brain.1 Definite diagnosis still relies on neuropathologic examination or the detection of the CJD-specific abnormal prion protein (PrPCJD) in the central nervous system tissue.2
However, patients with sporadic CJD show great variability in clinical signs and pathologic lesions, partially depending on the polymorphic methionine (M) or valine (V) at codon 129 and the glycotype of protease-resistant PrP (types 1 and 2) that accumulates in brain.3- 5 Because of this phenotypic variability, accurate and early intra vitam diagnosis of sporadic CJD is often challenging, requiring the combination of clinical signs and instrumental or biochemical findings that usually occur in the late stage of disease. The sensitivity of these diagnostic criteria for sporadic CJD based on the analysis of probable and definite cases has been 83%, with a specificity of 71%.1
The real-time quaking-induced conversion (RT-QuIC) assay detects femtograms of PrPCJD from all subtypes of sporadic CJD,6- 12 and previous applications of RT-QuIC to CSF (eg, PQ-CSF) have given diagnostic sensitivities of 77% to 91% and specificities of 98.5% to 100%.7,9,13- 15 A second-generation improved RT-QuIC assay for CSF samples (IQ-CSF) has increased sensitivity to 96%.9 Finally, the application of RT-QuIC to brushings from the olfactory mucosa (OM) has shown a sensitivity of at least 97% and a specificity of 100%.16,17
In the present study, we used RT-QuIC to analyze CSF and OM samples from 86 patients referred to the Italian CJD surveillance system to determine the accuracy of the test at the time of CJD diagnosis. In addition, we propose a diagnostic algorithm for optimal diagnosis of suspected CJD based on RT-QuIC analysis of CSF and OM.
JAMA Neurology 2016
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