Application of real-time quaking-induced conversion in Creutzfeldt–Jakob disease surveillance

BACKGROUND: Evaluation of the application of CSF real-time quaking-induced conversion in Creutzfeldt–Jakob disease surveillance to investigate test accuracy, influencing factors, and associations with disease incidence. METHODS: In a prospective surveillance study, CSF real-time quaking-induced conversion was performed in patients with clinical suspicion of prion disease (2014–2022). Clinically or histochemically characterized patients with sporadic Creutzfeldt–Jakob disease (n = 888) and patients with final diagnosis of non-prion disease (n = 371) were included for accuracy and association studies. RESULTS: The overall test sensitivity for sporadic Creutzfeldt–Jakob disease was 90% and the specificity 99%. Lower sensitivity was associated with early disease stage (p = 0.029) and longer survival (p < 0.001). The frequency of false positives was significantly higher in patients with inflammatory CNS diseases (3.7%) than in other diagnoses (0.4%, p = 0.027). The incidence increased from 1.7 per million person-years (2006–2017) to 2.0 after the test was added to diagnostic the criteria (2018–2021). CONCLUSION: We validated high diagnostic accuracy of CSF real-time quaking-induced conversion but identified inflammatory brain disease as a potential source of (rare) false-positive results, indicating thorough consideration of this condition in the differential diagnosis of Creutzfeldt–Jakob disease. The surveillance improved after amendment of the diagnostic criteria, whereas the incidence showed no suggestive alterations during the COVID-19 pandemic. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00415-022-11549-2.