Objective:

Identify the clinical, laboratory, and pathologic features associated with false negative real-time
quaking-induced conversion (RT-QuIC) testing for prions.

Background:

Heterogeneity in clinical presentation, abundant mimics, and potential for iatrogenic
transmission emphasize the need for accurate diagnostic tests for Creutzfeldt-Jakob disease
(CJD). While RT-QuIC is an excellent test, false negative results are recognized in clinical
practice.

Design/Methods:

One-hundred twelve patients with probable or definite prion disease were assessed at two tertiary
care centers from 2013-2021. RT-QuIC testing for prions was performed in cerebrospinal fluid
(CSF) in all patients via the National Prion Disease Pathology Surveillance Center (Cleveland,
OH). Demographic data, clinical features, and results of common tests and laboratory studies
were abstracted from electronic medical records, and differences between RT-QuIC positive and
negative patients considered using univariate statistics.

Results:

Initial RT-QuIC testing was negative in 12/112 patients (sensitivity 89%). Median age at
presentation was younger in RT-QuIC negative patients (56.9 vs 66 years, p<0.01), who were
also less likely to present with ataxia (3/12 vs 61/100, p=0.03). CSF cell count, protein, and
glucose levels were similar between cohorts, while rates of 14-3-3 positivity (2/12 vs 77/100,
p<0.01) and median CSF total tau levels were lower in RT-QuIC negative patients (2318 vs 4001
pg/mL, p<0.01). RT-QuIC negative patients also had a longer median days from symptom onset
to first presentation (125 vs 47, p=0.04), and longer symptomatic disease duration (530 vs 148,
p<0.01). Two RT-QuIC-negative patients underwent repeat testing, of which both were positive.

Conclusions:

RT-QuIC is a sensitive yet imperfect measure necessitating incorporation of other test results
when prion disease is suspected. Patients with negative RT-QuIC had lower CSF biomarkers of
neuronal damage (total-tau and 14-3-3) and longer symptomatic duration of prion disease raising
the possibility that false negative RT-QuIC testing may associate with a more indolent disease
course.