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RT-QuIC Nasal Brushing

A Test for Creutzfeldt–Jakob Disease Using Nasal Brushings

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Year of Publication: 2014

Authors: Christina D. Orrú, Matilde Bongianni, Giovanni Tonoli, ..., Gianluigi Zanusso

Journal: New England Journal of Medicine

Citation: N Engl J Med 2014;371:519-29

Link: https://www.nejm.org/doi/full/10.1056/NEJMoa1315200

PDF: https://www.nejm.org/doi/pdf/10.1056/NEJ...ticleTools=true

Clinical Question

Can RT-QuIC analysis of olfactory epithelium samples obtained via nasal brushings accurately diagnose Creutzfeldt-Jakob disease in living patients?

Bottom Line

RT-QuIC testing of nasal brushings demonstrated 97% sensitivity and 100% specificity for diagnosing CJD, outperforming CSF-based RT-QuIC (77% sensitivity) in the same patients. This minimally invasive approach detects substantial prion seeding activity in the olfactory epithelium and offers a promising method for definitive antemortem diagnosis of CJD.

        Major Points
        RT-QuIC of nasal brushings positive in 30/31 CJD patients (15/15 definite sCJD, 13/14 probable sCJD, 2/2 inherited E200K CJD)
All 43 non-CJD controls were RT-QuIC negative on nasal brushings
Olfactory mucosa samples gave significantly stronger and faster RT-QuIC responses than CSF (P<0.001)
Individual brushings contained approximately 10⁵ to 10⁷ prion seeds, several logs₁₀ greater concentration than in CSF
Nasal brushing is a safe, minimally invasive procedure requiring only local vasoconstrictor and fiberoptic rhinoscope
Method detected all CJD molecular subtypes (MM, MV, VV genotypes; types 1 and 2 PrPᶜᴶᴰ)
One false negative case (Patient 29) had typical tau and 14-3-3 levels but negative RT-QuIC on both OM and CSF
The presence of substantial prion seeds in the nasal vault raises biosafety considerations for medical instruments contacting this area

      

Design

Study Type: Prospective diagnostic accuracy study

Randomization:

Blinding: Blinded analysis; RT-QuIC testing performed on blinded sample sets

Enrollment Period: Not specified

Follow-up Duration: Not applicable (diagnostic study)

Centers: 2

Countries: Italy, United States

Sample Size: 74

Analysis: Sensitivity and specificity calculated with 95% confidence intervals using Wilson procedure; statistical comparison of ThT fluorescence responses using unpaired t-tests

Inclusion Criteria

CJD patients: Rapidly progressive dementia referred due to possible or probable CJD
Classified according to updated clinical diagnostic criteria (Puoti et al. 2012)
Controls with other neurological disorders: Probable Alzheimer's disease, probable Parkinson's disease, progressive supranuclear palsy, paraneoplastic limbic encephalitis
Controls without neurological disorders: Persons referred to ENT clinic for other purposes

Exclusion Criteria

Not explicitly stated

Baseline Characteristics

CJD Patients (N=31):

Definite sporadic CJD: 15
Probable sporadic CJD: 14
Inherited CJD (E200K): 2
Age range - years: 29-83
Sex - male/female: 15/16
PRNP codon 129 MM genotype: 14
PRNP codon 129 MV genotype: 9
PRNP codon 129 VV genotype: 2
Genotype not available: 4
Disease duration - months (range): 2.0-31.0
Typical MRI findings - n: 22/31
PSWCs on EEG - n: 13/31
14-3-3 positive - n: 28/31
CSF tau >2400 pg/mL - n: 23/25

Controls with Other Neurological Disorders (N=12):

Mean age - years: 70.8 ± 8.8
Age range - years: 48-82
Sex - male/female: 4/8
Probable Alzheimer's disease: 5
Probable Parkinson's disease: 4
Progressive supranuclear palsy: 2
Paraneoplastic limbic encephalitis: 1

Controls without Neurological Disorders (N=31):

Mean age - years: 52.1 ± 15.0
Age range - years: 24-81
Sex - male/female: 20/11

Arms

Field	CJD Patients	Control
Intervention	Olfactory mucosa obtained via nasal brushing; CSF obtained via lumbar puncture; samples analyzed by RT-QuIC assay	Olfactory mucosa obtained via nasal brushing; CSF obtained via lumbar puncture (subset); samples analyzed by RT-QuIC assay
Duration	Single time point diagnostic testing	Single time point diagnostic testing

Outcomes

Outcome	Type	Control	Intervention	P-value
Diagnostic accuracy of RT-QuIC assay on olfactory mucosa samples for detecting CJD	Primary	Sensitivity - Olfactory Mucosa: 97% (30/31 CJD positive) · 95% CI Sensitivity: 82 to 100% · Specificity - Olfactory Mucosa: 100% (0/43 controls positive) · 95% CI Specificity: 90 to 100%
RT-QuIC sensitivity on CSF samples \| Result: 77% (23/30 CJD positive); 95% CI: 57 to 89%; Specificity: 100% (0/46 controls positive)	Secondary
RT-QuIC sensitivity in definite sporadic CJD (olfactory mucosa) \| Result: 100% (15/15); 95% CI: 75 to 100%	Secondary
RT-QuIC sensitivity in probable sporadic CJD (olfactory mucosa) \| Result: 93% (13/14)	Secondary
Mean ThT fluorescence comparison OM vs CSF \| Result: OM samples significantly higher than CSF	Secondary			<0.001
Prion seed concentration in olfactory mucosa \| Result: 3.4 to 4.1 log₁₀ SD₅₀ per µL of packed pellet	Secondary
Prion seed concentration in CSF \| Result: 0.2 to 0.5 log₁₀ SD₅₀ per µL (i.e., <0.1 log₁₀)	Secondary
Prion seed concentration in brain tissue \| Result: 7.2 to 8.95 log₁₀ SD₅₀ per mg	Secondary
14-3-3 assay sensitivity \| Result: 90% (28/31)	Secondary
CSF tau >2400 pg/mL sensitivity \| Result: 92% (23/25)	Secondary
Nasal brushing procedure	Adverse		Description: Minimally invasive procedure using local vasoconstrictor (1% epinephrine) and rigid fiberoptic rhinoscope with disposable sheath; Complications: None reported

Subgroup Analysis

RT-QuIC detected all CJD molecular subtypes: MM genotype (14/14), MV genotype (8/9), VV genotype (2/2), and both type 1 and type 2 PrPᶜᴶᴰ. The single false negative (Patient 29, MV genotype) was RT-QuIC negative on both OM and CSF despite having clinical features and biomarkers typical of sporadic CJD.

Criticisms

Relatively small sample size (31 CJD patients, 43 controls); larger validation studies needed
Single-center sampling (Italy) for CJD patients limits generalizability
One false negative case suggests method may not detect all CJD cases
Time between symptom onset and OM brushing varied widely (0.5-28 months); effect of disease stage on test performance unclear
Control population had significantly different age distribution than CJD patients
Biosafety implications of prion-contaminated medical instruments not fully addressed
Study did not compare performance to brain biopsy (true gold standard in living patients)
Only sporadic and E200K inherited CJD tested; performance in other inherited forms unknown
Requires specialized laboratory expertise and equipment for RT-QuIC assay

Funding

Intramural Research Program of the National Institute of Allergy and Infectious Diseases (NIAID); Fondazione Cariverona; Italian Ministry of Health (RF2009-1474758); Creutzfeldt-Jakob Disease Foundation; Programma Master and Back–Percorsi di rientro fellowship; NIAID Gift Fund donations

Based on: RT-QuIC Nasal Brushing (New England Journal of Medicine, 2014)