The Generative Brain

How prion disease is diagnosed: research

Plain explanationMore detail

Diagnosis of sporadic CJD in life rests on a clinical syndrome plus supportive investigations, now including RT-QuIC on cerebrospinal fluid and cortical ribboning on diffusion-weighted MRI. Under the revised international surveillance criteria, in-life sensitivity reached 92.2 percent against 77.5 percent under the previous criteria, with specificity unchanged, and neuropathology remains the only route to a definite diagnosis.

The usual route to a diagnosis
  1. SymptomsChanges that progress quickly.
  2. Neurological examA specialist looks for other causes first.
  3. MRI and EEGBrain scan and brain wave test.
  4. Spinal fluid testsIncluding RT-QuIC, where available.
  5. Specialist reviewCriteria give a probable diagnosis.
  6. ConfirmationA definite diagnosis needs brain tissue, usually after death.

The order differs by hospital and country.

Diagnostic classification in prion disease is organised around the categories definite, probable and possible used by the international surveillance network. Definite requires neuropathology. Probable requires a compatible clinical syndrome, supportive investigations and exclusion of alternatives. The research questions concern how much of the diagnostic load the in-life investigations can carry, and which cases they fail on.

This page states the performance figures and their limits. Plain language versions are at how it is diagnosed and how it is diagnosed: more detail.

What do the revised criteria add, and how much?

Watson and colleagues validated the revised criteria on 501 sporadic CJD cases and 146 non-cases from the United Kingdom, France, Germany and Italy. In-life sensitivity was 92.2 percent, against 77.5 percent under the previous criteria, with specificity about 81 percent in both. Among patients who had the complete investigation panel, sensitivity was 97.8 percent against 76.2 percent, with specificity again unchanged.

The two added investigations performed differently in that cohort. Cortical ribboning on MRI gave 67.9 percent sensitivity and 86.5 percent specificity. RT-QuIC gave 91.6 percent sensitivity and 100 percent specificity.

What does each investigation contribute?

The 2026 Viruses review sets out the current sequence. Diffusion-weighted MRI is the most sensitive imaging test, with cortical ribboning and basal ganglia involvement typical in sporadic CJD; early scans can be normal, which is why serial imaging is used. FDG-PET and SPECT are supportive and less specific. EEG shows periodic sharp wave complexes in about two thirds of sporadic cases and is neither universal nor specific. Cerebrospinal fluid 14-3-3 and total tau are elevated but lack specificity. RT-QuIC is the most informative CSF test, with specificity around 99 percent and sensitivity above 90 percent for second generation assays, and can be run on olfactory mucosa brushings. Neurofilament light and phosphorylated neurofilament heavy are mainly research tools. PRNP sequencing is described as essential when genetic disease is suspected.

Practice follows this. The Italian National CJD Registry offers PrP RT-QuIC on cerebrospinal fluid and genetic analysis to physicians, with consent forms covering CSF, urine, olfactory mucosa and saliva, and states that it no longer performs the CSF 14-3-3 test. The tests as a patient meets them are listed in tests.

Which patients test negative?

Ng and colleagues characterised the negative results in the United Kingdom surveillance programme. Of 250 definite sporadic CJD cases, 27, or 10.8 percent, were CSF RT-QuIC negative. Those patients were younger at onset, with a median of 62 against 68 years, and had a longer disease duration. They were less likely to have gait difficulties, at 73 percent against 93 percent, or motor symptoms, at 62 percent against 80 percent. EEG and diffusion-weighted MRI sensitivity were similar in both groups. The VV1 and MM2 subtypes were overrepresented among the negatives, at 32 percent against 1 percent and 21 percent against 3 percent, and co-occurring neurodegenerative disease was found in 9 of the 27.

A negative RT-QuIC therefore carries different weight depending on the clinical picture. The subtype pattern behind this is set out in sporadic CJD subtypes.

Can peripheral tissue replace a lumbar puncture?

Mammana and colleagues tested 71 skin punch biopsy samples from 35 CJD patients, five of them sampled in life, and reported 89 percent sensitivity and 100 percent specificity for skin prion RT-QuIC. Seeding activity appeared higher in the sporadic subtypes associated with the V2 strain, VV2 and MV2K, than in typical MM1, which the authors describe as resting on a limited number of cases.

Assay format also affects what is detectable. Cheng and colleagues compared an end point readout with real-time RT-QuIC on 91 retrospective cerebrospinal fluid samples, 45 confirmed CJD against 46 non-CJD, obtaining 98 percent sensitivity and 91 percent specificity for the end point format against 96 percent and 98 percent for RT-QuIC, and 84 percent and 70 percent for 14-3-3. The cut-offs were derived from the same panel, which limits what the figures establish about prospective use.

What does neuropathology still provide?

Definite diagnosis requires tissue. Method development here is older and well characterised. Schulz-Schaeffer and colleagues described the paraffin-embedded tissue blot, which transfers sections to a nitrocellulose membrane, digests with high concentration proteinase K to remove normal prion protein, then probes with monoclonal antibodies. They reported moderate to strong staining across 42 sporadic CJD cases covering 15 methionine homozygous, 13 heterozygous and 14 valine homozygous codon 129 genotypes, with no staining in any of 24 control brains spanning Alzheimer disease, multi-infarct dementia, cerebral lymphoma and other conditions. In mice infected with the ME7 strain, the method detected faint signal at 30 days after inoculation against 120 days for Western blot, with clinical signs at 177 days.

Neuropathology at Homburg combines this blot with a membrane adsorption assay on native tissue, Western blot typing that distinguishes prion type 1 from type 2 by fragment size after enzyme digestion, and immunohistochemistry. Which disease the tissue shows is the subject of disease research.

How much diagnosis does surveillance actually capture?

National figures show the gap between notification and classification. The Public Health Agency of Canada factsheet reports 90 people diagnosed with CJD in Canada in 2022 and gives the breakdown as about 93 percent sporadic, about 6 percent inherited and under 1 percent acquired. The public dashboard, with data current to 30 September 2026 and last updated on 29 October 2026, instead states that genetic CJD makes up 5 to 15 percent of diagnosed cases, so the two Canadian sources do not give the same figure for the inherited share. The dashboard also counts suspected case notifications separately and notes that some do not end up meeting the surveillance case definitions.

Comparative performance across the assay formats is collected in comparing the tests, and the marker work behind the next round of assays in biomarkers.

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