Neuropsychiatric disorder + positive RT-QuIC in CSF or other tissues OR Rapidly progressive dementia; and at least 2 out of 4 following clinical features: Myoclonus Visual or cerebellar signs Pyramidal/extrapyramidal signs Akinetic mutism AND at least 1 positive result on one of the following laboratory tests: a typical EEG (periodic sharp wave complexes) during an illness of any duration a positive 14-3-3 protein CSF assay in patients with a disease duration of less than 2 years hyperintensity in caudate nucleus/putamen on brain MRI or at least 2 cortical regions (temporal, parietal, occipital) either on diffusion-weighted imaging (DWI) or fluid attenuated inversion recovery (FLAIR) Routine investigations should not suggest an alternative diagnosis.