RPD + myoclonus
Sporadic prion disease (sCJD)
TriadRPD + startle myoclonus → akinetic mutism
SurvivalMean ~5 mo; 90% die within 1 yr
Best early testMRI DWI cortical ribboning
Most specificCSF RT-QuIC (~99–100%)
RPD + startle myoclonus + akinetic mutism? Think prion — but rule out treatable mimics first.
Key clinical features
- Rapidly progressive dementia + startle/stimulus-sensitive myoclonus
- Akinetic mutism (late) — awake but immobile & mute
- ± cerebellar, visual/cortical, pyramidal signs
- MRI DWI cortical ribboning + caudate/putamen (DWI > FLAIR) — most useful early
- EEG periodic sharp waves ~1–2 Hz, late, ~64% (MM1)
- CSF WBC >5 argues AGAINST CJD → reconsider treatable causes
◆ Signature clue
RPD + startle myoclonus + akinetic mutism → sporadic CJD — but ~20–25% of RPDs are treatable; exclude autoimmune encephalitis, SREAT, and other mimics before calling it prion.
Diagnosis
CSF RT-QuIC = most specific antemortem test (~99–100%), has largely superseded 14-3-3 in practice. MRI DWI ribboning + caudate/putamen restriction is the best early clue; EEG PSWCs are late.
Management
No disease-modifying therapy — supportive care & counseling. First priority is to chase the treatable RPD mimics (autoimmune/paraneoplastic, SREAT, Whipple, NCSE).