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# Prion diseases

- Lesion

Prion diseases are caused by a misfolded protein that converts normal copies; they cause rapid dementia and are always fatal.

Updated Nov 12, 2026

## Key points

- Spongiform change: small round vacuoles in the neuropil and neurons of the cortex and deep grey matter.
- Sporadic CJD: rapidly progressive dementia with startle myoclonus; periodic sharp waves on EEG, 14-3-3 and RT-QuIC positive CSF.
- Variant CJD: younger patients, psychiatric onset, florid plaques (kuru-type plaque surrounded by vacuoles); linked to BSE.
- Familial forms: familial CJD, Gerstmann-Sträussler-Scheinker, fatal familial insomnia (thalamic degeneration).
- Prions resist standard sterilisation; iatrogenic cases came from grafts, hormones and instruments.

## What it is

Prion diseases are caused by a misfolded form of the normal prion protein (PrPc) called PrPsc, which is resistant to proteases and converts normal molecules into its shape. They can be sporadic (most cases), inherited (PRNP mutations) or acquired (contaminated tissue or, in variant CJD, beef from cattle with bovine spongiform encephalopathy). The brain shows spongiform change, neuron loss and gliosis without inflammation. Death usually comes within months of the first symptoms.

## Step by step

- Normal PrPc is a membrane protein rich in alpha-helix.
- A misfolded beta-sheet form (PrPsc) arises spontaneously, from a mutation or from outside.
- PrPsc binds PrPc and converts it into more PrPsc, a chain reaction.
- PrPsc aggregates, resists proteases and spreads through the brain.
- Neurons die, the neuropil becomes spongy and astrocytes proliferate.

## Forms of prion disease

| Form | Cause | Distinguishing feature |
| --- | --- | --- |
| [Sporadic CJD](https://durgical.com/en/conditions/prion-diseases/) | Spontaneous misfolding | Older adults, months-long rapid dementia, myoclonus |
| Familial CJD, GSS, fatal familial insomnia | PRNP mutations, autosomal dominant | Insomnia and thalamic loss in FFI; ataxia and plaques in GSS |
| Iatrogenic CJD | Contaminated grafts, hormones, instruments | Long incubation |
| Variant CJD | BSE prions in food | Young adults, florid plaques, prion in lymphoid tissue |
| Kuru | Ritual cannibalism | Historical; plaques, ataxia |

## Markers

- PrP immunostain after protease digestion
- 14-3-3 protein in CSF
- RT-QuIC assay

## Clinical notes

- Suspected CJD calls for special infection-control measures for surgery and autopsy instruments.
- Prion disease is a notifiable condition in many countries.

## Memory aid

A bad fold that teaches good folds to go bad: sponge holes, no inflammation, months to live.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the infectious agent in prion disease?

A misfolded, protease-resistant form of the prion protein (PrPsc) that converts normal prion protein into its abnormal shape.

## What is the histologic hallmark of prion disease?

Spongiform change: vacuoles in the neuropil with neuron loss and gliosis, without inflammation.

## What distinguishes variant CJD from sporadic CJD?

Younger age, psychiatric onset, florid plaques and a link to eating BSE-contaminated beef.

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## Elsewhere in DurgiPedia

- [Prion protein (PrP)](https://durgical.com/en/biochemistry/enzymes/prion-protein/)

## Connections

## Related 2

- [Neurodegeneration: the protein table](https://durgical.com/en/general-pathology/neurodegeneration-the-protein-table/)
- [Alzheimer disease: plaques and tangles](https://durgical.com/en/general-pathology/alzheimer-disease-plaques-and-tangles/)

## Related conditions 2

- [Prion diseases (Creutzfeldt–Jakob)](https://durgical.com/en/conditions/prion-diseases/)
- [Dementia (major neurocognitive disorder)](https://durgical.com/en/conditions/dementia/)

## Microorganisms 1

- [Prions](https://durgical.com/en/microbiology/prions/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Creutzfeldt-Jakob Disease | CJD | MedlinePlus](https://medlineplus.gov/creutzfeldtjakobdisease.html) (MedlinePlus, US National Library of Medicine, 2026); [Prion disease: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/prion-disease/) (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/prion-diseases/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/prion-diseases/