Prion diseases

1. Big picture

Prion diseases are rare, fatal, transmissible neurodegenerative diseases caused by abnormal misfolded prion protein. They are important in the neurology exam because they cause rapidly progressive dementia, usually with myoclonus, ataxia, extrapyramidal/pyramidal signs, and characteristic supportive findings on MRI, CSF, and EEG.

The key exam sentence:

Think of prion disease when a patient develops rapidly progressive dementia over weeks to months, especially with myoclonus, ataxia, pyramidal or extrapyramidal signs, and typical MRI/EEG/CSF findings.

The most important exam trap:

Prions are “protein-only” infectious agents without nucleic acid, resistant to ordinary sterilization, and there is no curative treatment.

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2. Definition

Prion diseases, also called transmissible spongiform encephalopathies, are progressive neurodegenerative disorders caused by conversion of normal cellular prion protein into an abnormal misfolded form.

Normal prion protein:

PrPᶜ = normal cellular prion protein.

Abnormal prion protein:

PrPˢᶜ = misfolded, pathogenic, protease-resistant prion protein.

The abnormal prion protein induces normal prion proteins to misfold, causing a self-propagating chain reaction.

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3. Classification of human prion diseases