A 55-year-old man presents with rapidly progressive dementia, myoclonus, and visual disturbances. EEG shows periodic sharp wave complexes. Brain biopsy shows spongiform vacuolation of the cortex with gliosis but no inflammatory infiltrate. What is the causative agent?

• A JC virus causing demyelination of white matter
• B Abnormally folded prion protein (PrPSc) causing conformational change of normal PrPC ✓
• C HSV-1 causing temporal lobe encephalitis
• D Autoantibodies against NMDA receptors causing limbic encephalitis

Explanation

The clinical triad of rapidly progressive dementia, myoclonus, and periodic EEG complexes with spongiform cortical vacuolation on biopsy are pathognomonic of Creutzfeldt-Jakob disease (CJD), a prion disease. The causative agent is PrPSc — an abnormally folded isoform of normal prion protein (PrPC) that acts as a template for conformational conversion of normal PrPC into the pathological form, propagating without nucleic acid. The absence of inflammation distinguishes prion diseases from viral encephalitis.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.