Rapidly progressive dementia and prion disease (MEQ)

(i) Assessment and investigation — 6 marks

Start with tempo, not mood. Date-anchored collateral, a function-based timeline, and the question "what could he do three months ago that he cannot do today?" A family who can name a week is describing a rapidly progressive dementia, and that reordering of the differential is the mark-earning move.^[11]

Examine as a physician. Startle myoclonus, gait and limb ataxia, cortical visual function, tone, reflexes and primitive reflexes — the signs that were present in prion-negative as well as prion-positive patients, and which are missed if you only take a psychiatric history.^[12][1]

Investigations, sequenced:^[11][1][2]

• Bloods for reversible causes: B12, thiamine status, thyroid function, liver and renal function, calcium, glucose, syphilis and HIV serology, autoimmune and paraneoplastic screens.
• MRI with DWI and ADC — the request that decides the diagnosis; a routine sequence set can be reported normal when DWI is diagnostic.
• EEG, including consideration of non-convulsive status epilepticus.
• CSF: cell count, protein, 14-3-3, total tau, RT-QuIC, cytology and autoimmune encephalitis antibodies.
• PRNP sequencing where indicated, through the appropriate pathway.^{[1][2][13][17]}