DLB and PDD — structured clinical viva

Opening move

Structure: stop harmful prescribing → safety/risk → diagnosis (cores + 1-year rule) → differentials → investigations → ChEI plan with doses → psychosis ladder → RBD → prognosis. Do not debate nosology while high-potency dopamine blockade continues.[1][3]

Expected discussion points

1. Immediate safety

• Hold/stop high-dose risperidone or any high-potency D2 strategy; observe for rigidity, reduced consciousness, autonomic instability (neuroleptic sensitivity).[3]
• Exclude delirium precipitants.

2. Nosology

• Probable DLB if dementia + ≥2 core features (fluctuation, VH, RBD, spontaneous parkinsonism) or 1 core + indicative biomarker.[1]
• PDD if dementia after established PD ≥1 year (Emre).[2]
• Same Lewy continuum; temporal label differs.[1]

3. Work-up

• Standard labs, ECG, MRI; collateral for RBD.
• DaT SPECT when uncertainty remains — reduced uptake supports DLB.[9]

4. Treatment

• Non-drug and deprescribe anticholinergics first.[8]
• ChEI: rivastigmine start 1.5 mg PO BD titrate toward trial doses, or donepezil 5→10 mg daily; monitor GI, HR, falls.[4][5][8]
• Psychosis residual: clozapine low-dose with FBC monitoring; pimavanserin where available; quetiapine weak evidence — never high-potency typicals first-line.[6][7][8]

5. RBD and disposition

• Environmental safety; melatonin over clonazepam in frail elderly when meds needed.[1]
• Multidisciplinary follow-up, carer support, advance care planning.

Examiner traps

Defending high-dose antipsychotic as "just psychosis treatment"; calling this uncomplicated late-onset schizophrenia without organic LB frame; unable to name ChEI dose; equating PDD and DLB without 1-year rule; promising pimavanserin without regional access caveat.[1][3][8]

Model synthesis (30–40 seconds)

"This is probable DLB — fluctuation, visual hallucinations, RBD, and spontaneous parkinsonism with dementia, not primary late-onset schizophrenia. I will stop high-potency dopamine blockade because of neuroleptic sensitivity, complete delirium/organic work-up, start a cholinesterase inhibitor with cardiac and GI monitoring, manage residual psychosis only with specialist low-D2 strategies if needed, secure the sleep environment for RBD, and arrange joint old-age psychiatry and neurology follow-up."[1][3][4][8]