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DaTSCAN in DLB — MRCPsych Paper B MCQ

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HardOld Age PsychiatryDaTSCAN in DLBMRCPsych Paper B

A 69-year-old man has progressive cognitive decline, recurrent formed visual hallucinations, marked cognitive fluctuations and spontaneous parkinsonism. The differential diagnosis remains dementia with Lewy bodies versus Alzheimer's disease. An iodine-123 ioflupane SPECT scan (DaTSCAN) is requested. Which biological signal is this scan primarily designed to assess?

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Correct answer: A — Striatal presynaptic dopamine transporter availability

DaTSCAN uses iodine-123-labelled ioflupane, which binds predominantly to presynaptic dopamine transporters in the striatum. Striatal uptake therefore reflects dopamine transporter availability and acts as a surrogate marker of the integrity of nigrostriatal dopaminergic terminals. Reduced uptake supports dementia with Lewy bodies rather than Alzheimer's disease, although a normal scan does not independently exclude DLB and the scan cannot distinguish DLB from Parkinson's disease dementia. Amyloid-beta burden is assessed using amyloid PET, while glucose utilisation is assessed using FDG-PET. Perfusion SPECT uses different tracers to measure regional blood flow. Ioflupane has some lower-affinity serotonin-transporter binding, but this is not the primary diagnostic signal measured by DaTSCAN.

Reference: Electronic Medicines Compendium. DaTSCAN 74 MBq/ml solution for injection: Summary of Product Characteristics, sections 4.1 and 5.1. Updated July 2026. https://www.medicines.org.uk/emc/product/14810/smpc