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Brain nuclear medicine — dementia, parkinsonism, epilepsy and tumours

In the brain nuclear medicine measures function before structure changes: FDG shows neuronal metabolism, amyloid PET shows plaques, DaTscan shows the presynaptic dopamine terminal, and ictal SPECT shows the seizure focus.

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Why it matters in the exam

Dementia on FDG: Alzheimer disease — reduced uptake in temporoparietal cortex and the posterior cingulate and precuneus; frontotemporal — reduced uptake in the frontal lobe and anterior temporal lobe; Lewy body — occipital reduction with a preserved posterior cingulate (the "cingulate island"). A negative amyloid PET excludes Alzheimer disease as the cause; a positive one supports it, but plaques are also found in Lewy body disease, amyloid angiopathy, Down syndrome and some healthy older adults. Imaging is also used to select patients for anti-amyloid antibodies.

DaTscan (I-123 ioflupane) binds the presynaptic dopamine transporter: reduction, first in the putamen so the striatum changes from a "comma" to a "full stop", occurs in Parkinson disease, MSA, PSP and Lewy body disease; the study is normal in essential tremor, drug-induced parkinsonism and psychogenic parkinsonism. Drugs such as sertraline, bupropion, methylphenidate, amphetamines and cocaine interfere with binding. The thyroid is blocked before the study. Imaging of the postsynaptic D2 receptor separates: preserved in Parkinson disease, reduced in atypical parkinsonian syndromes.

Epilepsy: ictal SPECT — injection of HMPAO or ECD within seconds of seizure onset shows increased perfusion at the focus; interictal FDG shows reduced metabolism at the focus, usually in the temporal lobe; combining with MRI guides surgery. Brain tumours: FDG is hard to read because of the brain's high uptake; amino acid PET (FET, F-DOPA, methionine) is better for defining glioma and for separating recurrence from radiation necrosis. Brain death: absent intracranial perfusion, sometimes with a "hot nose".

Key points

• FDG — dementia patterns by region.
• Negative amyloid excludes Alzheimer disease.
• DaTscan — reduced in Parkinson, normal in essential tremor and drug-induced parkinsonism.
• Epilepsy — increased ictal perfusion, reduced interictal metabolism.
• Glioma — amino acid PET.

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Sources

• EANM Procedure Guidelines for Brain PET Imaging Using F-18 FDG Version 3, 2022 — Dementia patterns and epilepsy
• EANM Practice Guideline/SNMMI Procedure Standard for Dopaminergic Imaging in Parkinsonian Syndromes 1.0, 2020 — Interfering drugs and interpretation
• Joint EANM/SNMMI Guideline on Amyloid PET, 2022 — Appropriate use and interpretation
• PET Imaging in Glioma: Joint EANM/EANO/RANO Practice Guidelines/SNMMI Procedure Standards, 2019 — Amino acid PET for recurrence versus treatment change

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.