I-123-Ioflupane (DaTscan)¹²³I-ioflupane

Quick Answer

I-123-ioflupane binds the presynaptic dopamine transporter (DAT) in the striatum, imaging the integrity of nigrostriatal dopaminergic neurons. It distinguishes neurodegenerative parkinsonism (Parkinson disease and related disorders — reduced striatal uptake) from conditions with intact dopaminergic terminals such as essential tremor and drug-induced/psychogenic parkinsonism (normal uptake). It does not distinguish Parkinson disease from atypical parkinsonism (MSA/PSP). The thyroid is blocked with stable iodine before injection.

Mechanism

Ioflupane (FP-CIT) is a cocaine analog that binds the DAT on presynaptic dopaminergic nerve terminals in the caudate and putamen. Uptake reflects the density of functioning presynaptic terminals, which falls with nigrostriatal degeneration. It is a presynaptic marker — distinct from postsynaptic D2-receptor imaging.

Biodistribution & Preparation

Target uptake in the striatum against low brain background; free iodide goes to the thyroid unless blocked. Block the thyroid with stable iodine (e.g. potassium iodide/perchlorate) before injection, and review medications — certain stimulants, cocaine, and some agents alter DAT binding.

Clinical Indications

• Differentiating degenerative parkinsonian syndromes (abnormal) from essential tremor and drug-induced/psychogenic parkinsonism (normal).
• Supporting dementia with Lewy bodies vs Alzheimer disease (DLB shows reduced striatal uptake; AD is typically normal).
• Clarifying uncertain/atypical clinical presentations.

Interpretation

• Normal: symmetric comma/crescent-shaped striatal uptake (caudate + putamen).
• Abnormal: reduced/absent putaminal uptake, usually asymmetric, progressing toward a "period/full-stop" shape — indicating presynaptic dopaminergic degeneration.
• Quantification: striatal specific binding ratios (SBR, striatum-to-background) support the visual read.

What It Can and Cannot Tell You

An abnormal scan shows a dopaminergic deficit — not a specific disease: Parkinson disease, MSA, and PSP can all be abnormal. Its diagnostic power is the flip side — a normal scan is strong evidence against degenerative parkinsonism (confirming essential tremor, drug-induced, or psychogenic parkinsonism, and the "SWEDD" phenomenon — scans without evidence of dopaminergic deficit). To separate PD from atypical parkinsonism, other data (clinical course, MRI, cardiac MIBG, and other imaging) are needed.

Complementary Tests

• Cardiac I-123-MIBG (postganglionic sympathetic denervation) supports PD/DLB over MSA.
• FDG-PET metabolic patterns and MRI help separate atypical parkinsonian syndromes.

Reporting Checklist

• Describe striatal symmetry, putaminal involvement, and overall shape (comma → period).
• State whether the pattern indicates a dopaminergic deficit (present/absent) — not a specific disease.
• Report SBR/quantitative values supporting the visual read.
• Confirm thyroid blockade and note interfering medications.

Common Pitfalls

• Reading it as disease-specific — it only shows presence/absence of a dopaminergic deficit.
• Ignoring medication effects (certain stimulants, cocaine, some antidepressants) on DAT binding.
• Inadequate thyroid blockade (free-iodide thyroid uptake, image degradation).
• Over-relying on visual read without quantitative support in equivocal cases.

Board Pearls

DaTscan images the presynaptic dopamine transporter, so an abnormal scan shows a dopaminergic deficit — not a specific disease (Parkinson disease, MSA, PSP, and DLB can all be abnormal). Its power is the flip side: a normal scan is strong evidence against degenerative parkinsonism (confirming essential tremor or drug-induced/psychogenic parkinsonism).

Normal striata form a symmetric comma/crescent (caudate + putamen); degeneration reduces putaminal uptake first and asymmetrically, evolving toward a "period" shape. Block the thyroid with stable iodine and review DAT-altering medications.

To separate PD from atypical parkinsonism (MSA/PSP), DaTscan alone is insufficient — add clinical course, MRI, and cardiac MIBG (reduced in PD/DLB, relatively preserved in MSA). Quantitative specific binding ratios support the visual read in equivocal cases, and reduced striatal uptake also supports DLB over Alzheimer disease.

Related Pages

• Related CNS: Brain FDG & dementia imaging (DLB vs AD), amyloid & tau PET.
• Tracer: I-123-MIBG (cardiac innervation complement).
• Pitfalls: Pearls, pitfalls & normal variants.

Figure / Diagram Suggestions

• A comma → period shape-evolution plate (normal vs progressive putaminal loss).
• A presynaptic vs postsynaptic dopaminergic-imaging schematic.
• A PD vs atypical parkinsonism work-up flow (DaTscan + MIBG + MRI).

Self-Check (Board-Style)