What is the recommended PET study for an older adult patient with suspected Parkinsonism, presenting with tremors, rigidity, and bradykinesia?

Recommended PET Study for Parkinsonism

For patients with suspected Parkinsonism presenting with tremors, rigidity, and bradykinesia, I-123 ioflupane SPECT/CT (DaTscan) is the recommended nuclear medicine study, not PET. 1

Primary Imaging Recommendation

I-123 ioflupane SPECT/CT is the gold standard nuclear medicine study for evaluating Parkinsonian syndromes because it:

• Differentiates true Parkinsonian syndromes (PD, MSA, PSP, CBD) from essential tremor and drug-induced tremor 1
• Demonstrates abnormality early in the disease course compared to anatomic imaging 1
• Shows decreased radiotracer uptake in the striatum, typically progressing from putamen to caudate nuclei 1, 2
• A normal I-123 ioflupane SPECT/CT essentially excludes Parkinsonian syndromes 1, 3

Role of FDG-PET/CT

FDG-PET/CT has limited utility for initial Parkinsonian syndrome evaluation 1:

• There is very limited good-quality evidence supporting its use in Parkinsonian syndromes 1
• It can help differentiate PSP from idiopathic PD by showing characteristic hypometabolism patterns (medial frontal and anterior cingulate cortices, striatum, and midbrain in PSP) 1
• FDG-PET/CT is NOT the first-line nuclear medicine study for suspected Parkinsonism 1

Structural Imaging First

Before any nuclear medicine study, obtain MRI brain without IV contrast as the optimal initial imaging modality 1, 2:

• Superior soft-tissue characterization and sensitivity to iron deposition 1
• Rules out structural causes, focal lesions, or vascular disease 1
• Often normal in early PD but essential to exclude alternative diagnoses 1, 2

Clinical Algorithm

1. Clinical diagnosis remains primary: Bradykinesia plus resting tremor and/or rigidity 2
2. MRI brain without contrast first to exclude structural mimics 1, 2
3. I-123 ioflupane SPECT/CT when diagnosis is uncertain or to differentiate from essential tremor 1, 2, 3
4. FDG-PET/CT only if atypical features suggest PSP or other specific Parkinson-plus syndromes 1

Critical Pitfalls to Avoid

• Do not order amyloid PET/CT - there is no relevant literature supporting its use in Parkinsonian syndrome evaluation 1
• Do not order tau PET/CT for initial Parkinsonian syndrome workup 1
• Do not skip structural imaging - MRI is essential before functional imaging 1, 2
• Remember that I-123 ioflupane SPECT/CT cannot differentiate between different Parkinsonian syndromes (PD, MSA, PSP, CBD all show abnormal patterns) - it only separates them from non-degenerative causes 1, 4

Emerging Technologies

Note that newer PET tracers targeting postsynaptic dopamine receptors (11C-raclopride-PET, I-123-iodobenzamide SPECT) are not yet FDA-approved for clinical use 1.