Files

T

Ross 9c86b32c3b .

2025-10-20 21:15:33 +01:00

27 KiB

Raw Permalink Blame History

title, docid, authors, breadcrumbs, category, cmeTopicId, documentVersionId, imageCount, lastUpdated, pageDescription, pageKeywords, pageTitle, enhancedTitle, type, references, breadcrumbs

title

docid

authors

breadcrumbs

KEY FACTS

Terminology
- Chronic, progressive brain disorder characterized by loss of dopaminergic neurons that leads to tremors at rest, rigidity, slowed movements, and shuffling gait
Imaging
- Dopamine transporters typically decreased for all Parkinson syndromes [Parkinson disease (PD) and atypical parkinsonism syndromes (APS)]
- Loss of dopaminergic neurons visualized on I-123 ioflupane (DaT) SPECT and F-18 fluorodopa (FDOPA) PET
- I-123 ioflupane (DaT, FP-CIT) SPECT - Molecular imaging agent that binds to dopamine transporters located on presynaptic nigrostriatal axons
- F-18 FDOPA PET - F-18 FDOPA is decarboxylated by amino acid decarboxylase to F-18 fluorodopamine and stored in presynaptic vesicles in dopaminergic nerve terminals
- Sensitivity > 90% for differentiating PD and essential tremor
- Normal DaT and FDOPA scans demonstrate comma-shaped uptake on axial images
- Abnormal scans demonstrate - Asymmetric putamen activity - Symmetrically decreased or absent putamen activity with preservation of caudate - Decreased or absent putamen activity with significantly decreased/absent caudate uptake
- Patient should be off all interfering dopaminergic medications
Top Differential Diagnoses
- PD
- Multiple system atrophy
- Progressive supranuclear palsy
- Dementia with Lewy bodies
- Corticobasal degeneration

TERMINOLOGY

Definitions
- Parkinsonian syndrome (PS) - Clinical syndrome presenting with any combination of bradykinesia, resting tremor, rigidity, and autonomic instability
- Parkinson disease **(**PD) (α-synucleinopathy) - Chronic progressive disorder caused by degenerative loss of dopaminergic neurons - Classically present with bradykinesia and at least 1 of (i) tremor &/or (ii) rigidity - Normal DaT scan considered essentially exclusionary for diagnosis
- Atypical PS (APS) - Characterized by more rapid progression and poorer prognosis than PD - Includes progressive supranuclear palsy (PSP; 4R-tauopathy), multiple system atrophy (MSA; α-synucleinopathy), and corticobasal degeneration (CBD; 4R-tauopathy)
- Dementia with Lewy bodies (DLB) (α-synucleinopathy) - Dementia + visual hallucinations, parkinsonism, cognitive fluctuations, dysautonomia, sleep disorders, and neuroleptic sensitivity
- Drug-induced parkinsonism (DIP) - Secondary parkinsonism, usually reversible
- Vascular parkinsonism (VP) - Small vessel disease, multiple lacunar infarcts in basal ganglia
- Essential tremor (ET) - Most common cause of action tremor in adults - Slow, gradual progression

IMAGING

General Features
- Loss of dopaminergic neurons on I-123 ioflupane (DaT) SPECT or F-18 fluorodopa (FDOPA) PET
- Relatively normal F-18 FDG PET/CT - Distinct abnormal patterns in APS

Imaging Recommendations

Best imaging tool

- **I-123 ioflupane (DaT, FP-CIT) SPECT**
        - Molecular imaging agent that binds to dopamine (DA) transporters located on presynaptic nigrostriatal axons
        - DA transporters typically decreased for all Parkinson syndromes (PD and APSs)
        - DA transporters are located in putamen and caudate nuclei
        - Demonstrates loss of dopaminergic neurons
        - Sensitivity > 90% for differentiating PD and ET
        - May be symmetric or asymmetric
        - Differentiates PD and APS from ET and DIP
        - PD and APS demonstrate decreased activity in putamen and caudate
        - Does **not** differentiate PD from APS or between APSs
        - Image interpretation
                  - Normal scans demonstrate comma-shaped uptake on axial images
                  - Abnormal scans demonstrate period-shaped uptake on axial images indicating more pronounced loss of uptake in putamen
                  - Abnormal uptake may be initially detected in contralateral putamen relative to clinical symptoms
                  - Abnormal patterns
                              - Asymmetric putamen activity
                              - Symmetrically decreased or absent putamen activity with preservation of caudate
                              - Decreased or absent putamen activity with significantly decreased/absent caudate uptake
- **F-18 FDOPA PET**
        - F-18 FDOPA is decarboxylated by amino acid decarboxylase to F-18 fluorodopamine and stored in presynaptic vesicles in dopaminergic nerve terminals
        - Accumulation of F-18 fluorodopamine in striatum is visually detected on PET
        - Similar uptake pattern as I-123 ioflupane in normal and disease states but benefits from better quality of PET
        - Normal scan: Comma-shaped uptake on axial images visualizing caudate and putamen
        - Abnormal scan: Asymmetric or decreased putamen activity with normal or decreased caudate activity
- **F-18 FDG PET/CT**
        - Typically normal in PD
                  - Preserved F-18 FDG PET/CT in basal ganglia differentiates PD from PS
- **MIBG cardiac SPECT**
        - Absent myocardial tracer binding in PD and LBD
        - Typically preserved in APDs, DIP, VP, ET

Protocol advice

- **I-123 ioflupane**
        - Patient should be off all interfering dopaminergic medications
                  - Cocaine, amphetamines, and methylphenidate severely decrease binding
                  - Ephedrine and phentermine may decrease binding
                  - Bupropion, fentanyl, and some anesthetics may decrease binding
        - Patient preparation
                  - Pretreat with thyroid blocker (400 mg of oral potassium solution or single dose of Lugol solution) 1 hour before tracer injection
                  - Pregnancy category C: Unknown whether I-123 can cause fetal damage or early termination of pregnancy
        - Radiopharmaceutical: I-123 ioflupane
        - Dose: 3-5 mCi (111-185 MBq) intravenously
        - Dosimetry: Striata receives highest radiation exposure, followed by bladder, bowel, and lungs (assuming thyroid is blocked)
        - Image acquisition: 3-6 hours after injection
                  - SPECT or SPECT/CT acceptable but attenuation correction is recommended
                  - Photopeak should be set to 159 keV ± 10%
                  - Low-energy, high-resolution collimator
                  - 128 x 128 matrix is recommended
                  - 30-second projection time (120 projections)
- **F-18 FDOPA**
        - Patient preparation 
                  - Premedicate with 150 mg of carbidopa orally at least 60 minutes (and no longer than 120 minutes) prior to administration of F-18 FDOPA injection
                  - Carbidopa blocks systemic/peripheral decarboxylation of F-18 FDOPA to increase uptake in brain
        - Patient should be off all interfering dopaminergic medications for at least 12 hours prior to F-18 FDOPA injection 
                  - Aromatic L-amino acid decarboxylase (AADC) inhibitors (e.g., carbidopa, benserazide, etc.)
                  - DA agonists, DA reuptake inhibitors, DA-releasing agents (DRAs), such as psychostimulants of amphetamine class, peripheral catechol-O-methyltransferase (COMT) inhibitors, and monoamine oxidase (MAO) inhibitors
        - Radiopharmaceutical: F-18 FDOPA
        - Dose: 5 mCi (185 MBq) intravenously
        - Image acquisition: 80-100 minutes after injection
                  - PET attenuation correction CT
        - Dosimetry: Critical organ is bladder wall
- F-18 FDG PET/CT
        - Patient preparation
                  - Patient should fast, stop IV fluids containing dextrose, stop parenteral feeding for 4-6 hours
                  - Blood sugar should be 150-200 mg/dL
                  - Patient should be placed in quiet, dimly lit room prior to and after injection for 30 minutes
        - Radiopharmaceutical: F-18 FDG
        - Dose: 5-20 mCi (185-740 MBq)
        - Dosimetry: Urinary bladder receives largest dose
        - Image acquisition: 30-60 minutes after injection

Artifacts and Quality Control
- Certain medications can significantly alter scan appearance and should be discontinued/documented
- Ensure patient is off competing medications if activity is diffusely low

DIFFERENTIAL DIAGNOSIS

Parkinson Disease
- I-123 ioflupane/F-18 FDOPA positive
- Amyloid PET negative
- F-18 FDG PET grossly normal, but PD-related metabolic pattern reported as increased pallidal, thalamic, and motor cortical metabolic activity associated with decreased lateral premotor and parietooccipital cortical activity
- MR T2* can show loss of swallowtail sign in substantia nigra
Atypical Parkinsonian Syndromes
- MSA - Family of neurodegenerative disorders - Symptoms include parkinsonism, ataxia, and autonomic dysfunction - Cerebellar dominant (MSA-C) and parkinsonian dominant (MSA-P) - F-18 FDG PET - MSA-C shows decreased activity in cerebellum - MSA-P shows decreased putamen activity - Amyloid PET negative - I-123 ioflupane/F-18 FDOPA positive - MR shows volume loss/T2 hyperintensity in cerebellum, middle cerebellar peduncles, and putamen
- PSP - Symptoms include parkinsonism, bradykinesia, rigidity, vertical gaze palsy, dysphagia, dysarthria - Amyloid PET negative - Ioflupane SPECT positive - Decreased F-18 FDG activity in basal ganglia, frontal lobes, anterior cingulate, midbrain - Volume loss in midbrain with relatively preserved pons, MR hummingbird sign or Mickey Mouse sign
- DLB - Symptoms include dementia, visual hallucinations, parkinsonism - I-123 ioflupane/F-18 FDOPA positive - Amyloid PET is positive in > 50% of patients - F-18 FDG PET/CT shows generalized reduced cortical uptake most pronounced in occipital region and sparing posterior cingulate gyrus cingulate island sign
- CBD - Cognitive/behavioral symptoms precede movement dysfunction - Symptoms include akinesia, rigidity, dystonia, apraxia, executive dysfunction, aphasia, "alien limb" phenomenon - Patients do not respond to levodopa - I-123 ioflupane/F-18 FDOPA positive, typically asymmetric and decreased contralateral to symptoms - Amyloid PET negative - F-18 FDG PET/CT relative decreased activity in contralateral cortex and basal ganglia - May be caused by increased ipsilateral uptake
Benign Essential Tremor
- Negative I-123 ioflupane/F-18 FDOPA
Vascular Parkinsonism
- Negative I-123 ioflupane/F-18 FDOPA
Drug-Induced Parkinsonism
- Negative I-123 ioflupane/F-18 FDOPA

PATHOLOGY

General Features
- PD accounts for > 70% of parkinsonian patients
- α-synuclein skin biopsy shows high sensitivity for PD, MSA, and DLB
- Loss of dopaminergic neurons - Affected neurons project from substantia nigra (midbrain) to putamen and caudate - Putamen typically affected earlier and more severely - Symptoms begin to show after ~ 50% of neurons are affected

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Rigidity, tremor, bradykinesia, autonomic instability

Demographics
- Prevalence of ~ 1% in adults > 65 years

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls
- I-123 ioflupane SPECT/F-18 FDOPA each differentiate between diseases related to DA loss (PD and APS) and those that mimic them clinically (benign tremor and VP)
- Cardiac MIBG may be helpful in diagnosing PD and DLB, though is typically normal in other PSs
Reporting Tips
- Reporting scheme in literature - Normal: 2 comma-shaped areas of uptake - Abnormal grade 1: Asymmetric uptake [normal (comma shape) on one side and abnormal (period shape) on other side] - Abnormal grade 2: Abnormal (period shape) reduced putamen activity bilaterally - Abnormal grade 3: Markedly reduced uptake bilaterally

cc5405dd-1797-4f98-b1a1-127b9159f5f1

References

Selected References

Images

Selected Images

Axial graphic demonstrates brain anatomy and expected area of uptake (blue) in the head of the caudate and putamen .

Axial graphic shows normal uptake (orange) of I-123 ioflupane or F-18 FDOPA overlaid on the head of the caudate and putamen .

Axial I-123 ioflupane SPECT shows normal putamen activity and caudate activity . These finding are not consistent with Parkinson disease (PD) or atypical parkinsonism syndromes (APS).

Axial I-123 ioflupane SPECT shows absent left putamen activity , preserved but decreased right putamen activity , and preserved caudate activity . These findings are consistent with PD or APS.

Axial I-123 ioflupane SPECT shows absent bilateral putamen activity and preserved caudate activity . These finding are consistent with PD or APS.

Axial I-123 ioflupane SPECT shows absent bilateral putamen activity and almost absent caudate activity. These findings are consistent with PD or APS if patient was not on any interfering medications.

Quantitative analysis of I-123 ioflupane SPECT shows the bilateral caudates have abnormally low uptake of radiotracer compared with normal controls. Note that this would be difficult to discern on visual analysis alone .

Quantitative analysis of I-123 ioflupane SPECT in the same patient shows the bilateral posterior putamina have abnormally low uptake of radiotracer compared with normal controls. Visual analysis of the putamina supports the quantitative analysis.

Axial I-123 ioflupane SPECT images in a patient with suspected PD show no significant uptake in the caudate or putamen . After the scan, it was revealed that the patient was taking modafinil, which has been reported to bind to the dopamine transporter and inhibit dopamine reuptake.

Axial I-123 ioflupane SPECT images in the same patient after discontinuation of modafinil show significant uptake in the caudate but decreased/absent uptake in the putamen .

Additional Images

Axial I-123 ioflupane SPECT shows bilateral a comma-shaped appearance, consistent with a normal study. Note the slight asymmetry between sides, which may be secondary to head positioning.

Axial I-123 Ioflupane SPECT images of the same patient from superior to inferior demonstrate the full appearance of caudate heads and putamen.

27 KiB Raw Permalink Blame History Unescape Escape

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

TERMINOLOGY

Definitions

IMAGING

General Features

Imaging Recommendations

Best imaging tool

Protocol advice

Artifacts and Quality Control

DIFFERENTIAL DIAGNOSIS

Atypical Parkinsonian Syndromes

Benign Essential Tremor

Vascular Parkinsonism

Drug-Induced Parkinsonism