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KEY FACTS

Terminology
- Progressive neurodegenerative disease characterized by parkinsonism, visual hallucinations, fluctuations in cognition (alertness/attention), and other cognitive impairments leading to functional decline
Imaging
- Low dopamine transporter uptake in basal ganglia on I-123 FP-CIT SPECT similar to parkinsonian syndromes - Decreased tracer binding may be more symmetric and diffuse when compared to typical cases of Parkinson disease (PD)
- Cardiac sympathetic denervation on MIBG
- Significant occipital lobe glucose hypometabolism relative to Alzheimer disease (AD) with preservation of posterior cingulate gyrus
Top Differential Diagnoses
- PD and PD dementia (PDD)
- AD, including posterior cortical atrophy
- Frontotemporal dementia (FTD)
Pathology
- Intraneuronal aggregates of α-synuclein result in neurodegeneration
- Significant amount of Lewy body dementia (LBD) cases involve comorbid Alzheimer pathology, which can complicate decisions about amyloid-targeting therapies (ATTs)
Clinical Issues
- Parkinsonism
- Fluctuating cognition, especially in attention/alertness
- Recurrent visual hallucinations
- Progressive impairment of cognition with motor complications leading to loss of functional independence
- REM sleep behavioral disorders
- No current disease-modifying treatment for LBD

TERMINOLOGY

Abbreviations
- Lewy body dementia (LBD)
Synonyms
- Dementia with Lewy bodies
Definitions
- Progressive neurodegenerative disease of brain characterized by - Visual hallucinations - Parkinsonism (bradykinesia, rigidity, tremor) - Fluctuations in cognition (alertness/attention) - REM sleep behavioral disorder

IMAGING

General Features

Best diagnostic clue

- Indicative imaging criteria
        - Abnormally low dopamine transporter (DaT) binding in basal ganglia on DaT SPECT study
        - Absent myocardial uptake on MIBG [sympathetic denervation can also be seen with primary heart disease and diabetic neuropathy as well as Parkinson disease (PD) dementia (PDD)]
- Supportive imaging criteria
        - Medial temporal lobe hypometabolism less severe than Alzheimer disease (AD) on FDG PET
        - Significant occipital lobe glucose hypometabolism relative to AD on FDG PET
        - Preservation of posterior cingulate gyrus on FDG PET (cingulate island sign)

Location

- Cortical, subcortical, and brainstem structures; midbrain, basal ganglia, occipital lobe

Imaging Recommendations

Best imaging tool

- DaT SPECT with I-123 ioflupane (FP-CIT)
        - Binds to DaT predominantly in presynaptic striata
        - Normal uptake in caudate and putamen
        - Abnormal DaT imaging indicative feature for LBD diagnosis
        - Compared to PD, DaT findings in LBD can be more uniformly decreased between caudate and putamen and less likely asymmetric
        - DaT imaging differentiates between LBD (abnormal DaT) and AD (normal DaT)
        - Cannot reliably distinguish between other disorders with parkinsonism
- I-123 MIBG cardiac exam
        - Norepinephrine analogue taken up by sympathetic cardiac nerves
        - Cardiac sympathetic denervation seen with PD, PDD, and LBD
        - Usually preserved with atypical parkinsonian syndromes, AD, and frontotemporal dementia (FTD)
- F-18 FDG PET
        - Generalized glucose hypometabolism with significant occipital lobe hypometabolism
                  - Occipital lobe involvement may help distinguish from classic AD-like pattern of hypometabolism
                  - Similar hypometabolic pattern seen in PD and PDD
        - Medial temporal lobe hypometabolism less severe than in AD
- F-18 amyloid PET
        - Can be positive in 50% or more of LBD patients, possibly reflecting AD-LBD copathology
        - Important to consider DaT scan in patients with positive amyloid and any clinical concern for LBD before starting amyloid-targeting therapy (ATTs)

Protocol advice

- I-123 ioflupane
        - Patient preparation
                  - Patient should be off all interfering dopaminergic medications
                  - Pretreat with thyroid blocker (oral potassium solution, Lugol) 1 hour before tracer injection
                  - Pregnancy category C: Unknown whether I-123 ioflupane can cause fetal damage or early termination of pregnancy
        - Radiopharmaceutical: I-123 ioflupane
        - Dose: 3-5 mCi (111-185 MBq)
        - Dosimetry: Striata receives highest radiation exposure, followed by bladder, bowel, and lungs (assuming thyroid is blocked)
        - Image acquisition: 3-6 hours after injection
- I-123 MIBG 
        - Patient preparation
                  - Patient should be off all interfering medications
                  - Pretreatment with Lugol (KI) solution
        - Dose: 3-10 mCi (111-370 MBq)
        - Dosimetry: Bladder (assuming thyroid is blocked)
        - Image acquisition: Anterior planar imaging early (15 min) after injection and delayed (4 hours) after injection; can perform SPECT as well
        - Heart:mediastinum ratio calculated on delayed anterior planar image (< 1.8 concerning for denervation)
- F-18 FDG PET
        - 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 min
        - Radiopharmaceutical: F-18 FDG
        - Dose: 5-20 mCi (185-740 MBq)
        - Dosimetry: Urinary bladder receives largest dose
        - Image acquisition: 30-60 min after injection

DIFFERENTIAL DIAGNOSIS

Parkinson Disease and Parkinson Disease Dementia
- Neurodegenerative disease that often presents with cogwheel rigidity, shuffled gate, pill-rolling tremor at rest, bradykinesia
- Shares similar Lewy body-related neuropathology with LBD
- Dementia may develop but generally 10 years after onset of motor symptoms - PDD: PD cases where dementia is diagnosed 1 year after onset of motor symptoms
Posterior Cortical Atrophy (Visual Alzheimer Disease Variant)
- Most commonly resulting from amyloid-β and τ protein aggregates, similar to classic AD
- Visuospatial and visuoperception deficits most common, simultanagnosia
- FDG PET often shows hypometabolism in classic areas (precuneus, posterior cingulate, posterior temporal lobes) with atypical occipital involvement
- Unlike LBD, tends to involve posterior cingulate, typically more occipital asymmetric hypometabolism than LBD, negative DaT and MIBG
Alzheimer Disease
- Most common cause of dementia
- Impairments in episodic memory and other cognitive domains
- Preservation of motor functions
- Early F-18 FDG hypometabolism in parietotemporal and posterior cingulate cortices - F-18 FDG PET hypometabolism spares occipital visual cortex
- Related to aggregation of amyloid-β and τ proteins - Positive on amyloid PET
Frontotemporal Dementia
- Commonly presents with personality and behavioral changes
- Atrophy of frontal and anterior temporal lobes
- F-18 FDG PET hypometabolism primarily in frontal/anterior temporal lobes

PATHOLOGY

General Features

Etiology

- Abnormal aggregates of α-synuclein protein within neurons
- More diffusely seen than in PD

Associated abnormalities

- Significant amount of LBD cases involve comorbid Alzheimer pathology, which can complicate decisions about ATTs
        - LBD is diagnosed when dementia is present before or concurrently with parkinsonian features

Gross Pathologic & Surgical Features
- Relative preservation of total brain volume relative to other dementias
- Increased volume of lateral ventricles relative to healthy controls
- Decreased pigmentation within substantia nigra (midbrain) and loci cerulei (pons)

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Parkinsonism
- Fluctuating cognition, especially in attention/alertness
- Recurrent visual hallucinations
- REM sleep behavioral disorder

Other signs/symptoms

- Severe neuroleptic sensitivity
- Hallucinations (other than visual)
- Depression
- Severe autonomic dysfunction

Clinical profile

- 3 main types of dementia related to continuum of Lewy body clinicopathology
        - Diffuse LBD (isolated)
                  - Dementia with diffuse cortical LB pathology
                  - No other significant pathology (minimal plaques/tangles)
        - PDD
                  - PD patients diagnosed with dementia 1 year after onset of motor symptoms
                  - Onset of dementia in PD is generally 10 years after onset of motor symptoms
        - LBD-AD copathology
                  - Pathology consistent with cortical LB (α-synuclein) and AD-like pathologic changes (amyloid plaques/neurofibrillary tangles)
                  - Most common presentation, occurring in ~ 70% of LBD cases

Natural History & Prognosis
- Progressive impairment of cognition with motor complications leading to loss of functional independence - Core features include fluctuating cognition with impact on alertness/attention, visual hallucinations, and features of parkinsonism
- Memory loss is less prominent early symptom in LBD but may develop with progression of disease - Significant distinction from AD, where memory is common early symptom
Treatment
- No current disease-modifying treatment for LBD
- Several therapies may help alleviate common symptoms
- Levodopa can be used for some motor symptoms
- Cholinesterase inhibitors may be used for some cognitive symptoms
- Can have neuroleptic malignant syndrome if given some antipsychotic medications that interact with dopamine

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls
- I-123 ioflupane - Abnormally low DaT binding in basal ganglia on DaT SPECT study
- I-123 MIBG - Sympathetic cardiac denervation
- F-18 FDG PET/CT - Occipital lobe hypometabolism and normal posterior cingulate gyrus (cingulate island sign) to distinguish LBD from AD
- F-18 amyloid PET - Consider recommending DaT scan in patients with positive amyloid biomarkers and any clinical concern for LBD before starting ATTs

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References

Selected References

Images

Selected Images

Sagittal graphic of the brain depicts the territory of the primary visual cortex in the occipital lobe along the banks of the calcarine sulcus (blue) that is decreased in Lewy body dementia (LBD) on F-18 FDG PET.

Transaxial graphic of the brain outlines the occipital lobe in blue.

Posterior F-18 FDG PET with quantitative mapping shows decreased activity posteriorly (blue/purple), predominantly in the occipital lobe (red outline).

Left lateral F-18 FDG PET with quantitative mapping shows decreased activity posteriorly (blue/purple) in the same patient, predominantly in the occipital lobe (red outline). These findings are typical for LBD.

Axial F-18 FDG PET in a patient with advanced LBD shows decreased activity throughout the cortex, including the occipital lobe .

Surface images with quantitative mapping show decreased activity in the posterior cingulate gyrus, precuneus and temporal lobes (blue/purple) with sensorimotor sparing , concerning for Alzheimer disease (AD) copathology. DaT scan was not performed.

Axial F-18 FDG PET in a patient with advanced amnestic AD shows decreased activity throughout the cortex with sparing of the occipital lobe , which distinguishes it from LBD.

Surface images with quantitative mapping show decreased metabolism in a patient with AD. There is characteristic hypometabolism with sparing of the sensorimotor cortex . In contrast to LBD, there is significant sparing of the posterior visual areas in the occipital lobe .

I-123 ioflupane scan demonstrates significant abnormally decreased activity in the putamen bilaterally as can be seen in LBD, Parkinson disease, and parkinsonian syndromes.

I-123 ioflupane scan demonstrates normal symmetric activity in the head of the caudate and putamen bilaterally , effectively ruling out LBD.

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KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

TERMINOLOGY

Abbreviations

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Imaging Recommendations

Best imaging tool

Protocol advice

DIFFERENTIAL DIAGNOSIS

Posterior Cortical Atrophy (Visual Alzheimer Disease Variant)

PATHOLOGY

General Features

Etiology

Associated abnormalities

Gross Pathologic & Surgical Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Other signs/symptoms

Clinical profile

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Image Interpretation Pearls

References

Selected References

Images

Selected Images

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