PET Imaging in Movement Disorders

Spatiotemporal Progression Patterns of Dopamine Availability and Deep Gray Matter Volume in Parkinson Disease-Related Cognitive Impairment

BACKGROUND AND OBJECTIVES

Cognitive impairment is a frequent nonmotor symptom in patients with Parkinson disease (PD), and early cognitive decline is often attributed to dopaminergic system dysfunction. We aimed to explore spatiotemporal progression patterns of striatal dopamine availability and regional brain volume based on cognitive status among patients with PD.

METHODS

This retrospective, cross-sectional study included patients with newly diagnosed PD who were not taking medication for this condition who visited a university-affiliated hospital in Seoul between January 2018 and December 2020. Patients were classified as having normal cognition (PD-NC), mild cognitive impairment (PD-MCI), or PD dementia (PDD) based on Seoul Neuropsychological Screening Battery-II, which includes 31 subsets covering activities of daily living and 5 cognitive domains. They all had brain imaging with MRI and PET with 18F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane at baseline. Subsequently, standardized uptake value ratios (SUVRs) for regional dopamine availability and regional gray matter volumes were obtained using automated segmentation. These metrics were compared across cognitive status groups, and spatiotemporal progression patterns were analyzed using the Subtype and Stage Inference machine learning technique.

RESULTS

Among 168 patients (mean age, 73.3 ± 6.1 years; 81 [48.2%] women), 65 had PD-NC, 65 had PD-MCI, and 38 had PDD. Patients with PD-MCI exhibited lower SUVRs (3.61 ± 1.31, p < 0.001) in the caudate than patients with PD-NC (4.43 ± 1.21) but higher SUVRs than patients with PDD (2.39 ± 1.06). Patients with PD-NC had higher thalamic SUVRs (1.55 ± 0.16, p < 0.001) than patients with both PD-MCI (1.45 ± 0.16) and PDD (1.38 ± 0.19). Regional deep gray matter volumes of the caudate (p = 0.015), putamen (p = 0.012), globus pallidus (p < 0.001), thalamus (p < 0.001), hippocampus (p < 0.001), and amygdala (p < 0.001) were more reduced in patients with PD-MCI or PDD than in patients with PD-NC, and the SUVR of the caudate correlated with caudate volume (r = 0.187, p = 0.015). Hippocampal atrophy was the initial change influencing cognitive impairment. The reduced dopamine availability of the thalamus preceded reductions in volume across most deep gray matter regions.

DISCUSSION

Our finding underscores the association between decreased dopamine availability and volume of the caudate and thalamus with cognitive dysfunction in PD. The dopamine availability of the caudate and thalamus was reduced before the volume of the caudate and thalamus was decreased, highlighting the spatiotemporal association between dopaminergic and structural pathology in cognitive impairment in PD.

Obstructive Sleep Apnea and Striatal Dopamine Availability in Parkinson's Disease

BACKGROUND

Sleep disorders are frequently associated with Parkinson's disease. Obstructive sleep apnea syndrome is one of these sleep disorders and is associated with the severity of motor symptoms in Parkinson's disease. Obstructive sleep apnea can lead to dopaminergic neuronal cell degeneration and may impair the clearance of α-synuclein in Parkinson's disease. Striatal dopamine uptake is a surrogate marker of nigral dopaminergic cell damage.

OBJECTIVE

We aimed to investigate the differences in striatal dopamine availability between Parkinson's disease patients with or without obstructive sleep apnea.

METHODS

A total of 85 de novo and nonmedicated Parkinson's disease patients were enrolled. Full-night polysomnography was performed for all patients, and obstructive sleep apnea was diagnosed as apnea/hypopnea index ≥5. Positron emission tomography was performed with 18 F-N-(3-fluoropropyl)-2β-carbon ethoxy-3β-(4-iodophenyl) nortropane, and the regional standardized-uptake values were analyzed using a volume-of-interest template and compared between groups with or without obstructive sleep apnea.

RESULTS

Dopamine availability in the caudate nucleus of the obstructive sleep apnea group was significantly lower than that of the nonobstructive sleep apnea group. On subgroup analysis, such association was found in female but not in male patients. In other structures (putamen, globus pallidus, and thalamus), dopamine availability did not differ between the two groups.

CONCLUSION

This study supports the proposition that obstructive sleep apnea can contribute to reduced striatal dopamine transporter availability in Parkinson's disease. Additional studies are needed to assess the causal association between obstructive sleep apnea and the neurodegenerative process in Parkinson's disease. © 2023 International Parkinson and Movement Disorder Society.

Reliability and validity of visual analysis of [ 18 F]FE-PE2I PET/CT in early Parkinsonian disease

OBJECTIVE

[ 18 F]FE-PE2I (FE-PE2I) is a new radiotracer for dopamine transporter (DAT) imaging with PET. The aim of this study was to evaluate the visual interpretation of FE-PE2I images for the diagnosis of idiopathic Parkinsonian syndrome (IPS). The inter-rater variability, sensitivity, specificity, and diagnostic accuracy for visual interpretation of striatal FE-PE2I compared to [ 123 I]FP-CIT (FP-CIT) single-photon emission computed tomography (SPECT) was evaluated.

METHODS

Thirty patients with newly onset parkinsonism and 32 healthy controls with both an FE-PE2I and FP-CIT were included in the study. Four patients had normal DAT imaging, of which three did not fulfil the IPS criteria at the clinical reassessment after 2 years. Six raters evaluated the DAT images blinded to the clinical diagnosis, interpreting the image as being 'normal' or 'pathological', and assessed the degree of DAT-reduction in the caudate and putamen. The inter-rater agreement was assessed with intra-class correlation and Cronbach's α . For calculation of sensitivity and specificity, DAT images were defined as correctly classified if categorized as normal or pathological by ≥4/6 raters.

RESULTS

The overall agreement in visual evaluation of the FE-PE2I- and FP-CIT images was high for the IPS patients ( α  = 0.960 and 0.898, respectively), but lower in healthy controls (FE-PE2I: α  = 0.693, FP-CIT: α  = 0.657). Visual interpretation gave high sensitivity (both 0.96) but lower specificity (FE-PE2I: 0.86, FP-CIT: 0.63) with an accuracy of 90% for FE-PE2I and 77% for FP-CIT.

CONCLUSION

Visual evaluation of FE-PE2I PET imaging demonstrates high reliability and diagnostic accuracy for IPS.

Premorbid cancer and motor reserve in patients with Parkinson's disease

Decreased cancer risk has been reported in patients with Parkinson’s disease (PD), and cancer prior to PD can have a protective effect on PD risk. We investigated cancer history prior to PD diagnosis to determine if such history can enhance motor reserve in PD by assessing the association between motor deficits and striatal subregional dopamine depletion. A total of 428 newly diagnosed, drug-naïve PD patients was included in the study. PD patients were categorized into three groups of no prior neoplasia, premorbid precancerous condition, and premorbid malignant cancer before PD diagnosis. Parkinsonian motor status was assessed using the Unified Parkinson’s Disease Rating Scale (UPDRS) motor score and modified Hoehn and Yahr stage score. All patients underwent positron emission tomography (PET) with ¹⁸F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane (¹⁸F-FP-CIT), and the regional standardized uptake value ratios (SUVRs) were analyzed with a volume-of-interest template among the groups. The UPDRS motor score negatively correlated with SUVRs in the posterior putamen for all patient groups. Groups with neoplasia, especially those with premorbid cancer, showed lower motor scores despite similar levels of dopamine depletion in the posterior putamen relative to those without neoplasia. These results suggest that premorbid cancer acts as a surrogate for motor reserve in patients with PD and provide imaging evidence that history of cancer has a protective effect on PD.

Molecular Imaging of Neurodegenerative Parkinsonism

Advances in molecular PET imaging of neurodegenerative parkinsonism are reviewed with focus on neuropharmacologic radiotracers depicting terminals of selectively vulnerable neurons in these conditions. Degeneration and losses of dopamine, norepinephrine, serotonin, and acetylcholine imaging markers thus far do not differentiate among the parkinsonian conditions. Recent studies performed with [¹⁸F]fluorodeoxyglucose PET are limited by the need for automated image analysis tools and by lack of routine coverage for this imaging indication in the United States. Ongoing research engages use of novel molecular modeling and in silico methods for design of imaging ligands targeting these specific proteinopathies.

Comparison of 6-[18F]FDOPA PET with Nigrosome 1 detection in patients with parkinsonism

Background

The functional 6-[¹⁸F]FDOPA positron emission tomography (PET) can be a helpful tool in differentiating parkinsonism with dopaminergic deficiency from clinically similar differential diagnoses. Furthermore, in T2*/susceptibility-weighted imaging (SWI) magnetic resonance imaging (MRI) sequences the structural integrity of the Nigrosome 1 (N1) can be assessed by checking the presence of the swallow tail sign (STS). We therefore retrospectively compared the performance of the 6-[¹⁸F]FDOPA PET with the N1 detection in patients suspected with parkinsonian diseases. Forty-three consecutive patients (m: 23, f: 20, mean age: 63 ± 12 years) were included in the study. They underwent clinically indicated 6-[¹⁸F]FDOPA PET/MRI scans as part of their neurological evaluation of uncertain parkinsonian syndromes. Visual and semi-quantitative PET imaging results were statistically compared with visual N1 assessment on 3 T SWI. As the gold standard, we defined the clinical diagnosis at the last follow-up, which included idiopathic Parkinson syndrome (IPS; n = 18), atypical parkinsonian syndromes (APS; n = 9) and other neurological diseases without dopaminergic deficit (n = 16).

Results

Thirty-five of 43 patients (81%, Kappa 0.611) had corresponding results in 6-[¹⁸F]FDOPA PET and SWI. Seven of the remaining 8 patients were correctly diagnosed by 6-[¹⁸F]FDOPA PET alone. Sensitivity, specificity and accuracy for 6-[¹⁸F]FDOPA and N1 imaging were 93%, 94%, 93% and 82%, 75%, 79%, respectively.

Conclusions

6-[¹⁸F]FDOPA PET and Nigrosome 1 evaluation had an overall good intermodality agreement. Diagnostic agreement was very good in cases of clinically suspected idiopathic Parkinson syndrome and fair in atypical parkinsonian syndromes, but poor in patients with non-parkinsonian disorders. 6-[¹⁸F]FDOPA PET showed higher sensitivity, specificity and accuracy in discriminating parkinsonian syndromes from non-parkinsonian disorders than the N1 evaluation. In summary, the additional benefit of N1 assessment in patients with APS or parkinsonism without dopaminergic deficit needs to be proven by prospective studies.

11C- and 18F-Radiotracers for In Vivo Imaging of the Dopamine System: Past, Present and Future

The applications of positron emission tomography (PET) imaging to study brain biochemistry, and in particular the aspects of dopamine neurotransmission, have grown significantly over the 40 years since the first successful in vivo imaging studies in humans. In vivo PET imaging of dopaminergic functions of the central nervous system (CNS) including dopamine synthesis, vesicular storage, synaptic release and receptor binding, and reuptake processes, are now routinely used for studies in neurology, psychiatry, drug abuse and addiction, and drug development. Underlying these advances in PET imaging has been the development of the unique radiotracers labeled with positron-emitting radionuclides such as carbon-11 and fluorine-18. This review focuses on a selection of the more accepted and utilized PET radiotracers currently available, with a look at their past, present and future.

Molecular Imaging of Extrapyramidal Movement Disorders With Dementia: The 4R Tauopathies

Two pathologically distinct neurodegenerative conditions, progressive supranuclear palsy and corticobasal degeneration, share in common deposits of tau proteins that differ both molecularly and ultrastructurally from the common tau deposits diagnostic of Alzheimer disease. The proteinopathy in these disorders is characterized by fibrillary aggregates of 4R tau proteins. The clinical presentations of progressive supranuclear palsy and of corticobasal degeneration are often confused with more common disorders such as Parkinson disease or subtypes of frontotemporal lobar degeneration. Neither of these 4R tau disorders has effective therapy, and while there are emerging molecular imaging approaches to identify patients earlier in the course of disease, there are as yet no reliably sensitive and specific approaches to diagnoses in life. In this review, aspects of the clinical syndromes, neuropathology, and molecular biomarker imaging studies applicable to progressive supranuclear palsy and to corticobasal degeneration will be presented. Future development of more accurate molecular imaging approaches is proposed.

Synuclein in neurodegeneration

Neurodegenerative diseases are a heterogeneous group of disorders characterized by gradual progressive neuronal loss in the central nervous system. Unfortunately, the pathogenesis of many of these diseases remains unknown. Synucleins are a family of small, highly charged proteins expressed predominantly in neurons. Following their discovery, much has been learned about their structure, function, interaction with other proteins and role in neurodegenerative disease over the last two decades. One of these proteins, α-Synuclein (α-Syn), appears to be involved in many neurodegenerative disorders. These include Parkinson's disease (PD), dementia with Lewy bodies (DLB), Rapid Eye Movement Sleep Behavior Disorder (RBD) and Pure Autonomic Failure (PAF), i.e., collectively termed α-synucleinopathies. This review focuses on α-Syn dysfunction in neurodegeneration and assesses its role in synucleinopathies from a biochemical, genetic and neuroimaging perspective.

Dopamine transporter imaging in neurodegenerative movement disorders: PET vs. SPECT

Purpose

The dopamine transporter (DAT) serves as biomarker for parkinsonian syndromes. DAT can be measured in vivo with single-photon emission computed tomography (SPECT) and positron emission tomography (PET). DAT-SPECT is the current clinical molecular imaging standard. However, PET has advantages over SPECT measurements, and PET radioligands with the necessary properties for clinical applications are on the rise. Therefore, it is time to review the role of DAT imaging with SPECT compared to PET.

Methods

PubMed and Web of Science were searched for relevant literature of the previous 10 years. Four topics for comparison were used: diagnostic accuracy, quantitative accuracy, logistics, and flexibility.

Results

There are a few studies directly comparing DAT-PET and DAT-SPECT. PET and SPECT both perform well in discriminating neurodegenerative from non-neurodegenerative parkinsonism. Clinical DAT-PET imaging seems feasible only recently, thanks to simplified DAT assessments and better availability of PET radioligands and systems. The higher resolution of PET makes more comprehensive assessments of disease progression in the basal ganglia possible. Additionally, it has the possibility of multimodal target assessment.

Conclusion

DAT-SPECT is established for differentiating degenerative from non-degenerative parkinsonism. For further differentiation within neurodegenerative Parkinsonian syndromes, DAT-PET has essential benefits. Nowadays, because of wider availability of PET systems and radioligand production centers, and the possibility to use simplified quantification methods, DAT-PET imaging is feasible for clinical use. Therefore, DAT-PET needs to be considered for a more active role in the clinic to take a step forward to a more comprehensive understanding and assessment of Parkinson’s disease.

New markers in Parkinson's disease

Parkinson's disease (PD) is a chronic, debilitating neurodegenerative disorder characterized clinically by a variety of progressive motor and nonmotor symptoms. Currently, there is a dearth of diagnostic tools available to predict, diagnose or mitigate disease risk or progression, leading to a challenging dilemma within the healthcare management system. The search for a reliable biomarker for PD that reflects underlying pathology is a high priority in PD research. Currently, there is no reliable single biomarker predictive of risk for motor and cognitive decline, and there have been few longitudinal studies of temporal progression. A combination of multiple biomarkers might facilitate earlier diagnosis and more accurate prognosis in PD. In this review, we focus on the recent developments of serial biomarkers for PD from a variety of clinical, biochemical, genetic and neuroimaging perspectives.