[18F]-FDopa positron emission tomography imaging in corticobasal syndrome

PURPOSE

First, to investigate the patterns of [18F]-FDOPA positron emission tomography imaging in corticobasal syndrome using visual and semi-quantitative analysis and to compare them with patterns found in Parkinson's disease and progressive supranuclear palsy. Then, to search for correlations with clinical features and [18F]-FDG positron emission tomography imaging.

METHODS

27 corticobasal syndrome patients who underwent [18F]-FDOPA positron emission tomography imaging were retrospectively studied. They were compared to 27 matched Parkinson's disease patients, 12 progressive supranuclear palsy patients and 53 normal controls. Scans were visually assigned to one of the following patterns: normal; unilateral homogeneous striatal uptake reduction; putamen uptake reduction with putamen-caudate gradient. A semi-quantitative analysis of striatal regional uptake and asymmetry was performed and correlated to clinical features and [18F]-FDG positron emission tomography patterns.

RESULTS

[18F]-FDOPA positron emission tomography appeared visually abnormal in only 33.5% of corticobasal syndrome patients. However, semi-quantitative analysis found putaminal asymmetry in 63%. Striatal uptake was homogeneously reduced in both putamen and caudate nucleus in corticobasal syndrome patients unlike in Parkinson's disease and progressive supranuclear palsy. No correlation was found between [18F]-FDOPA positron emission tomography and clinical features. Half of corticobasal syndrome patients presented a corticobasal degeneration pattern on [18F]-FDG positron emission tomography.  CONCLUSION: [18F]-FDOPA positron emission tomography can often be normal in corticobasal syndrome patients. Semi-quantitative analysis is useful to unmask a significant asymmetry in many of them. Homogeneous striatal uptake reduction contralateral to the clinical signs is highly suggestive of corticobasal syndrome. This finding can be helpful to better characterize this syndrome with respect to Parkinson's disease and progressive supranuclear palsy.

Dopamine transporter SPECT imaging in Parkinson's disease and atypical Parkinsonism: a study of 137 patients

INTRODUCTION

Differential diagnosis between Parkinson's disease (PD) and multiple system atrophy-parkinsonian type (MSA-P), corticobasal degeneration (CBD), and progressive supranuclear palsy (PSP), collectively termed atypical Parkinsonism (AP), is challenging. Dopamine transporter density imaging with Ioflupane I¹²³ (DaTscan) is a marker of presynaptic nigrostriatal dysfunction. The primary aim of this study was to investigate the utility of DaTscan in the differential diagnosis of MSA-P, CBD, and PSP.

METHODS

Patients examined at Eginition Hospital (2011-2021), with available DaTscan data and a diagnosis of probable AP, clinically established PD, as well as a neurological control (NC) group were included. Mean binding specific index (BSI), BSI of the most affected side, asymmetry index, laterality, and caudate/putamen ratio were recorded. Analyses were performed by Kruskal-Wallis and ANCOVA.

RESULTS

137 patients were included (CBD: [Formula: see text]; MSA-P: [Formula: see text]; PSP: [Formula: see text]; PD: [Formula: see text]; NC: [Formula: see text]). There were significant differences when comparing CBS, PSP, and NC vs. all other groups combined. Pairwise between-group comparisons revealed significant differences between PSP and CBD (mean striatum BSI>1.95; sensitivity 74.1%; specificity 85.0%), CBD and MSA-P (mean striatum BSI>2.04; sensitivity 70.4%; specificity 86.7%), and CBD and PD (mean striatum BSI>2.11; sensitivity 66.7%; specificity 100.0%). There were no differences between PSP, MSA-P, and PD. PSP, MSA-P, and PD differed from NC subjects, with 100% specificity and high sensitivity. Differentiation of NC from CBD was suboptimal.

DISCUSSION

CBD patients exhibit relatively mild DaTscan abnormalities. DaTscan may assist in the differentiation of CBD from PSP. DaTscan does not differentiate among PD, MSA-P, and PSP.

Dopamine transporter SPECT imaging in corticobasal syndrome: A peak into the underlying pathology?

BACKGROUND

Multiple pathologies may underlie corticobasal syndrome (CBS), including Alzheimer's disease (AD). Dopamine transporter density imaging with Ioflupane ¹²³ I SPECT (DaTscan) may be normal in CBS. No studies to date have examined the relationship between DaTscan status and underlying pathology in CBS.

OBJECTIVES

The main objective of the study was to test whether a normal DaTscan in CBS patients is indicative of an underlying AD pathology, as determined by cerebrospinal fluid (CSF) biomarkers.

METHODS

Eighteen CBS patients were included. They were divided into patients with an AD and a non-AD disease pathology, based on their cerebrospinal fluid biochemical profile. A typical AD CSF profile was defined as an increase in total and phosphorylated at threonine 181 tau protein in addition to a decrease in amyloid-beta with 42 amino acids. DaTscan data were compared in these two groups.

RESULTS

Eight of the 18 CBS patients (44%) had a normal DaTscan. Seven of the 18 CBS patients (39%) had an AD cerebrospinal fluid biochemical profile. Two of seven CBS patients with AD biomarker profile had abnormal DaTscans. Three of 11 CBS patients with a non-AD biomarker profile had normal DaTscans. A normal DaTscan was indicative of AD pathology with suboptimal (~70%) sensitivity and specificity. Semi-quantitative DaTscan analysis did not differentiate between AD from non-AD CSF biomarker profile in CBS.

CONCLUSION

A normal DaTscan is indicative of AD in CBS, but the sensitivity and specificity of DaTscan as an in vivo marker of AD pathology is suboptimal.

VNTR polymorphism in the SLC6A3 gene does not influence dopamine transporter availability measured by [18F]FE-PE2I PET or [123I]FP-Cit SPECT

OBJECTIVE

To investigate the potential impact of polymorphism in the 3'-untranslated region (3'UTR) of the SLC6A3 gene (DAT1) on normal variation in dopamine transporter (DAT) imaging with [18F]FE-PE2I PET and [123I]FP-Cit SPECT.

METHODS

Thirty-six individuals (mean age 70.4±5.4 years) with normal [18F]FE-PE2I PET and [123I]FP-Cit SPECT were genotyped for variable number of tandem repeats (VNTR) in the 3'UTR of the DAT1 gene. The DAT-availability in the caudate and putamen as measured with [18F]FE-PE2I PET and [123I]FP-Cit SPECT, as well as in the substantia nigra with [18F]FE-PE2I PET were compared between the participants carrying one or two 9-repeat alleles (i.e. 9R+10R or 9R+9R; 47%) and the participants without a 9R allele (i.e. 10R+10R or 10R+11R; 53%). Nonparametric tests, linear regression analysis and mixed model analysis were used to assess any statistical difference in measured DAT availability between the two allele groups.

RESULTS

The measured DAT-availability in PET- and SPECT-imaging tended to be slightly higher in the 9R-group; however, the difference did not reach statistical significance in either the caudate or the putamen or the substantia nigra. Instead, age did have a significant effect on the DAT level (P < 0.05) notwithstanding the genotype.

CONCLUSION

No significant effect of DAT1-genotype was detectable in imaging with [18F]FE-PE2I PET or [123I]FP-Cit, instead, age accounted for the normal variation in DAT-PET and DAT-SPECT.

Individual Brain Metabolic Signatures in Corticobasal Syndrome

BACKGROUND

Corticobasal syndrome (CBS) is the usual clinical presentation of patients with corticobasal degeneration pathology. Nevertheless, there are CBS individuals with postmortem neuropathology typical of Alzheimer's disease (AD).

OBJECTIVE

In this study, we aim to detect FDG-PET metabolic signatures at the single-subject level in a CBS sample, also evaluated with cerebrospinal fluid (CSF) markers for AD pathology.

METHODS

21 patients (68.9±6.4 years; MMSE score = 21.7±6.3) fulfilling current criteria for CBS were enrolled. All underwent a clinical-neuropsychological assessment and an instrumental evaluation for biomarkers of neurodegeneration, amyloid and tau pathology (i.e., FDG-PET imaging and CSF Aβ42 and tau levels) at close intervals. CBS subjects were classified according to the presence or absence of CSF markers of AD pathology (i.e., low Aβ42 and high phosphorylated tau levels). Optimized voxel-based SPM procedures provided FDG-PET metabolic patterns at the single-subject and group levels.

RESULTS

Eight CBS had an AD-like CSF profile (CBS-AD), while thirteen were negative (CBS-noAD). The two subgroups did not differ in demographic characteristics or global cognitive impairment. FDG-PET SPM t-maps identified different metabolic signatures. Namely, all CBS-AD patients showed the typical AD-like hypometabolic pattern involving posterior cingulate cortex, precuneus and temporo-parietal cortex, whereas CBS-noAD cases showed bilateral hypometabolism in fronto-insular cortex and basal ganglia that is typical of the frontotemporal lobar degeneration spectrum.

DISCUSSION

These results strongly suggest the inclusion of FDG-PET imaging in the diagnostic algorithm of individuals with CBS clinical phenotype in order to early identify functional metabolic signatures due to different neuropathological substrates, thus improving the diagnostic accuracy.

Dopamine Receptors in Parkinson's Disease: A Meta-Analysis of Imaging Studies

Dopamine receptors are abundant along the central nigrostriatal tract and are expressed as 5 subtypes in two receptor families. In PD, compensatory changes in dopamine receptors emerge as a consequence of the loss of dopamine nerve terminals or dopaminergic pharmacotherapy. We performed a systematic review and meta-analysis of the available PET and single-photon emission computed tomography studies that have investigated dopamine receptors in PD, PSP and MSA. The inclusion criteria were studies including human PET or single-photon emission computed tomography imaging; dopamine receptor tracers (D1-like or D2-like) and idiopathic PD, PSP, or MSA patients compared with healthy controls. The 67 included D2-like studies had 1925 patients. Data were insufficient for an analysis of D1-like studies. PD patients had higher striatal binding early in the disease, but after a disease duration of 4.36 years, PD patients had lower binding values than healthy controls. Striatal D2R binding was highest in unmedicated early PD patients and in the striatum contralateral to the predominant motor symptoms. PSP and MSA-P patients had lower striatal D2R binding than PD patients (14.2% and 21.8%, respectively). There is initial upregulation of striatal D2Rs in PD, which downregulate on average 4 years after motor symptom onset, possibly because of agonist-induced effects. The consistent upregulation of D2Rs in the PD striatum contralateral to the predominant motor symptoms indicates that receptor changes are driven by neurodegeneration and loss of striatal neuropil. Both PSP and MSA patients have clearly lower striatal D2R binding values than PD patients, which offers an opportunity for differential diagnostics. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

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.

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.

Corticobasal degeneration

Corticobasal degeneration (CBD) is a rare neurodegenerative disease characterized by the predominance of pathological 4 repeat tau deposition in various cell types and anatomical regions. Corticobasal syndrome (CBS) is one of the clinical phenotypes associated with CBD pathology, manifesting as a progressive asymmetric akinetic-rigid, poorly levodopa-responsive parkinsonism, with cerebral cortical dysfunction. CBD can manifest as several clinical phenotypes, and similarly, CBS can also have a pathologic diagnosis other than CBD. This chapter discusses the clinical manifestations of pathologically confirmed CBD cases, the current diagnostic criteria, as well as the pathologic and neuroimaging findings of CBD/CBS. At present, therapeutic options for CBD remain symptomatic. Further research is needed to improve the clinical diagnosis of CBD, as well as studies on disease-modifying therapies for this relentlessly progressive neurodegenerative disorder.

Presynaptic Striatal Dopaminergic Function in Atypical Parkinsonism: A Metaanalysis of Imaging Studies

Multiple-system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal syndrome (CBS) have signs and symptoms overlapping those of Parkinson disease (PD), complicating their clinical diagnosis. Although presynaptic dopaminergic brain imaging with PET and SPECT is clinically widely used for patients with suspected PD, the benefit of functional imaging in atypical parkinsonism syndromes remains unclear. We compared striatal presynaptic dopaminergic function in MSA parkinsonism variant (MSA-P), MSA cerebellar variant (MSA-C), PSP, CBS, and PD using combined quantitative data from all published studies. Methods: The PubMed database was searched from inception to August 2018 for the terms "dopamine" OR "dopaminergic" AND "PET" OR "SPECT" OR "SPET" and keywords related to PD, MSA, PSP, and CBS. In total, 1,711 publications were identified. PET or SPECT studies comparing patients with atypical parkinsonism to another diagnostic group (PD, MSA, PSP, or CBS) were included. Tracers for dopamine transporter (DAT), aromatic amino acid decarboxylase (AADC), or vesicular monoamine type 2 were investigated. Tracer binding data were extracted from the original articles. Heterogeneity of the data was examined using I ² statistics, and a random-effects model was used to summarize data. Hedges g was used as an estimator of effect size in group comparisons. Results are reported according to PRISMA guidelines. Results: Thirty-five studies (29 DAT, 6 AADC, no vesicular monoamine type 2 studies) with 356 MSA-P patients, 204 PSP patients, 79 CBS patients, and 62 MSA-C patients were included in the metaanalysis. Caudate nucleus and putamen DAT function was clearly lower in PSP than in PD (caudate: 34.1% difference, g = -1.08, 95% confidence interval [CI] = -1.52 to -0.64; putamen: 18.2%, g = -0.86, 95% CI = -1.50 to -0.21) and MSA-P (striatum: 31.4%, g = -0.70, 95% CI = -1.21 to -0.19) and was clearly lower in MSA-P than in MSA-C (striatum: 46.0%, g = 1.46, 95% CI = 0.23 to 2.68). Although not significant because of limited data, aromatic l-AADC results paralleled the DAT findings. Conclusion: Striatal presynaptic DAT function is clearly lower in PSP patients than in PD and MSA-P patients and is clearly lower in MSA-P patients than in MSA-C patients.

Corticobasal syndrome: neuroimaging and neurophysiological advances

Corticobasal degeneration (CBD) is a neurodegenerative condition characterized by 4R tau protein deposition in several brain regions that clinically manifests itself as a heterogeneous atypical parkinsonism typically expressed in adulthood. The prototypical clinical phenotype of CBD is corticobasal syndrome (CBS). Important insights into the pathophysiological mechanisms underlying motor and higher cortical symptoms in CBS have been gained by using advanced neuroimaging and neurophysiological techniques. Structural and functional neuroimaging studies often show asymmetric cortical and subcortical abnormalities, mainly involving perirolandic and parietal regions and basal ganglia structures. Neurophysiological investigations including electroencephalography and somatosensory evoked potentials provide useful information on the origin of myoclonus and on cortical sensory loss. Transcranial magnetic stimulation demonstrates heterogeneous and asymmetric changes in the excitability and plasticity of primary motor cortex and abnormal hemispheric connectivity. Neuroimaging and neurophysiological abnormalities in multiple brain areas reflect asymmetric neurodegeneration, leading to asymmetric motor and higher cortical symptoms in CBS.

FDG-PET patterns associated with underlying pathology in corticobasal syndrome

OBJECTIVE

To evaluate brain ¹⁸Fluorodeoxyglucose PET (FDG-PET) differences among patients with a clinical diagnosis of corticobasal syndrome (CBS) and distinct underling primary pathologies.

METHODS

We studied 29 patients with a diagnosis of CBS who underwent FDG-PET scan and postmortem neuropathologic examination. Patients were divided into subgroups on the basis of primary pathologic diagnosis: CBS-corticobasal degeneration (CBS-CBD) (14 patients), CBS-Alzheimer disease (CBS-AD) (10 patients), and CBS-progressive supranuclear palsy (CBS-PSP) (5 patients). Thirteen age-matched healthy patients who underwent FDG-PET were the control group (HC). FDG-PET scans were compared between the subgroups and the HC using SPM-12, with a threshold of p _FWE < 0.05.

RESULTS

There were no differences in Mattis Dementia Rating Scale or finger tapping scores between CBS groups. Compared to HC, the patients with CBS presented significant hypometabolism in frontoparietal regions, including the perirolandic area, basal ganglia, and thalamus of the clinically more affected hemisphere. Patients with CBS-CBD showed a similar pattern with a more marked, bilateral involvement of the basal ganglia. Patients with CBS-AD presented with posterior, asymmetric hypometabolism, including the lateral parietal and temporal lobes and the posterior cingulate. Finally, patients with CBS-PSP disclosed a more anterior hypometabolic pattern, including the medial frontal regions and the anterior cingulate. A conjunction analysis revealed that the primary motor cortex was the only common area of hypometabolism in all groups, irrespective of pathologic diagnosis.

DISCUSSION AND CONCLUSIONS

In patients with CBS, different underling pathologies are associated with different patterns of hypometabolism. Our data suggest that FDG-PET scans could help in the etiologic diagnosis of CBS.

Dopamine transporter imaging with [18F]FE-PE2I PET and [123I]FP-CIT SPECT-a clinical comparison

Background

Dopamine transporter (DAT) imaging may be of diagnostic value in patients with clinically suspected parkinsonian disease. The purpose of this study was to compare the diagnostic performance of DAT imaging with positron emission computed tomography (PET), using the recently developed, highly DAT-selective radiopharmaceutical [¹⁸F]FE-PE2I (FE-PE2I), to the commercially available and frequently used method with [¹²³I]FP-CIT (FP-CIT) single-photon emission computed tomography (SPECT) in early-stage idiopathic parkinsonian syndrome (PS).

Methods

Twenty-two patients with a clinical de novo diagnosis of PS and 28 healthy controls (HC) participating in an on-going clinical trial of FE-PE2I were analyzed in this study. Within the trial protocol, participants are clinically reassessed 2 years after inclusion. A commercially available software was used for automatic calculation of FP-CIT-specific uptake ratio (SUR). MRI-based volumes of interest combined with threshold PET segmentation were used for FE-PE2I binding potential relative to non-displaceable binding (BP_ND) quantification and specific uptake value ratios (SUVR).

Results

PET with FE-PE2I revealed significant differences between patients with a clinical de novo diagnosis of PS and healthy controls in striatal DAT availability (p < 0.001), with excellent accuracy of predicting dopaminergic deficit in early-stage PS. The effect sizes were calculated for FE-PE2I BP_ND (Glass’s Δ = 2.95), FE-PE2I SUVR (Glass’s Δ = 2.57), and FP-CIT SUR (Glass’s Δ = 2.29). The intraclass correlation (ICC) between FE-PE2I BP_ND FP-CIT SUR was high in the caudate (ICC = 0.923), putamen (ICC = 0.922), and striatum (ICC = 0.946), p < 0.001. Five of the 22 patients displayed preserved striatal DAT availability in the striatum with both methods. At follow-up, a non-PS clinical diagnosis was confirmed in three of these, while one was clinically diagnosed with corticobasal syndrome. In these patients, FE-PE2I binding was also normal in the substantia nigra (SN), while significantly reduced in the remaining patients. FE-PE2I measurement of the mean DAT availability in the putamen was strongly correlated with BP_ND in the SN (R = 0.816, p < 0.001). Olfaction and mean putamen DAT availability was correlated using both FE-PE2I BP_ND and FP-CIT SUR (R ≥ 0.616, p < 0.001).

Conclusion

DAT imaging with FE-PE2I PET yields excellent basic diagnostic differentiation in early-stage PS, at least as good as FP-CIT SPECT.

A systematic review of lessons learned from PET molecular imaging research in atypical parkinsonism

PURPOSE

To systematically review the previous studies and current status of positron emission tomography (PET) molecular imaging research in atypical parkinsonism.

METHODS

MEDLINE, ISI Web of Science, Cochrane Library, and Scopus electronic databases were searched for articles published until 29th March 2016 and included brain PET studies in progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and corticobasal syndrome (CBS). Only articles published in English and in peer-reviewed journals were included in this review. Case-reports, reviews, and non-human studies were excluded.

RESULTS

Seventy-seven PET studies investigating the dopaminergic system, glucose metabolism, microglial activation, hyperphosphorilated tau, opioid receptors, the cholinergic system, and GABA_A receptors in PSP, MSA, and CBS patients were included in this review. Disease-specific patterns of reduced glucose metabolism have shown higher accuracy than dopaminergic imaging techniques to distinguish between parkinsonian syndromes. Microglial activation has been found in all forms of atypical parkinsonism and reflects the known distribution of neuropathologic changes in these disorders. Opioid receptors are decreased in the striatum of PSP and MSA patients. Subcortical cholinergic dysfunction was more severe in MSA and PSP than Parkinson's disease patients although no significant changes in cortical cholinergic receptors were seen in PSP with cognitive impairment. GABA_A receptors were decreased in metabolically affected cortical and subcortical regions in PSP patients.

CONCLUSIONS

PET molecular imaging has provided valuable insight for understanding the mechanisms underlying atypical parkinsonism. Changes at a molecular level occur early in the course of these neurodegenerative diseases and PET imaging provides the means to aid differential diagnosis, monitor disease progression, identify of novel targets for pharmacotherapy, and monitor response to new treatments.