SPECT and PET imaging of the dopaminergic system in Parkinson's disease

A sporadic Parkinson's disease model via silencing of the ubiquitin-proteasome/E3 ligase component, SKP1A

Our and other's laboratory microarray-derived transcriptomic studies in human PD substantia nigra pars compacta (SNpc) samples have opened an avenue to concentrate on potential gene intersections or cross-talks along the dopaminergic (DAergic) neurodegenerative cascade in sporadic PD (SPD). One emerging gene candidate identified was SKP1A (p19, S-phase kinase-associated protein 1A), found significantly decreased in the SNpc as confirmed later at the protein level. SKP1 is part of the Skp1, Cullin 1, F-box protein (SCF) complex, the largest known class of sophisticated ubiquitin-proteasome/E3-ligases and was found to directly interact with FBXO7, a gene defective in PARK15-linked PD. This finding has led us to the hypothesis that a targeted site-specific reduction of Skp1 levels in DAergic neuronal cell culture and animal systems may result in a progressive loss of DAergic neurons and hopefully recreate motor disabilities in animals. The second premise considers the possibility that both intrinsic and extrinsic factors (e.g., manipulation of selected genes and mitochondria impairing toxins), alleged to play central roles in DAergic neurodegeneration in PD, may act in concert as modifiers of Skp1 deficiency-induced phenotype alterations ('dual-hit' hypothesis of neurodegeneration). To examine a possible role of Skp1 in DAergic phenotype, we have initially knocked down the expression of SKP1A gene in an embryonic mouse SN-derived cell line (SN4741) with short hairpin RNA (shRNA) lentiviruses (LVs). The deficiency of SKP1A closely recapitulated cardinal features of the DAergic pathology of human PD, such as decreased expression of DAergic phenotypic markers and cell cycle aberrations. Furthermore, the knocked down cells displayed a lethal phenotype when induced to differentiate exhibiting proteinaceous round inclusion structures, which were almost identical in composition to human Lewy bodies, a hallmark of PD. These findings support a role for Skp1 in neuronal phenotype, survival, and differentiation. The identification of Skp1 as a key player in DAergic neuron function suggested that a targeted site-specific reduction of Skp1 levels in mice SNpc may result in a progressive loss of DAergic neurons and terminal projections in the striatum. The injected LV SKP1shRNA to mouse SN resulted in decreased expression of Skp1 protein levels within DAergic neurons and loss of tyrosine hydroxylase immunoreactivity (TH-IR) in both SNpc and striatum that was accompanied by time-dependent motor disabilities. The reduction of the vertical movements, that is rearing, may be reminiscent of the early occurrence of hypokinesia and axial, postural instability in PD. According to the 'dual-hit' hypothesis of neurodegenerative diseases, it is predicted that gene-gene and/or gene-environmental factors would act in concert or sequentially to propagate the pathological process of PD. Our findings are compatible with this conjecture showing that the genetic vulnerability caused by knock down of SKP1A renders DAergic SN4741 cells especially sensitive to genetic reduction of Aldh1 and exposure to the external stressors MPP+ and DA, which have been implicated in PD pathology. Future consideration should be given in manipulation SKP1A expression as therapeutic window, via its induction genetically or pharmacological, to prevent degeneration of the nigra striatal dopamine neurons, since UPS is defective.

Parkinson's Disease Subtyping Using Clinical Features and Biomarkers: Literature Review and Preliminary Study of Subtype Clustering

The second most common progressive neurodegenerative disorder, Parkinson’s disease (PD), is characterized by a broad spectrum of symptoms that are associated with its progression. Several studies have attempted to classify PD according to its clinical manifestations and establish objective biomarkers for early diagnosis and for predicting the prognosis of the disease. Recent comprehensive research on the classification of PD using clinical phenotypes has included factors such as dominance, severity, and prognosis of motor and non-motor symptoms and biomarkers. Additionally, neuroimaging studies have attempted to reveal the pathological substrate for motor symptoms. Genetic and transcriptomic studies have contributed to our understanding of the underlying molecular pathogenic mechanisms and provided a basis for classifying PD. Moreover, an understanding of the heterogeneity of clinical manifestations in PD is required for a personalized medicine approach. Herein, we discuss the possible subtypes of PD based on clinical features, neuroimaging, and biomarkers for developing personalized medicine for PD. In addition, we conduct a preliminary clustering using gait features for subtyping PD. We believe that subtyping may facilitate the development of therapeutic strategies for PD.

Dopamine transporter (DAT) imaging in Parkinson's disease and related disorders

This review gives an insight into the beginnings of dopamine transporter (DAT) imaging in the early 1990s, focussing on single photon emission tomography (SPECT). The development of the method and its consolidation as a now widely used clinical tool is described. The role of DAT-SPECT in the diagnosis and differential diagnosis of PD, atypical parkinsonian syndromes and several other different neurological disorders is reviewed. Finally the clinical research using DAT-SPECT as a biomarker for the progression of PD, for the detection of a preclinical dopaminergic lesion and its correlation with neuropathological findings is outlined.

Neurophysiological Biomarkers of Parkinson's Disease

BACKGROUND

There is a need for reliable and robust Parkinson's disease biomarkers that reflect severity and are sensitive to disease modifying investigational therapeutics.

OBJECTIVE

To demonstrate the utility of EEG as a reliable, quantitative biomarker with potential as a pharmacodynamic endpoint for use in clinical assessments of neuroprotective therapeutics for Parkison's disease.

METHODS

A multi modal study was performed including aquisition of resting state EEG data and dopamine transporter PET imaging from Parkinson's disease patients off medication and compared against age-matched controls.

RESULTS

Qualitative and test/retest analysis of the EEG data demonstrated the reliability of the methods. Source localization using low resolution brain electromagnetic tomography identified significant differences in Parkinson's patients versus control subjects in the anterior cingulate and temporal lobe, areas with established association to Parkinson's disease pathology. Changes in cortico-cortical and cortico-thalamic coupling were observed as excessive EEG beta coherence in Parkinson's disease patients, and correlated with UPDRS scores and dopamine transporter activity, supporting the potential for cortical EEG coherence to serve as a reliable measure of disease severity. Using machine learning approaches, an EEG discriminant function analysis classifier was identified that parallels the loss of dopamine synapses as measured by dopamine transporter PET.

CONCLUSION

Our results support the utility of EEG in characterizing alterations in neurophysiological oscillatory activity associated with Parkinson's disease and highlight potential as a reliable method for monitoring disease progression and as a pharmacodynamic endpoint for Parkinson's disease modification therapy.

Longitudinal Change of DAT SPECT in Parkinson's Disease and Multiple System Atrophy

BACKGROUND

Both Parkinson's disease (PD) and multiple system atrophy (MSA) are neurodegenerative disorder affecting striatonigral system. Although various lines of evidence demonstrate that dopaminergic neuron degeneration emerges before the onset of motor symptoms in PD, preclinical/prodromal progression of neurodegeneration is far less understood in MSA.

OBJECTIVE

The aim of this study was to clarify the difference in the progression of dopaminergic degeneration in MSA and PD using dopamine transporter single-photon emission computed tomography (DAT SPECT).

METHODS

We analyzed longitudinal data of the specific binding ratio (SBR), a measure of striatal radiotracer uptake, in DAT SPECT from 7 patients with MSA-C, 5 patients with MSA-P, and 18 patients with PD. We performed 2.7±0.7 scans with an interval of 9.85±6.00 months for MSA and 2 scans with an interval of 2.16±0.16 years for PD.

RESULTS

The rate of SBR decline was faster in both subtypes of MSA compared with PD, but the value was similar between MSA-P and MSA-C. The estimated SBR at the onset of initial motor symptoms was lower in PD and MSA-P than in MSA-C, especially in the predominantly affected side. SBR of the predominantly affected side starts to decrease before the onset of motor symptoms in PD and MSA-P, whereas the initiation of SBR decline is around the onset in MSA-C individuals. The decline of SBR in the less affected side was not clearly shown before the onset in MSA-P or MSA-C.

CONCLUSIONS

Our results suggest that the SBR in DAT SPECT analysis is an important pathophysiological marker reflecting the disease- and subtype-specific progression of dopaminergic degeneration in MSA and PD.

99mTc-TRODAT-1 SPECT/CT imaging as a complementary biomarker in the diagnosis of parkinsonian syndromes

INTRODUCTION

Parkinson's disease (PD) and Parkinson plus syndromes (PPS) are neurodegenerative movement disorders caused by loss of dopamine in the basal ganglia. The diagnosis of both PD and PPS is complex as it is made solely on the basis of clinical features, with no established imaging modality to aid in the diagnosis. Technetium-99m-labeled tropane derivative (Tc-TRODAT-1) binds to the dopamine transporters present in the presynaptic membrane of the dopaminergic nerve terminal. The aim of this prospective study was to investigate the potential usefulness of Tc-TRODAT-1 imaging in the diagnosis of PD and PPS.

PATIENTS AND METHODS

Fifty-eight patients with a clinical diagnosis of idiopathic PD or PPS were recruited. The severity of the disease was assessed using the Hoehn and Yahr scale. Patients in stage I and II were considered as cases of Early PD. Twenty-five apparently healthy volunteers served as controls. Brain single-photon emission computed tomography/computed tomography in all the participants was performed 3-4 h after an injection of Tc-TRODAT-1. Specific uptake ratios (SURs) of striatum were calculated for both the left and right striatum, and the values were compared between PD, PPS, and healthy volunteers.

RESULTS

A significant lower uptake of tracer activity was found in either of the striatum in PD and PPS cases compared with the control group, which showed a symmetrical comma-shaped striatal uptake. This was also reflected in the SUR values, which were significantly higher in the control group in comparison with the PD and PPS patients (P<0.001). A significant difference was also found in the SUR values between the cases of early PD and control group (P<0.001).No significant difference was noted among the SUR values in different Hoehn and Yahr stages.

CONCLUSION

For clinical practice, both the visual analysis and the quantitative parameters of Tc-TRODAT-1 single-photon emission computed tomography/computed tomography showed usefulness in distinguishing cases of PD and PPS from the healthy individuals.

In Vivo Molecular Imaging for Biomedical Analysis and Therapies

In vivo molecular imaging is a powerful tool to analyze the human body. Precision medicine is receiving high attention these days, and molecular imaging plays an important role as companion diagnostics in precision medicine. Nuclear imaging with PET or SPECT and optical imaging technologies are used for in vivo molecular imaging. Nuclear imaging is superior for quantitative imaging, and whole-body analysis is possible even for humans. Optical imaging is superior due to its ease of use, and highly targeted specific imaging is possible with activatable agents. However, with optical imaging using fluorescence, it is difficult to obtain a signal from deep tissue and quantitation is difficult due to the attenuation and scattering of the fluorescent signal. Recently, to overcome these issues, optoacoustic imaging has been used in in vivo imaging. In this article, we review in vivo molecular imaging with nuclear and optical imaging and discuss their utility for precision medicine.

Cognitive Impairment Associated with Parkinson's Disease: Role of Mitochondria

Parkinson's disease (PD) is a movement disorder and is associated with some of the intellectual disabilities like cognitive dysfunctions. PD associated cognitive dysfunctions have been proved well in both preclinical and clinical set ups. Like other neurodegenerative diseases, insults to mitochondria have a significant role in the pathobiology of PD associated dementia (PDD). Neurotoxins like MPTP, mutations of the mitochondrial genes, oxidative stress, imbalanced redox mechanisms and dysregulated mitochondrial dynamics have been implicated in mitochondrial dysfunctions and have paramount importance in the pathobiology of PDD. However, the extent of contribution of mitochondrial dysfunctions towards cognitive deficits in PD has not been characterized completely. In this review we highlight on the contribution of mitochondrial dysfunction to PDD. We also highlight different behavioural tests used in nonhuman primate and rodent models for assessing cognitive deficits and some common techniques for evaluation of mitochondrial dysfunction in PDD.

Structural and functional imaging in parkinsonian syndromes

Movement disorders with parkinsonian features are common, and in recent years imaging has assumed a greater role in diagnosis and management. Thus, it is important that radiologists become familiar with the most common imaging patterns of parkinsonism, especially given the significant clinical overlap and diagnostic difficulty associated with these disorders. The authors review the most common magnetic resonance (MR) and molecular imaging patterns of idiopathic Parkinson disease and atypical parkinsonian syndromes. They also discuss the interpretation of clinically available molecular imaging studies, including assessment of cerebral metabolism with 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET), cortical amyloid deposition with carbon 11 ((11)C) Pittsburgh compound B and fluorine 18 ((18)F) florbetapir PET, and dopaminergic activity with iodine 123 ((123)I) ioflupane single photon emission computed tomography (SPECT). Although no single imaging test is diagnostic, a combination of tests may help narrow the differential diagnosis. Findings at (123)I ioflupane SPECT can confirm the loss of dopaminergic neurons in patients with parkinsonism and help distinguish these syndromes from treatable conditions, including essential tremor and drug-induced parkinsonism. FDG PET uptake can demonstrate patterns of neuronal dysfunction that are specific to a particular parkinsonian syndrome. Although MR imaging findings are typically nonspecific in parkinsonian syndromes, classic patterns of T2 signal change can be seen in multiple system atrophy and progressive supranuclear palsy. Finally, positive amyloid-binding PET findings can support the diagnosis of dementia with Lewy bodies. Combined with a thorough clinical evaluation, multimodality imaging information can afford accurate diagnosis, allow selection of appropriate therapy, and provide important prognostic information.

Flow cytometry analysis of synaptosomes from post-mortem human brain reveals changes specific to Lewy body and Alzheimer's disease

Synaptic dysfunction is thought to have an important role in the pathophysiology of neurodegenerative diseases, such as Alzheimer's disease (AD) and Lewy body disease (LBD). To improve our understanding of synaptic alterations in health and disease, we investigated synaptosomes prepared from post-mortem human cerebral cortex, putamen (PT), and two regions of the caudate nucleus, dorso-lateral (DL) and ventro-medial (VM), regions commonly affected in AD and LBD. We observed that the fraction of synaptosomal particles with reactivity for dopamine transporter (DAT) was significantly reduced in the PT and VM caudate of patients with neuropathological diagnosis of LBD. As expected, these differences also were reflected in direct measurements of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in caudate and PT of LBD patients. The fraction of synaptosomal particles positive for amyloid β (Aβ) was significantly increased in frontal cortical samples of patients with the neuropathological diagnosis of severe AD, and was positively correlated with disease progression. We also prepared synaptosomes from the striatum of mice with severe loss of DA neurons (Slc6a3-DTR mice) and wild-type littermate controls. We observed markedly reduced levels of DAT-positive synaptosomes in Slc6a3-DTR mice following exposure to diphtheria toxin (DT). Striatal levels of DA and DOPAC in Slc6a3-DTR mice also were reduced significantly following DT exposure. We conclude that flow cytometric analysis of synaptosomes prepared from human or mouse brain provides an opportunity to study expression of pathology-associated proteins and also the specific loss of dopaminergic nerve terminals. Hence, we believe it is a valid method to detect pathological changes at the level of the synapse in LBD as well as AD.

Deranged NMDAergic cortico-subthalamic transmission underlies parkinsonian motor deficits

Parkinson's disease (PD) is the most prevalent hypokinetic movement disorder, and symptomatic PD pathogenesis has been ascribed to imbalances between the direct and indirect pathways in the basal ganglia circuitry. Here, we applied glutamate receptor blockers to the subthalamic nucleus (STN) of parkinsonian rats and evaluated locomotor behaviors via single-unit and local-field recordings. Using this model, we found that inhibition of NMDAergic cortico-subthalamic transmission ameliorates parkinsonian motor deficits without eliciting any vivid turning behavior and abolishes electrophysiological abnormalities, including excessive subthalamic bursts, cortico-subthalamic synchronization, and in situ beta synchronization in both the motor cortex and STN. Premotor cortex stimulation revealed that cortico-subthalamic transmission is deranged in PD and directly responsible for the excessive stimulation-dependent bursts and time-locked spikes in the STN, explaining the genesis of PD-associated pathological bursts and synchronization, respectively. Moreover, application of a dopaminergic agent via a microinfusion cannula localized the therapeutic effect to the STN, without correcting striatal dopamine deficiency. Finally, optogenetic overactivation and synchronization of cortico-subthalamic transmission alone sufficiently and instantaneously induced parkinsonian-associated locomotor dysfunction in normal mice. In addition to the classic theory emphasizing the direct-indirect pathways, our data suggest that deranged cortico-subthalamic transmission via the NMDA receptor also plays a central role in the pathophysiology of parkinsonian motor deficits.

Pre- and postsynaptic dopamine SPECT in idiopathic Parkinsonian diseases: a follow-up study

We prospectively evaluated the diagnostic contribution of (123)I-FP-Cit (DAT) and (123)I-IBZM (IBZM) SPECT in 29 patients with Parkinson's disease (PD) (74.4 ± 4.2 years) and 28 patients with atypical parkinsonian diseases (APD) (74.3 ± 9.2 years). Twelve had multiple system atrophy (MSA) and 16 progressive supranuclear palsy (PSP). Sixteen age-matched healthy controls (HC) were included. DAT and IBZM SPECTs were made at baseline and after 1 year in all PD patients and in 20 (DAT) and 18 (IBZM) of the APD patients, and after 3 years in 22 (DAT) and 17 (IBZM) of the PD patients and in 10 (DAT) and 10 (IBZM) of the APD patients. The relative DAT uptake decrease was faster in PD and PSP than in HC and MSA. In PSP the DAT uptake was lower than in MSA after 1 year but not after 3 years. Baseline IBZM uptake was not significantly different between patients and HC or between PD and APD. One year after initiated dopaminergic treatment the mean IBZM uptake in the MSA patients remained high compared to PSP and after 3 years compared to PD, PSP, and HC. Thus, the pattern of uptake of these ligands over time may be of value in discriminating between these diagnoses.

Aging of the dopaminergic system and motor behavior in mice intoxicated with the parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication of mice is a standard model of Parkinson's disease (PD). However, it does not reproduce functionally PD. Given the occurrence of PD during aging, symptoms might only be detected in MPTP-intoxicated mice after aging. To address this, mice injected with MPTP at 2.5 months were followed up to a maximum age of 21 months. There was no loss of dopamine cells with aging in control mice; moreover, the initial post-MPTP intoxication decrease in dopamine cell was no longer significant at 21 months. With aging, striatal dopamine level remained constant, but concentrations of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were markedly reduced in both groups. There was also a late impairment of fine motor skills. After MPTP intoxication, hyperactivity was immediately detected and it became greater than in control mice from 14 months of age; fine motor skills were also more impaired; both these symptoms were correlated with striatal dopamine, DOPAC and HVA concentrations. In bothgroups, neither motor symptoms nor dopamine changes worsened with age. These findings do not support the notion that PD develops with age in mice after MPTP intoxication and that the motor deficits seen are because of an aging process.

The significance of neuronal lateralisation in Parkinson's disease

The destruction of the dopaminergic neurons in the substantia nigra (SN) and consequent depletion of striatal dopamine elicits the main movement deficits related to Parkinson's disease (PD). In the early stages of the illness, the motor symptoms are often exhibited asymmetrically. Thus, the onset of PD features starts on either the right or left side. The side of onset appears to determine the prognosis of the disorder and other features, such as right-side tremor dominance has a better prognosis in contrast to left-side dominant bradykinesia-rigidity. In addition, left-side onset of motor features is associated with cognitive decline. Therefore, an intricate relation appears to exist between the side of disease onset and progression/severity and other non-motor symptoms. Unilateral PD in turn corresponds to neuronal nigrostriatal degeneration in the contralateral hemisphere. Indeed positron emission tomography has demonstrated a positive correlation between symptom asymmetry and brain function (Hoorn et al. Parkinsonism Relat Disord 17:58-60, 2011), which corresponds to a unilateral pattern of degeneration. This phenomenon appears to be exclusive to PD. Additionally, the variation in motor symptom(s) dominance exhibited in the disorder conforms to the notion that PD is a spectrum disease with many sub-groups. Thus, clinical and post mortem studies on "lateralisation" may serve as a vital tool in understanding the mechanism(s) eliciting the characteristic destruction of the SN neurons. Additionally, it may be employed as a predictive indicator for the symptomology and prognosis of the illness thus allowing selective treatment strategies targeted at the pronounced hemispheric degeneration.

Metabolomic profiling in LRRK2-related Parkinson's disease

Background

Mutations in LRRK2 gene represent the most common known genetic cause of Parkinson's disease (PD).

Methodology/Principal Findings

We used metabolomic profiling to identify biomarkers that are associated with idiopathic and LRRK2 PD. We compared plasma metabolomic profiles of patients with PD due to the G2019S LRRK2 mutation, to asymptomatic family members of these patients either with or without G2019S LRRK2 mutations, and to patients with idiopathic PD, as well as non-related control subjects. We found that metabolomic profiles of both idiopathic PD and LRRK2 PD subjects were clearly separated from controls. LRRK2 PD patients had metabolomic profiles distinguishable from those with idiopathic PD, and the profiles could predict whether the PD was secondary to LRRK2 mutations or idiopathic. Metabolomic profiles of LRRK2 PD patients were well separated from their family members, but there was a slight overlap between family members with and without LRRK2 mutations. Both LRRK2 and idiopathic PD patients showed significantly reduced uric acid levels. We also found a significant decrease in levels of hypoxanthine and in the ratios of major metabolites of the purine pathway in plasma of PD patients.

Conclusions/Significance

These findings show that LRRK2 patients with the G2019S mutation have unique metabolomic profiles that distinguish them from patients with idiopathic PD. Furthermore, asymptomatic LRRK2 carriers can be separated from gene negative family members, which raises the possibility that metabolomic profiles could be useful in predicting which LRRK2 carriers will eventually develop PD. The results also suggest that there are aberrations in the purine pathway in PD which may occur upstream from uric acid.

Current concepts in stereotactic radiosurgery - a neurosurgical and radiooncological point of view

Stereotactic radiosurgery is related to the history of "radiotherapy" and "stereotactic neurosurgery". The concepts for neurosurgeons and radiooncologists have been changed during the last decade and have also transformed neurosurgery. The gamma knife and the stereotactically modified linear accelerator (LINAC) are radiosurgical equipments to treat predetermined intracranial targets through the intact skull without damaging the surrounding normal brain tissue. These technical developments allow a more precise intracranial lesion control and offer even more conformal dose plans for irregularly shaped lesions. Histological determination by stereotactic biopsy remains the basis for any otherwise undefined intracranial lesion. As a minimal approach, it allows functional preservation, low risk and high sensitivity. Long-term results have been published for various indications. The impact of radiosurgery is presented for the management of gliomas, metastases, brain stem lesions, benign tumours and vascular malformations and selected functional disorders such as trigeminal neuralgia. In AVM's it can be performed as part of a multimodality strategy including resection or endovascular embolisation. Finally, the technological advances in radiation oncology as well as stereotactic neurosurgery have led to significant improvements in radiosurgical treatment opportunities. Novel indications are currently under investigation. The combination of both, the neurosurgical and the radiooncological expertise, will help to minimize the risk for the patient while achieving a greater treatment success.

Subacute hemicorporal parkinsonism in 5 patients with infarcts of the basal ganglia

In 1929, Critchley introduced the term "vascular parkinsonism" (VP), which has been the subject of considerable controversy in neurology. Parkinsonism does not appear to be a frequent consequence of striatal infarcts, although unilateral parkinsonism has been reported as an acute or subacute onset syndrome following strategic infarcts in the striatum. Previous 123-I ioflupane SPECT (DaTSCAN) studies involving radioisotope labeling of the dopamine transporter protein at presynaptic level in patients with IPD (idiopathic Parkinson's disease) have found this technique to be highly sensitive in exploring the nigrostriatal pathway. Previous studies of VP with DatSCAN have been inconclusive. The present study correlates clinical data (unilateral parkinsonism following contralateral lenticular infarction), and radiological (CT/MRI) and functional neuroimaging findings (DatSCAN) in 5 patients with CT/MRI criteria for striatal infarcts. Finally, in 2 of these patients a diagnosis of IPD was made because of the follow-up of clinical signs and pathological DaTSCAN findings not concordant with the size and location of the vascular lesion.

Does combined imaging of the pre- and postsynaptic dopaminergic system increase the diagnostic accuracy in the differential diagnosis of parkinsonism?

PURPOSE

We hypothesized that combining pre- and postsynaptic quantitative information about the dopaminergic system would provide a higher diagnostic accuracy in the differential diagnosis of parkinsonism than specific striatal D(2) receptor binding alone. Therefore, the aim of the study was to introduce new semi-quantitative parameters and evaluate their ability to discriminate between Parkinson's disease (IPS) and non-idiopathic parkinsonian syndromes (non-IPS).

METHODS

In 100 patients (69 IPS, 31 non-IPS), postsynaptic [(123)I]IBZM and presynaptic [(123)I]FP-CIT SPECT scans were evaluated by observer-independent techniques. The diagnostic performances of striatal dopamine transporter (DAT) and D(2) receptor binding, their respective asymmetries, and a combination of pre- and postsynaptic asymmetry were evaluated with ROC analyses. A logistic regression model was generated combining factors to calculate the probability for each patient of belonging to either diagnostic group.

RESULTS

D(2) receptor binding provided a sensitivity of 87.1% and a specificity of 72.5% with an area under the curve (AUC) of 0.866. The AUCs of other single parameters were lower than that of D(2) binding. A gain of diagnostic power (p = 0.026) was reached with a model combining pre- and postsynaptic asymmetries and D(2) binding (sensitivity 90.3%, specificity 73.9%, AUC 0.893).

CONCLUSION

The combination of quantitative parameters of presynaptic DAT and postsynaptic D(2) receptor binding demonstrates superior diagnostic power in the differentiation of patients with IPS and non-IPS than the established approach based on D(2) binding alone. Striatal D(2) receptor binding and the combination of DAT and IBZM binding asymmetries are the factors contributing most in separating these diagnostic groups.

Brain SPECT imaging in multiple system atrophy

Clinical diagnosis of multiple system atrophy (MSA) relays on signs and symptoms that are often difficult to identify particularly at early stage. Indeed neuropathological studies have demonstrated that MSA is the first cause of misdiagnosis in a cohort of patients presenting with parkinsonian features. Dopamine transporter imaging (DAT) shows striatal decrements in both MSA and Parkinson's disease (PD) making it not sensitive for differential diagnosis. Studies of dopamine D2 receptors with IBZM may help revealing striatal degeneration but a large overlap exist particularly if PD patients with advanced disease are included. We have measured brain flow with technetium-99m ethyl cysteinate dimer (ECD-SPECT) in 36 MSA patients and compared it with 43 PD and 39 age-matched controls. Using Statistical Parametric Mapping (SPM99) we found areas of significant reduced perfusion in the striatum, brain stem and cerebellum in MSA compared to the other groups. We believe that ECD-SPECT imaging may offer significant advantages compared to other imaging techniques in the assessment of neuronal degeneration in MSA and may help the clinician in the diagnostic characterization of patients presenting with atypical parkinsonism.

Translational research in central nervous system drug discovery

Of all the therapeutic areas, diseases of the CNS provide the biggest challenges to translational research in this era of increased productivity and novel targets. Risk reduction by translational research incorporates the "learn" phase of the "learn and confirm" paradigm proposed over a decade ago. Like traditional drug discovery in vitro and in laboratory animals, it precedes the traditional phase 1-3 studies of drug development. The focus is on ameliorating the current failure rate in phase 2 and the delays resulting from suboptimal choices in four key areas: initial test subjects, dosing, sensitive and early detection of therapeutic effect, and recognition of differences between animal models and human disease. Implementation of new technologies is the key to success in this emerging endeavor.

Possible impact of dopamine SPECT on decision-making for drug treatment in Parkinsonian syndrome

Single-photon emission computed tomography (SPECT) markers allow measuring the integrity of the brain dopaminergic system in vivo. We used dopamine transporter (DAT) SPECT with [(123)I]FP-CIT and dopamine D(2)/D(3) receptor SPECT with [(123)I]IBZM to evaluate whether there is a reduction of DAT and/or D(2)/D(3) receptor SPECT in treated and untreated patients with Parkinsonian syndrome (PS). We found that almost a quarter of our patients treated with anti-Parkinsonian medication prior to SPECT imaging did not show evidence of a presynaptic dopaminergic deficit while 37% of untreated patients were diagnosed as having Parkinson's disease. 17% of treated patients had additional loss of D(2)/D(3) receptor binding capacity in concordance with the clinical follow-up diagnoses of multiple system atrophy, progressive nuclear palsy, and vascular Parkinsonism. Apart from 38% clinically uncertain cases, SPECT was in concordance with 75% of initial clinical diagnoses. 25% were reclassified as indicated by SPECT findings and confirmed by a 1.5-year clinical follow-up. We conclude that dopamine SPECT may support establishing or refuting the clinical diagnosis and, therefore, help to make the decision for or against dopaminomimetic treatment in cases with PS.

Thiethylperazine-induced parkinsonism: in vivo demonstration of dopamine D2 receptors blockade

Thiethylperazine (Torecan) is a piperazine phenothiazine employed to relieve vertigo. Its use may be associated with extrapyramidal side effects (dystonia, akathisia, tardive dyskinesia) (Sulkava, 1984), but parkinsonism has rarely been described. We describe a woman who, 1 month after the onset of thiethylperazine treatment, developed parkinsonism that disappeared 2 months after withdrawal of the drug. However, cerebral single-photon emission computed tomography (SPECT) with the dopamine (DA) D2 receptors ligand 123I-iodobenzamide (123I-IBZM) revealed a persistent reduced DA D2 receptors activity (by 45%) in the basal ganglia (BG), which may be clinically not effective.

The dopamine D2 receptor ligand 18F-desmethoxyfallypride: an appropriate fluorinated PET tracer for the differential diagnosis of parkinsonism

For therapeutic and prognostic reasons it is important to differentiate between idiopathic parkinsonian syndrome (IPS, Parkinson's disease) and atypical parkinsonian syndromes (APS) like multiple system atrophy or progressive supranuclear palsy. Whereas IPS patients usually show a normal or upregulated postsynaptic dopamine D2 receptor profile, APS patients present decreased postsynaptic tracer binding. The aim of this prospective study was to evaluate the D2 receptor antagonist fluorine-18 desmethoxyfallypride (18F-DMFP), a recently developed positron emission tomography (PET) tracer with better clinical availability than carbon-11 raclopride, for the differential diagnosis of IPS versus APS. The study included 16 healthy control subjects and 35 patients with clinically diagnosed parkinsonism (16 IPS patients, 19 APS patients). All patients underwent PET imaging after injection of 180-200 MBq 18F-DMFP. Receiver operating characteristic (ROC) analyses were performed in order to assess the diagnostic performance of 18F-DMFP PET. We found the striatal 18F-DMFP uptake ratio to be significantly (P<0.01) reduced in the APS patients (2.44+/-0.42) compared with the healthy control subjects (3.61+/-0.43) and the IPS patients (3.21+/-0.78), whereas the uptake ratios of the IPS patients and the control subjects did not differ significantly. For the differential diagnosis of APS versus IPS, the ROC analysis of caudate 18F-DMFP binding showed a specificity, sensitivity and accuracy of 100%, 74% and 86%, respectively, as well as positive and negative predictive values of 100% and 76%, respectively. Based on these first clinical results, we consider 18F-DMFP to be an appropriate PET tracer for the differential diagnosis of parkinsonian syndromes, with the advantage of better clinical availability than 11C-labelled D2 radioligands.