Early differential diagnosis of Parkinson's disease with 18F-fluorodeoxyglucose and positron emission tomography

The diagnosis of Parkinson's disease

The correct diagnosis of Parkinson's disease is important for prognostic and therapeutic reasons and is essential for clinical research. Investigations of the diagnostic accuracy for the disease and other forms of parkinsonism in community-based samples of patients taking antiparkinsonian medication confirmed a diagnosis of parkinsonism in only 74% of patients and clinically probable Parkinson's disease in 53% of patients. Clinicopathological studies based on brain bank material from the UK and Canada have shown that clinicians diagnose the disease incorrectly in about 25% of patients. In these studies, the most common reasons for misdiagnosis were presence of essential tremor, vascular parkinsonism, and atypical parkinsonian syndromes. Infrequent diagnostic errors included Alzheimer's disease, dementia with Lewy bodies, and drug-induced parkinsonism. Increasing knowledge of the heterogeneous clinical presentation of the various parkinsonisms has resulted in improved diagnostic accuracy of the various parkinsonian syndromes in specialised movement-disorder units. Also genetic testing and various other ancillary tests, such as olfactory testing, MRI, and dopamine-transporter single-photon-emission computed-tomography imaging, help with clinical diagnostic decisions.

Quantitative 1H magnetic resonance spectroscopic imaging determines therapeutic immunization efficacy in an animal model of Parkinson's disease

Nigrostriatal degeneration, the pathological hallmark of Parkinson's disease (PD), is mirrored by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. MPTP-treated animals show the common behavioral, motor, and pathological features of human disease. We demonstrated previously that adoptive transfer of Copaxone (Cop-1) immune cells protected the nigrostriatal dopaminergic pathway in MPTP-intoxicated mice. Herein, we evaluated this protection by quantitative proton magnetic resonance spectroscopic imaging (1H MRSI). 1H MRSI performed in MPTP-treated mice demonstrated that N-acetyl aspartate (NAA) was significantly diminished in the substantia nigra pars compacta (SNpc) and striatum, regions most affected in human disease. When the same regions were coregistered with immunohistochemical stains for tyrosine hydroxylase, numbers of neuronal bodies and termini were similarly diminished. MPTP-intoxicated animals that received Cop-1 immune cells showed NAA levels, in the SNpc and striatum, nearly equivalent to PBS-treated animals. Moreover, adoptive transfer of immune cells from ovalbumin-immunized to MPTP-treated mice failed to alter NAA levels or protect dopaminergic neurons and their projections. These results demonstrate that 1H MRSI can evaluate dopaminergic degeneration and its protection by Cop-1 immunization strategies. Most importantly, the results provide a monitoring system to assess therapeutic outcomes for PD.

Evidence from biomarkers and surrogate endpoints

The use of physiological, anatomical, and other biological tests is commonplace in the practice of medicine. In neurology, objectively measured tests termed biomarkers (BMs) are playing an increasing role in diagnosis and management of disease, both in clinical practice and in experimental therapeutics. This article will discuss the various applications of BMs to the assessment of therapies for neurological diseases and will use examples from neurological diseases to elucidate the strengths and potential weaknesses of BMs. As the understanding of the pathophysiology of many neurological diseases has improved, new BMs have been developed, and efforts have been made to use these as proxies for clinical endpoints. A BM used in this manner is referred to as a surrogate endpoint (SE). There are many potential advantages and disadvantages of using SEs in the evaluation of new therapies, and these will be reviewed as well. Furthermore, the evidence required for the development of an SE and the nature of the evidence that can be derived from the use of BMs and SEs will be discussed.

Neuroimaging and therapeutics in movement disorders

In this review, we discuss the role of neuroimaging in assessing treatment options for movement disorders, particularly Parkinson's disease (PD). Imaging methods to assess dopaminergic function have recently been applied in trials of potential neuroprotective agents. Other imaging methods using regional metabolism and/or cerebral perfusion have been recently introduced to quantify the modulation of network activity as an objective marker of the treatment response. Both imaging strategies have provided novel insights into the mechanisms underlying a variety of pharmacological and stereotaxic surgical treatment strategies for PD and other movement disorders.

Functional neuroimaging studies in restless legs syndrome

Functional neuroimaging studies may contribute to elucidate pathophysiological mechanisms of the restless legs syndrome (RLS) which still remain unclear. Studies in patients with RLS have been performed using functional magnetic resonance imaging (fMRI), single photon emission computed tomography (SPECT) and, more recently, positron emission tomography (PET). SPECT and PET studies revealed some controversial results of the pre- and postsynaptic dopaminergic neurotransmission system and cerebral metabolism in RLS probably reflecting a dysfunction of the central dopaminergic system. However, it still has to be determined whether these alterations affect the nigrostriatal and/or other central dopaminergic systems like the diencephalospinal or mesolimbic pathway and whether they are the primary mechanisms or only secondary phenomena within the manifestation of RLS symptoms. A subtle receptor dysfunction or a synaptic dopaminergic deficit may play a major role. fMRI investigations of RLS patients revealed an activation in the red nuclei and brainstem close to the reticular formation during the symptomatic period, suggesting that subcortical cerebral generators are involved in the pathogenesis of RLS. However, both techniques are not yet clinically relevant methods to differentiate RLS from other movement disorders during sleep. Further investigations, especially at night when RLS symptoms are most pronounced, will lead to a better understanding of the mechanisms underlying RLS.

Voxel based comparison of glucose metabolism in the differential diagnosis of the multiple system atrophy using statistical parametric mapping

OBJECTIVE

A differential diagnosis of idiopathic parkinsonian disease (IPD) and multiple system atrophy (MSA) is difficult due to their common signs and symptoms. The aim of this 18F-2-fluoro-2 deoxyglucose (18F-FDG) positron emission tomography (PET) study was to compare the regional cerebral glucose metabolism in MSA with that in IPD by statistical parametric mapping (SPM) and image registration.

METHODS

The 18F-FDG PET images of MSA and IPD patients were assessed by SPM and image registration to determine metabolic patterns that may be useful in differentiating between the two groups. Eleven patients with MSA, eight patients with IPD and 22 healthy controls participated in the study.

RESULTS

The IPD patients were found to have a significant glucose hypometabolism in comparison with the healthy controls in the prefrontal, lateral frontal, and parietotemporal cortices, and the cingulate and caudate areas (p< or =0.01, 100 voxel-level). In patients with MSA, hypometabolism was observed in the putamen, pons, and cerebellum in comparison with the healthy controls and IPD patients.

CONCLUSION

The voxel-based analysis of 18F-FDG PET images showed detailed differences between IPD and MSA, which may be useful in differentiating the two disease entities, as evidenced by the correlation of glucose metabolism with disease severity and dopamine agonist medication. The mapping analysis of 18F-FDG PET images might be a useful adjunctive method of a differential diagnosis for parkinsonism in a clinical setting.

Brain networks associated with cognitive reserve in healthy young and old adults

In order to understand the brain networks that mediate cognitive reserve, we explored the relationship between subjects' network expression during the performance of a memory test and an index of cognitive reserve. Using H2(15)O positron emission tomography, we imaged 17 healthy older subjects and 20 young adults while they performed a serial recognition memory task for nonsense shapes under two conditions: low demand, with a unique shape presented in each study trial; and titrated demand, with a study list size adjusted so that each subject recognized shapes at 75% accuracy. A factor score that summarized years of education, and scores on the NART and the WAIS-R Vocabulary subtest was used as an index of cognitive reserve. The scaled subprofile model was used to identify a set of functionally connected regions (or topography) that changed in expression across the two task conditions and was differentially expressed by the young and elderly subjects. The regions most active in this topography consisted of right hippocampus, posterior insula, thalamus, and right and left operculum; we found concomitant deactivation in right lingual gyrus, inferior parietal lobe and association cortex, left posterior cingulate, and right and left calcarine cortex. Young subjects with higher cognitive reserve showed increased expression of the topography across the two task conditions. Because this topography, which is responsive to increased task demands, was differentially expressed as a function of reserve level, it may represent a neural manifestation of innate or acquired reserve. In contrast, older subjects with higher cognitive reserve showed decreased expression of the topography across tasks. This suggests some functional reorganization of the network used by the young subjects. Thus, for the old subjects this topography may represent an altered, compensatory network that is used to maintain function in the face of age-related physiological changes.

Assessment of disease progression in parkinsonism

In this brief article, we report preliminary results from an NIH-funded project to use functional brain imaging to study the natural history of neurodegeneration during the earliest clinical stages of PD. We used positron emission tomography (PET) to measure DAT binding (18F-FPCIT), resting glucose metabolism (18FFDG), and brain activation (H215O) responses in 20 newly diagnosed PD patients. The longitudinal study is being conducted at three time points for each measurement during a 5-year period. The interim results indicate the evolution of abnormal metabolic brain networks and activation responses occurring in parallel with presynaptic nigrostriatal dopamine dysfunction in early PD.

Different metabolic patterns analysis of Parkinsonism on the 18F-FDG PET

Idiopathic Parkinson's disease (IPD), progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) are the most common movement disorders associated with neurodegenerative disease. A clinical differential diagnosis of IPD and atypical Parkinsonian disorders, such as MSA and PSP, is often complicated by the presence of symptoms common to both groups. Since Parkinsonism has a different pathophysiology in the cortical and subcortical brain structures, assessing the regional cerebral glucose metabolism may assist in making a differential diagnosis of Parkinsonism. The 18F-FDG PET images of IPD, MSA and PSP were assessed using statistical parametric mapping (SPM) in order to determine the useful metabolic patterns. Twenty-four patients with Parkinsonism: eight patients (mean age 67.9 +/- 10.7 years; M/F: 3/5) with IPD, nine patients (57.9 +/- 9.2 years; M/F: 4/5) with MSA and seven patients (67.6 +/- 4.8 years; M/F: 3/4) with PSP were enrolled in this study. All patients with Parkinsonism and 22 age-matched normal controls underwent 18F-FDG PET, (after 370 MBq 18F-FDG). The three groups and the individual IPD, MSA and PSP patients were compared with a normal control group using a two-sided t-test of SPM (uncorrected P < 0.01, extent threshold > 100 voxel). The IPD, MSA and PSP groups showed significant hypometabolism in the cerebral neocortex compared to the normal control group. The MSA group showed significant hypometabolism in the putamen, pons and cerebellum compared to the normal controls and IPD groups. In addition, PSP showed significant hypometabolism in the caudate nucleus, the thalamus, midbrain and the cingulate gyrus compared to the normal controls, the IPD and the MSA groups. In conclusion, an assessment of the 18F-FDG PET images using SPM may be a useful adjunct to a clinical examination when making a differential diagnosis of Parkinsonism.

Covariance PET patterns in early Alzheimer's disease and subjects with cognitive impairment but no dementia: utility in group discrimination and correlations with functional performance

Although multivariate analytic techniques might identify diagnostic patterns that are not captured by univariate methods, they have rarely been used to study the neural correlates of Alzheimer's disease (AD) or cognitive impairment. Nonquantitative H2(15)O PET scans were acquired during rest in 17 probable AD subjects selected for mild severity [mean-modified Mini Mental Status Examination (mMMS) 46/57; SD 5.1], 16 control subjects (mMMS 54; SD 2.5) and 23 subjects with minimal to mild cognitive impairment but no dementia (mMMS 53; SD 2.8). Expert clinical reading had low success in discriminating AD and controls. There were no significant mean flow differences among groups in traditional univariate SPM Noxel-wise analyses or region of interest (ROI) analyses. A covariance pattern was identified whose mean expression was significantly higher in the AD as compared to controls (P = 0.03; sensitivity 76-94%; specificity 63-81%). Sites of increased concomitant flow included insula, cuneus, pulvinar, lingual, fusiform, superior occipital and parahippocampal gyri, whereas decreased concomitant flow was found in cingulate, inferior parietal lobule, middle and inferior frontal, supramarginal and precentral gyri. The covariance analysis-derived pattern was then prospectively applied to the cognitively impaired subjects: as compared to subjects with Clinical Dementia Rating (CDR) = 0, subjects with CDR = 0.5 had significantly higher mean covariance pattern expression (P = 0.009). Expression of this pattern correlated inversely with Selective Reminding Test total recall (r = -0.401, P = 0.002), delayed recall (r = -0.351, P = 0.008) and mMMS scores (r = -0.401, P = 0.002) in all three groups combined. We conclude that patients with AD may differentially express resting cerebral blood flow covariance patterns even at very early disease stages. Significant alterations in expression of resting flow covariance patterns occur even for subjects with cognitive impairment. Expression of covariance patterns correlates with cognitive and functional performance measures, holding promise for meaningful associations with underlying biopathological processes.

Evaluation of animal models of Parkinson's disease for neuroprotective strategies

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of dopaminergic nigral neurons and striatal dopamine. Despite the advances of modern therapy to treat the symptoms of PD, most of the patients will eventually experience debilitating disability. The need for neuroprotective strategies that will slow or stop the progression of the disease is clear. The progress in the understanding of the cause and pathogenesis of PD is providing clues for the development of disease-modifying strategies. In that regard, animal models of PD and non-human primate models in particular, are essential for the preclinical evaluation and testing of candidate therapies. However, the diversity of models and different outcome measures used by investigators make it challenging to compare results between neuroprotective agents. In this review we will discuss methods for the selection, development and assessment of animal models of PD, the role of non-human primates and the concept of "multiple models/multiple endpoints" to predict the success in the clinic of neuroprotective strategies.

Functional imaging in Parkinson's disease and dementia with Lewy bodies

Functional imaging modalities (positron emission tomography, single photon emission tomography, magnetic resonance spectroscopy, and functional magnetic resonance) allow aspects of regional cerebral function to be evaluated in various neuropsychiatric disorders. This review will summarize the use of such techniques in current imaging studies involving Parkinson's disease and dementia with Lewy bodies, with respect to assessing regional changes, using them in differential diagnosis, and monitoring disease progression and treatment effects.

Functional brain imaging in the differential diagnosis of Parkinson's disease

The accurate diagnosis of idiopathic Parkinson's disease (IPD) is not only important for deciding on treatment strategies and providing a prognosis, but also crucial for studies designed to investigate the aetiology and pathogenesis of parkinsonian disorders. Over recent decades, improvements in the characterisation of the parkinsonian syndromes have led to improvements in clinical diagnostic accuracy; however, clinical criteria alone are not always sufficient to distinguish between IPD and other parkinsonian syndromes, particularly in the early stages of disease and in atypical presentations. Therefore, in addition to the development and implementation of diagnostic clinical assessments, there is a need for available objective markers to aid the physician in the differential diagnosis of IPD. Functional neuroimaging holds the promise of improved diagnosis and allows assessment in early disease. In this review, the use of PET and single photon emission CT in the differential diagnosis of IPD are discussed.

Differentiation of idiopathic Parkinson's disease, multiple system atrophy, progressive supranuclear palsy, and healthy controls using magnetization transfer imaging

The differentiation of multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) from idiopathic Parkinson's disease (IPD) is difficult. Magnetization transfer imaging (MTI), a measure that correlates with myelination and axonal density, was employed in this study in the attempt to distinguish between these disorders. Measurements were carried out in 15 patients with IPD, 12 patients with MSA, 10 patients with PSP, and in 20 aged-matched healthy control subjects. The main finding was a change in the magnetization transfer ratio in the globus pallidus, putamen, caudate nucleus, substantia nigra, and white matter in IPD, MSA, and PSP patients, matching the pathological features of the underlying disorder. Furthermore, stepwise linear discriminant analysis provided a good classification of the individual patients into the different disease groups. All IPD patients and control subjects were correctly separated from the MSA and PSP cohort, and all PSP patients and 11 of 12 MSA patients were correctly separated from the IPD and control cohort. There was also a fairly good discrimination of IPD patients from control subjects and of MSA from PSP patients. In conclusion, MTI revealed degenerative changes in patients with different parkinsonian syndromes matching the underlying pathological features of the different diseases, underlining the high potential of this method in distinguishing MSA and PSP from IPD.

Mapping of brain function after MPTP-induced neurotoxicity in a primate Parkinson's disease model

Neurophysiological studies of the brain in normal and Parkinson's disease (PD) patients have indicated intricate connections for basal ganglia-induced control of signaling into the motor cortex. To investigate if similar mechanisms are controlling function in the primate brain (Macaca fascicularis) after MPTP-induced neurotoxicity, we conducted PET studies of cerebral blood flow, oxygen and glucose metabolism, dopamine transporter, and D2 receptor function. Our observations after MPTP-induced dopamine terminal degeneration of the caudate and putamen revealed increased blood flow (15%) in the globus pallidus (GP), while blood flow was moderately decreased (15-25%) in the caudate, putamen, and thalamus and 40 % in the primary motor cortex (PMC). Oxygen extraction fraction was moderately increased (10-20%) in other brain areas but the thalamus, where no change was observable. Oxygen metabolism was increased in the GP and SMA (supplementary motor area including premotor cortex, Fig. 3) by a range of 20-40% and decreased in the putamen and caudate and in the PMC. Glucose metabolism was decreased in the caudate, putamen, thalamus, and PMC (range 35-50%) and enhanced in the GP by 15%. No change was observed in the SMA. In the parkinsonian primate, [(11)C]CFT (2beta-carbomethoxy-3beta-(4-fluorophenyltropane) dopamine transporter binding was significantly decreased in the putamen and caudate (range 60-65%). [(11)C]Raclopride binding of dopamine D(2) receptors did not show any significant changes. These experimental results obtained in primate studies of striato-thalamo-cortico circuitry show a similar trend as hypothetized in Parkinson's disease-type degeneration.

Looking Backward to Move Forward: Early Detection of Neurodegenerative Disorders

Early detection of neurodegenerative disorders would provide clues to the underlying pathobiology of these diseases and would enable more effective diagnosis and treatment of patients. Recent advances in molecular neuroscience have begun to provide the tools to detect diseases like Alzheimer's disease, Parkinson's disease, and others early in their course and potentially even before the development of clinical manifestations of disease. These genetic, imaging, clinical, and biochemical tools are being validated in a number of studies. Early detection of these slowly progressive diseases offers the promise of presymptomatic diagnosis and, ultimately, of disease-modifying medications for use early in disease and during the presymptomatic period.

New concepts and tools in imaging for the study of neurodegenerative disease

Existing technologies permit the detection of changes in neurotransmitter and/or neuroreceptor expression. This may be useful for diagnosis, for monitoring disease progression, and for assessing the pathogenesis of complications associated with long-term treatment. Although the binding of [11C]raclopride to D2 receptors is subject to competition from endogenous dopamine, this can be exploited to estimate changes in synaptic levels of dopamine. Assessment of processes downstream to the receptor will require the development of new approaches.

Functional imaging of cognition in Parkinson's disease

PURPOSE OF REVIEW

Cognitive deficits that occur even early in the course of Parkinson's disease have received increasing attention in current imaging research. The exact physio-pathological processes mediating the deficits and the complex relationship of cognitive signs and antiparkinsonian treatment are not well understood. A clearer understanding of these mechanisms could potentially influence treatment choices, drug development and, ultimately, patient care.

RECENT FINDINGS

Abnormal networks identified in studies of resting state metabolism in Parkinson's disease represent metabolic markers for remote effects of striato-nigral degeneration. These metabolic changes include subcortico-cortical networks, in particular cognitive cortico-striato-pallidal-thalamocortical loops. Recent brain studies focus on intervention-related brain changes. They illustrate different task-specific changes in brain activation with deep brain stimulation and with levodopa. Variable results of stimulation can be attributed to different effects on segregated cortico-striato-pallidal-thalamocortical loops during stimulation. By contrast, the heterogeneity observed in studies with levodopa possibly reflects the disease-stage and task-specific effects of levodopa. A decline in caudate dopamine modulated basal ganglia outflow appears to contribute to executive dysfunction and to brain activation changes in these loops at early Parkisnon's disease stages, while mesocortical degeneration mediated increases of inefficient dorsolateral prefrontal cortex activation may display a feature of more advanced disease stages only.

SUMMARY

Despite evidence for the role of dopamine and cortico-striato-pallidal-thalamocortical loops in cognition, the specific contributions of mesocortical dopamine depletion and striatal dysfunction with downstream consequences on the loops remain to be separated. Additionally, more research is needed into the role of non-dopaminergic pathology in cognitive decline in Parkinson's disease.

99mTc-TRODAT-1 SPECT in healthy and 6-OHDA lesioned parkinsonian monkeys: comparison with 18F-FDOPA PET

Parkinson's disease (PD) is a degeneration of the nigrostriatal dopaminergic pathway, leading to a selective loss of dopamine in the striatum. 99mTc-TRODAT-1 is a recently developed radiotracer that selectively binds to the dopamine transporters, which are significant because loss of these transporters corresponds with a loss of dopaminergic neurons. The present investigation compared 99mTc-TRODAT-1 single photon emission computed tomography (SPECT) with 18F-FDOPA positron emission tomography (PET) in the evaluation of PD using a primate model. Three monkeys, including one 6-hydroxydopamine lesioned PD model and two controls, were examined by both 99mTc-TRODAT-1 SPECT and 18F-FDOPA PET. For the PD monkey, expression of parkinsonian behaviour and 18F-FDOPA PET were used to evaluate the severity of the lesion. 99Tc-TRODAT-1 was prepared from a lyophilized kit. After intravenous injection of the radiotracer, SPECT was acquired over 4 h using a dual-head camera equipped with ultra-high resolution fan-beam collimators. Both uptake measurement and visual assessment were performed. Data were compared with motor behaviour and PET imaging. The striatal uptake in both healthy and PD monkeys increased continuously during the study, although the gradient of increase was less prominent in the diseased monkey. The increased uptake in the controls appeared to become blunt around 4 h after injection. A profound decrease of 99Tc-TRODAT-1 uptake was found in the striatum of the PD monkey compared with the controls (0.91 vs 2.16). In the PD monkey, the decrease of striatal uptake contralateral to the more affected side of the body was more prominent compared to the ipsilateral side (0.77 vs 1.06). In addition, greater loss occurred in the contralateral side of the putamen (0.54 vs 1.04). Changes of uptake ratios in the striatum and its subnuclei of the PD monkey were significantly correlated with those measured from PET. The loss of striatal uptake appeared greater in SPECT than the corresponding PET with both visual and uptake analyses. In conclusion, our data in a limited series of cases indicate that 99Tc-TRODAT-1 with a conventional nuclear medicine camera system may provide a suitable tool in evaluating parkinsonism in a primate model.

Do dopamine agonists or levodopa modify Parkinson's disease progression?

During the past decade, in vivo imaging of the nigrostriatal dopaminergic system has been developed as a research tool to monitor progressive dopaminergic neuron loss in Parkinson's disease (PD) and to assess the effect of medication on imaging outcomes. Recently two similar studies compared the effect of initial treatment with a dopamine agonist (pramipexole (CALM-PD CIT) or ropinirole (REAL-PET)) or levodopa on the progression of PD as measured by [123I]beta-CIT or [18F]Dopa imaging. These two clinical imaging studies targeting dopamine function with different imaging ligands and technology both demonstrate slowing in the rate of loss of [123I]beta-CIT or [18F]Dopa uptake in early PD patients treated with dopamine agonists compared with levodopa. The relative reduction in the per cent loss from baseline of [123I]beta-CIT uptake in the pramipexole versus the levodopa group was 47% at 22 months, 44% at 34 months and 37% at 46 months after initiating treatment. The relative reduction of 18F-dopa uptake in the ropinirole group versus the levodopa group was 35% at 24 months. These results should be very cautiously interpreted with regard to the effect of dopamine agonists or levodopa on clinical disease progression. These data highlight the need to compare imaging outcomes of dopamine neuronal loss with multiple meaningful clinical endpoints of disease progression in placebo controlled, larger and long-term studies.

Tc-99m ethylene cysteinate dimer SPECT in the differential diagnosis of parkinsonism

Positron emission tomography (PET) and network analysis have been used to identify a reproducible pattern of regional metabolic covariation that is associated with idiopathic Parkinson's disease (PD). The activity of this PD-related pattern can be quantified in individual subjects and used to discriminate PD patients from atypical parkinsonians. Because PET is not commonly available, we sought to determine whether similar discrimination could be achieved using more routine single photon emission computed tomography (SPECT) perfusion methods. Twenty-three subjects with PD (age, 63 +/- 9 years), 22 subjects with multiple system atrophy (MSA; age, 64 +/- 7 years), and 20 age-matched healthy controls (age, 62 +/- 13 years) underwent SPECT imaging of regional cerebral perfusion with Tc-99m ethylene cysteinate dimer (ECD). Using network analysis, we determined whether a PD-related pattern existed in the SPECT data, and whether its expression discriminated PD from MSA patients. Additionally, we compared the accuracy of group discrimination achieved by this pattern with that of the PET-derived PD-related pattern applied to the SPECT data. Network analysis of the SPECT data identified a significant pattern characterized by relative increases in cerebellar, lentiform, and thalamic perfusion covarying with decrements in the frontal operculum and in the medial temporal cortex. Subject scores for this pattern discriminated PD patients from controls (P < 0.01) and from MSA patients (P < 0.03). Subject scores for the PET-derived PD-related pattern computed in the individual SPECT scans more accurately distinguished PD patients from controls (P < 0.005) and from MSA patients (P = 0.0002). A significant PD-related covariance pattern can be identified in SPECT perfusion data. Moreover, the disease related pattern identified previously with PET can be applied to individual SPECT perfusion scans to provide group discrimination between PD patients, healthy controls, and individuals with MSA. Because of significant individual subject overlap between groups, however, the clinical utility of this method in the differential diagnosis of Parkinsonism remains uncertain.

Combination of dopamine transporter and D2 receptor SPECT in the diagnostic evaluation of PD, MSA, and PSP

It is often difficult to differentiate clinically between Parkinson's disease (PD), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP). The objective of this work was to investigate whether combined pre- and postsynaptic dopaminergic single photon emission computed tomography (SPECT) scanning can reliably demonstrate changes in the nigrostriatal dopaminergic system and help differentiate between normal controls, PD, MSA, and PSP patients. We performed SPECT evaluation of the dopamine transporter (DAT) and dopamine D2 receptors (D2). SPECT scans using [123I]beta-CIT (for DAT) and [123I]IBF (for D2) were performed in 18 patients with PD (12 dopa-naïve and 6 on levodopa and/or dopamine agonists), 7 with MSA of the striatonigral degeneration type, 6 with PSP, and 29 normal controls. Antiparkinsonian drugs were withheld for at least 12 hours before the scans. DAT and D2 binding potentials (Rv = V3/V2) were measured for caudate, anterior, and posterior putamen on the sides ipsilateral and contralateral to the worst motor symptoms. DAT binding in the posterior putamen was markedly reduced in all patients. However, D2 binding in posterior putamen was significantly increased in dopa-untreated PD, being greater than the normal range in 4 of 12 (33%), and it was significantly reduced in MSA, being below the normal range in 5 of 7 (71%). None of the patients with PD showed reduced D2 binding below the normal range in posterior putamen. The degree of DAT binding could not discriminate between the patient groups. The ratio of posterior putamen to caudate percentage D2 Rv compared with the controls showed an opposite pattern between PD or PSP and MSA; the caudate was greater in 16 of 18 with PD and 6 of 6 with PSP, whereas caudate was less in 5 of 7 with MSA. These findings suggest that DAT SPECT may be useful in differentiating parkinsonism from controls and D2 SPECT in further differentiating MSA from Parkinson's disease and possibly PSP.

Resting regional cerebral glucose metabolism in advanced Parkinson's disease studied in the off and on conditions with [(18)F]FDG-PET

Studies of resting regional cerebral glucose consumption (rCMRGlc) in nondemented patients with Parkinson's disease (PD) have produced conflicting results, reporting both reduced and normal metabolism in advanced disease and reduced or normal metabolism after dopaminergic therapy. To investigate these issues, [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) was performed in 11 nondemented PD patients with advanced disease and 10 age-matched controls. PD patients were studied after withdrawal of all dopaminergic medication to produce a practically defined off condition, and a second time 1 hour after levodopa, resulting in a clinical on state. Dynamic PET scans and simultaneous arterialised venous blood samples of [(18)F] activity were obtained. A graphical approach was used to generate parametric images of rCMRGlc and statistical parametric mapping to localise significant metabolic changes in PD. Compared with controls, global rCMRGlc was reduced in the on but not in the off condition in PD. In both states, significant regional reductions of glucose uptake were found in the parietal, frontal, temporal cortex, and caudate nucleus. Reductions correlated with the severity of disability in frontal and temporal cortex. Direct comparison between on and off conditions revealed relatively greater reductions of uptake in the ventral/orbital frontal cortex and the thalamus during on. Results suggest that cortical and caudate hypometabolism are common in advanced PD and that caution is mandatory if [(18)F]FDG PET is being used to differentiate advanced PD from dementia and progressive supranuclear palsy where similar reductions are seen. Furthermore, in PD, administration of levodopa is associated with further hypometabolism in orbitofrontal cortex; an area known to be relevant for reversal learning where performance is typically impaired after dopaminergic treatment.

Functional brain networks in Parkinson's disease

With the advent of new methods of network analysis, we have utilized metabolic data acquired through positron emission tomography (PET) to identify disease-related patterns of functional pathology in the movement disorders. In Parkinson's disease (PD), we have used [(18)F]-fluorodeoxyglucose (FDG)/PET to identify a disease-related regional metabolic covariance pattern characterized by lentiform and thalamic hypermetabolism associated with regional metabolic decrements in the lateral premotor cortex, the supplementary motor area, the dorsolateral prefrontal cortex, and the parieto-occipital association regions. The expression of this network is modulated in a predictable fashion by levodopa therapy and by stereotaxic interventions for PD.We have extended this network analytical approach from studies of glucose metabolism in the resting state to dynamic studies of brain activation during motor performance. These PET studies utilized [(15)O]-water (H(2) (15)O) to measure cerebral blood flow activation responses during the execution of simple and complex motor tasks. In addition to the modulation of abnormal resting metabolic networks, effective PD therapy can enhance brain activation responses during motor execution, with specific regional associations with improvements in timing and spatial accuracy.This approach is also useful in identifying specific brain networks mediating the learning of sequential information. We have found that the normal relationship between brain networks and learning performance are altered in the earliest stages of PD with a functional shift from striatal to cortical processing. Brain activation PET studies during therapeutic interventions for PD demonstrate how normal brain-behavior relationships can be restored with successful therapy. Thus, functional brain imaging with network analysis can provide insights into the mechanistic basis of basal ganglia disorders and their treatment.

Hypermetabolism in the ventrolateral thalamus in unilateral Parkinsonian resting tremor: a positron emission tomography study

Tremorogenesis in Parkinson's disease (PD) is assumed to involve a cerebral network including the thalamus. An imaging study was performed on eight PD patients with strictly unilateral resting tremor using fluorodeoxyglucose positron emission tomography coregistered to 3-dimensional magnetic resonance imaging. Increased metabolic activity of high statistical significance (P<0.001) was found in the anterior ventrolateral nuclear group of the thalamus located contralateral to the tremor side. The metabolic changes significantly covaried with tremor amplitudes. For the first time, it could be demonstrated that thalamic metabolic changes associated with tremor in PD are localized in the ventral lateral anterior nucleus (VLa). The results are discussed with respect to previous studies on tremor generation.

Cardiovascular reflex testing contributes to clinical evaluation and differential diagnosis of Parkinsonian syndromes

The differentiation between Parkinson's disease (PD), progressive supranuclear palsy (PSP), and multiple system atrophy (MSA) may be difficult but is important for prognostic and therapeutic purposes. Varying degrees of autonomic failure have been described in PD and MSA, whereas its involvement in PSP remains controversial. The aim of this study was to investigate autonomic function in patients fulfilling strict clinical diagnostic criteria for the disorders above, to evaluate the diagnostic capacity of laboratory autonomic tests. The study group was consecutively recruited among patients referred to a movement disorder unit. Thirty-four patients with PD, 15 patients with PSP, and 47 patients with MSA were compared with 18 healthy age-matched controls. Autonomic tests included analysis of heart rate variability (HRV) in temporal domain, at rest and during forced respiration, as well as blood pressure (BP) changes during 75 degrees head-up tilt. HRV did not differ between groups during quiet breathing but was significantly reduced during forced respiration in MSA (P < 0.01), while PD and PSP groups did not differ from controls. Hypotensive responses during orthostatic provocation were seen in PD (P < 0.01) and MSA (P < 0.001), whereas BP remained stable in most PSP patients, not differing from the healthy control group. On an individual basis, decreased HRV and severe hypotensive responses were seen in MSA patients regardless of age and disease duration, whereas PD patients showed this combination only at high age and long duration. In PSP, only a few cases with decreased HRV and limited hypotensive responses were found. We conclude that cardiovascular reflex tests can supplement the clinical differentiation of Parkinsonian syndromes.

Radiosynthesis of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta (4' methylphenyl) nortropane (FPCMT)

A synthetic procedure for the routine preparation of [18F] N-3-fluoropropyl-2-beta-carbomethoxy-3-beta-(4' methylphenyl) nortropane (18F FPCMT) has been developed. The synthesis is based on alkylation of nortropane with 18F labeled fluoropropyl tosylate. Purification of the final product was achieved by a preparative HPLC procedure using Alltech Econosil column. Separation of the desired compound was achieved and the product was clean. The radiochemical yield (without decay correction) is 4 to 5%, calculated at the end of the synthesis based on the total amount of fluorine recovered from the target. Radiochemical purity was in the range of 98 to 99%.

Rapid-onset dystonia-parkinsonism: linkage to chromosome 19q13

Rapid-onset dystonia-parkinsonism (RPD) is an autosomal dominant movement disorder characterized by sudden onset of persistent dystonia and parkinsonism, generally during adolescence or early adulthood. Symptoms evolve over hours or days, and generally stabilize within a few weeks, with slow or no progression. Other features include little or no response to L-dopa, and low levels of homovanillic acid in the central nervous system. Neuroimaging studies indicate no degeneration of dopaminergic nerve terminals in RDP, suggesting that this disorder results from a functional deficit, as in dystonia, rather than neuronal loss, as in Parkinson's disease. We studied 81 members of two midwestern US families with RDP, 16 of whom exhibited classic features of RDP. We found significant evidence for linkage in these two families to markers on chromosome 19q13, with the highest multipoint LOD score at D19S198 (z = 5.77 at theta = 0.0). The flanking markers D19S587 and D19S900 define a candidate region of approximately 8 cM. Although RDP itself is a rare condition, it is important because it has clinical and biochemical similarities to both Parkinson's disease and dystonia. Identification of the genetic defect in RDP holds promise for understanding the underlying disease processes of both of these more common diseases.

Differential diagnosis of Parkinson's disease

The differential diagnosis of PD includes other neurodegenerative disorders; hereditary disorders; and symptomatic causes, such as structural lesions, infections, metabolic abnormalities, hydrocephalus, and drugs or toxins. A good history of symptom evaluation, drug use, and family illness is just as essential as a careful neurologic examination when evaluating a patient with parkinsonism. Although there is no definitive diagnostic test for PD at this time, tests to rule out other causes should be considered and then treatment started.

Emission tomography contribution to clinical neurology

The role of functional neuroimaging techniques in furthering the understanding of pathophysiological mechanisms of neurological diseases and in the assessment of neurological patients is increasingly important. Here, we review data mainly from emission tomography techniques, namely positron emission tomography (PET) and single photon emission computerized tomography (SPECT), that have helped elucidate the pathophysiology of a number of neurological diseases and have suggested strategies in the treatment of neurological patients. We also suggest possible future developments of functional neuroimaging applied to clinical populations and briefly touch on the emerging role of functional magnetic resonance imaging (fMRI) in clinical neurology and neurosurgery.

Positron emission tomographic studies in restless legs syndrome

We studied six restless legs syndrome (RLS) patients with [F18]fluorodeoxyglucose (FDG) positron emission tomography (PET). We also studied four of these same patients with [F18]fluorodopa (FDOPA) PET. The patients' FDG and FDOPA PET scans were compared with those from age-matched healthy control subjects. No significant differences between the two groups were found for any regional blood flow values derived from the FDG scans or for any binding constants derived from the FDOPA scans. These results suggest that any abnormal resting brain metabolic activity or putative presynaptic dopaminergic defect in RLS is likely either to be so subtle that it is below the threshold for ready detection by PET or that it is located in an area of neural tissue inaccessible to the current scanner. No substantial defect is likely to involve the dopaminergic nigrostriatal axis.

Functional brain networks in DYT1 dystonia

Early-onset idiopathic torsion dystonia (ITD) is an autosomal dominant hyperkinetic movement disorder with incomplete penetrance, associated with a 3 base-pair deletion in the DYT1 gene on chromosome 9q34. To determine the metabolic substrates of brain dysfunction in DYT1 dystonia, we scanned 7 nonmanifesting and 10 affected DYT1 carriers and 14 normal volunteers with [18F]fluorodeoxyglucose and positron emission tomography. We found that DYT1 dystonia is mediated by the expression of two independent regional metabolic covariance patterns. The first pattern, identified in an analysis of nonmanifesting gene carriers was designated movement free (MF). This abnormal pattern was characterized by increased metabolic activity in the lentiform nuclei, cerebellum, and supplementary motor areas. The MF pattern was present in DYT1 carriers with and without clinical manifestations and persisted in DYT1 dystonia patients in whom involuntary movements were suppressed by sleep. The second pattern, identified in an analysis of affected gene carriers with sustained contractions at rest, was designated movement related (MR). This pattern was characterized by increased metabolic activity in the midbrain, cerebellum, and thalamus. The expression of the MR pattern was increased in waking DYT1 patients with sustained dystonia, compared with DYT1 carriers who were unaffected or who had dystonia only on action, as well as normal controls. MR subject scores declined significantly with sleep in affected DYT1 patients but not in normal controls. These findings indicate the penetrance of the DYT1 gene is considerably greater than previously assumed. ITD is mediated through the interaction of functional brain networks relating separately to gene status and to abnormal movement.

123I-beta-CIT and 123I-IBZM-SPECT scanning in levodopa-naive Parkinson's disease

Striatal dopamine transporter function and dopamine D2 receptor status were evaluated in 15 patients with early untreated Parkinson's disease using single photon emission tomography (SPECT) with 123I-Iodo-2beta-carboxymethoxy-3beta-(4-idiophenyl)tropane (beta-CIT) and 123I-Iodobenzamide (IBZM) as pre- and postsynaptic ligands. Symptoms were unilateral in five patients and bilateral but asymmetric in 10 patients. Patients with bilateral symptoms had significantly lower 18-hour striatal/cerebellar beta-CIT binding ratios (3.59 +/- 0.79) than hemiparkinsonian patients (5.76 +/- 1.48, p < 0.05) reflecting more advanced disease in this subgroup. Patients with bilateral parkinsonism were also found to have a significant side-to-side difference in striatal beta-CIT binding with more marked reduction contralateral to the presenting limb (18-hour striatal/cerebellar ratio: 4.13 +/- 0.78 [ipsilateral] versus 3.59 +/- 0.79 [contralateral], p < 0.05). Dopamine D2 receptor binding as measured by IBZM was significantly elevated contralateral to the affected side in hemiparkinsonian patients (striatal/cerebellar ratio: 2.42 +/- 0.90 [contralateral] versus 2.19 +/- 0.80 [ipsilateral], p < 0.05). This asymmetric upregulation was absent in the patients with bilateral parkinsonism (striatal/cerebellar ratio: 1.85 +/- 0.43 [contralateral to more severely affected side] versus 1.83 +/- 0.34 [ipsilateral], p > 0.05). Our data suggest that postsynaptic dopamine receptor upregulation contralateral to the presenting side occurs in untreated unilateral PD and disappears in untreated bilateral (asymmetric) PD despite a greater loss of dopamine transporter function. Combined beta-CIT and IBZM SPECT studies may be helpful to monitor the progression of nigrostriatal dysfunction in early PD.

Differential diagnosis of parkinsonism with [18F]fluorodeoxyglucose and PET

The clinical differentiation between typical idiopathic Parkinson's disease (IPD) and atypical parkinsonian disorders (APD) is complicated by the presence of signs and symptoms common to both forms of parkinsonism. Metabolic brain imaging with [18F]fluorodeoxyglucose (FDG) and positron emission tomography (PET) may be a useful adjunct in differentiating APD from IPD. To explore this possibility, we studied 48 parkinsonian patients suspected as having possible APD because of a deteriorating response to dopaminergic treatment, the development of autonomic dysfunction, or both. A group of 56 patients with likely IPD served as control subjects. We used quantitative FDG/PET to measure regional rates of cerebral glucose use in IPD and APD patients. We used discriminant analysis to categorize IPD and APD patients based on their regional metabolic data. We found that a linear combination of caudate, lentiform, and thalamic values accurately discriminated APD from IPD patients (p < 0.0001). Significant metabolic abnormalities were present in the striatum and the thalamus of 36 of 48 (75%) APD patients. Our findings show that measurements of regional glucose metabolism can be used to discriminate patients with suspected APD from their counterparts with classic IPD. FDG/PET may be a useful adjunct to the clinical examination in the differential diagnosis of parkinsonism.

Asymmetry of basal ganglia glucose metabolism and dopa responsiveness in parkinsonism

We investigated, by positron emission tomography (PET) with [18F]fluoro-2-deoxy-d-glucose (FDG) (FDG-PET), brain glucose metabolism in 19 patients with parkinsonian features. We compared local pattern of FDG uptake and asymmetry indexes in patients with therapeutic response to levodopa (L-dopa) (group 1, presumed Parkinson's disease, n = 9) and patients without L-dopa therapeutic response (group 2, presumed striatonigral degeneration, n = 10). Limb dystonia was present in 11% of patients in group 1 and in 40% of patients in group 2. Asymmetry in basal ganglia metabolism was distributed differently in the two groups (analysis of variance, p < 0.04). In superior and inferior putamen, superior and middle caudate, ventral striatum, and inferior thalamus, relative reduction in metabolism on the side contralateral to predominant parkinsonian signs was associated with L-dopa unresponsiveness. On the contrary, in middle caudate, ventral striatum, and inferior thalamus, a relative increase in metabolism on the side contralateral to the predominant side, parkinsonian signs were found in L-dopa-responsive patients. Our FDG-PET study using simple statistical procedures demonstrates inverse asymmetry of basal ganglia glucose metabolism in parkinsonian patients grouped on the sole basis of L-dopa responsiveness.

Increased cerebrospinal fluid levels of neurofilament protein in progressive supranuclear palsy and multiple-system atrophy compared with Parkinson's disease

More reliable tools are needed for the differentiation of Parkinson's disease (PD) from other parkinsonian disorders. The neurofilament protein (NFL) and the glial fibrillary acidic protein (GFAP) are main structural proteins of axons and fibrillary astroglial cells. By using enzyme-linked immunosorbent assays, these proteins were quantified in the cerebrospinal fluid (CSF) of 49 patients referred to the Department of Neurology for diagnostic consideration or treatment of parkinsonism of different etiologies. All patients were first diagnostically evaluated by strict clinical criteria. The procedure included a neurologic and neuro-ophthalmologic examination as well as computed tomography or magnetic resonance imaging. These were performed independently and in advance of the CSF analysis. A total of 19 patients were diagnosed as having PD, 12 had progressive supranuclear palsy (PSP), and 10 had multiple-system atrophy (MSA). Eight were diagnosed as having other diseases, such as arteriosclerotic parkinsonism and undefined parkinsonian syndromes. The content of NFL was significantly higher both in the PSP group (p < 0.001) and in the MSA group (p < 0.0001) compared with the PD group. The high values of NFL indicate an ongoing neuronal degeneration affecting mainly the axonal compartment in the PSP and MSA groups, whereas there was no difference in glial involvement as measured by GFAP in the PD, PSP, and MSA groups. There was a relation between high CSF levels of NFL in the various patient groups and the occurrence of pyramidal symptoms (p < 0.001), possibly reflecting the axonal damage to the corticospinal tract. Furthermore, mortality at 24-month follow up was associated with high NFL levels (p < 0.01). We conclude that analysis of NFL in CSF may become useful in the differential diagnosis of parkinsonian syndromes.

Pathophysiology of movement disorders studied using PET

PET radiotracer methods can measure various biochemical features of brain tissue in the living human brain. Here, local brain energy consumption and striatal dopaminergic function will be discussed in the light of the neurodegenerative processes underlying Parkinson's disease. Particularly, disease progression and its consequences for protective and restorative strategies will be outlined. Also, an example will be given to demonstrate how the effect of neurotrophic factors on the striatal dopaminergic system can be monitored by PET tracer methods.

Regional metabolic correlates of surgical outcome following unilateral pallidotomy for Parkinson's disease

Stereotaxic ventral pallidotomy has been employed in the symptomatic treatment of patients with advanced Parkinson's disease (PD). To understand the pathophysiology of clinical outcome following this procedure, we studied 10 PD patients (5 men and 5 women; mean age 60.0 +/- 6.1 years; mean Hoehn and Yahr stage 3.8 +/- 1.0) with quantitative 18F-fluorodeoxyglucose (FDG) and positron emission tomography (PET). All patients were scanned preoperatively; 8 of 10 patients were rescanned 6 to 8 months following surgery. Clinical performance was assessed off medications before and after surgery using standardized timed motor tasks. We found that preoperative lentiform metabolism correlated significantly with improvement in contralateral motor tasks at 1 week, 3 months, and 6 months following unilateral pallidotomy (p<0.03). Postoperatively, significant metabolic increases were noted in the primary motor cortex, lateral premotor cortex, and dorsolateral prefrontal cortex (p<0.01) of the hemisphere that underwent surgery. Improvement in contralateral limb motor performance correlated significantly with surgical declines in thalamic metabolism (p<0.01) and increases in lateral frontal metabolism (p<0.05). Principal components analysis disclosed a significant covariance pattern characterized by postoperative declines in ipsilateral lentiform and thalamic metabolism associated with bilateral increase in supplementary motor control metabolism. Subject scores for this pattern correlated significantly with improvements in both contralateral and ipsilateral limb performance (p<0.005). These results suggest that pallidotomy reduced the preoperative overaction of the inhibitory pallidothalamic projection. Clinical improvement may be associated with modulations in regional brain metabolism occurring remote from the lesion site.