The metabolic topography of parkinsonism

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.

Differentiating multiple system atrophy from Parkinson's disease: contribution of striatal and midbrain MRI volumetry and multi-tracer PET imaging

OBJECTIVES

The differential diagnosis between typical idiopathic Parkinson's disease (PD) and the striatonigral variant of multiple system atrophy (MSA-P) is often difficult because of the presence of signs and symptoms common to both forms of parkinsonism, particularly at symptom onset. This study investigated striatal and midbrain findings in MSA-P and PD patients in comparison with normal controls with the use of positron emission tomography (PET) and three dimensional magnetic resonance imaging (3D MRI) based volumetry to increase the differential diagnostic accuracy between both disease entities.

METHODS

Nine patients with MSA-P, 24 patients with PD, and seven healthy controls were studied by MRI and PET with 6-[(18)F]-fluoro-L-dopa (FDOPA), [(18)F]fluoro-deoxyglucose (FDG), and 11-C-Raclopride (RACLO). Striatal and extrastriatal volumes of interest (VOI) were calculated on the basis of the individual MRI data. The PET data were transferred to the VOI datasets and subsequently analysed.

RESULTS

MSA-P differed significantly from PD patients in terms of decreased putaminal volume, glucose metabolism, and postsynaptic D2 receptor density. The striatal FDOPA uptake was equally impaired in both conditions. Neither MRI volumetry nor PET imaging of the midbrain region further contributed to the differential diagnosis between PD and MSA-P.

CONCLUSIONS

The extent and spatial distribution of functional and morphological changes in the striatum permit the differentiation of MSA-P from PD. Both, multi-tracer PET and 3D MRI based volumetry, may be considered equivalent in the assessment of different striatal abnormality in both disease entities. In contrast, MRI and PET imaging of the midbrain does not provide a further gain in diagnostic accuracy.

Surgical therapy for Parkinson's disease

Surgical therapies for Parkinson's disease (PD) are now being performed with increasing frequency due to the limitations of conventional dopaminergic therapies, improvements in operative procedures, and increased information on the organization of the basal ganglia in normal and pathologic conditions. Ablation procedures have now been largely replaced with deep brain stimulation, which permits benefits to be obtained without the need to make a destructive brain lesion. Several studies now demonstrate the value of stimulating the subthalamic nucleus or the globus pallidus pars interna in patients with advanced PD. Nonetheless, there are limitations associated with these procedures and benefits do not exceed those obtained with levodopa, albeit with reduced motor complications. Fetal transplantation remains an experimental procedure that has shown limited benefits in a double-blind trial and is complicated by persistent dyskinesia. Stem cell, trophic factor, and gene therapy approaches are promising and are currently under intensive investigation.

Functional imaging of the dopamine system: in vivo evaluation of dopamine deficiency and restoration

Dopamine deficiency causes a severe impairment in motor function in patients with Parkinson's disease (PD) and in experimental animal models. Recent developments in neuroimaging techniques provide a means to assess in vivo the state of the dopamine system. From a functional perspective, four levels need to be operative and integrated in the system: the dopamine cell (pre-synaptic), the striatal dopamine receptors (post-synaptic), adequate release of dopamine (intra-synaptic), and the cortico-subcortical motor projections. Neuroimaging functional methods can be used to estimate, at these four levels, dopamine cell degeneration, adaptive responses to injury and, importantly, the effect of therapeutic interventions. In this respect, data from functional imaging studies at clinical and pre-clinical stages, support the idea that cell replacement therapy might achieve a more physiological restoration of the dopamine motor system than other therapies (such as ablative surgery, administration of precursor, deep brain stimulation) that currently are equally or more effective in relieving motor symptoms.

Subthalamotomy for advanced Parkinson disease

Object. The aim of this study was to determine if subthalamotomy is effective in treating advanced Parkinson disease (PD).

Methods. The authors performed microelectrode mapping—guided stereotactic surgery on the subthalamic nucleus in eight patients with PD. Lesioning was performed using radiofrequency heat coagulation and confirmed with magnetic resonance imaging. Three patients who underwent unilateral and four with bilateral subthalamotomy were evaluated for up to 18 months according to the Unified PD Rating Scale (UPDRS). One patient who underwent unilateral subthalamotomy died 6 months postsurgery.

At 3 months into the “off” period after surgery, there were significant improvements in contralateral bradykinesia (p < 0.0002), rigidity (p < 0.0001), tremor (p < 0.01), axial motor features (p < 0.02), gait (p < 0.03), postural stability (p < 0.03), total UPDRS scores (p < 0.03), and Schwab and England scores (p < 0.04). The benefits were sustained at 6, 12, and 18 months, except for the improvement in tremor. At 12 months into the “on” period, significant benefits were present for motor fluctuation (p < 0.04), on dyskinesia (p < 0.006), off duration (p < 0.05), total UPDRS score (p < 0.02), and contralateral tremor (p < 0.05). Benefits for motor fluctuation, off duration, and off-period tremor were lost after the 18-month follow-up period. The levodopa requirement was reduced by 66% for the unilateral and 38% for the bilaterally treated group. Bilateral subthalamotomy offered more benefits than did unilateral surgery for various parkinsonian features in both the on and off periods. Three patients suffered hemiballismus, two recovered spontaneously, and one died of aspiration pneumonia after discontinuation of levodopa.

Conclusions. These findings indicate that subthalamotomy can ameliorate the cardinal symptoms of PD, reduce the dosage of levodopa, diminish complications of the drug therapy, and improve the quality of life.

Monosymptomatic resting tremor and Parkinson's disease: a multitracer positron emission tomographic study

We sought to elucidate the relationship between monosymptomatic resting tremor (mRT) and Parkinson's disease (PD). We studied eight mRT patients (mean Hoehn and Yahr [H&Y], 1.1 +/- 0.4), eight patients with PD (mean H&Y, 1.5 +/- 0.8), who showed all three classic parkinsonian symptoms, and seven age-matched healthy subjects. Subjects underwent cerebral magnetic resonance imaging (MRI) and multitracer positron emission tomography (PET) with 6-[(18)F]fluoro-L-dopa (F-dopa), [(18)F]fluorodeoxyglucose (FDG), and [(11)C]raclopride (RACLO). PD and mRT patients did not show significant differences in F-dopa-, RACLO-, or FDG-PET scans. In F-dopa- and RACLO-PET, significant differences between the pooled patient data and control subjects were found for the following regions: anterior and posterior putamen ipsilateral and contralateral to the more affected body side, and ipsilateral and contralateral putaminal gradients of the K(i) values. Furthermore, we found a difference for the normalized glucose values of the whole cerebellum between the control group (0.94 +/- 0.06) and PD patients (1.01 +/- 0.04; P < 0.05) but not for the mRT group (0.97 +/- 0.03). Our findings indicate that monosymptomatic resting tremor represents a phenotype of Parkinson's disease, with a nearly identical striatal dopaminergic deficit and postsynaptic D2-receptor upregulation in both patient groups. We suggest that the cerebellar metabolic hyperactivity in PD is closer related to akinesia and rigidity rather than to tremor.

Neurophysiological refinement of subthalamic nucleus targeting

OBJECTIVE

Advances in image-guided stereotactic surgery, microelectrode recording techniques, and stimulation technology have been the driving forces behind a resurgence in the use of functional neurosurgery for the treatment of movement disorders. Despite the dramatic effects of deep brain stimulation (DBS) techniques in ameliorating the symptoms of Parkinson's disease, many critical questions related to the targeting, effects, and mechanisms of action of DBS remain unanswered. In this report, we describe the methods used to localize the subthalamic nucleus (STN) and we present the characteristics of encountered cells.

METHODS

Twenty-six patients with idiopathic Parkinson's disease underwent simultaneous, bilateral, microelectrode-refined, DBS electrode implantation into the STN. Direct and indirect magnetic resonance imaging-based anatomic targeting was used. Cellular activity was analyzed for various neurophysiological parameters, including firing rates and interspike intervals. Physiological targeting confirmation was obtained by performing macrostimulation through the final DBS electrode.

RESULTS

The average microelectrode recording time for each trajectory was 20 minutes, with a mean of 5.2 trajectories/patient. Typical trajectories passed through the anterior thalamus, zona incerta/fields of Forel, STN, and substantia nigra-pars reticulata. Each structure exhibited a characteristic firing pattern. In particular, recordings from the STN exhibited an increase in background activity and an irregular firing pattern, with a mean rate of 47 Hz. The mean cell density was 5.6 cells/mm, with an average maximal trajectory length of 5.3 mm. Macrostimulation via the DBS electrode yielded mean sensory and motor thresholds of 4.2 and 5.7 V, respectively.

CONCLUSION

The principal objectives of microelectrode recording refinement of anatomic targeting are precise identification of the borders of the STN and thus determination of its maximal length. Microelectrode recording also allows identification of the longest and most lateral segment of the STN, which is our preferred target for STN DBS electrode implantation. Macrostimulation via the final DBS electrode is then used primarily to establish the side effect profile for postoperative stimulation. Microelectrode recording is a helpful targeting adjunct that will continue to facilitate our understanding of basal ganglion physiological features.

Postural asymmetries following unilateral subthalomotomy for advanced Parkinson's disease

Two cases of postural asymmetries following unilateral stereotaxic subthalamotomy were observed with head and body tilting to the side contralateral to the STN lesion, which corrected itself completely or partially with levodopa treatment. After subsequent contralateral STN surgery, the postural asymmetry disappeared in both patients. Possible mechanism is discussed.

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.

Contributions of PET and SPECT to the understanding of the pathophysiology of Parkinson's disease

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) provide the means to studying in vivo the neurochemical, hemodynamic or metabolic consequences of the degeneration of the nigrostriatal dopaminergic system in Parkinson's disease (PD). The extent of striatal dopaminergic denervation can be quantified with radiotracers as [18F]FDopa for PET and [123I]tropanes for SPECT. There are other radiotracers such as [11C]Dopa and meta-tyrosines as well as PET tracers for uptake sites. Striatal uptake of [18F]FDopa and [123I]tropanes is markedly decreased in PD, more in the putamen than in the caudate nucleus, and inversely correlates with the severity of motor signs and with duration of disease. PET and SPECT make possible the assessment by noninvasive means of the changes in dopamine receptor density, the effect of neuronal transplants or neuroprotective treatments in PD patients, or the nigrostriatal dopaminergic function in at-risk subjects. Activation studies using cerebral blood flow and metabolism measurements during a motor task reveal an impaired ability to activate the supplementary motor area and dorsolateral prefrontal cortex in PD. This functional disability is reversed by the use of dopaminergic medication or by surgical treatment by pallidotomy or deep brain stimulation. The differential diagnosis between PD and multiple system atrophy, progressive supranuclear palsy or corticobasal degeneration is not yet clearly established by PET and SPECT, even though these syndromes have some particular neurochemical and metabolic profiles. On the other hand, PET and SPECT are useful for distinguishing PD from Dopa-responsive dystonia, or for assessing the integrity of the nigrostriatal dopaminergic pathway in atypical cases of postural tremor or iatrogenic parkinsonian syndromes.

Metabolic changes following subthalamotomy for advanced Parkinson's disease

We studied 6 advanced-stage Parkinson's disease patients with [18F] fluorodeoxyglucose/positron emission tomography before and 3 months after unilateral ablation of the subthalamic nucleus performed with microelectrode mapping. Operative changes in glucose metabolism were assessed by comparing baseline and postoperative scans. We also quantified operative changes in the activity of an abnormal Parkinson's disease-related metabolic network that we had identified in previous [18F] fluorodeoxyglucose/positron emission tomography studies. Following unilateral subthalamic nucleus ablation, a highly significant reduction in glucose utilization was present in the midbrain ipsilateral to the lesion site, most pronounced in the vicinity of the substantia nigra pars reticularis. Significant metabolic reductions were also present in the ipsilateral internal globus pallidus, ventral thalamus, and pons. Operative changes in Parkinson's disease network activity differed significantly for the lesioned and unlesioned hemispheres. In the lesioned hemisphere, network activity declined significantly following surgery, but was unaltered in the contralateral, unlesioned hemisphere. These results suggest that subthalamotomy reduces basal ganglia output through internal globus pallidus/substantia nigra pars reticularis and also influences downstream neural activity in the pons and ventral thalamus. This procedure also reduces the activity of abnormal Parkinson's disease-related metabolic brain networks, suggesting a widespread modulation of motor circuitry.

Patterns of cortical activity and memory performance in Alzheimer's disease

BACKGROUND

Declarative memory changes are the hallmark of Alzheimer's disease, although their functional neuroanatomy is not restricted to a single structure. Factor analysis provides statistical methods for evaluating patterns of cerebral changes in regional glucose uptake.

METHODS

Thirty-three Alzheimer's patients and 33 age- and gender-matched control subjects were studied with magnetic resonance imaging and positron emission tomography with [(18)F] deoxyglucose. During the tracer-uptake period, subjects performed a serial verbal learning task. Cortical activity was measured in 32 regions of interest, four in each lobe on both hemispheres.

RESULTS

Factor analysis with varimax rotation identified seven factors explaining 80% of the variance ("parietal cortex," "occipital cortex," "right temporo-prefrontal areas," "frontal cortex," "motor strip," "left temporal cortex," and "posterior temporal cortex"). Relative to control subjects, Alzheimer's patients showed significantly reduced values on the factors occipital cortex, right temporo-prefrontal areas, frontal cortex, and left temporal cortex. The factor temporo-prefrontal areas showed large differences between patients with good and poor performance, but little difference when control subjects were similarly divided.

CONCLUSIONS

Findings suggest that Alzheimer's disease is characterized by altered patterns of cortical activity, rather than deficits in a single location, and emphasize the importance of right temporo-prefrontal circuitry for understanding memory deficits.

Repetitive transcranial magnetic stimulation to SMA worsens complex movements in Parkinson's disease

OBJECTIVES

To evaluate the therapeutic potential of repetitive transcranial magnetic stimulation (rTMS) for Parkinson's disease (PD) by delivering stimulation at higher intensity and frequency over longer time than in previous research. Promising beneficial effects on movement during or after rTMS have been reported.

METHODS

Ten patients with idiopathic PD were enrolled in a randomized crossover study comparing active versus sham rTMS to the supplementary motor area (SMA). Assessments included reaction and movement times (RT/MT), quantitative spiral analysis, timed motor performance tests, United Parkinson's Disease Rating Scale (UPDRS), patient self-report and guess as to stimulation condition.

RESULTS

Two of 10 patients could not tolerate the protocol. Thirty to 45 min following stimulation, active rTMS as compared with sham stimulation worsened spiral drawing (P=0.001) and prolonged RT in the most affected limb (P=0.030). No other significant differences were detected.

CONCLUSIONS

We sought clinically promising improvement in PD but found subclinical worsening of complex and preparatory movement following rTMS to SMA. These results raise safety concerns regarding the persistence of dysfunction induced by rTMS while supporting the value of rTMS as a research tool. Studies aimed at understanding basic mechanisms and timing of rTMS effects are needed.

FDG positron emission tomography in diffuse Lewy body disease: a case report

Lewy body disease is a clinicopathologic condition that includes Parkinson's disease at one end and diffuse Lewy body disease at the other hand. The latter is often associated with progressive cognitive deterioration, levodopa-responsive parkinsonism, fluctuations of cognitive and motor functions, and visual and auditory hallucinations. In addition, it can be a familial disease. Clinical and positron emission tomographic findings are described in a patient with atypical dementia and movement disorder and a pathologically proved diagnosis of diffuse Lewy body disease.

Continuous dopamine-receptor stimulation in early Parkinson's disease

Chronic L-dopa therapy is associated with the development of motor complications in the majority of Parkinson's disease (PD) patients. Although the precise mechanism responsible for these events is not known, increasing laboratory and clinical evidence points to a sequence of events that is initiated by abnormal pulsatile stimulation of dopamine receptors by the intermittent administration of agents with short half-lives such as L-dopa. Initiating therapy with a long-acting dopamine agonist has been shown to delay the onset and reduce the severity of motor complications in MPTP monkeys and PD patients. Administering L-dopa with a catechol-O-methyltransferase (COMT) inhibitor to block its peripheral metabolism increases its plasma half-life and might have a similar effect. Thus, a rational strategy for treating PD would be to initiate therapy with a long-acting dopamine-receptor agonist and supplement at the appropriate time with L-dopa combined with a COMT inhibitor.

Role of dopamine in learning and memory: implications for the treatment of cognitive dysfunction in patients with Parkinson's disease

Along with dementia, Parkinson's disease (PD) is associated with subtle but widespread cognitive impairment even in the absence of clinically apparent cognitive decline. Many of the deficits are reminiscent of those observed in patients with lesions of the prefrontal cortex, that is, failure in executive function that involves skills required for anticipation, planning, initiation and monitoring of goal-directed behaviours. This paper reviews the dopaminergic brain circuitry, and preclinical and clinical evidence supporting the regulation of prefrontal cortex activity by dopamine, and the role of dopamine in cognitive impairment in patients with PD. It addresses the need to integrate these facts and the findings of positive, neutral or detrimental frontal cognitive response to dopaminergic drugs in PD which should be viewed mainly in the context of methodological differences for subject selection. The cognitive effect of levodopa does not much depend on a neuropsychological specificity of the drug, the years of evolution of the disease or the severity of the motor signs. Instead, it may be a function of the level of dopamine depletion in different parts of the basal ganglia and prefrontal cortex. Consequently, dopaminergic agents may enhance cognitive functions in some patients and impair them in others. De novo patients tend to improve during the first year of treatment; stable responders to oral levodopa tend to show no changes; and wearing-off responders tend to deteriorate with acute levodopa challenge. Enhancement and impairment of cognitive function with dopaminergic treatment is incomplete and task-specific, suggesting the need to integrate the above dopamine facts with other neurotransmitter systems findings in PD. Meanwhile, such cognitive dissociation can be useful in refining the definition of the cognitive deficit in PD patients without dementia and emphasising the need to develop new and specific strategies for treatment.

Acute immediate-early gene response to 6-hydroxydopamine infusions into the medial forebrain bundle

Although the long-term neurobiological and behavioral effects of nigrostriatal lesions are well characterized, the events occurring soon after injury are not. These acute events can provide insight into the mechanisms underlying long-term adaptations to nigrostriatal lesions. The present experiments examined the basal ganglia immediate-early gene response to infusions of the catecholamine neurotoxin 6-hydroxydopamine into the nigrostriatal pathway in rats. Following 6-hydroxydopamine infusions into the medial forebrain bundle in awake, behaving rats, there was a rapid and transient induction of striatal c-fos and zif/268 messenger RNAs. Both immediate-early genes were maximally induced by 45min post-infusion, and returned to control levels by 1.5h (c-fos) or 3h (zif/268) post-infusion. Double-labeling experiments revealed that striatal c-fos expression occurred preferentially in preproenkephalin-expressing neurons. 6-Hydroxydopamine-induced c-fos messenger RNA was also observed in the substantia nigra pars reticulata and entopeduncular nucleus, but not the globus pallidus, 45 min after medial forebrain bundle 6-hydroxydopamine infusions. Finally, the role of ionotropic striatal glutamate receptors in nigrostriatal injury-induced striatal c-fos was examined by combining medial forebrain bundle 6-hydroxydopamine infusions with intrastriatal glutamate antagonist infusions. Both the N-methyl-D-aspartate antagonist, (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid, and the non-N-methyl-D-aspartate antagonist, 6,7-dinitroquinoxaline-2, 3-dione, blocked striatal induction of c-fos messenger RNA following 6-hydroxydopamine infusions into the medial forebrain bundle. These results provide evidence of rapidly developing, glutamate-dependent molecular responses in the basal ganglia which may contribute to some of the well-described long-term adaptations of this system to nigrostriatal injury.

Cerebral blood flow and metabolism in late-life depression and dementia

Late-life depression (LLD) is characterized by abnormalities in cerebral blood flow (CBF) and cerebral metabolic rate (CMR) for glucose. Unlike younger adults with major depression, global cortical CBF and CMR reductions have been reported in LLD. Patients with LLD are also characterized by topographic abnormalities, most commonly involving selective prefrontal, superior temporal, and anterior parietal cortex. The fate of these abnormalities with response to antidepressant treatment is highly uncertain, and heterogeneous findings have been reported in younger samples with major depression. The limited data in LLD suggest that response to electroconvulsive therapy or antidepressant medications does not involve reversal of baseline abnormalities but rather accentuation of prefrontal deficits. At minimum, these paradoxical findings suggest that abnormalities in CBF and CMR may be persistent in LLD and a trait characteristic. Characteristic profiles of CBF and CMR abnormalities have also been demonstrated in samples with Alzheimer's disease (AD) and other types of dementia. Functional imaging has shown sensitivity to disease severity and progression. Nonetheless, there is limited information regarding the sensitivity and specificity of the functional imaging modalities in the differential diagnosis of dementias. At present, the evidence does not support the use of functional imaging in isolation as a diagnostic tool. Rather, these imaging modalities may be considered as an adjunct to careful clinical assessment, either to improve diagnosis in early cases or to assist in subtyping difficult cases.

Cortical dysfunction in non-demented Parkinson's disease patients: a combined (31)P-MRS and (18)FDG-PET study

Regional cerebral phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) was performed in 10 non- demented Parkinson's disease patients and nine age-matched control subjects. Five of the patients undergoing (31)P-MRS and four additional Parkinson's disease patients had cerebral 2-[(18)F]fluoro-2-deoxy-D-glucose PET ((18)FDG-PET), the results of which were compared with those of eight age-matched control subjects. All Parkinson's disease patients underwent neuropsychological testing including performance and verbal subtests of the Wechsler Adult Intelligence Scale-Revised, Boston Naming Test, Controlled Oral Word Association test (FAS Test) and California Learning Test to exclude clinical dementia. (31)P MR spectra from right and left temporo-parietal cortex, occipital cortex and a central voxel incorporating basal ganglia and brainstem were obtained. (31)P MR peak area ratios of signals from phosphomonoesters (PMEs), inorganic phosphate (P(i)), phosphodiesters (PDEs), alpha-ATP, gamma-ATP and phosphocreatine (PCr) relative to beta-ATP were measured. Relative percentage peak areas of PMEs, P(i), PDEs, PCr, and alpha-, beta- and gamma-ATP signals were also measured with respect to the total (31)P-MRS signal. Significant bilateral increases in the P(i)/beta-ATP ratio were found in temporoparietal cortex (P = 0.002 right and P = 0.014 left cortex) for the non-demented Parkinson's disease patients compared with controls. In the right temporoparietal cortex, there was also a significant increase in the mean relative percentage P(i) (P = 0.001). (18)FDG-PET revealed absolute bilateral reductions in glucose metabolism after partial volume effect correction in posterior parietal and temporal cortical grey matter (P < 0.01 and P < 0.05, respectively) for the Parkinson's disease group, using both volume of interest analysis and statistical parametric mapping. There were significant correlations between right temporoparietal P(i)/beta-ATP ratios and estimated reductions in performance IQ (r = 0.96, P < 0.001). Left temporoparietal P(i)/beta-ATP ratios correlated with full scale IQ and verbal IQ (r = -0.82, P = 0.006, r = -0.86, P = 0.003, respectively). In summary, temporoparietal cortical hypometabolism was seen in non-demented Parkinson's disease patients with both (31)P-MRS and (18)FDG-PET, suggesting that both glycolytic and oxidative pathways are impaired. This dysfunction may reflect either the presence of primary cortical pathology or deafferentation of striato-cortical projections. (31)P-MRS and (18)FDG-PET may both provide useful predictors of future cognitive impairment in a subset of Parkinson's disease patients who go on to develop dementia.

The impact of brain imaging technology on our understanding of motor function and dysfunction

Brain imaging techniques have demonstrated functional specialisation of multiple areas within the motor system. They have also defined the patterns of interactions between these regions during normal motor function and in motor disorders. Functional imaging makes visible the changes in cortical activity that take place over time during motor functions, from the activations a fraction of a second before voluntary action to cortical neuronal plasticity several weeks after injury. Recently, the functional abnormalities underlying various acquired and developmental motor disorders have been described, as well as the effects of therapeutic intervention.

Usefulness of a dopamine transporter PET ligand [(18)F]beta-CFT in assessing disability in Parkinson's disease

OBJECTIVES

The usefulness of a novel dopamine transporter PET ligand, [(18)F]beta-CFT in assessing disability in Parkinson's disease was studied.

METHODS

Twenty seven patients with Parkinson's disease in different disability stages (of which nine were patients with early disease) and nine healthy controls were studied. The regions of interest were drawn on a magnetic resonance image resliced according to the PET image.

RESULTS

There was a significant reduction in [(18)F]beta-CFT uptake in the posterior putamen (to 18% of the control mean, p<0.00001), anterior putamen (28%, p<0.00001), and caudate nucleus (51%, p<0.00001) in the total population of patients with Parkinson's disease. The reduction in [(18)F]beta-CFT uptake was more pronounced with more severe disability of the patients, the correlations between the total motor score of the unified Parkinson's disease rating scale (UPDRS) and [(18)F]beta-CFT uptake being significant in the posterior putamen (r=-0.62 p=0.0005), anterior putamen (r=-0.64, p=0.0003), and the caudate nucleus (r=-0.62, p=0.0006). There was a significant negative correlation with putaminal [(18)F]beta-CFT uptake and the hypokinesia and rigidity scores, but not with the tremor score of the UPDRS motor part. In nine patients with early disease and without any antiparkinsonian medication the reduction in the [(18)F]beta-CFT uptake (average of ipsilateral and contralateral side) was reduced in the total putamen to 34% of the mean control value (p<0.00001). The corresponding figures in the other brain areas were: posterior putamen 21% (p<0.00001), anterior putamen 43% (p<0.00001), and caudate nucleus 76% (p<0.01). The reductions in [(18)F]beta-CFT uptake were more severe in the contralateral than in the ipsilateral side. Individually, [(18)F]beta-CFT uptake in the putamen in all patients was below 3 SD from the control mean.

CONCLUSIONS

[(18)F]beta-CFT is a sensitive marker of nigrostriatal dopaminergic dysfunction in Parkinson's disease and can be used in the diagnosis, assessment of disease severity, and follow up of patients.

Drug development for neurodegenerative diseases: role of PET

There are few relevant animal models for neurodegenerative diseases to be used for human drug development. Most current drugs for neurodegenerative diseases act through different neurotransmitter systems. Positron emission tomography (PET) is a unique tool in the study of neurodegenerative diseases as it enables quantitative measurements of oxygen consumption, blood flow, energy metabolism and functioning of various neurotransmitter systems. There are several possibilities in the use of PET in drug development. It is possible to radiolabel the drug itself or to study the effect of an unlabelled drug on blood flow, energy metabolism or function of neurotransmitter systems. All these approaches have been used in drug development for neurodegenerative diseases. However, in spite of the important role of PET in pathophysiological studies of neurodegenerative diseases, thus far the versatile possibilities of PET in drug development for neurodegenerative diseases have not been fully exploited.

Sensory processing in Parkinson's and Huntington's disease: investigations with 3D H(2)(15)O-PET

There is conjoining experimental and clinical evidence supporting a fundamental role of the basal ganglia as a sensory analyser engaged in central somatosensory control. This study was aimed at investigating the functional anatomy of sensory processing in two clinical conditions characterized by basal ganglia dysfunction, i.e. Parkinson's and Huntington's disease. Based on previously recorded data of somatosensory evoked potentials, we expected deficient sensory-evoked activation in cortical areas that receive modulatory somatosensory input via the basal ganglia. Eight Parkinson's disease patients, eight Huntington's disease patients and eight healthy controls underwent repetitive H(2)(15)O-PET activation scans during two experimental conditions in random order: (i) continuous unilateral high-frequency vibratory stimulation applied to the immobilized metacarpal joint of the index finger and (ii) rest (no vibratory stimulus). In the control cohort, the activation pattern was lateralized to the side opposite to stimulus presentation, including cortical [primary sensory cortex (S1); secondary sensory cortex (S2)] and subcortical (globus pallidus, ventrolateral thalamus) regional cerebral blood flow (rCBF) increases (P < 0.001). Between-group comparisons (P < 0.01) of vibration-induced rCBF changes between patients and controls revealed differences in central sensory processing: (i) in Parkinson's disease, decreased activation of contralateral sensorimotor (S1/M1) and lateral premotor cortex, contralateral S2, contralateral posterior cingulate, bilateral prefrontal cortex (Brodmann area 10) and contralateral basal ganglia; (ii) in Huntington's disease, decreased activation of contralateral S2, parietal areas 39 and 40, and lingual gyrus, bilateral prefrontal cortex (Brodmann areas 8, 9, 10 and 44), S1 (trend only) and contralateral basal ganglia; (iii) in both clinical conditions relative enhanced activation of ipsilateral sensory cortical areas, notably caudal S1, S2 and insular cortex. Our data show that Parkinson's disease and Huntington's disease, beyond well-established deficits in central motor control, are characterized by abnormal cortical and subcortical activation on passive sensory stimulation. Furthermore, the finding that activation increases in ipsilateral sensory cortical areas may be interpreted as an indication of either altered central focusing and gating of sensory impulses, or enhanced compensatory recruitment of associative sensory areas in the presence of basal ganglia dysfunction. Altered sensory processing is thought to contribute to pertinent motor deficits in both conditions.

The relation of putamen and caudate nucleus 18F-Dopa uptake to motor and cognitive performances in Parkinson's disease

The contribution of striatal (caudate nucleus-putamen) dopaminergic deficiency to the severity of motor signs is well established in Parkinson's disease (PD), while its role in the occurrence of cognitive and mood changes remains unresolved. We therefore measured in 27 non-demented PD patients and 10 age-matched controls striatal uptake of [18F]-6-fluoro-L-Dopa (F-Dopa) with PET, and mood (Beck depression), memory (Grober-Buschke), frontal executive functions (verbal fluency and Wisconsin card sorting), and attentional processing of sensory stimuli (N2-P3 auditory event-related potentials--ERPs). Locomotor disability of patients was assessed by Hoehn and Yahr score and Unified Parkinson's Disease Rating Scale (UPDRS). ANOVA showed that memory, but neither frontal lobe functions nor ERPs, was significantly altered in PD patients, whereas indices of depression were found only in advanced PD. The F-Dopa rate constant Ki was significantly reduced in the striatum, more in putamen than caudate nucleus, and inversely correlated with disease duration. A significant inverse correlation was found between both putamen and caudate nucleus Ki and Hoehn and Yahr score, and between putamen--but not caudate nucleus Ki --and UPDRS motor score. Principal components analysis (PCA) of PD patients Ki values and mood, cognitive and ERP parameters gave a three-factor solution. Variables contributing to factor 1 were memory score and N2-P3 ERP latencies, those to factor 2 were striatal Ki values, and those to factor 3 frontal executive performances. Depression did not segregate with any variable. Our findings suggest that unlike locomotor disability, cognitive abilities and mood state of non-demented PD patients are for the most part unrelated to striatal dopaminergic depletion and may result from dysfunction of extra-striatal dopaminergic or from non-dopaminergic systems.

Phosphorus magnetic resonance spectroscopy in multiple system atrophy and Parkinson's disease

We performed in vivo phosphorus magnetic resonance spectroscopy on the occipital lobes of 15 patients with multiple system atrophy (MSA; eight with olivopontocerebellar atrophy [OPCA] and seven with the striatonigral degeneration variant [SND]), 13 patients with idiopathic Parkinson's disease (PD), and 16 age-matched healthy subjects. The MSA group showed significantly reduced phosphocreatine (PCr), increased inorganic phosphate (Pi), and unchanged cytosolic free [Mg2+], and pH. We did not find any significant difference between the OPCA and SND variants. However, patients with PD showed significantly increased content of Pi, decreased cytosolic free [Mg2+], and unchanged [PCr] and pH. Comparing the MSA and PD groups, [PCr] was significantly lower in MSA than in PD, whereas cytosolic free [Mg2+] was significantly lower in PD. Despite a certain degree of overlap of [PCr] and [Mg2+] values between the two groups, by considering both variables at the same time it was possible to classify correctly 93% of cases by discriminant analysis. We conclude that phosphorus magnetic resonance spectroscopy discloses abnormal phosphate metabolite and ion contents in both MSA and PD, respectively, and may provide noninvasive diagnostic help to differentiate MSA from PD.

The distribution of cerebral activity related to visuomotor coordination indicating perceptual and executional specialization

The distribution of increased regional cerebral blood flow (rCBF) related to visuomotor coordination was studied by means of positron emission tomography (PET) in normal subjects. An experimental condition, in which a vertically presented zigzag figure had to be copied in a horizontal orientation, was compared with a control condition in which the same horizontal drawing was made, guided by a horizontally presented example. Cognitive components dealing with the mismatch in visual orientation resulted in activation of (i) right dorsal premotor cortex, (ii) right posterior parietal cortex, (iii) visual cortex (area V1) and (iv) left fusiform gyrus. In a second experiment, conditions were compared in which the same horizontal zigzag figure was copied in either a vertical or a horizontal orientation. Now, the motor components of the transformation of orientation appeared to be associated only with left premotor cortex activation. The differential distribution of activations is regarded to reflect the selective effort to cope with either the visual or the motor component of spatial incongruity, and indicates specialization for perceptual and executive components in visuomotor control. We propose that the perceptual component of visuomotor transformation in our experiment relates to a realignment of the coordinates of a percept to an internally defined coordinate system. The executive component relates to guidance of movement within an internal representation of space. In a preceding behavioural experiment, a majority of patients with Parkinson's disease (PD) failed on the task in which they had to make a horizontal copy of a vertically presented picture. This finding may suggest a deficit in the maintenance of an internal spatial representation to guide movement.

Parkinsonism associated with Sjögren's syndrome: three cases and a review of the literature

Sjögren's syndrome (SS) is a common multisystem autoimmune disorder. As with other autoimmune disorders such as systemic lupus erythematosus (SLE), SS has been associated with a wide range of neurologic abnormalities. Parkinsonism has been reported previously in five SS patients. We present three additional cases of SS with parkinsonism.

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.

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.

PET and the investigation of dementia in the parkinsonian patient

Parkinsonism and dementia are present in a number of neurodegenerative conditions. They may be a manifestation of isolated brain stem (Parkinson's disease) or diffuse Lewy body disease (DLBD), or be secondary to combined Lewy body and Alzheimer's disease (AD) pathologies. Positron emission tomography (PET) studies show a resting pattern of fronto-temporo-parietal hypometabolism in both, AD and in parkinsonism-dementia (PD-dementia) patients, even when only isolated brain stem Lewy body disease is found at pathology. We have studied three patients fulfilling clinical criteria for diagnosis of DLBD. Their 18F-fluorodeoxyglucose (FDG) PET results showed an AD pattern of fronto-temporo-parietal hypometabolism, though these patients had only mild cognitive dysfunction. Parkinsonism associated with apraxia is observed in corticobasal degeneration (CBD) while impairment of frontal functions, such as planning and sorting, is seen in patients with progressive supranuclear palsy (PSP). PET studies in CBD patients have shown an asymmetric hypometabolism of cortex and thalamus contralateral to the affected limbs, while in PSP patients there is a global metabolic reduction most pronounced in frontal areas and the basal ganglia. These results suggest that metabolic PET studies can help to distinguish PD-dementia, PSP and CBD, but are unable to distinguish PD-dementia from AD. Further studies with post-mortem confirmation are required to establish if DLBD is associated with a distinctive pattern of resting hypometabolism.

The treatment of Parkinson's disease in older people

Parkinson's disease is characterised by a variable combination of tremor, rigidity, bradykinesia and impaired righting reflexes. The cumulative life-time risk is one in 40. Levodopa remains the single most effective treatment in older patients, and the minimum dose to achieve maximum functional benefit should be employed. When fluctuations occur, controlled release preparations and selegiline can improve function. Oral dopamine agonists have a role but the combined side effect profile with levodopa should be monitored. COMT inhibitors have recently become available. Subcutaneous apomorphine can be helpful when "on-off" phenomena are marked. The concept of neuroprotection continues to be debated. Surgery is an option for fitter older people but neurotransplantation remains essentially a research tool.

Decreased habituation of midlatency auditory evoked responses in Parkinson's disease

The P1 midlatency auditory evoked potential was studied in patients with Parkinson's disease and compared to that in age-matched controls. Habituation of the potential was determined by using a two-click stimulus paradigm in which the stimuli were presented at 250-, 500-, and 1,000-ms interstimulus intervals. Results showed that habituation of the P1 potential had a statistically significant decrease at the 250-ms and 500-ms interstimulus intervals in patients with Parkinson's disease compared to normal controls. The degree of decreased habituation was found to increase with severity of the disease such that stage 5 patients showed greater decreases in habituation compared to stage 4, as did stage 4 compared to stage 3. These findings may be explained by the presence of a dysregulation of sensory processing, possibly by elements of the reticular activating system, including the pedunculopontine nucleus, in Parkinson's disease.

Globus pallidus stimulation activates the cortical motor system during alleviation of parkinsonian symptoms

Studies of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in monkeys suggest that excessive inhibitory outflow from the internal segment of the globus pallidus (GPi) suppresses the motor thalamus, which reduces activation of the cerebral cortex motor system, resulting in the slowness and poverty of movement of Parkinson's disease (PD). This hypothesis is supported by reports of high rates of spontaneous neuronal discharges and hypermetabolism in GPi (ref. 4-7) and impaired activation of the supplementary motor area (SMA) and dorsolateral prefrontal regions in PD patients. Furthermore, lesion or chronic high-frequency electrical (likely inactivating) stimulation of GPi (ref. 10-14) is associated with marked improvements in akinesia and rigidity, and the impaired activation of SMA is reversed when the akinesia is treated with dopamine agonists. To test whether improvement in motor function with pallidal surgery can be attributed to increased activity in premotor cortical regions, we assessed the changes in regional cerebral blood flow (rCBF) and parkinsonian symptoms during disruption of GPi activity with high-frequency stimulation delivered through implanted brain electrodes. Positron emission tomography (PET) revealed an increase in rCBF in ipsilateral premotor cortical areas during GPi stimulation, which improved rigidity and bradykinesia. These results suggest that disrupting the excessive inhibitory output of the basal ganglia reverses parkinsonism, via a thalamic relay, by activation of brain areas involved in the initiation of movement.

Age-related impaired affinity maturation and differential D-JH gene usage in human VH6-expressing B lymphocytes from healthy individuals

To elucidate the basic molecular events underlying humoral immunity during ontogeny and senescence, we analyzed a panel of 179 polymerase chain reaction-derived VH6-D-JH rearrangements from cord blood, peripheral blood, and spleen. Nucleotide sequence analysis of the CDR3 region shows that there is a difference in D and JH gene usage in functional rearrangements between lymphocytes from peripheral blood and spleen. Analysis of the VH6 gene shows that the mutational frequencies rise from 0.81% in cord blood to 1.96% in peripheral blood lymphocytes derived from young adults, and decrease to 0.80% in samples from individuals older than 50 years. The number of rearrangements carrying mutations follows a similar pattern: 22% in cord blood, 73% in the age group 20-49 years, and 57% in the age group over 50 years. The mutational frequencies among the mutated genes are, however, similar for cord blood and young adults, 2.76% and 2.51%, respectively, and 1.3% in older adults. These data show an age-related impaired affinity maturation which might relate to the decrease in immunological responsiveness among the elderly.

Infectious morbidity in long-term survivors of allogeneic marrow transplantation is associated with low CD4 T cell counts

Survivors of allogeneic marrow transplants are immunodeficient for at least 1 year after grafting. Multiple defects of immunity have been found; however, it is not known which defect primarily accounts for the high infectious morbidity of these patients. Twenty-nine allograft recipients who were in complete remission of the original disease were examined for the following parameters of immunity at 1 year after transplant: infection score (gauging the number and severity of infections within the 6 months prior to the annual exam), serum total IgM, IgG, and IgA, anti-Haemophilus influenzae IgG, anti-Streptococcus pneumoniae IgG, skin test reactivity, and the blood counts of B cells, CD4+ T cells, CD8+ T cells, and their subsets. THe only parameter inversely correlated with the infection score was CD4+ T cell count (P = 0.005 in univariable analysis, P = 0.06 in multivariable analysis). We conclude that infectious morbidity of long-term transplant survivors is related to the reconstitution of CD4+ T cells.

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.

Which clinical sign of Parkinson's disease best reflects the nigrostriatal lesion?

Clinical scales, based on the major signs of Parkinson's disease (PD), are commonly used to assess the effect of symptomatic treatment of PD. With the appearance of therapy aiming to rescue or protect the nigrostriatal neurons in PD, it becomes essential to define which of these signs best reflects the underlying neuronal deficit. Fluorodopa positron emission tomography has been shown to correlate with postmortem nigral cell counts. We correlated the major signs of PD with positron emission tomography results in 35 PD patients. We found that in the "practically defined off" state, (1) Purdue pegboard scores correlated best with the nigrostriatal dopaminergic deficit; (2) of the subscales of the modified Columbia score, the bradykinesia subscale correlated best; (3) rigidity and postural disturbance correlated less highly than bradykinesia, and their inclusion in a multiple regression did not improve the correlation of pegboard or bradykinesia scores alone; and (4) tremor did not correlate with the nigrostriatal dopaminergic deficit. We conclude that pegboard and bradykinesia scores represent the best clinical measures for studying the effect of treatment on the evolution of the nigrostriatal lesion of PD. Inclusion of other clinical signs provides additional information only for the study of functional impairments.