Motor associations of iron accumulation in deep grey matter nuclei in Parkinson's disease: a cross-sectional study of iron-related magnetic resonance imaging susceptibility.

BACKGROUND AND PURPOSE: To determine whether iron deposition in deep brain nuclei assessed using high-pass filtered phase imaging plays a role in motor disease severity in Parkinson's disease (PD). METHODS: Seventy patients with mild to moderate PD and 20 age- and gender-matched healthy volunteers (HVs) underwent susceptibility-weighted imaging on a 3 T magnetic resonance imaging scanner. Phase shifts (radians) in deep brain nuclei were derived from high-pass filtered phase images and compared between groups. Analysis of clinical laterality and correlations with motor severity (Unified Parkinson's Disease Rating Scale, Part III, UPDRS-III) were performed. Phase shifts (in radians) were compared between HVs and three PD subgroups divided according to UPDRS-III scores using analysis of covariance, adjusting for age and regional area. RESULTS: Parkinson's disease patients had significantly (P < 0.001) higher radians than HVs bilaterally in the putamen, globus pallidus and substantia nigra (SN). The SN contralateral to the most affected side showed higher radians (P < 0.001) compared to the less affected side. SN radians positively correlated with UPDRS-III and bradykinesia-rigidity subscores, but not with tremor subscores. ancova followed by post hoc Bonferroni-adjusted pairwise comparisons revealed that SN radians were significantly greater in the PD subgroup with higher UPDRS-III scores compared to both lowest UPDRS-III PD and HV groups (P < 0.001). CONCLUSIONS: Increased nigral iron accumulation in PD appears to be stratified according to disease motor severity and correlates with symptoms related to dopaminergic neurodegeneration. This semi-quantitative in vivo iron assessment could prove useful for objectively monitoring PD progression, especially in clinical trials concerning iron chelation therapies.

Cortical Lewy bodies and Aß burden are associated with prevalence and timing of dementia in Lewy body diseases.

AIMS: Our main objective was to determine the neuropathological correlates of dementia in patients with Lewy body disease (LBD). Furthermore, we used data derived from clinical, neuropathological and genetic studies to investigate boundary issues between Dementia with Lewy bodies (DLB) and Parkinson's disease with (PDD) and without (PDND) dementia. METHODS: One hundred and twenty-one cases with a neuropathological diagnosis of LBD and clinical information on dementia status were included in the analysis (55 PDD, 17 DLB and 49 PDND). We carried out topographical and semi-quantitative assessment of Lewy bodies (LB), Aß plaques and tau-positive neuropil threads (NT). The APOE genotype and MAPT haplotype status were also determined. RESULTS: The cortical LB (CLB) burden was the only independent predictor of dementia (OR: 4.12, P < 0.001). The total cortical Aß plaque burden was an independent predictor of a shorter latency to dementia from onset of motor signs (P = 0.001). DLB cases had a higher LB burden in the parietal and temporal cortex, compared to PDD. Carrying at least one APOE ϵ4 allele was associated with a higher cortical LB burden (P = 0.02), particularly in the neocortical frontal, parietal and temporal regions. CONCLUSIONS: High CLB burden is a key neuropathological substrate of dementia in LBD. Elevated cortical LB pathology and Aß plaque deposition are both correlated with a faster progression to dementia. The higher CLB load in the temporal and parietal regions, which seems to be a distinguishing feature of DLB, may account for the shorter latency to dementia and could be mediated by the APOE ϵ4 allele.

Positron emission tomography imaging in multiple sclerosis-current status and future applications.

BACKGROUND: Multiple Sclerosis (MS) is traditionally considered as a central nervous system (CNS) white matter inflammatory disease. However, recent studies have focused on the neurodegenerative aspects of the disease, which occur early in the pathological process, providing an opportunity for therapeutic intervention and application of neuroprotective strategies. The relationship between neural inflammation and cell death remains controversial. The recent development of new radiolabelled ligands provides positron emission tomography (PET) imaging with a role for studying early aspects of the MS pathology. METHODS: We provide an overview of current PET research in MS, particularly focussing on possible applications of new radioligands for studying inflammation and neurodegenerative processes. RESULTS: Pathological aspects of neuroinflammation, axonal degeneration and neuronal repair may be explored in vivo with selective PET tracers. Specific radioligands for the cannabinoid system may be applied in MS research to understand the role of this neurotransmitter system in the pathogenesis of the disease. CONCLUSIONS: PET imaging represents a promising tool for elucidating controversial aspects of MS pathology and for the assessment of selective and potentially neuroprotective therapies.

Depressive symptoms in PD correlate with higher 5-HTT binding in raphe and limbic structures.

BACKGROUND: Depression associated with Parkinson disease (PD) has a different symptom profile to endogenous depression. The etiology of depression in PD remains uncertain though abnormal serotonergic neurotransmission could play a role. OBJECTIVE: To assess with PET serotonergic function via in vivo serotonin transporter (5-HTT) availability in antidepressant-naive patients with PD. METHODS: Thirty-four patients with PD and 10 healthy matched control subjects had a clinical battery of tests including the patient-report Beck Depression Inventory-II (BDI-II), the clinician-report Hamilton Rating Scale for Depression (HRSD), and the structured clinical interview for DSM-IV Axis I Disorders (SCID-I). They underwent ¹¹C-DASB PET, a selective in vivo marker of 5-HTT binding in humans. RESULTS: BDI-II scores correlated with HRSD scores. Ten of 34 patients with PD (29.4%) had BDI-II and HRSD scores above the discriminative cutoff for PD depression though only half of these patients could be classed on SCID-I criteria as having an anxiety/mood disorder. Patients with PD with the highest scores for depression symptoms showed significantly raised ¹¹C-DASB binding in amygdala, hypothalamus, caudal raphe nuclei, and posterior cingulate cortex compared to low score cases, while ¹¹C-DASB binding values in other regions were similarly decreased in depressed and nondepressed patients with PD compared to healthy controls. CONCLUSION: Depressive symptoms in antidepressant-naive patients with PD correlate with relatively higher 5-HTT binding in raphe nuclei and limbic structures possibly reflecting lower extracellular serotonin levels. Our data are compatible with a key role of abnormal serotonergic neurotransmission contributing to the pathophysiology of PD depression and justify the use of agents acting on 5-HTT.

Parkinson disease and impulse control disorders: a review of clinical features, pathophysiology and management.

Impulse control disorders (ICDs) are a heterogeneous group of conditions involving repetitive, excessive and compulsive activities that interfere with life functioning. Examples are pathological gambling, compulsive shopping and hypersexuality. Over the last decade, ICDs have become increasingly recognised as being associated with Parkinson disease (PD), with the literature highlighting a link between dopamine replacement therapy and the development of ICDs. Patients who develop ICDs in the context of compulsive anti-Parkinsonian drug use are described as having dopamine dysregulation syndrome (DDS), which is associated with repetitive complex stereotyped behaviours called punding. Case-control and observational studies have further noted that patients with PD who develop ICDs are more likely to have younger-onset PD, a history of alcohol dependence, novelty-seeking personality traits and psychiatric comorbidities. The pathophysiology of underlying mechanisms is not fully understood, but recent evidence suggests that dopaminergic drugs, particularly dopamine agonists, coupled with changes in reward pathways involving the ventral striatal and related circuitry, may play a role. Neuroimaging studies using positron emission tomography and functional MRI have provided valuable information in this area: patients with DDS have been found to show enhanced dopamine release in the ventral striatum, suggesting functional abnormalities in the mesolimbic networks. Management of ICDs in patients with PD can be challenging, as they may not be aware of a change in their behaviour or may conceal their symptoms to avoid embarrassment. Currently, there is no clear evidence of an optimal treatment. Management is based on a careful balance of dopaminergic drugs with control of the aberrant behaviour, supported by psychological interventions. This review aims to summarise the current literature on ICDs, their phenomenology, epidemiology, clinical features, pathophysiology and management.

Long-term clinical and positron emission tomography outcome of fetal striatal transplantation in Huntington's disease.

Two patients with moderate Huntington's disease (HD) received bilateral fetal striatal allografts. One patient demonstrated, for the first time, increased striatal D2 receptor binding, evident with 11C-raclopride positron emission tomography, and prolonged clinical improvement over 5 years, suggesting long term survival and efficacy of the graft. The other patient did not improve clinically or radiologically. Our results indicate that striatal transplantation in HD may be beneficial but further studies are needed to confirm this.

Characterization of dopaminergic dysfunction in familial progressive supranuclear palsy: an 18F-dopa PET study.

We analyzed (18)F-dopa PET data from 11 members of kindreds with familial progressive supranuclear palsy (PSP) to characterize their cerebral dopaminergic dysfunction. Three clinically-affected PSP patients showed reduced (18)F-dopa uptake in the striatum, orbitofrontal cortex and amygdala. One asymptomatic subject exhibited progressive putamen dopaminergic dysfunction. 60% of subjects with abnormal (18)F-dopa scans developed PSP subsequently. This is the first in vivo documentation of cortical dopaminergic deficiency in PSP. Reduced striatal (18)F-dopa uptake in susceptible relatives may predict later clinical disease.

Clinical correlates of levodopa-induced dopamine release in Parkinson disease: a PET study.

OBJECTIVE: To evaluate the relationship between clinical improvement and in vivo synaptic dopamine (DA) release after a single oral dose of levodopa (LD) in patients with advanced Parkinson disease (PD). METHODS: We studied 16 patients with advanced PD with [(11)C]raclopride (RAC) PET. Each patient had RAC PET twice: once when medication had been withdrawn and once after an LD challenge. On the day of the LD challenge scan, oral 250 mg LD/25 mg carbidopa was given before scanning. Unified Parkinson's Disease Rating Scale (UPDRS) motor scores were rated in an "off" state before LD and again at the end of PET. RESULTS: All the patients were still in "on" state at the end of their LD challenge RAC PET scans. Following LD, mean caudate and putamen RAC binding potentials (BPs) were significantly lower vs baseline, consistent with increased synaptic DA. Individual LD-induced improvements in UPDRS score correlated significantly with reductions in putaminal BP. Additionally, large putaminal RAC BP changes were associated with higher dyskinesia scores. When motor UPDRS subitems were examined, improvements in rigidity and bradykinesia, but not in tremor or axial symptoms, correlated with putamen DA release. CONCLUSION: In advanced Parkinson disease, the improvement of rigidity and bradykinesia and the presence of dyskinesias after a single dose of oral levodopa are governed by the level of dopamine generated at striatal D2 receptors. In contrast, relief of parkinsonian tremor and axial symptoms is not related to striatal synaptic dopamine levels and presumably occurs via extrastriatal mechanisms.

Microglial activation correlates with severity in Huntington disease: a clinical and PET study.

BACKGROUND: Huntington disease (HD) is characterized by the progressive death of medium spiny dopamine receptor bearing striatal GABAergic neurons. In addition, microglial activation in the areas of neuronal loss has recently been described in postmortem studies. Activated microglia are known to release neurotoxic cytokines, and these may contribute to the pathologic process. METHODS: To evaluate in vivo the involvement of microglia activation in HD, the authors studied patients at different stages of the disease using [(11)C](R)-PK11195 PET, a marker of microglia activation, and [(11)C]raclopride PET, a marker of dopamine D2 receptor binding and hence striatal GABAergic cell function. RESULTS: In HD patients, a significant increase in striatal [(11)C](R)-PK11195 binding was observed, which significantly correlated with disease severity as reflected by the striatal reduction in [(11)C]raclopride binding, the Unified Huntington's Disease Rating Scale score, and the patients' CAG index. Also detected were significant increases in microglia activation in cortical regions including prefrontal cortex and anterior cingulate. CONCLUSIONS: These [(11)C](R)-PK11195 PET findings show that the level of microglial activation correlates with Huntington disease (HD) severity. They lend support to the view that microglia contribute to the ongoing neuronal degeneration in HD and indicate that [(11)C](R)-PK11195 PET provides a valuable marker when monitoring the efficacy of putative neuroprotecting agents in this relentlessly progressive genetic disorder.

Dopaminergic dysfunction in unrelated, asymptomatic carriers of a single parkin mutation.

Parkin disease is usually autosomal recessive; however, two studies have shown that asymptomatic heterozygotes have nigrostriatal dysfunction and even manifest subtle extrapyramidal signs. The authors used 18F-dopa PET to study 13 asymptomatic parkin heterozygotes and found a significant reduction of (18)F-dopa uptake in caudate, putamen, ventral, and dorsal midbrain compared with control subjects. Four had subtle extrapyramidal signs. Parkin heterozygosity is a risk factor for nigrostriatal dysfunction and in some may contribute to late-onset Parkinson disease.

Applications of positron emission tomography (PET) in neurology.

Positron emission tomography (PET) is a powerful imaging technique which enables in vivo examination of brain functions. It allows non-invasive quantification of cerebral blood flow, metabolism, and receptor binding. In the past PET has been employed mainly in the research setting due to the relatively high costs and complexity of the support infrastructure, such as cyclotrons, PET scanners, and radiochemistry laboratories. In recent years, because of advancements in technology and proliferation of PET scanners, PET is being increasingly used in clinical neurology to improve our understanding of disease pathogenesis, to aid with diagnosis, and to monitor disease progression and response to treatment. This article aims to provide an overview of the principles of PET and its applications to clinical neurology.

Two large British kindreds with familial Parkinson's disease: a clinico-pathological and genetic study.

We present the findings of a study of two large unrelated kindreds with autosomal dominant Parkinson's disease. The affected members were assessed clinically and with [(18)F]6-fluorodopa-PET and were indistinguishable from patients with the sporadic form of Parkinson's disease. In one kindred, an affected member was examined subsequently at autopsy and Lewy bodies were present in a distribution typical of sporadic Parkinson's disease. These kindreds are distinct from other Parkinsonian kindreds with identified genetic loci (PARK1-4) and provide further evidence for genetic heterogeneity in familial Parkinson's disease.

Familial progressive supranuclear palsy: detection of subclinical cases using 18F-dopa and 18fluorodeoxyglucose positron emission tomography.

BACKGROUND: Progressive supranuclear palsy (PSP) is generally considered to be a sporadic disease; however, occasional cases of familial PSP have been described. The rarity of reports of familial PSP may be attributed in part to an inability to detect subclinical disease in affected relatives who subsequently die before symptoms clinically develop. OBJECTIVE: To study regional cerebral dopaminergic function and glucose metabolism in members of 2 large kindreds with familial PSP to identify subclinical cases. METHODS: Three clinically affected members from the 2 PSP kindreds were scanned with both (18)F-dopa and (18)fluorodeoxyglucose ((18)FDG) positron emission tomography (PET). Fifteen asymptomatic first-degree relatives were scanned with (18)F-dopa PET; 10 of them also underwent a second PET study with (18)FDG. RESULTS: All 3 clinically affected PSP patients showed a significant reduction in caudate and putamen (18)F-dopa uptake along with a significant reduction in striatal, lateral, and medial premotor area and dorsal prefrontal cortex glucose metabolism. In 4 of the 15 asymptomatic relatives, caudate and putamen (18)F-dopa uptake was 2.5 SDs lower than the normal mean. These 4 subjects and a fifth asymptomatic relative with normal (18)F-dopa uptake showed a significant reduction of cortical and striatal glucose metabolism in a pattern similar to that of their affected relatives. CONCLUSION: (18)F-dopa and (18)FDG PET allowed us to identify 5 cases with subclinical metabolic dysfunction among 15 subjects (33%) at risk for PSP, suggesting that this approach is useful for characterizing the pattern of aggregation in PSP kindreds.

Delayed recovery of movement-related cortical function in Parkinson's disease after striatal dopaminergic grafts.

Intrastriatal transplantation of dopaminergic neurones aims to repair the selective loss of nigrostriatal projections and the consequent dysfunction of striatocortical circuitries in Parkinson's disease (PD). Here, we have studied the effects of bilateral human embryonic dopaminergic grafts on the movement-related activation of frontal cortical areas in 4 PD patients using H2 15O positron emission tomography and a joystick movement task. At 6.5 months after transplantation, mean striatal dopamine storage capacity as measured by 18F-dopa positron emission tomography was already significantly elevated in these patients. This was associated with a modest clinical improvement on the Unified Parkinson's Disease Rating Scale, whereas the impaired cortical activation was unchanged. At 18 months after surgery, there was further significant clinical improvement in the absence of any additional increase in striatal 18F-dopa uptake. Rostral supplementary motor and dorsal prefrontal cortical activation during performance of joystick movements had significantly improved, however. Our data suggest that the function of the graft goes beyond that of a simple dopamine delivery system and that functional integration of the grafted neurones within the host brain is necessary to produce substantial clinical recovery in PD.

Bilateral caudate and putamen grafts of embryonic mesencephalic tissue treated with lazaroids in Parkinson's disease.

Five parkinsonian patients were transplanted bilaterally into the putamen and caudate nucleus with human embryonic mesencephalic tissue from between seven and nine donors. To increase graft survival, the lipid peroxidation inhibitor tirilazad mesylate was administered to the tissue before implantation and intravenously to the patients for 3 days thereafter. During the second postoperative year, the mean daily L-dopa dose was reduced by 54% and the UPDRS (Unified Parkinson's Disease Rating Scale) motor score in 'off' phase was reduced by a mean of 40%. At 10-23 months after grafting, PET showed a mean 61% increase of 6-L-[(18)F]fluorodopa uptake in the putamen, and 24% increase in the caudate nucleus, compared with preoperative values. No obvious differences in the pattern of motor recovery were observed between these and other previously studied cases with putamen grafts alone. The amount of mesencephalic tissue implanted in each putamen and caudate nucleus was 42 and 50% lower, respectively, compared with previously transplanted patients from our centre. Despite this reduction in grafted tissue, the magnitudes of symptomatic relief and graft survival were very similar. These findings suggest that tirilazad mesylate may improve survival of grafted dopamine neurons in patients, which is in agreement with observations in experimental animals.

The catechol-O-methyltransferase (COMT) inhibitor entacapone enhances the pharmacokinetic and clinical response to Sinemet CR in Parkinson's disease.

OBJECTIVES: Entacapone is a specific, potent, peripherally acting catechol-O-methyltransferase (COMT) inhibitor. It has been shown to improve the bioavailability of plasma levodopa and extend its clinical effect when used as an adjunct to standard levodopa preparations, but there is little experience of the effect of entacapone on controlled release levodopa preparations. METHODS: A double blind, placebo controlled, single dose, randomised, cross over trial was performed in 14 patients with Parkinson's disease with motor fluctuations to investigate the clinical effect of a single dose of entacapone (200 mg) when administered with either standard levodopa-carbidopa (Sinemet) or controlled release levodopa-carbidopa preparations (Sinemet CR). RESULTS: When entacapone was administered with standard Sinemet the duration of the clinical response to standard Sinemet was longer in comparison with the response after placebo (p=0.02). Moreover, in the same patients, entacapone significantly increased the duration of the clinical response to Sinemet CR (p=0.05) without prolonging the latency of response or enhancing dyskinesias. CONCLUSIONS: These data confirm the clinical efficacy of entacapone-standard Sinemet combination. They also indicate that adding entacapone to controlled release levodopa preparations might provide a useful treatment option in patients with Parkinson's disease with motor fluctuations. A double blind clinical trial with a chronically administered entacapone-Sinemet CR combination is, however, required to verify this viewpoint.

Neuroimaging of dyskinesia.

Dyskinesias are observed in the majority of Parkinson's disease (PD) patients who have been chronically exposed to levodopa, and these may result from supersensitivity of postsynaptic striatal dopamine D1 and D2 receptors following loss of nigral dopaminergic projections. Dyskinetic and nondyskinetic PD patients were studied using 11C-SCH23390 and 11C-raclopride positron emission tomography (PET). No difference in mean putamen or caudate D1 or D2 receptor binding between the two patient subgroups was found, suggesting that dyskinesias are unlikely to arise from a primary disturbance of dopamine receptor availability. When dyskinetic and nondyskinetic patients were studied with 11C-diprenorphine PET, the former showed a significant reduction (p < 0.05) in striatal and thalamic opioid site availability, compatible with the presence of raised levels of endogenous opioid peptides. H2(15)O PET activation studies of patients with focal limb dyskinesias showed that resting levels of regional cerebral blood flow after oral levodopa were increased during dyskinesias in lentiform nuclei, motor, premotor and dorsal prefrontal cortex. These results suggest that dyskinesias are associated with derangement of basal ganglia opioid transmission, resulting in overactivity of basal ganglia-frontal projections.

Diurnal motor variations to repeated doses of levodopa in Parkinson's disease.

Patients with Parkinson's disease (PD) in long-term levodopa therapy often complain of worsening of motor symptoms in the afternoon and evening. The pathophysiology of this phenomenon is not known. We evaluated the motor response to repeated doses of levodopa during a 12-hour period in 52 parkinsonian patients (19 de novo, 20 stable, and 13 wearing-off). On the day of the study, all patients received standard doses of levodopa/carbidopa at 8:00 a.m., 12:00 noon, and 4:00 p.m. Motor measurements such as tapping test, walking time, and tremor score, and blood samples for levodopa and 3-O-methyldopa (3OMD) plasma analysis, were performed hourly. Mean motor scores and pharmacokinetic data, evaluated for a period of 3 hours after each levodopa dose, were compared. In de novo patients, we did not observe diurnal changes in motor score, whereas a progressive daytime worsening was visible in stable and wearing-off patients. No significant difference in levodopa pharmacokinetics after each levodopa dose was observed within each patient group, whereas 3OMD plasma levels significant increased with repeated levodopa administrations. However, no significant correlation between motor scores and 3OMD plasma levels was observed, suggesting that the diminishing motor response to afternoon and evening doses of levodopa in patients in long-term levodopa therapy does not relate to the pharmacokinetics of the drug. It is possible that this phenomenon may be an expression of the occurrence of tolerance to repeated doses of levodopa.

Dopamine release from nigral transplants visualized in vivo in a Parkinson's patient.

Synaptic dopamine release from embryonic nigral transplants has been monitored in the striatum of a patient with Parkinson's disease using [11C]-raclopride positron emission tomography to measure dopamine D2 receptor occupancy by the endogenous transmitter. In this patient, who had received a transplant in the right putamen 10 years earlier, grafts had restored both basal and drug-induced dopamine release to normal levels. This was associated with sustained, marked clinical benefit and normalized levels of dopamine storage in the grafted putamen. Despite an ongoing disease process, grafted neurons can thus continue for a decade to store and release dopamine and give rise to substantial symptomatic relief.