99mTc-TRODAT-1 SPECT study in early Parkinson's disease and essential tremor

Reviewing the Diagnostic Performance of 99mTc-TRODAT-1 Imaging in Distinguishing Idiopathic Parkinson's Disease from Parkinson-Plus Syndromes

Aim  Diagnosing movement disorders can be challenging owing to their similar clinical presentations with other neurodegenerative and basal ganglia disorders, like idiopathic Parkinson's disease (IPD), essential tremors (ET), vascular parkinsonism, multiple system atrophy (MSA), and progressive supranuclear palsy (PSP). Technetium-99m labeled tropane derivative (99mTc-TRODAT-1) imaging can help in diagnosing Parkinson's disease at an early stage to help early initiation of the treatment. The current study aimed to evaluate the role of 99mTc-TRODAT-1 imaging in differentiating IPD and Parkinson-plus syndromes (PPS). Material and Methods  We have analyzed 38 patients, referred to our department for 99mTc-TRODAT imaging. These patients were thoroughly evaluated in the movement disorder clinic at our institute and had a possible/ probable diagnosis of IPD, Hoehn and Yahr (H&Y) stage I/II ( n  = 28) or PPS (PSP [ n  = 06] and MSA [ n  = 04]). Striatal uptake ratio (SUR) was calculated in all the patients and data was statistically analyzed. Results  The mean age of IPD, PSP, and MSA groups was 56.5 ± 12.15, 65.2 ± 11.1, and 51.2 ± 3.9 years, respectively. On qualitative evaluation, all patients had reduced striatal uptake on 99mTc-TRODAT imaging, with 31/38 patients showed a greater reduction in putaminal uptake compared with the caudate nucleus. On semiquantitative evaluation, mean total SUR was 0.58 ± 0.27, 0.53 ± 0.31, and 0.91 ± 0.20 in IPD, PSP, and MSA groups, respectively. The total SUR was lowest in the PSP group followed by IPD, but MSA had relatively higher SUR, although the difference was not statistically significant. Among the IPD patient group, 25/28 patients (89.3%) experienced a greater reduction in SUR values in the striatum contralateral to the side, where motor symptoms first manifested at disease onset. Conclusion  99mTc-TRODAT is a potential imaging biomarker for the evaluation of presynaptic dopaminergic dysfunction in patients with movement disorders. In our study cohort, mean SUR values were lowest for the PSP group followed by IPD and MSA group, which was in concordance with previous studies. However, the difference between SUR values in these two groups was not statistically significant. The present study emphasizes that the capacity of 99mTc-TRODAT-1 imaging alone for diagnosing IPD from PPS is constrained, although it offers a precise approach for distinguishing patients with IPD from those with essential tremors, drug-induced, or psychogenic parkinsonism. Consequently, more specific imaging biomarkers are needed to effectively differentiate between patients with IPD and those with PPS.

Parkinson's Disease in Patients with Essential Tremor: A Prospective Clinical and Functional Neuroimaging Assessment

Introduction:

Patients with essential tremor (ET) have 3.5 times greater risk of developing Parkinson's disease (PD) throughout their lives, also known as PD with antecedent ET (ET-PD). Single photon emission computed tomography with radiotracer imaging of dopamine transporters (TRODAT-SPECT) can help differentiate these two diseases.

Method:

Relate the results of TRODAT-SPECT imaging in patients with ET to potential progress to ET-PD. Thirty-six patients with ET were evaluated by neurological examination, the Archimedes spiral, and the MDS-UPDRS III scale on two occasions, after a mean interval of three years. SPECT was performed on all patients after the first visit.

Results:

Overall, six patients (16.6%) progressed clinically to ET-PD. Patients with ET-PD were older, and the age of tremor onset was later. The ET-PD group scored higher on the MDS-UPDRS III scale, especially for the presence of bradykinesia. SPECT imaging was altered in 83.3% of the ET-PD patients compared to 33% of the ET patients (p=0.034). Changes on the SPECT with asymmetrical hypouptake suggested progress to ET-PD (p=0.025).

Conclusion:

Advanced age at the onset of tremor, the presence of bradykinesia, and asymmetrical alterations in SPECT may be related to progression to PD in patients with ET. Changes in neuroimaging suggest that SPECT-TRODAT can be used to predict progression to PD in selected patients.

The Pathophysiology and Treatment of Essential Tremor: The Role of Adenosine and Dopamine Receptors in Animal Models

Essential tremor (ET) is one of the most common neurological disorders that often affects people in the prime of their lives, leading to a significant reduction in their quality of life, gradually making them unable to independently perform the simplest activities. Here we show that current ET pharmacotherapy often does not sufficiently alleviate disease symptoms and is completely ineffective in more than 30% of patients. At present, deep brain stimulation of the motor thalamus is the most effective ET treatment. However, like any brain surgery, it can cause many undesirable side effects; thus, it is only performed in patients with an advanced disease who are not responsive to drugs. Therefore, it seems extremely important to look for new strategies for treating ET. The purpose of this review is to summarize the current knowledge on the pathomechanism of ET based on studies in animal models of the disease, as well as to present and discuss the results of research available to date on various substances affecting dopamine (mainly D3) or adenosine A1 receptors, which, due to their ability to modulate harmaline-induced tremor, may provide the basis for the development of new potential therapies for ET in the future.

Imaging the Pathophysiology of Essential Tremor-A Systematic Review

Background: The pathophysiology underlying essential tremor (ET) still is poorly understood. Recent research suggests a pivotal role of the cerebellum in tremor genesis, and an ongoing controversy remains as to whether ET constitutes a neurodegenerative disorder. In addition, mounting evidence indicates that alterations in the gamma-aminobutyric acid neurotransmitter system are involved in ET pathophysiology. Here, we systematically review structural, functional, and metabolic neuroimaging studies and discuss current concepts of ET pathophysiology from an imaging perspective. Methods: We conducted a PubMed and Scopus search from 1966 up to December 2020, entering essential tremor in combination with any of the following search terms and their corresponding abbreviations: positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and gamma-aminobutyric acid (GABA). Results: Altered functional connectivity in the cerebellum and cerebello-thalamico-cortical circuitry is a prevalent finding in functional imaging studies. Reports from structural imaging studies are less consistent, and there is no clear evidence for cerebellar neurodegeneration. However, diffusion tensor imaging robustly points toward microstructural cerebellar changes. Radiotracer imaging suggests that the dopaminergic axis is largely preserved in ET. Similarly, measurements of nigral iron content and neuromelanin are unremarkable in most studies; this is in contrast to Parkinson's disease (PD). PET and MRS studies provide limited evidence for cerebellar and thalamic GABAergic dysfunction. Conclusions: There is robust evidence indicating that the cerebellum plays a key role within a multiple oscillator tremor network which underlies tremor genesis. However, whether cerebellar dysfunction relies on a neurodegenerative process remains unclear. Dopaminergic and iron imaging do not suggest a substantial overlap of ET with PD pathophysiology. There is limited evidence for alterations of the GABAergic neurotransmitter system in ET. The clinical, demographical, and genetic heterogeneity of ET translates into neuroimaging and likely explains the various inconsistencies reported.

An Update on the Neurochemistry of Essential Tremor

Background:

The pathophysiology and neurochemical mechanisms of essential tremor (ET) are not fully understood, because only a few post-mortem studies have been reported, and there is a lack of good experimental model for this disease.

Objective:

The main aim of this review is to update data regarding the neurochemical features of ET. Alterations of certain catecholamine systems, the dopaminergic, serotonergic, GABAergic, noradrenergic, and adrenergic systems have been described, and are the object of this revision.

Methods:

For this purpose, we performed a literature review on alterations of the neurotransmitter or neuromodulator systems (catecholamines, gammaaminobutyric acid or GABA, excitatory amino acids, adenosine, T-type calcium channels) in ET patients (both post-mortem or in vivo) or in experimental models resembling ET.

Results and Conclusion:

The most consistent data regarding neurochemistry of ET are related with the GABAergic and glutamatergic systems, with a lesser contribution of adenosine and dopaminergic and adrenergic systems, while there is not enough evidence of a definite role of other neurotransmitter systems in ET. The improvement of harmaline-induced tremor in rodent models achieved with T-type calcium channel antagonists, cannabinoid 1 receptor, sphingosine-1-phosphate receptor agonists, and gap-junction blockers, suggests a potential role of these structures in the pathogenesis of ET.

Phase I clinical study with different doses of 99mTc-TRODAT-1 in healthy adults

OBJECTIVES

To study the pharmacokinetics, biodistribution, and injection doses of ^99mTc-TRODAT-1 in healthy adults.

METHODS

Thirty healthy individuals comprising 15 females and 15 males were randomly divided into three groups and the injection doses of ^99mTc-TRODAT-1 of group 1, 2, and 3 were 370 MBq, 740 MBq, and 1110 MBq, respectively. Assessments of subjective symptoms and tests were performed before and after injection. Blood and urine collections and whole-body planar imaging were analyzed at various time points. Bilateral brain striatal SPECT images obtained at 3.5 h PI were assessed visually and semiquantitatively.

RESULTS

No serious adverse events or deaths were observed in our study. The pharmacokinetic analysis showed that ^99mTc-TRODAT-1 was eliminated rapidly from the circulation, with just about 4% of the injected dose remaining in blood at 1 h post-injection. The mean cumulative urinary excretion over 24 h was just 2.96 ± 0.96%ID. The time-activity curve demonstrated that the radioactivity was mainly in liver and abdomen. The highest absorbed dose was in the dose-limiting organ, liver (20.88 ± 4.45 × 10^-3 mSv/MBq). The average effective dose was 5.22 ± 1.05 × 10^-3 mSv/MBq. The clarity of striatal images assessed visually in group 1 was worse than that in group 2 and 3. The semiquantitative analysis showed that there were no differences in striatum/cerebellum between the three groups (group 1: 1.77 ± 0.11, group 2: 1.62 ± 0.14, and group 3: 1.75 ± 0.20; P = 0.088).

CONCLUSIONS

^99mTc-TRODAT-1 was safe to use in humans and showed the status of dopaminergic neurons specifically and clearly. The injection dose we suggested was 740 MBq.

Linking Essential Tremor to the Cerebellum-Neuroimaging Evidence

Essential tremor (ET) is the most common pathological tremor disorder in the world, and post-mortem evidence has shown that the cerebellum is the most consistent area of pathology in ET. In the last few years, advanced neuroimaging has tried to confirm this evidence. The aim of the present review is to discuss to what extent the evidence provided by this field of study may be generalised. We performed a systematic literature search combining the terms ET with the following keywords: MRI, VBM, MRS, DTI, fMRI, PET and SPECT. We summarised and discussed each study and placed the results in the context of existing knowledge regarding the cerebellar involvement in ET. A total of 51 neuroimaging studies met our search criteria, roughly divided into 19 structural and 32 functional studies. Despite clinical and methodological differences, both functional and structural imaging studies showed similar findings but without defining a clear topography of neurodegeneration. Indeed, the vast majority of studies found functional and structural abnormalities in several parts of the anterior and posterior cerebellar lobules, but it remains to be established to what degree these neural changes contribute to clinical symptoms of ET. Currently, advanced neuroimaging has confirmed the involvement of the cerebellum in pathophysiological processes of ET, although a high variability in results persists. For this reason, the translation of this knowledge into daily clinical practice is again partially limited, although new advanced multivariate neuroimaging approaches (machine-learning) are proving interesting changes of perspective.

Neuroimaging essentials in essential tremor: a systematic review

Background

Essential tremor is regarded to be a disease of the central nervous system. Neuroimaging is a rapidly growing field with potential benefits to both diagnostics and research. The exact role of imaging techniques with respect to essential tremor in research and clinical practice is not clear. A systematic review of the different imaging techniques in essential tremor is lacking in the literature.

Methods

We performed a systematic literature search combining the terms essential tremor and familial tremor with the following keywords: imaging, MRI, VBM, DWI, fMRI, PET and SPECT, both in abbreviated form as well as in full form. We summarize and discuss the quality and the external validity of each study and place the results in the context of existing knowledge regarding the pathophysiology of essential tremor.

Results

A total of 48 neuroimaging studies met our search criteria, roughly divided into 19 structural and 29 functional and metabolic studies. The quality of the studies varied, especially concerning inclusion criteria. Functional imaging studies indicated cerebellar hyperactivity during rest and during tremor. The studies also pointed to the involvement of the thalamus, the inferior olive and the red nucleus. Structural studies showed less consistent results.

Discussion and conclusion

Neuroimaging techniques in essential tremor give insight into the pathophysiology of essential tremor indicating the involvement of the cerebellum as the most consistent finding. GABAergic dysfunction might be a major premise in the pathophysiological hypotheses. Inconsistencies between studies can be partly explained by the inclusion of heterogeneous patient groups. Improvement of scientific research requires more stringent inclusion criteria and application of advanced analysis techniques. Also, the use of multimodal neuroimaging techniques is a promising development in movement disorders research. Currently, the role of imaging techniques in essential tremor in daily clinical practice is limited.

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We conducted a systematic review of neuroimaging studies in essential tremor.

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Cerebellar involvement is the most consistent finding.

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GABAergic dysfunction is worthwhile investigating more intensively.

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We encourage multimodal neuroimaging focussing on brain networks.

Increased 99mTc TRODAT-1 uptake in anaplastic oligodendroglioma

(99m)Tc TRODAT-1, a selective dopamine transporter SPECT imaging agent, has demonstrated its efficacy in identifying patients with Parkinson disease. Primary or metastatic brain neoplasm uptake of TRODAT-1 is rarely reported in literatures. A 51-year-old female patient underwent TRODAT-1 study for bradykinesia and altered cognitive function; the images showed abnormal extrastriatal uptake in the right frontal lobe subsequent to operation, and pathological examination confirmed anaplastic oligodendroglioma. Care should be taken in interpreting TRODAT-1 image; any focus on abnormal accumulation of radiotracer should not be overlooked because it can be brain neoplasm as demonstrated in this case.

Smoking, dopamine transporter, and hand tremor

AIM

The purpose of the study was to evaluate the relationship between the number of packs smoked per day and specific uptake ratio (SUR) in the striatum on Tc-99m TRODAT, and frequency of hand tremor.

METHODS

It was a prospective, cross-sectional study. In all, 23 healthy nonsmokers and 37 current smokers were recruited in the study. All subjects underwent Tc-99m TRODAT SPECT, brain CT scan, thyroid function test, tremor measurement system, and neurologic examinations.

RESULTS

There were significant differences in the SUR in the striatum on Tc-99m TRODAT and in the frequency of hand tremor in rest state and in arm extended state among nonsmokers (grade I), current smokers with less than 1 pack smoked per day (grade II), and current smokers with equal or more than 1 pack smoked per day (grade III) by ANOVA (all P < 0.001). After adjusting for age and gender, there was a significantly negative correlation between smoke grade and SUR in the striatum on Tc-99m TRODAT by multiple linear regression (β = -0.45, P < 0.001). Smoke grade was the significant predictor for the frequency of hand tremor in rest state and in arm extended state, after adjusting for age and gender by multiple linear regression (β = 14.70, P < 0.001; β = 15.37, P < 0.001).

CONCLUSIONS

There is a dose-response relationship between the number of packs smoked per day and SUR in the striatum, and the frequency of hand tremor. Decreased dopamine transporter binding in the striatum and increased frequency of hand tremor in smokers may have important implications for evaluating the impact of smoking on the central and peripheral nerve systems.

Dose-response relationship between cumulative mercury exposure index and specific uptake ratio in the striatum on Tc-99m TRODAT SPECT

PURPOSE

Tc-99m TRODAT is an agent for dopamine transporters and measuring dopamine innervation of the striatum. An association between Parkinson disease and body burden mercury level has been reported in the scientific published data. The purpose of this study was to investigate the effect of mercury exposure on dopamine transporters in the striatum measured by Tc-99m TRODAT single-photon emission computed tomography (SPECT).

METHOD AND MATERIALS

Study subjects included 17 workers who worked in a lamp factory at risk for mercury vapor exposure and 15 age-matched healthy controls. All subjects received Tc-99m TRODAT SPECT, brain computed tomography scan, and neurologic examinations. Biologic urine mercury levels at the end of a work week were assessed for workers.

RESULTS

There were significant differences in specific uptake ratio (SUR) in the striatum, caudate, and putamen between mercury exposure workers and healthy controls on Tc-99m TRODAT SPECT (all P < 0.001). The results showed a significantly negative correlation between urine and cumulative mercury levels and SUR in the striatum on Tc-99m TRODAT SPECT by Pearson analysis (r = -0.501, P = 0.040; r = -0.563, P = 0.019). After adjusting for age, gender, and body mass index, cumulative mercury exposure index (Cum Hg) was demonstrated to be the statistically significant predictor for SUR in the striatum, caudate, and putamen on Tc-99m TRODAT SPECT by multiple linear regression analysis (β = -0.543, P = 0.018; β = -0.521, P = 0.033; β = -0.465, P = 0.048).

CONCLUSION

Mercury exposure has significantly negative effect on dopamine transporters in the striatum. There is dose-response relationship between cumulative mercury exposure index (Cum Hg) and SUR in the striatum on Tc-99m TRODAT brain SPECT.

The role of dopaminergic imaging in patients with symptoms of dopaminergic system neurodegeneration

Diagnosis of neurological and psychiatric conditions associated with disturbances of dopaminergic functioning can be challenging, especially in the early stages, and may be assisted with biomarkers such as dopamine system imaging. Distinguishing between Alzheimer's disease and dementia with Lewy bodies is a major diagnostic challenge. Clinical diagnosis of Parkinson's disease is straightforward with classic presentation, but accurate distinction among Parkinsonian variants may be difficult; non-Parkinson's disease conditions are commonly misdiagnosed as Parkinson's disease, and ~20% of patients with Parkinson's disease are not clinically diagnosed despite coming to medical attention. Early and accurate diagnosis is desirable to improve management. Imaging of the dopamine transporter using single-photon emission computed tomography may be of particular utility in this regard. Abnormal imaging indicates underlying nigrostriatal neurodegeneration, supportive of a diagnosis of Parkinson's disease, atypical parkinsonism or dementia with Lewy bodies, and identifies patient groups in whom dopaminergic therapy may be beneficial. Normal imaging supports diagnosis of a condition not involving nigrostriatal neurodegeneration such as Alzheimer's disease, essential tremor or drug-induced parkinsonism and hence a different therapeutic approach. In patients in whom there was diagnostic uncertainty between degenerative parkinsonism and non-degenerative tremor disorders, baseline imaging with the dopamine transporter ligand [(123)I]ioflupane (DaTscan™) has shown 78% sensitivity and 97% specificity with reference to clinical diagnosis at 3 years, versus 93% and 46%, respectively, for baseline clinical diagnosis. In a Phase III trial of [(123)I]ioflupane in patients with initial clinical diagnosis of probable or possible dementia with Lewy bodies or non-Lewy body dementia, mean specificity for excluding non-Lewy body dementia (predominantly Alzheimer's disease) was 90.4%. Using clinical diagnosis as a reference against which to assess sensitivity and specificity of dopamine transporter imaging is a limitation, but definitive diagnosis via pathological confirmation is generally not feasible. In a series of patients with post-mortem brain examination, imaging using [(123)I]ioflupane has demonstrated higher sensitivity (88%) and specificity (100%) for differentiating dementia with Lewy bodies from non-Lewy body dementia than clinical diagnosis (75% and 42%, respectively). Dopaminergic system imaging may be particularly valuable in patients with clinically inconclusive parkinsonism or a clinical diagnosis of possible dementia with Lewy bodies; it is not helpful in differentiating between Parkinson's disease and atypical parkinsonism, although postsynaptic dopaminergic imaging may be of utility. Other potential uses of dopamine transporter imaging include identification of patients with premotor Parkinson's disease, monitoring disease progression in testing novel therapeutics, and as an inclusion criterion for entry into clinical trials.

Dual-isotope single-photon emission computed tomography for dopamine and serotonin transporters in normal and Parkinsonian monkey brains

INTRODUCTION

Parkinson's disease (PD) affects both dopaminergic and serotonergic systems. In this study, we simultaneously evaluated dopamine and serotonin transporters in primates using dual-isotope single-photon emission computed tomography (SPECT) imaging and compared the results with traditional single-isotope imaging.

METHODS

Four healthy and one 6-OHDA-induced PD monkeys were used for this study. SPECT was performed over 4 h after individual or simultaneous injection of [(99m)Tc]TRODAT-1 (a dopamine transporter imaging agent) and [(123)I]ADAM (a serotonin transporter imaging agent).

RESULTS

The results showed that the image quality and uptake ratios in different brain regions were comparable between single- and dual-isotope studies. The striatal [(99m)Tc]TRODAT-1 uptake in the PD monkey was markedly lower than that in normal monkeys. The uptake of [(123)I]ADAM in the midbrain of the PD monkey was comparable to that in the normal monkeys, but there were decreased uptakes in the thalamus and striatum of the PD monkey.

CONCLUSIONS

Our results suggest that dual-isotope SPECT using [(99m)Tc]TRODAT-1 and [(123)I]ADAM can simultaneously evaluate changes in dopaminergic and serotonergic systems in a PD model.

Distinguishing Parkinson's disease and essential tremor with transcranial sonography

OBJECTIVES

Until today there is no reliable test that can clearly distinguish Parkinson's disease (PD) from the essential tremor (ET). Our aim was to determine the usefulness of the transcranial sonography (TCS) in the differential diagnosis of the PD and ET as well as the interobserver reliability for this method.

METHODS

Transcranial sonography of substantia nigra and clinical examination were performed on 80 PD patients, 30 ET patients, and 80 matched controls by two independent physicians.

RESULTS

Bilateral SN hyperechogenicity over the margin of 0.20 cm(2) was found in 91% of PD patients, 10% of healthy subjects, and in 13% patients with ET. Interobserver agreement for this method was significant (Student's t-test, P = 1.000).

CONCLUSIONS

Substantia nigra hyperechogenicity on TCS is a highly specific finding of PD, where in healthy individuals or in ET patients, it might correspond to an increased risk of developing PD later in life or might also be because of the impairment of nearby area of nucleus ruber in ET patients, as suggested by positron emission tomography studies. TCS may serve as a practical and sufficiently sensitive neuroimaging tool in PD diagnoses and in distinguishing it from ET; its repeatability and accuracy might add to its practical value.

Exploring the relationship between essential tremor and Parkinson's disease

Although essential tremor (ET) and Parkinson's disease (PD) are considered distinct disorders, there is overlap in some clinical features. In some PD patients, a long-standing postural tremor in the hands may precede the onset of parkinsonian features by several years or decades. Furthermore, large families with both ET and PD phenotypes have been described and autopsy studies have demonstrated Lewy body pathology in brains of ET patients. Functional neuroimaging suggests that some ET patients have dopaminergic deficit. We examine here the evidence for and against an association between ET and PD, and critically review data supporting the notion that a subset of ET patients is predisposed to developing PD.

Essential tremor: emerging views of a common disorder

Essential tremor (ET) is the most prevalent tremor disorder. ET has traditionally been viewed as a monosymptomatic disorder characterized by a kinetic arm tremor, but this definition is gradually being replaced. The clinical spectrum has come to include several motor features, including tremor and ataxia, and several non-motor features, including possible cognitive impairment and personality disturbances. Postmortem studies are revealing several different patterns of pathology. The emerging view is that ET might be a family of diseases, unified by the presence of kinetic tremor, but further characterized by etiological, clinical and pathological heterogeneity. Effective pharmacological treatments for the disorder remain limited, although new insights into disease mechanisms might result in more-effective therapies. In addition, recent investigations of environmental toxicants that might be linked to ET open the way towards primary disease prevention through a reduction in exposure to these factors.

Early diagnosis of Parkinson’s disease

The clinical methods of olfactory testing and color discrimination as well as apparative methods such as transcranial ultrasound, dopamine transporter imaging and MIBG scintigraphy reveal a high sensitivity concerning the diagnosis of idiopathic Parkinson's disease (PD). The specificity of the presented methods, in particular of the dopamine transporter imaging--seems to be limited. All these methods and primarily their combination allow the detection of PD in early and--probably--preclinical stages. This requires sufficient therapeutic strategies to prevent and treat preclinical and early PD.