Differentiation of Parkinson's disease and multiple system atrophy in early disease stages by means of I-123-MIBG-SPECT

Towards a biological diagnosis of PD

Since the original description by James Parkinson, Parkinson's disease (PD) has intrigued us for over 200 years. PD is a progressive condition that is incurable so far, and affects millions of people worldwide. Over the years, our knowledge has expanded tremendously, and a range of criteria have been put forward and used to try to define PD. However, owing to the complexity of the problem, it is still not consensual how to diagnose and classify a disease that manifests with diverse features, and that responds differently to existing therapies and to those under development. We are now living a time when 'biological' information is becoming abundant, precise, and accessible enabling us to attempt to incorporate different sources of information to classify different forms of PD. These refinements are essential for basic science, as they will enable us to develop improved models for studying PD, and to implement new findings into clinical practice, as this will be the path towards effective personalized medicine.

Clinical Trial-Ready Patient Cohorts for Multiple System Atrophy: Coupling Biospecimen and iPSC Banking to Longitudinal Deep-Phenotyping

Multiple system atrophy (MSA) is a fatal neurodegenerative disease of unknown etiology characterized by widespread aggregation of the protein alpha-synuclein in neurons and glia. Its orphan status, biological relationship to Parkinson's disease (PD), and rapid progression have sparked interest in drug development. One significant obstacle to therapeutics is disease heterogeneity. Here, we share our process of developing a clinical trial-ready cohort of MSA patients (69 patients in 2 years) within an outpatient clinical setting, and recruiting 20 of these patients into a longitudinal "n-of-few" clinical trial paradigm. First, we deeply phenotype our patients with clinical scales (UMSARS, BARS, MoCA, NMSS, and UPSIT) and tests designed to establish early differential diagnosis (including volumetric MRI, FDG-PET, MIBG scan, polysomnography, genetic testing, autonomic function tests, skin biopsy) or disease activity (PBR06-TSPO). Second, we longitudinally collect biospecimens (blood, CSF, stool) and clinical, biometric, and imaging data to generate antecedent disease-progression scores. Third, in our Mass General Brigham SCiN study (stem cells in neurodegeneration), we generate induced pluripotent stem cell (iPSC) models from our patients, matched to biospecimens, including postmortem brain. We present 38 iPSC lines derived from MSA patients and relevant disease controls (spinocerebellar ataxia and PD, including alpha-synuclein triplication cases), 22 matched to whole-genome sequenced postmortem brain. iPSC models may facilitate matching patients to appropriate therapies, particularly in heterogeneous diseases for which patient-specific biology may elude animal models. We anticipate that deeply phenotyped and genotyped patient cohorts matched to cellular models will increase the likelihood of success in clinical trials for MSA.

Orthostatic hypotension: Review and expert position statement

Orthostatic hypotension is defined as a drop in systolic blood pressure of at least 20mmHg or a drop in diastolic blood pressure of at least 10mmHg within 3minutes of standing. It is a common disorder, especially in high-risk populations such as elderly subjects and patients with neurological diseases, and is associated with markedly increased morbidity and mortality. Its management can be challenging, particularly in cases where supine hypertension is associated with severe orthostatic hypotension. Education of the patient, non-pharmacological measures, and drug adaptation are the cornerstones of treatment. Pharmacological treatment should be individualized according to the severity, underlying cause, 24-hour blood pressure profile, and associated coexisting conditions. First-line therapies are midodrine and fludrocortisone, which may need to be combined for optimal care of severe cases.

Cardiac 123I-Metaiodobenzylguanidine (MIBG) Scintigraphy in Parkinson's Disease: A Comprehensive Review

Cardiac sympathetic denervation, as documented on 123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy, is relatively sensitive and specific for distinguishing Parkinson's disease (PD) from other neurodegenerative causes of parkinsonism. The present study aims to comprehensively review the literature regarding the use of cardiac MIBG in PD. MIBG is an analog to norepinephrine. They share the same uptake, storage, and release mechanisms. An abnormal result in the cardiac MIBG uptake in individuals with parkinsonism can be an additional criterion for diagnosing PD. However, a normal result of cardiac MIBG in individuals with suspicious parkinsonian syndrome does not exclude the diagnosis of PD. The findings of cardiac MIBG studies contributed to elucidating the pathophysiology of PD. We investigated the sensitivity and specificity of cardiac MIBG scintigraphy in PD. A total of 54 studies with 3114 individuals diagnosed with PD were included. The data were described as means with a Hoehn and Yahr stage of 2.5 and early and delayed registration H/M ratios of 1.70 and 1.51, respectively. The mean cutoff for the early and delayed phases were 1.89 and 1.86. The sensitivity for the early and delayed phases was 0.81 and 0.83, respectively. The specificity for the early and delayed phases were 0.86 and 0.80, respectively.

Vagus Nerve Ultrasonography Helps Distinguish Multiple System Atrophy from Other Parkinsonian Syndromes

Background

Distinguishing multiple system atrophy from other parkinsonian syndromes is challenging.

Objectives

To evaluate vagus nerve ultrasonography for differentiating parkinsonian syndromes.

Methods

A single-center, cross-sectional, observational study assessed 85 consecutive adult patients with de novo parkinsonism between June 2020 and December 2022, using 12 MHz ultrasonography of the vagus nerve cross-sectional area.

Results

Bilateral vagus nerves were smaller in multiple system atrophy than in other parkinsonian syndromes. The area under the receiver operating characteristic curve for differentiating multiple system atrophy was 0.79 on the right side and 0.74 on the left. The cut-off values to diagnose multiple system atrophy were 0.71 and 0.86 mm2 on the right and left sides, respectively, with sensitivities of 82.6% and 87.0%, specificities of 74.2% and 64.5%, positive predictive values of 54% and 47.6%, and negative predictive values of 92.0% and 93.0%.

Conclusions

Vagus nerve ultrasonography may differentiate multiple system atrophy from other parkinsonian syndromes.

Pupil light reflex dynamics in Parkinson's disease

Introduction

Visual disturbance is common symptom in Parkinson's disease (PD), and defective pupil light reflex (PLR) is an anticipated contributing factor that may be associated to the presence of autonomic dysfunction, which is a common non-motor feature of PD. Studies investigating the intercorrelation between PLR and dysautonomia in PD are limited.

Methods

The aim of this study was to investigate differences of PLR parameters, measured by eye-tracker, between patients with PD, with and without signs of dysautonomia, and healthy controls (HC). In total, 43 HC and 50 patients with PD were recruited and PLR parameters were measured with Tobii Pro Spectrum, during a long (1,000 ms) and a short (100 ms) light stimulus. Presence of orthostatic hypotension (OH) was used as proxy marker of dysautonomia. Linear mixed-effects model and non-parametric comparative statistics were applied to investigate differences among groups.

Results

Peak constriction velocity was slower in PD compared with HC, after adjustment for age and sex in the mixed model, and the difference was greater in the subgroup of PD with OH (unadjusted). Dilation amplitude and velocity were also gradually slower in HC vs. PD without OH vs. PD with OH (unadjusted for confounders). In the mixed model, age was significant predictor of dilation response.

Discussion

Our results support previous observations on defective PLR in PD, evaluated with eye-tracker, and show a possible association with autonomic dysfunction. Further studies with more patients and rigorous evaluation of autonomic dysfunction are needed to validate these findings.

Cardiac sympathetic denervation could be associated with dysphagia in Parkinson's disease

Background

Dysphagia is an important non-motor symptom that is closely associated with quality of living and mortality in Parkinson's disease (PD). However, the pathophysiology of dysphagia in PD remains inconclusive. We tried to confirm whether the occurrence of dysphagia could be related to sympathetic degeneration using cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphy.

Methods

We prospectively recruited 27 PD patients and classified them into two groups (PD with dysphagia vs. PD without dysphagia) by Swallowing Disturbance Questionnaire (SDQ) score and compared the clinical characteristics, videofluoroscopic swallowing study (VFSS) findings and parameters from cardiac MIBG scintigraphy.

Results

The mean early and late H/M ratios were significantly lower in the PD with dysphagia group than those in the PD without dysphagia group (1.39 ± 0.21 vs. 1.86 ± 0.21, p < 0.01; 1.26 ± 0.18 vs. 1.82 ± 0.29, p < 0.01). In the correlation analysis, both the early and late H/M ratios were negatively correlated with the SDQ score and total VDS score (r = −0.65, p < 0.01; r = −0.53, p < 0.01; r = −0.65, p < 0.01, r = −0.58, p < 0.01).

Conclusion

We confirmed that cardiac sympathetic denervation might be associated with the presence and severity of dysphagia. This finding indicates that dysphagia in PD could be associated with a nondopaminergic mechanism.

Differentiation of Parkinson’s disease and Parkinsonism predominant multiple system atrophy in early stage by morphometrics in susceptibility weighted imaging

Background and purpose

We previously established a radiological protocol to discriminate multiple system atrophy-parkinsonian subtype (MSA-P) from Parkinson’s disease (PD). However, we do not know if it can differentiate early stage disease. This study aimed to investigate whether the morphological and intensity changes in susceptibility weighted imaging (SWI) of the lentiform nucleus (LN) could discriminate MSA-P from PD at early stages.

Methods

We retrospectively enrolled patients with MSA-P, PD and sex- and age-matched controls whose brain MRI included SWI, between January 2015 and July 2020 at the Movement Disorder Center. Two specialists at the center reviewed the medical records and made the final diagnosis, and two experienced neuroradiologists performed MRI analysis, based on a defined and revised protocol for conducting morphological measurements of the LN and signal intensity.

Results

Nineteen patients with MSA-P and 19 patients with PD, with less than 2 years of disease duration, and 19 control individuals were enrolled in this study. We found that patients with MSA- P presented significantly decreased size in the short line (SL) and corrected short line (cSL), ratio of the SL to the long line (SLLr) and corrected SLLr (cSLLr) of the LN, increased standard deviation of signal intensity (SIsd_LN, cSIsd_LN) compared to patients with PD and controls (P < 0.05). With receiver operating characteristic (ROC) analysis, this finding had a sensitivity of 89.5% and a specificity of 73.7% to distinguish MSA- P from PD.

Conclusion

Compared to PD and controls, patients with MSA-P are characterized by a narrowing morphology of the posterior region of the LN. Quantitative morphological changes provide a reference for clinical auxiliary diagnosis.

The Movement Disorder Society Criteria for the Diagnosis of Multiple System Atrophy

BACKGROUND

The second consensus criteria for the diagnosis of multiple system atrophy (MSA) are widely recognized as the reference standard for clinical research, but lack sensitivity to diagnose the disease at early stages.

OBJECTIVE

To develop novel Movement Disorder Society (MDS) criteria for MSA diagnosis using an evidence-based and consensus-based methodology.

METHODS

We identified shortcomings of the second consensus criteria for MSA diagnosis and conducted a systematic literature review to answer predefined questions on clinical presentation and diagnostic tools relevant for MSA diagnosis. The criteria were developed and later optimized using two Delphi rounds within the MSA Criteria Revision Task Force, a survey for MDS membership, and a virtual Consensus Conference.

RESULTS

The criteria for neuropathologically established MSA remain unchanged. For a clinical MSA diagnosis a new category of clinically established MSA is introduced, aiming for maximum specificity with acceptable sensitivity. A category of clinically probable MSA is defined to enhance sensitivity while maintaining specificity. A research category of possible prodromal MSA is designed to capture patients in the earliest stages when symptoms and signs are present, but do not meet the threshold for clinically established or clinically probable MSA. Brain magnetic resonance imaging markers suggestive of MSA are required for the diagnosis of clinically established MSA. The number of research biomarkers that support all clinical diagnostic categories will likely grow.

CONCLUSIONS

This set of MDS MSA diagnostic criteria aims at improving the diagnostic accuracy, particularly in early disease stages. It requires validation in a prospective clinical and a clinicopathological study. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cardiac sympathetic innervation in Parkinson's disease versus multiple system atrophy

Purpose

The aims of this study were to evaluate the diagnostic accuracy of the dual imaging method combining cardiac iodine-¹²³-metaiodobenzylguanidine single-photon emission computed tomography combined with low-dose chest computed tomography compared to routine cardiac scintigraphy, and assess regional differences in tracer distribution and the relationships between imaging and autonomic function in Parkinson’s disease and multiple system atrophy.

Methods

A prospective study including 19 Parkinson’s disease and 12 multiple system atrophy patients was performed. Patients underwent clinical evaluation, iodine-¹²³-metaiodobenzylguanidine single-photon emission computed tomography combined with chest computed tomography, planar scintigraphy, and cardiovascular autonomic function tests.

Results

Co-registration of single-photon emission computed tomography and chest computed tomography resulted in three groups with distinct patterns of tracer uptake: homogeneous, non-homogeneously reduced and absent. There was a significant difference in group allocation among patients with multiple system atrophy and Parkinson’s disease (p = 0.001). Most multiple system atrophy patients showed homogeneous uptake, and the majority of Parkinson’s disease patients showed absent cardiac tracer uptake. We identified a pattern of heterogeneous cardiac tracer uptake in both diseases with reductions in the apex and the lateral myocardial wall. Sympathetic dysfunction reflected by a missing blood pressure overshoot during Valsalva manoeuvre correlated with cardiac tracer distribution in Parkinson’s disease patients (p < 0.001).

Conclusions

The diagnostic accuracy of the dual imaging method and routine cardiac scintigraphy were similar. Anatomical tracer allocation provided by the dual imaging method of cardiac iodine-¹²³-metaiodobenzylguanidine single-photon emission computed tomography and chest computed tomography identified a heterogeneous subgroup of Parkinson’s disease and multiple system atrophy patients with reduced cardiac tracer uptake in the apex and the lateral wall. Sympathetic dysfunction correlated with cardiac imaging in Parkinson’s disease patients.

Cardiac Autonomic Dysfunction Is Associated with Severity of REM Sleep without Atonia in Isolated REM Sleep Behavior Disorder

123I-metaiodobenzylguanidine (MIBG) cardiac scintigraphy was performed to assess cardiac autonomic dysfunction and demonstrate its correlation with clinical and polysomnographic characteristics in patients with isolated rapid eye movement (REM) sleep behavior disorder. All subjects including 39 patients with isolated REM sleep behavior disorder and 17 healthy controls underwent MIBG cardiac scintigraphy for cardiac autonomic dysfunction assessment. The isolated REM sleep behavior disorder was confirmed by in-lab overnight polysomnography. A receiver operating curve was constructed to determine the cut-off value of the early and delayed heart-to-mediastinum ratio in patients with isolated REM sleep behavior disorder. Based on each cut-off value, a comparison analysis of REM sleep without atonia was performed by dividing isolated REM sleep behavior disorder patients into two groups. MIBG uptake below the cut-off value was associated with higher REM sleep without atonia. The lower heart-to-mediastinum ratio had significantly higher REM sleep without atonia (%), both with cut-off values of early (11.0 ± 5.6 vs. 29.3 ± 23.2%, p = 0.018) and delayed heart-to-mediastinum ratio (9.1 ± 4.3 vs. 30.0 ± 22.9%, p = 0.011). These findings indicate that reduced MIBG uptake is associated with higher REM sleep without atonia in isolated REM sleep behavior disorder.

Postganglionic Sudomotor Dysfunction and Brain Glucose Hypometabolism in Patients with Multiple System Atrophy

BACKGROUND

Sudomotor dysfunction is common in patients with multiple system atrophy (MSA). Postganglionic sudomotor dysfunction in MSA, which can be assessed using quantitative sudomotor axon reflex testing (QSART), results from the degeneration of preganglionic sympathetic neurons and direct loss of postganglionic fibers.

OBJECTIVE

We investigate whether abnormal QSART responses in patients with MSA are associated with disease severity.

METHODS

In this retrospective study, patients with probable MSA who underwent both 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) and autonomic function tests were included. Autonomic function test results were integrated divided into three sub-scores, including sudomotor, cardiovagal, and adrenergic sub-scores. The sudomotor sub-score represented postganglionic sudomotor function. Unified Multiple System Atrophy Rating Scale (UMSARS) Part I, Part II, and sum of Part I and II scores (Part I + II) to reflect disease severity and 18F-FDG-PET/CT results were collected.

RESULTS

Of 74 patients with MSA, 62.2%demonstrated abnormal QSART results. The UMSARS Part I + II score was significantly higher in the abnormal QSART group than in the normal QSART group (p = 0.037). In the regression analysis, both UMSARS Part I (β= 1.185, p = 0.013) and Part II (β= 1.266, p = 0.021) scores were significantly associated with the sudomotor sub-score. On 18F-FDG-PET/CT, the abnormal QSART group exhibited more severely decreased metabolic activity in the cerebellum and basal ganglia in patients with MSA-P and MSA-C, respectively. The sudomotor sub-score was significantly associated with regional metabolism in these areas.

CONCLUSION

Patients with MSA and postganglionic sudomotor dysfunction may have worse disease severity and greater neuropathological burden than those without.

Imaging Familial and Sporadic Neurodegenerative Disorders Associated with Parkinsonism

In this paper, the structural and functional imaging changes associated with sporadic and genetic Parkinson's disease and atypical Parkinsonian variants are reviewed. The role of imaging for supporting diagnosis and detecting subclinical disease is discussed, and the potential use and drawbacks of using imaging biomarkers for monitoring disease progression is debated. Imaging changes associated with nonmotor complications of PD are presented. The similarities and differences in imaging findings in Lewy body dementia, Parkinson's disease dementia, and Alzheimer's disease are discussed.

Sympathetic and sensory nerve fiber function in multiple system atrophy and idiopathic Parkinson's disease

OBJECTIVE

To explore small fiber somatosensory and sympathetic function in PD and MSA.

METHODS

We recruited 20 PD patients (7 women, median age 65.5 years; IQR 54.75-70.0), 10 MSA patients (4 women; median age 68 years; IQR 66.25-74.0), and 10 healthy subjects (HC; 4 women, median age 68; IQR 59.0-71.0 years). Autonomic testing included forehead cooling, intradermal microdialysis of norepinephrine (NE; 10^-5; 10^-6; 10^-7; and 10^-8), and orthostatic hypotension (OH); somatosensory testing included quantitative sensory testing (QST) according to the protocol of the German Research Network on Neuropathic Pain (DFNS).

RESULTS

OH occurred more frequently in PD (p = 0.018) and MSA (p = 0.002) compared to HC. Vasoconstriction responses were stronger in PD compared to MSA during forehead cooling (p = 0.044) and microdialysis of physiologically concentrated NE solutions (10^-7; 10-8; p = 0.017). PD and MSA had impaired cold (PD: p < 0.01; MSA: p < 0.05) and warm detection thresholds (PD and MSA, both p < 0.05). The mechanical detection threshold was higher in PD (p < 0.01). Conversely, mechanical pain thresholds were decreased in PD and MSA (both p < 0.001), indicating mechanical hyperalgesia.

CONCLUSION

In contrast to MSA, we found evidence of peripheral adrenoreceptor hypersensitivity in PD, probably caused by peripheral sympathetic denervation. Sensory testing revealed peripheral neuropathy and central pain sensitization in PD and MSA. Jointly, our data demonstrate autonomic and somatosensory dysfunction in PD and MSA.

Fatigability and Cardiorespiratory Impairments in Parkinson's Disease: Potential Non-Motor Barriers to Activity Performance

Parkinson's disease (PD) is the second most common neurodegenerative condition after Alzheimer's disease, affecting an estimated 160 per 100,000 people 65 years of age or older. Fatigue is a debilitating non-motor symptom frequently reported in PD, often manifesting prior to disease diagnosis, persisting over time, and negatively affecting quality of life. Fatigability, on the other hand, is distinct from fatigue and describes the magnitude or rate of change over time in the performance of activity (i.e., performance fatigability) and sensations regulating the integrity of the performer (i.e., perceived fatigability). While fatigability has been relatively understudied in PD as compared to fatigue, it has been hypothesized that the presence of elevated levels of fatigability in PD results from the interactions of homeostatic, psychological, and central factors. Evidence from exercise studies supports the premise that greater disturbances in metabolic homeostasis may underly elevated levels of fatigability in people with PD when engaging in physical activity. Cardiorespiratory impairments constraining oxygen delivery and utilization may contribute to the metabolic alterations and excessive fatigability experienced in individuals with PD. Cardiorespiratory fitness is often reduced in people with PD, likely due to the combined effects of biological aging and impairments specific to the disease. Decreases in oxygen delivery (e.g., reduced cardiac output and impaired blood pressure responses) and oxygen utilization (e.g., reduced skeletal muscle oxidative capacity) compromise skeletal muscle respiration, forcing increased reliance on anaerobic metabolism. Thus, the assessment of fatigability in people with PD may provide valuable information regarding the functional status of people with PD not obtained with measures of fatigue. Moreover, interventions that target cardiorespiratory fitness may improve fatigability, movement performance, and health outcomes in this patient population.

Can Autonomic Testing and Imaging Contribute to the Early Diagnosis of Multiple System Atrophy? A Systematic Review and Recommendations by the Movement Disorder Society Multiple System Atrophy Study Group

Background

In the current consensus diagnostic criteria, the diagnosis of probable multiple system atrophy (MSA) is based solely on clinical findings, whereas neuroimaging findings are listed as aid for the diagnosis of possible MSA. There are overlapping phenotypes between MSA-parkinsonian type and Parkinson's disease, progressive supranuclear palsy, and dementia with Lewy bodies, and between MSA-cerebellar type and sporadic adult-onset ataxia resulting in a significant diagnostic delay and misdiagnosis of MSA during life.

Objectives

In light of an ongoing effort to revise the current consensus criteria for MSA, the Movement Disorders Society Multiple System Atrophy Study Group performed a systematic review of original articles published before August 2019.

Methods

We included articles that studied at least 10 patients with MSA as well as participants with another disorder or control group for comparison purposes. MSA was defined by neuropathological confirmation, or as clinically probable, or clinically probable plus possible according to consensus diagnostic criteria.

Results

We discuss the pitfalls and benefits of each diagnostic test and provide specific recommendations on how to evaluate patients in whom MSA is suspected.

Conclusions

This systematic review of relevant studies indicates that imaging and autonomic function tests significantly contribute to increasing the accuracy of a diagnosis of MSA.

Advances in the Research of Risk Factors and Prodromal Biomarkers of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. With the advent of an aging population and improving life expectancy worldwide, the number of PD patients is expected to increase, which may lead to an urgent need for effective preventive and diagnostic strategies for PD. Although there is increasing research regarding the pathogenesis of PD, there is limited knowledge regarding the prevention of PD. Moreover, the diagnosis of PD depends on clinical criteria, which require the occurrence of bradykinesia and at least one symptom of rest tremor or rigidity. However, converging evidence from clinical, genetic, neuropathological, and imaging studies suggests the initiation of PD-specific pathology prior to the initial presentation of these classical motor clinical features by years or decades. This latent stage of neurodegeneration in PD is a particularly important stage for effective neuroprotective therapies, which might retard the progression or prevent the onset of PD. Therefore, the exploration of risk factors and premotor biomarkers is not only crucial to the early diagnosis of PD but is also helpful in the development of effective neuroprotection and health care strategies for appropriate populations at risk for PD. In this review, we searched and summarized ∼249 researches and 31 reviews focusing on the risk factors and prodromal biomarkers of PD and published in MEDLINE.

Autoimmune autonomic ganglionopathy: an update on diagnosis and treatment

INTRODUCTION

Autoimmune autonomic ganglionopathy (AAG) is an acquired immune-mediated disorder that leads to autonomic failure. The disorder is associated with autoantibodies to the ganglionic nicotinic acetylcholine receptor (gAChR). We subsequently reported that AAG is associated with an overrepresentation of psychiatric symptoms, sensory disturbance, autoimmune diseases, and endocrine disorders. Area covered: The aim of this review was to describe AAG and highlight its pivotal pathophysiological aspects, clinical features, laboratory examinations, and therapeutic options. Expert commentary: AAG is a complex neuroimmunological disease, these days considered as an autonomic failure with extra-autonomic manifestations (and various limited forms). Further comprehension of the pathophysiology of this disease is required, especially the mechanisms of the extra-autonomic manifestations should be elucidated. There is the possibility that the co-presence of antibodies that were directed against the other subunits in both the central and peripheral nAChRs in the serum of the AAG patients. Some patients improve with immunotherapies such as IVIg and/or corticosteroid and/or plasma exchange. ¹²³I-MIBG myocardial scintigraphy may be a useful tool to monitor the therapeutic effects of immunotherapies.

Advances in SPECT Methodology

The emerging role of molecular imaging has made possible to evaluate and quantify biochemical changes of molecular targets in specific neurochemical systems involved in movement disorders, providing neurochemical information of clinical changes before the pathological features occurred. In detail, radionuclides imaging techniques are frequently used for the in vivo study of neurotransmitter and receptor function, alterations in cerebral blood flow and metabolic activity, abnormal protein deposition, and inflammation, with a central role in molecular imaging for preclinical and clinical studies. The present chapter represents an overview of main use of single-photon emission computed tomography (SPECT) in movement disorders, with a focal attention on specific radiotracers used, recent advances in SPECT technology and reconstruction algorithm and added specific value of semiquantitative methods for images analysis. Finally, a brief paragraph is dedicated to description of SPECT/CT devices and advantages of using hybrid technology.

Roles of cardiac sympathetic neuroimaging in autonomic medicine

Sympathetic neuroimaging is based on the injection of compounds that either radiolabel sites of the cell membrane norepinephrine transporter (NET) or that are taken up into sympathetic nerves via the NET and radiolabel intra-neuronal catecholamine storage sites. Detection of the radioactivity is by planar or tomographic radionuclide imaging. The heart stands out among body organs in terms of the intensity of radiolabeling of sympathetic nerves, and virtually all of sympathetic neuroimaging focuses on the left ventricular myocardium. The most common cardiac sympathetic neuroimaging method worldwide is ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) scanning. ¹²³I-MIBG scanning is used routinely in Europe and East Asia in the diagnostic evaluation of neurogenic orthostatic hypotension (nOH), to distinguish Lewy body diseases (e.g., Parkinson disease with orthostatic hypotension (OH), pure autonomic failure) from non-Lewy body diseases (e.g., multiple system atrophy) and to distinguish dementia with Lewy bodies from Alzheimer's disease. In the USA, ¹²³I-MIBG scanning has been approved by the Food and Drug Administration for the evaluation of pheochromocytoma and some forms of heart failure-but not for the above-mentioned differential diagnoses. Positron emission tomographic methods based on imaging agents such as ¹⁸F-dopamine are categorized as research tools, despite more than a quarter century of clinical experience with these modalities. Considering that ¹²³I-MIBG scanning is available at most academic medical centers in the USA, cardiac sympathetic neuroimaging by this methodology merits consideration as an autonomic test, especially in patients with nOH.

Prospective study of relevance of 123I-MIBG myocardial scintigraphy and clonidine GH test to distinguish Parkinson's disease and multiple system atrophy

BACKGROUND

¹²³I-MIBG myocardial scintigraphy and clonidine growth hormone test (CGH test) may help to distinguish multiple system atrophy (MSA) from Parkinson's disease (PD). Their relevance in the first-stage parkinsonism of uncertain etiology is unknown.

METHODS

Patients experiencing parkinsonism of ambiguous etiology were clinically classified into the PD group or the MSA group as initial clinical diagnosis (ICD). Then, CGH test and myocardial scintigraphy were performed. Clinical assessment was repeated throughout the disease course until the final clinical diagnosis (FCD) could be established according to the criteria of PD and MSA, respectively.

RESULTS

Twenty-five patients with uncertain diagnosis were included (15 MSA and 10 PD as ICD). At the end of a 6-year follow-up, FCD was MSA in 11/25 patients and PD in 14/25. The CGH test and the scintigraphy showed a sensitivity of 82%, and a specificity of 71 and 93%, respectively, for the diagnosis of MSA. The combination of a normal scintigraphy (i.e., with myocardial MIBG uptake) with genitourinary dysfunction was the most relevant test to diagnose MSA, whereas an abnormal scintigraphy with a levodopa response of > 30% or an abnormal scintigraphy with the absence of OH was the most relevant combinations to diagnose PD. All these combinations had an accuracy superior than 90% and a specificity of 100%.

CONCLUSION

Combinations of myocardial scintigraphy with genitourinary dysfunction, levodopa response of > 30%, or orthostatic hypotension could be of interest for the distinction between PD and MSA when the clinical diagnosis remains ambiguous at the first stage of the disease.

Optimizing Parkinson's disease diagnosis: the role of a dual nuclear imaging algorithm

The diagnosis of Parkinson's disease (PD) currently relies almost exclusively on the clinical judgment of an experienced neurologist, ideally a specialist in movement disorders. However, such clinical diagnosis is often incorrect in a large percentage of patients, particularly in the early stages of the disease. A commercially available, objective and quantitative marker of nigrostriatal neurodegeneration was recently provided by 123-iodine ¹²³I-ioflupane SPECT imaging, which is however unable to differentiate PD from a variety of other parkinsonian syndromes associated with striatal dopamine deficiency. There is evidence to support an algorithm utilizing a dual neuroimaging strategy combining ¹²³I-ioflupane SPECT and the noradrenergic receptor ligand ¹²³I-metaiodobenzylguanidine (MIBG), which assesses the post-ganglion peripheral autonomic nervous system. Evolving concepts regarding the synucleinopathy affecting the central and peripheral autonomic nervous systems as part of a multisystem disease are reviewed to sustain such strategy. Data are presented to show how MIBG deficits are a common feature of multisystem Lewy body disease and can be used as a unique feature to distinguish PD from atypical parkinsonisms. We propose that the combination of cardiac (MIBG) and cerebral ¹²³I-ioflupane SPECT could satisfy one of the most significant unmet needs of current PD diagnosis and management, namely the early and accurate diagnosis of patients with typical Lewy body PD. Exemplary case scenarios will be described, highlighting how dual neuroimaging strategy can maximize diagnostic accuracy for patient care, clinical trials, pre-symptomatic PD screening, and special cases provided by specific genetic mutations associated with PD.

Extensive Delayed Brain Atrophy after Resuscitation in a Patient with Multiple System Atrophy

Brain magnetic resonance imaging (MRI) of multiple system atrophy (MSA) shows atrophy in the cerebrum, cerebellum, and brainstem. It is also characterized by specific patterns such as hyperintense lateral putaminal rim. MRI of hypoxic encephalopathy shows atrophy mainly in the gray matter, and laminar necrosis in the cerebral cortex is often observed. Here, we report an MSA patient damaged by hypoxic insult and resuscitated after 18-min cardiac arrest. The brain of the patient developed severe atrophy within a period of 10 months. Furthermore, brain atrophy was observed in the white and gray matter, which preserved the brain atrophy pattern in MSA. We assume that alpha-synuclein oligomerization is involved in the neural cell death and brain atrophy. It might have caused further neural cell death in the brain damaged by hypoxia. Alpha-synuclein, which is involved in the pathogenesis of MSA, is suggested to be a prion. Misfolded alpha-synuclein may propagate through cell-to-cell transmission and cause wide pathological change, visible as atrophied MR imaging.

Pure Autonomic Failure

Pure autonomic failure (PAF) is a rare sporadic neurodegenerative autonomic disorder characterized by slowly progressive pan autonomic failure without other features of neurologic dysfunctions. The main clinical symptoms result from neurogenic orthostatic hypotension and urinary and gastrointestinal autonomic dysfunctions. Autonomic failure in PAF is caused by neuronal degeneration of pre- and postganglionic sympathetic and parasympathetic neurons in the thoracic spinal cord and paravertebral autonomic ganglia. The presence of Lewy bodies and α-synuclein deposits in these neural structures suggests that PAF is one of Lewy body synucleinopathies, examples of which include multiple system atrophy, Parkinson disease, and Lewy body disease. There is currently no specific treatment to stop progression in PAF. Management of autonomic symptoms is the mainstay of treatment and includes management of orthostatic hypotension and supine hypertension. The prognosis for survival of PAF is better than for the other synucleinopathies.

123I-metaiodobenzylguanidine myocardial scintigraphy with early images alone is useful for the differential diagnosis of dementia with Lewy bodies

123I-metaiodobenzylguanidine cardiac scintigraphy (MIBG) is a useful imaging technique for the diagnosis of dementia with Lewy bodies (DLB). However, MIBG has a serious disadvantage in that it demands a long examination time. The objective of this study was to evaluate statistically the usefulness of the heart/mediastinum ratio (H/M) from the early phase of MIBG for the differential diagnosis of DLB. In total, 113 patients were examined, including 32 non-DLB (19 with Alzheimer's dementia) and 79 DLB patients. The mean early-H/M ratio was 2.83 in the non-DLB group and 1.95 in the DLB group. The mean delayed-H/M ratio was 3.0 in the non-DLB group and 1.76 in the DLB group. With a cutoff point of 2.27 on early images, the sensitivity, specificity, and diagnostic accuracy were 65%, 94%, and 73%, respectively, and the area under the curve was 0.82, indicating moderate accuracy. This analysis indicates that images from the early phase of MIBG alone are sufficient for the differential diagnosis of Alzheimer's disease and DLB.

131I-MIBG myocardial scintigraphy for differentiation of Parkinson's disease from multiple system atrophy or essential tremor in Chinese population

OBJECTIVE

Clinical distinction of Parkinson's disease (PD) from multiple system atrophy (MSA) or essential tremor (ET) is sometimes difficult. The purpose of this study was to assess changes in cardiac sympathetic nerve function in PD, MSA, and ET by ¹³¹I-MIBG myocardial scintigraphy METHODS: Patients with PD (25), MSA (18), or ET (11) and 10 healthy controls (HC) were enrolled. ¹³¹I-MIBG myocardial scintigraphy was performed for each subject, and heart/mediastinum (H/M) ratios were calculated at two sample times (15min and 4h after the injection of ¹³¹I-MIBG), representing the ¹³¹I-MIBG myocardial uptake ratios. The washout ratio (WOR) of MIBG which indicates the activity tone of the presynaptic sympathetic nerves was calculated for each subject.

RESULTS

The H/M ratios at the two sample times (15min and 4h) were 1.65±0.36 and 1.50±0.43 in the PD group, 1.97±0.36 and 2.08±0.57 in the MSA group, 2.34±0.34 and 2.46±0.51 in the ET group, and 2.41±0.26 and 2.66±0.47 in the HC group. The H/M ratios at the two sample times were lower in the PD group than in the MSA, ET, or HC groups, with statistical significance (all P<0.05). The H/M ratios at the two sample times were significantly lower in the MSA group than in the HC group (all P<0.05). There was no significant difference in H/M ratios at either sample time between the ET and HC group (all P>0.05). The washout ratios (WORs) of MIBG were significantly increased in PD group compared with those in MSA, ET and HC groups. In subgroup analysis, The H/M ratios at the two sample times were decreased in early PD group compared with those in early MSA and early ET groups, with statistical significance (all P<0.05).

CONCLUSIONS

Cardiac sympathetic dysfunction can occur in both PD and MSA patients, especially in PD patients, whereas it remains normal in ET patients. ¹³¹I-MIBG myocardial scintigraphy can help distinguish patients with PD from those with MSA or ET with good sensitivity and specificity.

Anhidrosis in multiple system atrophy involves pre- and postganglionic sudomotor dysfunction

BACKGROUND

The objective of this study was to characterize the degree, pattern, lesion site, and temporal evolution of sudomotor dysfunction in multiple system atrophy (MSA) and to evaluate differences by parkinsonian (MSA-parkinsonism) and cerebellar (MSA-cerebellar) subtypes.

METHODS

All cases of MSA evaluated at Mayo Clinic Rochester between 2005 and 2010 with postganglionic sudomotor testing and thermoregulatory sweat test were reviewed. Pattern and lesion site (preganglionic, postganglionic, or mixed) were determined based on thermoregulatory sweat test and postganglionic sudomotor testing.

RESULTS

The majority of the 232 patients were MSA-parkinsonism (145, 63%). Initial postganglionic sudomotor testing was abnormal in 59%, whereas thermoregulatory sweat test was abnormal in 95% of all patients. MSA-parkinsonism patients were more likely to have an abnormal thermoregulatory sweat test compared with MSA-cerebellar (98% versus 90%, P = 0.006) and had a higher mean percentage of anhidrosis (57%) compared with MSA-cerebellar (48%; P = 0.033). Common anhidrosis patterns were regional (38%) and global (35%). The site of the lesion was preganglionic in 47% and mixed (preganglionic and postganglionic) in 41%. The increase in anhidrosis per year was 6.2% based on 70 repeat thermoregulatory sweat tests performed on 29 patients. The frequency of postganglionic sudomotor abnormalities increased over time.

CONCLUSIONS

Our findings suggest: (1) sudomotor dysfunction is almost invariably present in MSA and even more common and severe in MSA-parkinsonism than MSA-cerebellar; (2) a preganglionic pattern of sweat loss is common in MSA; however, pre- and postganglionic abnormalities may coexist; and (3) the increasing frequency of postganglionic sudomotor dysfunction over time suggests involvement of postganglionic fibers or sweat glands later in the disease course. © 2016 International Parkinson and Movement Disorder Society.

Molecular imaging of dopamine transporters

The dopamine transporter (DAT) is responsible for clearance of dopamine from the synaptic cleft after its release. Imaging DAT availability provides a measure of dopamine terminal function and a method for detecting the striatal dopamine terminal dysfunction present in idiopathic Parkinson's disease (PD) and atypical neurodegenerative parkinsonian disorders such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). DAT imaging with positron emission tomography (PET) or single photon emission computed tomography (SPECT) can be used to support or refute a diagnosis of dopamine deficient parkinsonism in cases where this is unclear and rationalise a trial of dopamine replacement agents as therapy. It can also detect subclinical dopaminergic dysfunction when present in subjects at risk for PD such as relatives of patients, susceptibility gene mutation carriers, and subjects with late onset hyposmia or sleep disorders. The presence of normal DAT availability on imaging can help categorise "subjects without evidence of dopamine deficiency" (SWEDDs) who on occasion mimic PD and include dystonic tremors, drug-induced and psychogenic parkinsonism in their ranks. Reduced levels of baseline striatal DAT availability on PET or SPECT scanning, however, should be regarded as supportive rather than diagnostic of dopamine deficient parkinsonism.

(123)I-meta-iodobenzylguanidine (MIBG) cardiac scintigraphy in α-synucleinopathies

Cardiac meta-iodobenzylguanidine (MIBG) uptake on (123)I-MIBG cardiac scintigraphy is reduced in patients with Lewy body disease such as Parkinson's disease (PD), dementia with Lewy bodies (DLB), and pure autonomic failure, and has been reported to be useful for differentiating PD from other parkinsonian syndromes, as well as DLB from Alzheimer disease (AD). Postmortem studies have shown that the number of tyrosine hydroxylase (TH)-immunoreactive nerve fibers of the heart was decreased in pathologically-confirmed Lewy body disease, supporting the findings of reduced cardiac MIBG uptake in Lewy body diseases. Now, reduced cardiac MIBG uptake can be a potential biomarker for the presence of Lewy bodies in the nervous system. (123)I-MIBG cardiac scintigraphy can allow us to determine the presence of Lewy bodies.

Imaging synucleinopathies

In this review the structural and functional imaging changes associated with the synucleinopathies PD, MSA, and dementias associated with Lewy bodies are reviewed. The role of imaging for supporting differential diagnosis, detecting subclinical disease, and following disease progression is discussed and its potential use for monitoring disease progression is debated. © 2016 International Parkinson and Movement Disorder Society.

Cardiovagal Baroreflex Sensitivity in Parkinson's Disease and Multiple-System Atrophy

Background and Purpose

Parkinson's disease (PD) and multiple-system atrophy of the parkinsonian type (MSA-P) are progressive neurodegenerative disorders that in addition to dysfunction of the motor system also present with features of dysautonomia, frequently manifesting as orthostatic hypotension (OH). The pathophysiology of OH has been proposed to differ between these two disorders. This study investigated the spontaneous and cardiovagal baroreflex sensitivity (BRS) in Parkinson's disease patients with orthostatic hypotension (PD_OH) and multiple system atrophy of Parkinsonian type with orthostatic hypotension in an attempt to differentiate the two disorders.

Methods

Two methods were used for determining the BRS: a spontaneous method (spontaneous BRS) and the reflexive baroreflex gain (cardiovagal BRS) from phases II and IV of the Valsalva maneuver (VM) in PD_OH and MSA-P_OH.

Results

The spontaneous BRS (5.04±0.66 ms/mm Hg vs. 4.78±0.64 ms/mm Hg, p=0.54) and the cardiovagal BRS from phase II of the VM (0.96±0.75 ms/mm Hg vs. 1.34±1.51 ms/mm Hg, p=0.76) did not differ between PD_OH and MSA-P_OH, but the cardiovagal BRS from phase IV of the VM (0.03±0.07 ms/mm Hg vs. 2.86±2.39 ms/mm Hg, p=0.004) was significantly lower in PD_OH.

Conclusions

The cardiovagal BRS from phase IV of the VM has potential for differentiating PD_OH and MSA-P_OH, indicating a difference in the pathophysiological mechanisms underlying the autonomic dysfunction in the two disorders.

Imaging of genetic and degenerative disorders primarily causing Parkinsonism

In this chapter the structural and functional imaging changes associated with both genetic causes of Parkinson's disease and the sporadic condition are reviewed. The role of imaging for supporting diagnosis and detecting subclinical disease is discussed and the potential use and drawbacks of using imaging biomarkers for monitoring disease progression are debated. Additionally, the use of imaging for differentiating atypical parkinsonian syndromes from Parkinson's disease is presented.

Biomarkers in Parkinson's disease: Advances and strategies

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive motor disturbances and affects more than 1% of the worldwide population. Despite considerable progress in understanding PD pathophysiology, including genetic and biochemical causes, diagnostic approaches lack accuracy and interventions are restricted to symptomatic treatments. PD is a complex syndrome with different clinical subtypes and a wide variability in disorder course. In order to deliver better clinical management of PD patients and discovery of novel therapies, there is an urgent need to find sensitive, specific, and reliable biomarkers. The development of biomarkers will not only help the scientific community to identify populations at risk, but also facilitate clinical diagnosis. Furthermore, these tools could monitor progression, which could ultimately deliver personalized therapeutic strategies. The field of biomarker discovery in PD has attracted significant attention and there have been numerous contributions in recent years. Although none of the parameters have been validated for clinical practice, some candidates hold promise. This review summarizes recent advances in the development of PD biomarkers and discusses new strategies for their utilization.

Autonomic Function Tests and MIBG in Parkinson's Disease: Correlation to Disease Duration and Motor Symptoms

AIMS

Disorders of the autonomic nervous system (ANS) have a variable degree of clinical relevance in patients with Parkinson's disease (PD). Here, we assessed whether subclinical autonomic dysfunction, as evaluated by a complete battery of autonomic function tests (AFTs), correlates with PD progression.

METHODS

A series of 27 consecutive patients with PD underwent extensive ANS investigations including the head-up tilt test (HUTT), Valsalva maneuver, deep-breathing test, and handgrip test (HG); further, they performed 123I-meta-iodobenzylguanidine (MIBG) scintigraphy.

RESULTS

Seven of the 27 patients showed orthostatic hypotension (OH) at HUTT and pathological responses to the deep-breathing and HG test and Valsalva maneuver. The majority of the remaining 20 patients with PD showed pathological responses to deep-breathing (n = 13) and/or HG (n = 11). Only 3 of 27 suffered relevant OH. MIBG uptake of myocardium was decreased in 19 patients with PD (H/M ratio 1.3 ± 0.2). Prolonged clinical observation (>3 years), persistent response to levodopa, and MIBG repetition allowed us to exclude negative MIBG as attributable to atypical Parkinsonism. MIBG uptake did not correlate with OH and other AFTs. Both HG test response and MIBG did correlate with the Unified Parkinson's Disease Rating Scale (UPDRS) motor score and disease duration. A positive correlation emerged between diastolic blood pressure (DBP) response to HG test and MIBG and with systolic blood pressure (SBP) response at tilt test.

CONCLUSIONS

Our investigation suggests that ANS impairment affects the majority of patients with PD, even those PD patients showing negative MIBG, irrespective of clinical neurovegetative symptoms. The strict correlation that has been revealed with disease progression supports the routine utilization of AFTs as a reliable and inexpensive tool for monitoring peripheral sympathetic dysfunction in PD and optimizing therapy.

(123)I-Metaiodobenzylguanidine Myocardial Scintigraphy in Lewy Body-Related Disorders: A Literature Review

Lewy body-related disorders are characterized by the presence of Lewy bodies and Lewy neurites, which have abnormal aggregations of α-synuclein in the nigral and extranigral areas, including in the heart. ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy is a well-known tool to evaluate cardiac sympathetic denervation in the Lewy body-related disorders. MIBG scintigraphy showed low uptake of MIBG in the Lewy body-related disorders, including Parkinson’s disease, dementia with Lewy bodies, pure autonomic failure and rapid eye movement sleep behavior disorder. This review summarizes previous results on the diagnostic applications of MIBG scintigraphy in Lewy body-related disorders.

Clinical features of autoimmune autonomic ganglionopathy and the detection of subunit-specific autoantibodies to the ganglionic acetylcholine receptor in Japanese patients

Autoimmune autonomic ganglionopathy (AAG) is a rare acquired channelopathy that is characterized by pandysautonomia, in which autoantibodies to ganglionic nicotinic acetylcholine receptors (gAChR) may play a central role. Radioimmunoprecipitation (RIP) assays have been used for the sensitive detection of autoantibodies to gAChR in the serum of patients with AAG. Here, we developed luciferase immunoprecipitation systems (LIPS) to diagnose AAG based on IgGs to both the α3 and β4 gAChR subunits in patient serum. We reviewed the serological and clinical data of 50 Japanese patients who were diagnosed with AAG. With the LIPS testing, we detected anti-α3 and -β4 gAChR antibodies in 48% (24/50) of the patients. A gradual mode of onset was more common in the seropositive group than in the seronegative group. Patients with AAG frequently have orthostatic hypotension and upper and lower gastrointestinal tract symptoms, with or without anti-gAChR. The occurrence of autonomic symptoms was not significantly different between the seropositive and seronegative group, with the exception of achalasia in three patients from the seropositive group. In addition, we found a significant overrepresentation of autoimmune diseases in the seropositive group and endocrinological abnormalities as an occasional complication of AAG. Our results demonstrated that the LIPS assay was a useful novel tool for detecting autoantibodies against gAChR in patients with AAG.

Cardiac 123I-MIBG uptake in de novo Brazilian patients with Parkinson's disease without clinically defined dysautonomia

Myocardial scintigraphy with meta-iodo-benzyl-guanidine (123I cMIBG) has been studied in Parkinson's disease (PD), especially in Asian countries, but not in Latin America. Most of these studies include individuals with PD associated to a defined dysautonomia. Our goal is to report the cardiac sympathetic neurotransmission in de novo Brazilian patients with sporadic PD, without clinically defined dysautonomia. We evaluated retrospectively a series of 21 consecutive cases with PD without symptoms or signs of dysautonomia assessed by the standard bedside tests. This number was reduced to 14 with the application of exclusion criteria. 123I cMIBG SPECT up-take was low or absent in all of them and the heart/mediastinum ratio was low in 12 of 14. We concluded that 123I cMIBG has been able to identify cardiac sympathetic neurotransmission disorder in Brazilian de novo PD patients without clinically defined dysautonomia.

Dysautonomia in Parkinson disease

Dysautonomias are conditions in which altered function of one or more components of the autonomic nervous system (ANS) adversely affects health. This review updates knowledge about dysautonomia in Parkinson disease (PD). Most PD patients have symptoms or signs of dysautonomia; occasionally, the abnormalities dominate the clinical picture. Components of the ANS include the sympathetic noradrenergic system (SNS), the parasympathetic nervous system (PNS), the sympathetic cholinergic system (SCS), the sympathetic adrenomedullary system (SAS), and the enteric nervous system (ENS). Dysfunction of each component system produces characteristic manifestations. In PD, it is cardiovascular dysautonomia that is best understood scientifically, mainly because of the variety of clinical laboratory tools available to assess functions of catecholamine systems. Most of this review focuses on this aspect of autonomic involvement in PD. PD features cardiac sympathetic denervation, which can precede the movement disorder. Loss of cardiac SNS innervation occurs independently of the loss of striatal dopaminergic innervation underlying the motor signs of PD and is associated with other nonmotor manifestations, including anosmia, REM behavior disorder, orthostatic hypotension (OH), and dementia. Autonomic dysfunction in PD is important not only in clinical management and in providing potential biomarkers but also for understanding disease mechanisms (e.g., autotoxicity exerted by catecholamine metabolites). Since Lewy bodies and Lewy neurites containing alpha-synuclein constitute neuropathologic hallmarks of the disease, and catecholamine depletion in the striatum and heart are characteristic neurochemical features, a key goal of future research is to understand better the link between alpha-synucleinopathy and loss of catecholamine neurons in PD.

Unbiased approaches to biomarker discovery in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal dementia have several important features in common. They are progressive, they affect a relatively inaccessible organ, and we have no disease-modifying therapies for them. For these brain-based diseases, current diagnosis and evaluation of disease severity rely almost entirely on clinical examination, which may be only a rough approximation of disease state. Thus, the development of biomarkers-objective, relatively easily measured, and precise indicators of pathogenic processes-could improve patient care and accelerate therapeutic discovery. Yet existing, rigorously tested neurodegenerative disease biomarkers are few, and even fewer biomarkers have translated into clinical use. To find new biomarkers for these diseases, an unbiased, high-throughput screening approach may be needed. In this review, I will describe the potential utility of such an approach to biomarker discovery, using Parkinson's disease as a case example.

Characterizing Premotor Parkinson's Disease: Clinical Features and Objective Markers

Increasingly, it has been recognized that in order to affect underlying neurodegeneration in Parkinson's disease (PD), individuals must be identified before onset of the classic motor symptoms. Thus, for research purposes, a redefinition of PD has been proposed into preclinical, premotor, and motor phases. In the preclinical phase, no clinical signs or symptoms of PD are present. In the premotor phase, nonmotor manifestations are detectable. These include olfactory, neuropsychiatric, sleep, gastrointestinal, and autonomic changes. A multi-modal approach is needed to maximize both sensitivity and specificity of any assessment of the premotor phase. To that end, several objective markers, such as dopaminergic imaging and electrophysiologic techniques, exist and are of potential utility. This review discusses the candidate nonmotor features and potential objective measures that may be used to define the premotor phase of PD.