Clinical Aspects of the Differential Diagnosis of Parkinson's Disease and Parkinsonism

Cerebellar Contributions to Hypokinetic Symptoms in an Acute Lesion Parkinsonism Model

Background: Parkinsonism, characterized by motor symptoms, is typically attributed to basal ganglia dysfunction. Recent evidence suggests that the cerebellum may also influence these symptoms. This study investigated Crus II, the dentate nucleus (DN), and the inferior olive (IO) in a rat model of parkinsonism induced by a bilateral ventrolateral striatal (VLS) lesion. Materials and Methods: Twenty-four male Wistar rats were divided into control (n = 12) and experimental (n = 12) groups. Monopolar electrodes were implanted in target structures. The experimental group received a bilateral VLS lesion. Animals underwent four weekly sessions of electrophysiological recordings and blind behavioral assessments (resting, grooming, locomotion, rearing, sniffing) via video tracking. Power spectral density (PSD) in the 300-500 Hz band was computed. Statistical analyses included Mann-Whitney U, Friedman with Wilcoxon post hoc, and Spearman correlation tests. Results: During weeks one and two, there were significant PSD increases in the experimental group compared to the control, particularly in Crus II-grooming (p = 0.005), locomotion (p = 0.007), and rearing (p = 0.026); in IO-sniffing (p = 0.0167); and in DN-grooming (p < 0.001) and locomotion (p = 0.0008). Additionally, intragroup analysis revealed significant PSD elevations relative to baseline in these structures. Significant correlations were observed only for grooming (negative correlations) and sniffing (positive correlations) across all cerebellar regions. Conclusions: These findings suggest compensatory cerebellar hyperactivity induced by VLS lesion, potentially modulating hypokinetic symptoms and highlighting dynamic network interactions. Interpretation warrants caution due to limitations inherent to the acute lesion model and experimental duration.

Unravelling the Proteinopathic Engagement of α-Synuclein, Tau, and Amyloid Beta in Parkinson's Disease: Mitochondrial Collapse as a Pivotal Driver of Neurodegeneration

Parkinson's disease is a complex neurological ailment manifested by dopaminergic neurodegeneration in the substantia nigra of the brain. This study investigates the molecular tripartite interaction between Lewy bodies, amyloid beta, and tau protein in the pathogenesis of Parkinson's disease. Lewy bodies which have been found as the important pathological hallmark in the degenerative neurons of Parkinson's patients, are mainly composed of α-synuclein. The accumulation of α-synuclein has been directly and indirectly linked to the severity and degree of progression of the disease. In addition, approximately 50% of Parkinson's disease cases are also described by hyperphosphorylation of tau protein indicating its significant involvement in the disease. The study further explains how α-synuclein, tau and amyloid beta can spread via cross-seeding mechanisms and accelerate each other's aggregation leading to neuronal death. Both GSK-3β and CDK5 are involved in phosphorylation which among other effects contributes to the misfolding of both α-synuclein and tau proteins that lead to neurodegeneration in Alzheimer's disease. Several mediators, that contribute to mitochondrial damage through elevated oxidative stress pathology are clearly described. Because of the increase in the incidence of Parkinson's disease, as predicted to be 17 million when the study was being conducted, studying these pathological mechanisms is very important in trying to establish treatments. This work contributes a path to finding a multi-target treatment regimen to alleviate the burden of this devastating disease.

The Vestibulo-Ocular Reflex is Associated With Visuospatial Dysfunction in Patients With Parkinson's Disease

BACKGROUND

Visuospatial impairment is one of the most frequent cognitive deficits in patients with Parkinson's disease (PD). It remains unknown whether the vestibulo-ocular reflex (VOR) function affects visuospatial perception and memory in patients with PD.

OBJECTIVE

To delineate the relationship between VOR and visuospatial function in patients with PD.

METHODS

We prospectively evaluated video head-impulse tests in 151 patients with PD (mean age± $\; \pm \;$ standard deviation, 68± $\; \pm \;$ 9 years; 77 male). All patients conducted the Rey Complex Figure test (RCFT).

RESULTS

RCFT-copying and RCFT-delayed recall were impaired in 11 (11/151, 7%) and 15 (15/151, 10%) patients, respectively. The VOR gain was normal in 55 patients with PD (55/151, 36%). However, 69 patients overestimated VOR gain for at least one canal, and 34 patients showed a decreased gain for at least one canal (seven patients showed an overestimated gain for some canals and decreased gain for other canals). Multivariable logistic regression analysis showed that abnormal RCFT-copying was negatively associated with the VOR gain for the horizontal canal (odds ratio [OR]: 0.001, 95% confidence interval [CI]: 0.001-0.08, p = 0.007). In contrast, abnormal RCFT-delayed recall was negatively associated with Mini-Mental State Examination scores (0.70, 0.52-0.93, p = 0.013), positively with age (1.11, 1.00-1.22, p = 0.041), male sex (12.82, 1.17-142.86, p = 0.036), years of schooling (1.41, 1.09-1.82, p = 0.009), but not with the VOR gain for any canal.

CONCLUSIONS

The VOR function may be associated with deficits in visuospatial perception and learning in patients with PD. This implicates the development of more targeted therapeutic interventions and offers insights into the broader implications of PD on sensory-motor integration and cognitive function.

Glutathione S-transferase: A keystone in Parkinson's disease pathogenesis and therapy

Parkinson's disease is a progressive neurodegenerative disorder that predominantly affects motor function due to the loss of dopaminergic neurons in the substantia nigra. It presents significant challenges, impacting millions worldwide with symptoms such as tremors, rigidity, bradykinesia, and postural instability, leading to decreased quality of life and increased morbidity. The pathogenesis of Parkinson's disease is multifaceted, involving complex interactions between genetic susceptibility, environmental factors, and aging, with oxidative stress playing a central role in neuronal degeneration. Glutathione S-Transferase enzymes are critical in the cellular defense mechanism against oxidative stress, catalysing the conjugation of the antioxidant glutathione to various toxic compounds, thereby facilitating their detoxification. Recent research underscores the importance of Glutathione S-Transferase in the pathophysiology of Parkinson's disease, revealing that genetic polymorphisms in Glutathione S-Transferase genes influence the risk and progression of the disease. These genetic variations can affect the enzymatic activity of Glutathione S-Transferase, thereby modulating an individual's capacity to detoxify reactive oxygen species and xenobiotics, which are implicated in Parkinson's disease neuropathological processes. Moreover, biochemical studies have elucidated the role of Glutathione S-Transferase in not only maintaining cellular redox balance but also in modulating various cellular signalling pathways, highlighting its neuroprotective potential. From a therapeutic perspective, targeting Glutathione S-Transferase pathways offers promising avenues for the development of novel treatments aimed at enhancing neuroprotection and mitigating disease progression. This review explores the evident and hypothesized roles of Glutathione S-Transferase in Parkinson's disease, providing a comprehensive overview of its importance and potential as a target for therapeutic intervention.

Canine Multiple System Degeneration Associated with Sequence Variants in SERAC1

Canine multiple system degeneration (CMSD) is an early onset, progressive movement disorder affecting Kerry Blue Terriers and Chinese Crested dogs. The associated pathologic lesions include degeneration of the cerebellum, caudate nucleus, and substantia nigra. CMSD is inherited as an autosomal recessive trait in both dog breeds. Previous linkage mapping localized the CMSD locus to a 15 MB region on canine chromosome 1 (CFA1). Next-generation sequencing was used to generate whole-genome sequences from the DNA of an affected dog from each breed. The resulting sequence reads were aligned to the NCBI canine reference genome (build 3.1). Among the homozygous sequence variants within the CFA1 target region, a nonsense variant in exon 15 of SERAC1 was identified in the affected Kerry Blue Terrier, while in the Chinese Crested dog, a 4 bp deletion in the SERAC1 exon 4 acceptor splice site was found. RT-PCR showed that this deletion resulted in exon 4 skipping. Genotyping of large cohorts of Kerry Blue Terriers and Chinese Crested dogs for the respective breed-specific SERAC1 variants showed complete concordance between genotype and disease phenotype. Genotype-phenotype concordance was also observed in offspring generated by cross breeding between SERAC1-heterozygous Kerry Blue Terrier and Chinese Crested dogs, with only the compound heterozygotes exhibiting the disease phenotype, further confirming the recessive inheritance of CMSD. Variants in human SERAC1 are associated with disorders with a range of ages of disease onset and patterns of clinical signs, but that are all characterized by movement abnormalities similar to those of the dogs with CMSD. Canine CMSD could serve as a valuable model to elucidate the mechanisms underlying SERAC1-deficiency disorders and to evaluate potential therapeutic interventions.

Multifaceted Heparin: Diverse Applications beyond Anticoagulant Therapy

Heparin, a naturally occurring polysaccharide, has fascinated researchers and clinicians for nearly a century due to its versatile biological properties and has been used for various therapeutic purposes. Discovered in the early 20th century, heparin has been a key therapeutic anticoagulant ever since, and its use is now implemented as a life-saving pharmacological intervention in the management of thrombotic disorders and beyond. In addition to its known anticoagulant properties, heparin has been found to exhibit anti-inflammatory, antiviral, and anti-tumorigenic activities, which may lead to its widespread use in the future as an essential drug against infectious diseases such as COVID-19 and in various medical treatments. Furthermore, recent advancements in nanotechnology, including nano-drug delivery systems and nanomaterials, have significantly enhanced the intrinsic biofunctionalities of heparin. These breakthroughs have paved the way for innovative applications in medicine and therapy, expanding the potential of heparin research. Therefore, this review aims to provide a creation profile of heparin, space for its utilities in therapeutic complications, and future characteristics such as bioengineering and nanotechnology. It also discusses the challenges and opportunities in realizing the full potential of heparin to improve patient outcomes and elevate therapeutic interventions.

Ocular Vestibular-Evoked Myogenic Potential Assists in the Differentiation of Multiple System Atrophy From Parkinson's Disease

OBJECTIVE

Vestibular-evoked myogenic potentials (VEMPs) can help in assessing otolithic neural pathway in the brainstem, which may also contribute to the cardiovascular autonomic function. Parkinson's disease (PD) is associated with altered VEMP responses; however, the associations between VEMP abnormalities and multiple system atrophy (MSA) remain unknown. Therefore, we compared the extent of otolith dysfunction using ocular (oVEMP) and cervical VEMPs between patients with MSA and PD.

METHODS

We analyzed the clinical features, VEMP, and head-up tilt table test (HUT) findings using the Finometer in 24 patients with MSA and 52 with de novo PD who had undergone neurotologic evaluation at a referral-based university hospital in South Korea from January 2021 to March 2023.

RESULTS

MSA was associated with bilateral oVEMP abnormalities (odds ratio [95% confidence interval] = 9.19 [1.77-47.76], p = 0.008). The n1-p1 amplitude was negatively correlated with the Unified Multiple System Atrophy Rating Scale I-II score in patients with MSA (r = -0.571, p = 0.033), whereas it did not correlate with the Movement Disorder Society-Unified Parkinson's Disease Rating Scale-III score in patients with PD (r = -0.051, p = 0.687). The n1 latency was negatively correlated with maximum changes in systolic blood pressure within 15 s during HUT in patients with PD (r = -0.335, p = 0.040) but not in those with MSA (r = 0.277, p = 0.299).

CONCLUSION

Bilaterally abnormal oVEMP responses may indicate the extent of brainstem dysfunction in MSA. oVEMP reflects the integrity of otolith-autonomic interplay, reliably assists in differentiating between MSA and PD, and helps infer clinical decline.

The effects of combining repetitive transcranial magnetic stimulation with task-specific training on gait performance in individuals with Parkinson's disease: A review article

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor impairments, especially in the area of gait disturbances. Physiotherapy, with a focus on task-specific training, has demonstrated a level of efficacy as regards alleviating symptoms and enhancing functional capabilities in individuals with PD. Repetitive Transcranial Magnetic Stimulation (rTMS) has emerged as a potential therapeutic intervention for improving motor functions in individuals with PD.

AIMS

This review article aims to investigate the effects of combining rTMS with task-specific training on gait performance in individuals with PD.

MATERIALS AND METHODS

PubMed, Physiotherapy Evidence Database (PEDro), and Scopus were all searched for relevant studies. The focus of the search was on studies that investigated the efficacy of combining rTMS with task-specific training to improve gait performance in individuals with PD.

RESULTS

Four studies were identified as fulfilling the eligibility criteria and were included in the study. The combination of rTMS with specific treadmill training and weight-bearing exercises can significantly enhance walking efficiency, including improvements in walking speed, self-mobility, and step rate. In addition, the combination of rTMS and task-specific training, such as treadmill-based training, shows promise in enhancing gait performance in individuals with PD.

DISCUSSION AND CONCLUSION

High-frequency rTMS targeting the primary motor cortex (or M1) can result in improved walking speed, self-mobility, and step rate. However, limited research exists regarding low-frequency stimulation of the supplementary motor area (SMA) in individuals with gait issues. Further research is required to determine the optimal parameters of rTMS, such as strength, frequency, and duration of stimulation and it is worth considering the incorporation of additional training modalities, including cognitive exercises.

Vocal Fold Motion Impairment in Neurodegenerative Diseases

Vocal fold motion impairment (VFMI) is the inappropriate movement of the vocal folds during respiration, leading to vocal fold adduction and/or abduction problems and causing respiratory and vocal impairments. Neurodegenerative diseases (NDDs) are a wide range of disorders characterized by progressive loss of neurons and deposition of altered proteins in the brain and peripheral organs. VFMI may be unrecognized in patients with NDDs. VFMI in NDDs is caused by the following: laryngeal muscle weakness due to muscular atrophy, caused by brainstem and motor neuron degeneration in amyotrophic lateral sclerosis; hyperactivity of laryngeal adductors in Parkinson's disease; and varying degrees of laryngeal adductor hypertonia and abductor paralysis in multiple system atrophy. Management of VFMI depends on whether there is a presence of glottic insufficiency or insufficient glottic opening with/without severe dysphagia. VFMI treatment options for glottic insufficiency range from surgical interventions, including injection laryngoplasty and medialization thyroplasty, to behavioral therapies; for insufficient glottic opening, various options are available based on the severity and underlying cause of the condition, including continuous positive airway pressure therapy, botulinum toxin injection, tracheostomy, vocal fold surgery, or a combination of interventions. In this review, we outline the mechanisms, clinical features, and management of VFMI in NDDs and provide a guide for physicians who may encounter these clinical features in their patients. NDDs are always progressive; hence, timely evaluation, proper diagnosis, and appropriate management of the patient will greatly affect their vocal, respiratory, and swallowing functions as well as their quality of life.

Parkinson's disease and Parkinsonism syndromes: Evaluating iron deposition in the putamen using magnetic susceptibility MRI techniques - A systematic review and literature analysis

Magnetic resonance imaging (MRI) techniques, such as quantitative susceptibility mapping (QSM) and susceptibility-weighted imaging (SWI), can detect iron deposition in the brain. Iron accumulation in the putamen (PUT) can contribute to the pathogenesis of Parkinson's disease (PD) and atypical Parkinsonian disorders. This systematic review aimed to synthesize evidence on iron deposition in the PUT assessed by MRI susceptibility techniques in PD and Parkinsonism syndromes. The PubMed and Scopus databases were searched for relevant studies. Thirty-four studies from January 2007 to October 2023 that used QSM, SWI, or other MRI susceptibility methods to measure putaminal iron in PD, progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and healthy controls (HCs) were included. Most studies have found increased putaminal iron levels in PD patients versus HCs based on higher quantitative susceptibility. Putaminal iron accumulation correlates with worse motor scores and cognitive decline in patients with PD. Evidence regarding differences in susceptibility between PD and atypical Parkinsonism is emerging, with several studies showing greater putaminal iron deposition in PSP and MSA than in PD patients. Alterations in putaminal iron levels help to distinguish these disorders from PD. Increased putaminal iron levels appear to be associated with increased disease severity and progression. Thus, magnetic susceptibility MRI techniques can detect abnormal iron accumulation in the PUT of patients with Parkinsonism. Moreover, quantifying putaminal susceptibility may serve as an MRI biomarker to monitor motor and cognitive changes in PD and aid in the differential diagnosis of Parkinsonian disorders.

Distinct mechanisms underlying the therapeutic effects of low-molecular-weight heparin and chondroitin sulfate on Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder influenced by various factors, including age, genetics, and the environment. Current treatments provide symptomatic relief without impeding disease progression. Previous studies have demonstrated the therapeutic potential of exogenous heparin and chondroitin sulfate in PD. However, their therapeutic mechanisms and structure-activity relationships remain poorly understood. In this study, low-molecular-weight heparin (L-HP) and chondroitin sulfate (L-CS) exhibited favorable therapeutic effects in a mouse model of PD. Proteomics revealed that L-HP attenuated mitochondrial dysfunction through its antioxidant properties, whereas L-CS suppressed neuroinflammation by inhibiting platelet activation. Two glycosaminoglycan (GAG)-binding proteins, manganese superoxide dismutase (MnSOD2) and fibrinogen beta chain (FGB), were identified as potential targets of L-HP and L-CS, and we investigated their structure-activity relationships. The IdoA2S-GlcNS6S/GlcNAc6S unit in HP bound to SOD2, whereas the GlcA-GalNAc4S and GlcA-GalNAc4S6S units in CS preferred FGB. Furthermore, N-S and 2-O-S in L-HP, and 4-O-S, 6-O-S, and -COOH in L-CS contributed significantly to the binding process. These findings provide new insights and evidence for the development and use of glycosaminoglycan-based therapeutics for PD.

Practical Overview of 123I-Ioflupane Imaging in Parkinsonian Syndromes

Parkinsonian syndromes are a heterogeneous group of progressive neurodegenerative disorders involving the nigrostriatal dopaminergic pathway and are characterized by a wide spectrum of motor and nonmotor symptoms. These syndromes are quite common and can profoundly impact the lives of patients and their families. In addition to classic Parkinson disease, parkinsonian syndromes include multiple additional disorders known collectively as Parkinson-plus syndromes or atypical parkinsonism. These are characterized by the classic parkinsonian motor symptoms with additional distinguishing clinical features. Dopamine transporter SPECT has been developed as a diagnostic tool to assess the levels of dopamine transporters in the striatum. This imaging assessment, which uses iodine 123 (123I) ioflupane, can be useful to differentiate parkinsonian syndromes caused by nigrostriatal degeneration from other clinical mimics such as essential tremor or psychogenic tremor. Dopamine transporter imaging plays a crucial role in diagnosing parkinsonian syndromes, particularly in patients who do not clearly fulfill the clinical criteria for diagnosis. Diagnostic clarification can allow early treatment in appropriate patients and avoid misdiagnosis. At present, only the qualitative interpretation of dopamine transporter SPECT is approved by the U.S. Food and Drug Administration, but quantitative interpretation is often used to supplement qualitative interpretation. The authors provide an overview of patient preparation, common imaging findings, and potential pitfalls that radiologists and nuclear medicine physicians should know when performing and interpreting dopamine transporter examinations. Alternatives to 123I-ioflupane imaging for the evaluation of nigrostriatal degeneration are also briefly discussed. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material. See the invited commentary by Intenzo and Colarossi in this issue.

Botulinum toxin treatment in parkinsonism

Botulinum toxin (BoNT) was approved by the United States Food and Drug Administration (FDA) in 1989 for facial movement disorders and strabismus, but since that time its indications have been expanding beyond neurologic and ophthalmologic disorders. This article is a narrative review of the therapeutic use of BoNT in tremors, dystonia, sialorrhea, bladder and other autonomic symptoms, levodopa-induced dyskinesia and other problems occuring in the setting of parkinsonism. Though FDA approval is lacking for some of these indications, expert experiences have shown that BoNT is often beneficial in this group of patients.

The semicircular canal function is preserved with little impact on falls in patients with mild Parkinson's disease

INTRODUCTION

Postural instability is a cardinal symptom of Parkinson's disease (PD), which suggests the vestibular system may be affected in PD. This study aimed to determine whether vestibular dysfunction is associated with the risk of falls in PD.

METHODS

We prospectively recruited patients with de-novo PD at a tertiary medical center between December 2019 and March 2023. During initial assessment, each patient was queried about falls within the preceding year. All patients underwent evaluation of video head-impulse tests (video-HITs), motion analysis, mini-mental state examination (MMSE), and Montreal Cognitive Assessment (MOCA). We determined whether head impulse gain of the vestibulo-ocular reflex (VOR) was associated with clinical severity of PD or risk of falls.

RESULTS

Overall, 133 patients (mean age ± SD = 68 ± 10, 59 men) were recruited. The median Movement Disorder Society-Unified Parkinson's Disease Rating Scale motor part (MDS-UPDRS-III) was 23 (interquartile range = 16-31), and 81 patients (61 %) scored 2 or less on the Hoehn and Yahr scale. Fallers were older (p = 0.001), had longer disease duration (p = 0.001), slower gait velocity (p = 0.009), higher MDS-UPDRS-III (p < 0.001) and H&Y scale (p < 0.001), lower MMSE (p = 0.018) and MOCA scores (p = 0.001) than non-fallers. Multiple logistic regression showed that MDS-UPDRS-III had a positive association with falling (p = 0.004). Falling was not associated with VOR gain (p = 0.405). The VOR gain for each semicircular canal showed no correlation with the MDS-UPDRS-III or disease duration.

CONCLUSIONS

The semicircular canal function, as determined by video-HITs, is relatively spared and has little effect on the risk of falls in patients with mild-to-moderate PD.

Inability to suppress head rotation during the saccade test as a clinical biomarker for cognitive dysfunction in Parkinson's disease

BACKGROUND

There is a need for development of reliable and accessible clinical biomarker for detecting cognitive dysfunction in PD. This study aimed to investigate whether involuntary head rotation during the saccade test could serve as a potential biomarker for screening cognitive dysfunction in PD.

METHODS

A total of 27 PD patients and nine age- and sex-matched healthy controls were prospectively enrolled in this study. A custom-designed gyroscope was attached to the forehead of each participant, and a saccade test consisting of 20 trials was conducted. The entire test was recorded on video, and two movement disorder experts independently rated the degree of head rotation, blinded to the patients' clinical information. The peak angular velocity of head rotation was derived from the gyroscope data. Participants underwent Montreal Cognitive Assessment (MoCA) as the cognitive evaluation. Correlation analysis was performed to assess the relationship between head rotation and MoCA scores.

RESULTS

The mean peak angular velocity of head rotation significantly correlated with the MoCA scores (R = -0.52, p = 0.0023) including age, sex, disease duration, and education duration as cofactors. The optimal peak angular velocity thresholds for head rotation, which aligned with the manual ratings, were determined to be 5°/s and 10°/s for raters 1 and 2, respectively. The MoCA scores exhibited significant correlations with the number of head rotations, using both the 5°/s (R = -0.36, p = 0.042) and 10°/s (R = -0.49, p = 0.0048) thresholds. Furthermore, the mean angular velocity of the head demonstrated a 100% positive predictive value and specificity for the detection of cognitive impairment (MoCA < 26), based on the cut-offs of 5°/s and 10°/s.

CONCLUSION

Inability to suppress head rotation during saccades may serve as a potential clinical biomarker for screening cognitive dysfunction in PD.

Head-to-Head Comparison Between Rabbit Sign and EANM/SNMMI Criteria for the 18F-DOPA Visual Assessment of Parkinsonian Syndromes in PET/MRI: A Multiple Expert-Based and Blinded Controlled Study

PURPOSE

The aim of this study was to compare the diagnostic performance of the rabbit visual pattern versus the one endorsed by the EANM/SNMMI for the diagnosis of parkinsonian syndromes in PET/MRI.

PATIENTS AND METHODS

The 18F-DOPA PET images of 129 consecutive patients (65 Park+ and 64 controls) with 1 year of clinical follow-up were reviewed independently by 5 experienced readers on the same imaging workstation, blinded to the final clinical diagnosis. Two visual methods were assessed independently, with several days to months of interval: the criteria endorsed by EANM/SNMMI and the "rabbit" shape of the striate assessed on 3D MIP images. The sensitivities, specificities, likelihood ratios, and predictive values of the 2 diagnostic tests were estimated simultaneously by using the "comparison of 2 binary diagnostic tests to a paired design" method.

RESULTS

The estimated 95% confidence interval (CI) of sensitivities and specificities ranged from 49.4% to 76.5% and from 83.2% to 97.7%, respectively. The 95% CI estimates of positive and negative likelihood ratios ranged from 3.8 to 26.7 and from 0.26 to 0.56, respectively. The 95% CI estimates of the positive and negative predictive values ranged from 78.1% to 96.7% and from 60.3% to 81.4%, respectively. For all the parameters, no statistical difference was observed between the 2 methods (P > 0.05). The rabbit sign reduced the readers' discrepancies by 25%, while maintaining the same performance.

CONCLUSIONS

The rabbit visual pattern appears at least comparable to the current EANM/SNMMI reference procedure for the assessment of parkinsonian syndromes in daily clinical practice, without the need of any image postprocessing. Further multicenter prospective studies would be of relevance to validate these findings.

Patterns of striatal dopamine depletion and motor deficits in de novo Parkinson's disease

The background of this study is to investigate whether striatal dopamine depletion patterns (selective involvement in the sensorimotor striatum or asymmetry) are associated with motor deficits in Parkinson's disease (PD). We enrolled 404 drug-naïve patients with early stage PD who underwent dopamine transporter (DAT) imaging. After quantifying DAT availability in each striatal sub-region, principal component (PC) analysis was conducted to yield PCs representing the spatial patterns of striatal dopamine depletion. Subsequently, multivariate linear regression analysis was conducted to investigate the relationship between striatal dopamine depletion patterns and motor deficits assessed using the Unified PD Rating Scale Part III (UPDRS-III). Mediation analyses were used to evaluate whether dopamine deficiency in the posterior putamen mediated the association between striatal dopamine depletion patterns and parkinsonian motor deficits. Three PCs indicated patterns of striatal dopamine depletion: PC1 (overall striatal dopamine deficiency), PC2 (selective dopamine loss in the sensorimotor striatum), and PC3 (symmetric dopamine loss in the striatum). Multivariate linear regression analysis revealed that PC1 (β = - 1.605, p < 0.001) and PC2 (β = 3.201, p < 0.001) were associated with motor deficits (i.e., higher UPDRS-III scores in subjects with severe dopamine depletion throughout the whole striatum or more selective dopamine loss in the sensorimotor striatum), whereas PC3 was not (β = - 0.016, p = 0.992). Mediation analyses demonstrated that the effects of PC1 and PC2 on UPDRS-III scores were indirectly mediated by DAT availability in the posterior putamen, with a non-significant direct effect. Dopamine deficiency in the posterior putamen was most relevant to the severity of motor deficits in patients with PD, while the spatial patterns of striatal dopamine depletion were not a key determinant.