Differential patterns of functional connectivity in tremor dominant Parkinson's disease and essential tremor plus.

Tremor dominant Parkinson's disease (TDPD) and essential tremor plus (ETP) syndrome are commonly encountered tremor dominant neurological disorders. Although the basal ganglia thalamocortical (BGTC) and cerebello thalamocortical (CTC) networks are implicated in tremorogenesis, the extent of functional connectivity alterations across disorders is uncertain. This study aims to evaluate functional connectivity of the BGTC and CTC in TDPD and ETP. Resting state functional MRI was acquired for 25 patients with TDPD, ETP and 22 healthy controls (HC). Following pre-processing and denoising, seed-to-voxel based connectivity was carried out at FDR < 0.05 using ROIs belonging to the BGTC and CTC. Fahn-Tolosa-Marin tremor rating scale (FTMRS) was correlated with the average connectivity values at FDR < 0.05. Compared to HC, TDPD showed decreased connectivity between cerebellum and pre, post central gyrus. While, ETP showed decreased connectivity between pallidum and occipital cortex, precuneus, cuneus compared to HC. In comparison to ETP, TDPD showed increased connectivity between precentral gyrus, pallidum, SNc with the default mode network (DMN), and decreased connectivity between cerebellum with superior, middle frontal gyrus was observed. Tremor severity positively correlated with connectivity between SNc and DMN in TDPD, and negatively correlated with pallidal connectivity in ETP. Pattern of BGTC, CTC involvement is differential i.e., higher connectivity of the BGTC nodes in TDPD, and higher connectivity of cerebellar nodes in ETP. The interesting observation of pallidal involvement in ETP suggests the role of BGTC in the pathogenesis of ETP, and indicated similarities in concepts of tremor genesis in TDPD and ETP.

Morphometric alterations of the mesocorticolimbic network in Parkinson's disease with impulse control disorders.

Impulse control disorders (ICDs) are a group of non-motor symptoms of Parkinson disease (PD) leading to significant psychosocial detrimental outcome. The mesocorticolimbic network plays a distinctive role in reward learning and executive decision making and has been suggested to be involved in ICDs in PD. To study morphometric changes of the mesocorticolimbic network in PD with ICD. A total of 18 patients of PD with ICD (PD + ICD), 19 patients of PD without ICD (PD - ICD) and 19 healthy controls (HC) were included in the study. ICDs were diagnosed using Questionnaire for Impulsive-Compulsive Disorders in PD-Rating Scale (QUIP-RS). MRI was done using a 3T scanner and assessment of cortical thickness and subcortical volumes were done using FreeSurfer. Brain regions known to be part of the mesocorticolimbic network were extracted and included for statistical analysis. There was no difference between PD + ICD and PD - ICD with regard to duration of illness or total dopaminergic medication. In comparison to HC, patients with PD + ICD demonstrated atrophy of the left frontal pole, and this atrophy neared significance in comparison to PD - ICD. The QUIP-RS had a negative correlation with left caudate volume in PD + ICD. The PD + ICD group showed distinct morphometric changes in regions involved in the mesocorticolimbic system which may contribute to the presence of ICD.

Radiomics on routine T1-weighted MRI can delineate Parkinson's disease from multiple system atrophy and progressive supranuclear palsy.

OBJECTIVES: This study aimed to explore the feasibility of radiomics features extracted from T1-weighted MRI images to differentiate Parkinson's disease (PD) from atypical parkinsonian syndromes (APS). METHODS: Radiomics features were computed from T1 images of 65 patients with PD, 61 patients with APS (31: progressive supranuclear palsy and 30: multiple system atrophy), and 75 healthy controls (HC). These features were extracted from 19 regions of interest primarily from subcortical structures, cerebellum, and brainstem. Separate random forest classifiers were applied to classify different groups based on a reduced set of most important radiomics features for each classification as determined by the random forest-based recursive feature elimination by cross-validation method. RESULTS: The PD vs HC classifier illustrated an accuracy of 70%, while the PD vs APS classifier demonstrated a superior test accuracy of 92%. Moreover, a 3-way PD/MSA/PSP classifier performed with 96% accuracy. While first-order and texture-based differences like Gray Level Co-occurrence Matrix (GLCM) and Gray Level Difference Matrix for the substantia nigra pars compacta and thalamus were highly discriminative for PD vs HC, textural features mainly GLCM of the ventral diencephalon were highlighted for APS vs HC, and features extracted from the ventral diencephalon and nucleus accumbens were highlighted for the classification of PD and APS. CONCLUSIONS: This study establishes the utility of radiomics to differentiate PD from APS using routine T1-weighted images. This may aid in the clinical diagnosis of PD and APS which may often be indistinguishable in early stages of disease. KEY POINTS: • Radiomics features were extracted from T1-weighted MRI images. • Parkinson's disease and atypical parkinsonian syndromes were classified at an accuracy of 92%. • This study establishes the utility of radiomics to differentiate Parkinson's disease and atypical parkinsonian syndromes using routine T1-weighted images.

Abnormal structural connectivity in progressive supranuclear palsy-Richardson syndrome.

OBJECTIVES: Progressive supranuclear palsy-Richardson syndrome (PSP-RS) is characterized by symmetrical parkinsonism with postural instability and frontal dysfunction. This study aims to use the whole brain structural connectome (SC) to gain insights into the underlying disconnectivity which may be implicated in the clinical features of PSP-RS. METHODS: Sixteen patients of PSP-RS and 12 healthy controls were recruited. Disease severity was quantified using PSP rating scale (PSPRS), and mini-mental scale was applied to evaluate cognition. Thirty-two direction diffusion MRIs were acquired and used to compute the structural connectome of the whole brain using deterministic fiber tracking. Group analyses were performed at the edge-wise, nodal, and global levels. Age and gender were used as nuisance covariates for all the subsequent analyses, and FDR correction was applied. RESULTS: Network-based statistics revealed a 34-edge network with significantly abnormal edge-wise connectivity in the patient group. Of these, 25 edges were cortical connections, of which 68% were frontal connections. Abnormal deep gray matter connections were predominantly comprised of connections between structures of the basal ganglia. The characteristic path length of the SC was lower in PSP-RS, and nodal analysis revealed abnormal degree, strength, local efficiency, betweenness centrality, and participation coefficient in several nodes. CONCLUSIONS: Significant alterations in the structural connectivity of the whole brain connectome were observed in PSP-RS. The higher degree of abnormality observed in nodes belonging to the frontal lobe and basal ganglia substantiates the predominant frontal dysfunction and parkinsonism observed in PSP-RS. The findings of this study support the concept that PSP-RS may be a network-based disorder.

Microstructural abnormalities of substantia nigra in Parkinson's disease: A neuromelanin sensitive MRI atlas based study.

Microstructural changes associated with degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have been studied using Diffusion Tensor Imaging (DTI). However, these studies show inconsistent results, mainly due to methodological variations in delineation of SNc. To mitigate this, our work aims to construct a probabilistic atlas of SNc based on a 3D Neuromelanin Sensitive MRI (NMS-MRI) sequence and demonstrate its applicability to investigate microstructural changes on a large dataset of PD. Using manual segmentation and deformable registration we created a novel SNc atlas in the MNI space using NMS-MRI sequences of 27 healthy controls (HC). We first quantitatively evaluated this atlas and then employed it to investigate the micro-structural abnormalities in SNc using diffusion MRI from 133 patients with PD and 99 HCs. Our results demonstrated significant increase in diffusivity with no changes in anisotropy. In addition, we also observed an asymmetry of the diffusion metrics with a higher diffusivity and lower anisotropy in the left SNc than the right. Finally, a multivariate classifier based on SNc diffusion features could delineate patients with PD with an average accuracy of 71.7%. Overall, from this work we establish a normative baseline for the SNc region of interest using NMS-MRI while the application on PD data emphasizes on the contribution of diffusivity measures rather than anisotropy of white matter in PD.

Aberrant global and local efficiency of the executive subnetwork in essential tremor.

This study aims to use probabilistic tractography to ascertain the global (GE) and local efficiency (LE) of the executive subnetwork in essential tremor (ET). Significantly lower GE of the whole executive subnetwork and lower LE of the left rostral middle frontal gyrus, frontal pole, inferior frontal gyrus, bilateral anterior cingulate cortex, and medial orbitofrontal cortex. These results imply ineffective and inadequate communication of the executive subnetwork, and may be causally associated with the executive dysfunction observed in ET.

Comparison of effectiveness of trihexyphenidyl and levodopa on motor symptoms in Parkinson's disease.

Despite anti-cholinergics being the oldest type of medication used for the treatment of Parkinson's disease (PD), the mechanism of action and exact benefit is unclear. This study compared the effectiveness of trihexyphenidyl (THP) and levodopa (LD) on motor symptoms in patients with PD. Patients with PD who are currently taking or had taken THP were recruited. UPDRS-III was done following overnight medication OFF state and 30 min, 60 min, 90 min, and 120 min after THP (4 mg). After a forty-eight-hour interval, UPDRS-III was assessed one hour after Levodopa/carbidopa (200/50 mg) in an overnight OFF state. Twenty patients with a mean age of 57.9 ± 7.8 years and mean duration of illness of 5.1 ± 3.6 years were recruited. UPDRS-III score reduction (%) with THP was maximum in the tremor sub-score (53.8 ± 22.8) and was significantly better compared to improvement in total-UPDRS-III (27.0 ± 14.7), bradykinesia-UPDRS-III (22.2 ± 27.2), rigidity-UPDRS-III (29.5 ± 28.0) and axial-UPDRS-III (8.1 ± 13.3) sub-score. In comparison, respective LD improvement was 67.1 ± 22.9 (tremor-UPDRS-III), 61.3 ± 14.4 (total-UPDRS-III), 67.9 ± 32.1 (bradykinesia-UPDRS-III), 65.3 ± 25.5 (rigidity-UPDRS-III) and 50.7 ± 16.0 (axial-UPDRS-III). Improvement (%) in tre-UPDRS-III post-THP was comparable to that of post-LD (53.8 ± 22.8 vs. 67.1 ± 22.9, p = 0.057). Those with same or better tremor response with THP had significantly milder baseline tremor severity than those who had better response with LD (tre-UPDRS-III-OFF, 10.0 ± 2.8 vs. 5.8 ± 4.0, p = 0.013). Both THP and LD showed significant improvement in UPDRS-III. With THP, the maximum degree of improvement was in the tremor sub-score and not significantly different to that obtained by LD. Those with better tremor response on THP had milder tremor severity.

Clinical correlates of abnormal subcortical volumes in Essential Tremor.

Essential tremor (ET) is considered to be a neurodegenerative disorder and it is plausible that the observed motor and non-motor symptoms may be attributable to functional alterations secondary to abnormalities of subcortical nuclei. This study aims to compare the volumes of subcortical nuclei in patients with ET to ascertain neuroimaging correlates of motor and non-motor features of ET. Forty patients of ET and 40 age- and gender-matched healthy controls (HC) were enrolled in this study. Tremor severity was quantified with the Fahn-Tolosa-Marin tremor rating scale. Patients of ET with and without a rest tremor were also compared. Structural imaging was performed on a 3T scanner, and volumes of subcortical structures were obtained using Freesurfer. There was no difference in total brain volume between ET and HC. However, compared to HC, significantly lower volumes of bilateral thalamus, hippocampus, and ventral diencephalon were observed in patients with ET. A significantly higher volume was observed in the right caudate nucleus, pallidum, amygdala, and bilateral putamen, and nucleus accumbens. No difference was observed between patients of ET with and without a rest tremor. Patients with ET have significant alterations in volumes of subcortical nuclei, which are not limited to the motor domain and include structures involved in cognitive and behavioral functions. These results add to the growing concept of a neurodegenerative pathophysiology of ET with abnormalities extending beyond the cerebellum.

Abnormal hippocampal subfields are associated with cognitive impairment in Essential Tremor.

Multi-domain cognitive impairment (CI) has been frequently described in patients with essential tremor (ET). However, the exact neuroanatomical basis for this impairment is uncertain. This study aims to ascertain the role of the hippocampal formation in cognitive impairment in ET. Forty patients with ET and 40 age, gender and education matched healthy controls (HC) were enrolled. Cognition was assessed using a structured neuropsychological battery and patients were categorized as ET with CI (ETCI) and ET without CI (ETNCI). Automatic segmentation of hippocampal subfields was performed using FreeSurfer 6.0. The obtained volumes were correlated with scores of neuropsychological tests. Significant atrophy of the left subiculum, CA4, granule-cell layer of dentate gyrus, right molecular layer, and hypertrophy of bilateral parasubiculum, right hippocampus-amygdala-transition-area, bilateral hippocampal tail (HT) and widening of right hippocampal fissure was observed in ET. Trends toward atrophy of right subiculum, and widening of left HF was also observed. Comparison of HC and ETCI revealed atrophy of right subiculum, hypertrophy of bilateral parasubiculum, HT, and widening of left HF. ETCI showed a trend toward widening of right HF. ETNCI had isolated left parasubicular hypertrophy and in comparison, to ETNCI the ETCI subgroup had atrophy of bilateral fimbria. Significant correlations were observed between the volumes of HT, HF, fimbria and scores of tests for executive function, working and verbal memory. Patients with ET have significant volumetric abnormalities of several hippocampal subfields and these abnormalities may be important contributors for some forms of cognitive impairment observed in ET.

Atrophy of cerebellar peduncles in essential tremor: a machine learning-based volumetric analysis.

BACKGROUND: Subtle cerebellar signs are frequently observed in essential tremor (ET) and may be associated with cerebellar dysfunction. This study aims to evaluate the macrostructural integrity of the superior, middle, and inferior cerebellar peduncles (SCP, MCP, ICP) and cerebellar gray and white matter (GM, WM) volumes in patients with ET, and compare these volumes between patients with and without cerebellar signs (ETc and ETnc). METHODS: Forty patients with ET and 37 age- and gender-matched healthy controls were recruited. Atlas-based region-of-interest analysis of the SCP, MCP, and ICP and automated analysis of cerebellar GM and WM volumes were performed. Peduncular volumes were employed in a multi-variate classification framework to attempt discrimination of ET from controls. RESULTS: Significant atrophy of bilateral MCP and ICP and bilateral cerebellar GM was observed in ET. Cerebellar signs were present in 20% of subjects with ET. Comparison of peduncular and cerebellar volumes between ETnc and ETc revealed atrophy of right SCP, bilateral MCP and ICP, and left cerebellar WM in ETc. The multi-variate classifier could discriminate between ET and controls with a test accuracy of 86.66%. CONCLUSIONS: Patients with ET have significant atrophy of cerebellar peduncles, particularly the MCP and ICP. Additional atrophy of the SCP is observed in the ETc group. These abnormalities may contribute to the pathogenesis of cerebellar signs in ET. KEY POINTS: • Patients with ET have significant atrophy of bilateral middle and inferior cerebellar peduncles and cerebellar gray matter in comparison with healthy controls. • Patients of ET with cerebellar signs have significant atrophy of right superior cerebellar peduncle, bilateral middle and inferior cerebellar peduncle, and left cerebellar white matter in comparison with ET without cerebellar signs. • A multi-variate classifier employing peduncular volumes could discriminate between ET and controls with a test accuracy of 86.66%.

Altered structural connectivity of the motor subnetwork in multiple system atrophy with cerebellar features.

OBJECTIVES: To investigate the structural connectivity of the motor subnetwork in multiple system atrophy with cerebellar features (MSA-C), a distinct subtype of MSA, characterized by predominant cerebellar symptoms. METHODS: Twenty-three patients with MSA-C and 25 age- and gender-matched healthy controls were recruited for the study. Disease severity was quantified using the Unified Multiple System Atrophy Rating Scale (UMSARS). Diffusion MRI images were acquired and used to compute the structural connectomes (SCs) using probabilistic fiber tracking. The motor network with 12 brain regions and 26 cerebellar regions was extracted and was compared between the groups using analysis of variance at a global (network-wide), nodal (at each node), and edge (at each connection) levels, and was corrected for multiple comparisons. In addition, the acquired connectivity measures were correlated with duration of illness, total Unified MSA Rating Scale (UMSARS), and the motor component score. RESULTS: Significantly lower global network metrics-global density, transitivity, clustering coefficient, and characteristic path length-were observed in MSA-C (corrected p < 0.05). Reduced nodal strength was observed in the bilateral ventral diencephalon, the left thalamus, and several cerebellar regions. Network-based statistics revealed significant abnormal edge-wise connectivity in 40 connections (corrected p < 0.01), with majority of deficits observed in the cerebellum. Finally, significant negative correlations were observed between UMSARS scores and thalamic and cerebellar connectivity (p < 0.05) as well as between duration of illness and cerebellar connectivity. CONCLUSIONS: Abnormal connectivity of the basal ganglia and cerebellar network may be causally implicated for the motor features observed in MSA-C. KEY POINTS: • Structural connectivity of the motor subnetwork was explored in patients with multiple system atrophy with cerebellar features (MSA-C) using probabilistic tractography. • The motor subnetwork in MSA-C has significant alterations in both basal ganglia and cerebellar connectivity, with a higher extent of abnormality in the cerebellum. • These findings may be causally implicated for the motor features of cerebellar dysfunction and parkinsonism observed in MSA-C.

Clinical Utility of Longitudinal Measurement of Motor Threshold in Wilson's Disease.

This study describes the longitudinal changes of resting motor threshold (RMT) and central motor conduction time (CMCT) in 18 patients with Wilson's disease (WD). The RMT, CMCT, and Global Assessment Scale for Wilson Disease (GAS-WD) were measured at baseline and at follow-up after 12.94 ± 7.23 months. There was a significant decrease in the RMT (72.11 ± 18.62 vs. 63.7 ± 15.52%; p-value = 0.002) and GAS-WD scores (14.38 ± 5.35 vs. 9.77 ± 6.47 ms; p-value = 0.04). CMCT did not improve despite chelation therapy. Hence, RMT may serve as a marker of chelation efficacy in WD.

Phenotypic Variability of Essential Tremor Based on the Age at Onset.

BACKGROUND: Essential tremor (ET) is reported to have a bimodal distribution of age at onset (AAO) with phenotypic variability based on the AAO. This study aims to explore the distribution of AAO based on mathematical modeling and ascertain the differences, if any, in the clinical features of groups. METHODS: A chart review was conducted for 252 patients with ET diagnosed based on the Consensus statement of the Movement Disorder Society on Tremor. Finite mixture modeling was performed to identify groups of the cohort based on the AAO. RESULTS: Three groups were defined: early onset (EO): AAO ≤ 22 years, n = 63, intermediate onset (IO): 23 ≤ AAO ≤ 35 years, n = 43, and late onset (LO): AAO ≥ 36 years, n = 146. There were no significant differences related to family history or responsiveness to alcohol. The EO group had significantly higher prevalence of upper limb and lower limb tremor. Head tremor and voice tremor was more prevalent in the IO and LO groups. Cerebellar signs showed a significant increase with an increase in AAO. CONCLUSIONS: ET shows significant phenotypic variability based on the AAO. Patients with an early AAO are more likely to develop an appendicular tremor, whereas the probability of axial tremor and cerebellar signs increases with increasing AAO.

Probabilistic Tractography-Based Tremor Network Connectivity in Tremor Dominant Parkinson's Disease and Essential Tremor plus.

Background: The basal ganglia-thalamocortical (BGTC) and cerebello-thalamocortical (CTC) networks are implicated in tremor genesis; however, exact contributions across disorders have not been studied. Objective: Evaluate the structural connectivity of BGTC and CTC in tremor-dominant Parkinson's disease (TDPD) and essential tremor plus (ETP) with the aid of probabilistic tractography and graph theory analysis. Methods: Structural connectomes of the BGTC and CTC were generated by probabilistic tractography for TDPD (n = 25), ETP (ET with rest tremor, n = 25), and healthy control (HC, n = 22). The Brain Connectivity Toolbox was used for computing standard topological graph measures of segregation, integration, and centrality. Tremor severity was ascertained using the Fahn-Tolosa-Marin tremor rating scale (FTMRS). Results: There was no difference in total FTMRS scores. Compared with HC, TDPD had a lower global efficiency and characteristic path length. Abnormality in segregation, integration, and centrality of bilateral putamen, globus pallidus externa (GPe), and GP interna (GPi), with reduction of centrality of right caudate and cerebellar lobule 8, was observed. ETP showed reduction in segregation and integration of right GPe and GPi, ventrolateral posterior nucleus, and centrality of right putamen, compared with HC. Differences between TDPD and ETP were a reduction of strength of the right putamen, and lower clustering coefficient, local efficiency, and strength of the left GPi in TDPD. Conclusions: Contrary to expectations, TDPD and ETP may not be significantly different with regard to tremor pathogenesis, with definite overlaps. There may be fundamental similarities in network disruption across different tremor disorders with the same tremor activation patterns, along with disease-specific changes.

Free water imaging in Parkinson's disease and atypical parkinsonian disorders.

BACKGROUND: Free water (FW)-corrected diffusion measures are more precise compared to standard diffusion measures. This study comprehensively evaluates FW and corrected diffusion metrics for whole brain white and deep gray matter (WM, GM) structures in patients with Parkinson's disease (PD), progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) and attempts to ascertain the probable patterns of WM abnormalities. METHOD: Diffusion MRI was acquired for subjects with PD (n = 133), MSA (n = 25), PSP (n = 30) and matched healthy controls (HC) (n = 99, n = 24, n = 12). Diffusion metrics of FA, MD, AD, RD were generated and FW, corrected FA maps were calculated using a bi-tensor model. TBSS was carried out at 5000 permutations with significance at p < 0.05. For GM, diffusivity maps were extracted from the basal ganglia, and analyzed at an FDR with p < 0.05. RESULTS: Compared to HC, PD showed focal changes in FW. MSA showed changes in the cerebellum and brainstem, and PSP showed increase in FW involving supratentorial WM and midbrain. All three showed increased substantia nigra FW. MSA, PSP demonstrated increased FW in bilateral putamen. PD showed increased FW in left GP externa, and bilateral thalamus. Compared to HC, MSA had increased FW in bilateral GP interna, and left thalamic. PSP had an additional increase in FW of the right GP externa, right GP interna, and bilateral thalamus. CONCLUSION: The present study demonstrated definitive differences in the patterns of FW alterations between PD and atypical parkinsonian disorders suggesting the possibility of whole brain FW maps being used as markers for diagnosis of these disorders.