Trans-Spinal Direct Current Stimulation for Managing Primary Orthostatic Tremor.

BACKGROUND: Primary orthostatic tremor (POT) is a rare disorder, characterized by 13 to 18 Hz tremor in the legs when standing and is often refractory to medical treatment. Epidural spinal cord stimulation has been proposed as an alternative treatment. However, this approach is invasive, which limits its application. OBJECTIVE: Trans-spinal direct current stimulation (tsDCS) is a non-invasive method to modulate spinal cord circuits. The aim of this proof-of-concept study was to investigate the potential beneficial effect of tsDCS in POT. METHODS: We conducted a double-blind, sham-controlled study in 16 patients with POT. In two separate visits, patients received sham tsDCS first followed by active (either cathodal or anodal) tsDCS. The primary outcome was the change in time in standing position. Secondary outcomes comprised quantitative assessment of tremor, measurement of corticospinal excitability including short-latency afferent inhibition, and clinical global impression-improvement (CGI-I). Measurements were made at baseline, after sham tsDCS, 0-30 min, and 30-60 min after active conditions. RESULTS: Cathodal-tsDCS reduced tremor amplitude and frequency and lowered corticospinal excitability whereas anodal-tsDCS reduced tremor frequency only. CGI-I scores positively correlated with the time in standing position after both active tsDCS conditions. CONCLUSION: A single session of tsDCS can improve instability in POT. This opens a new vista for experimental treatment options using multiple sessions of spinal DC stimulation. © 2021 International Parkinson and Movement Disorder Society.

Motor cortex and hippocampus are the two main cortical targets in LGI1-antibody encephalitis.

Encephalitis associated with antibodies against leucine-rich glioma-inactivated 1 (LGI1) protein is increasingly recognized as an auto-immune disorder associated with characteristic tonic-dystonic seizures. The cortical or subcortical origin of these motor events is not clear. Some patients also present with different epileptic seizures and with cognitive impairment. The frequency of these features and their timing during the natural history of this encephalitis have not been fully described. We therefore reviewed data from 34 patients harbouring antibodies against LGI1 protein (21-81 years, median age 64) referred to the French Reference Centre for Neurological Paraneoplastic Syndrome. Three types of evidence suggested tonic-dystonic seizures were of cortical origin: (i) a slow, unilateral, frontal electroencephalographic wave, of duration ∼580 ms and amplitude ∼71 µV, preceded the contralateral tonic-dystonic seizures in simultaneous electroencephalographic and myographic records from seven of seven patients tested; (ii) 18-Fluorodeoxyglucose imaging revealed a strong hypermetabolism in primary motor cortex, controlateral to the affected limb, during encephalitis for five patients tested, as compared with data from the same patients after remission or from 16 control subjects; and (iii) features of polymyographic records of tonic-dystonic seizure events pointed to a cortical origin. Myoclonic patterns with brief, rhythmic bursts were present in three of five patients tested and a premyoclonic potential was identified in the cortex of one patient. Initially during encephalitis, 11 of 34 patients exhibited tonic-dystonic seizures (32%). Distinct epileptic syndromes were evident in 13 patients (38%). They were typically simple, focal seizures from the temporal lobe, consisting of vegetative symptoms or fear. At later stages, 22 of 32 patients displayed tonic-dystonic seizures (68%) and 29 patients presented frequent seizures (91%) including status epilepticus. Cognitive impairment, either anterograde amnesia or confusion was evident in 30 of 34 patients (88%). Brain imaging was normal in patients with isolated tonic-dystonic seizures; in patients with limbic symptoms it revealed initially a hippocampal hyperintensity in 8 of 19 patients (42%) and 17 of 24 patients (70%) at later stages. Our data suggest that the major signs of LGI1-antibody encephalitis can be linked to involvement of motor cortex and hippocampus. They occur in parallel with striatum involvement. One of these cortical targets is involved, often unilaterally at disease onset. As the encephalitis progresses, in the absence of immunomodulatory treatment, the second cortical target is affected and effects become bilateral. Progression to the second cortical target occurs with a variable delay of days to several months.

Orthostatic tremor: a cerebellar pathology?

SEE MUTHURAMAN ET AL DOI101093/AWW164 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Primary orthostatic tremor is characterized by high frequency tremor affecting the legs and trunk during the standing position. Cerebellar defects were suggested in orthostatic tremor without direct evidence. We aimed to characterize the anatomo-functional defects of the cerebellar motor pathways in orthostatic tremor. We used multimodal neuroimaging to compare 17 patients with orthostatic tremor and 17 age- and gender-matched healthy volunteers. Nine of the patients with orthostatic tremor underwent repetitive transcranial stimulation applied over the cerebellum during five consecutive days. We quantified the duration of standing position and tremor severity through electromyographic recordings. Compared to healthy volunteers, grey matter volume in patients with orthostatic tremor was (i) increased in the cerebellar vermis and correlated positively with the duration of the standing position; and (ii) increased in the supplementary motor area and decreased in the lateral cerebellum, which both correlated with the disease duration. Functional connectivity between the lateral cerebellum and the supplementary motor area was abnormally increased in patients with orthostatic tremor, and correlated positively with tremor severity. After repetitive transcranial stimulation, tremor severity and functional connectivity between the lateral cerebellum and the supplementary motor area were reduced. We provide an explanation for orthostatic tremor pathophysiology, and demonstrate the functional relevance of cerebello-thalamo-cortical connections in tremor related to cerebellar defects.

The long-term outcome of orthostatic tremor.

OBJECTIVES: Orthostatic tremor is a rare condition characterised by high-frequency tremor that appears on standing. Although the essential clinical features of orthostatic tremor are well established, little is known about the natural progression of the disorder. We report the long-term outcome based on the largest multicentre cohort of patients with orthostatic tremor. METHODS: Clinical information of 68 patients with clinical and electrophysiological diagnosis of orthostatic tremor and a minimum follow-up of 5 years is presented. RESULTS: There was a clear female preponderance (76.5%) with a mean age of onset at 54 years. Median follow-up was 6 years (range 5-25). On diagnosis, 86.8% of patients presented with isolated orthostatic tremor and 13.2% had additional neurological features. At follow-up, seven patients who initially had isolated orthostatic tremor later developed further neurological signs. A total 79.4% of patients reported worsening of orthostatic tremor symptoms. These patients had significantly longer symptom duration than those without reported worsening (median 15.5 vs 10.5 years, respectively; p=0.005). There was no change in orthostatic tremor frequency over time. Structural imaging was largely unremarkable and dopaminergic neuroimaging (DaTSCAN) was normal in 18/19 cases. Pharmacological treatments were disappointing. Two patients were treated surgically and showed improvement. CONCLUSIONS: Orthostatic tremor is a progressive disorder with increased disability although tremor frequency is unchanged over time. In most cases, orthostatic tremor represents an isolated syndrome. Drug treatments are unsatisfactory but surgery may hold promise.

Association of abnormal explicit sense of agency with cerebellar impairment in myoclonus-dystonia.

Non-motor aspects in dystonia are now well recognized. The sense of agency, which refers to the experience of controlling one's own actions, has been scarcely studied in dystonia, even though its disturbances can contribute to movement disorders. Among various brain structures, the cerebral cortex, the cerebellum, and the basal ganglia are involved in shaping the sense of agency. In myoclonus dystonia, resulting from a dysfunction of the motor network, an altered sense of agency may contribute to the clinical phenotype of the condition. In this study, we compared the explicit and implicit sense of agency in patients with myoclonus dystonia caused by a pathogenic variant of SGCE (DYT-SGCE) and control participants. We utilized behavioural tasks to assess the sense of agency and performed neuroimaging analyses, including structural, resting-state functional connectivity, and dynamic causal modelling, to explore the relevant brain regions involved in the sense of agency. Additionally, we examined the relationship between behavioural performance, symptom severity, and neuroimaging findings. We compared 19 patients with DYT-SGCE and 24 healthy volunteers. Our findings revealed that patients with myoclonus-dystonia exhibited a specific impairment in explicit sense of agency, particularly when implicit motor learning was involved. However, their implicit sense of agency remained intact. These patients also displayed grey-matter abnormalities in the motor cerebellum, as well as increased functional connectivity between the cerebellum and pre-supplementary motor area. Dynamic causal modelling analysis further identified reduced inhibitory effects of the cerebellum on the pre-supplementary motor area, decreased excitatory effects of the pre-supplementary motor area on the cerebellum, and increased self-inhibition within the pre-supplementary motor area. Importantly, both cerebellar grey-matter alterations and functional connectivity abnormalities between the cerebellum and pre-supplementary motor area were found to correlate with explicit sense of agency impairment. Increased self-inhibition within the pre-supplementary motor area was associated with less severe myoclonus symptoms. These findings highlight the disruption of higher-level cognitive processes in patients with myoclonus-dystonia, further expanding the spectrum of neurological and psychiatric dysfunction already identified in this disorder.

Clinical and Electrophysiological Characterization of Essential Tremor in 18 Children and Adolescents.

Background: Essential tremor (ET) is considered the most frequent abnormal movement in the general population, with childhood onset in 5 to 30% of the patients. Methods: A multicenter, descriptive cross-sectional study enrolled patients ⩽18 years with a definite diagnosis of ET according to the International Parkinson and Movement Disorders Society criteria. Demographic data, clinical and electrophysiological characteristics of the tremor, neurological examination and impact on quality of life were collected. Results: 9 males and 9 females were included (mean age of 13.9 years). Tremor was characterized by : upper limb onset at a mean age of 6.5 years; at enrollment, upper limbs localization, and involvement of an additional body region in 28% of the patients; kinetic tremor in all of the patients combined with postural tremor in 17 and rest tremor in 3; tremor mean frequency of 7.6 Hz, mean burst duration of 82.7 ms; identification of mild myoclonic jerks on the polymyographic recordings in 7 patients; altered quality of life with worse emotional outcomes in girls and when a disease duration >5 years was suggested. Discussion: Childhood-onset ET is associated with delayed diagnosis and remarkable functional impact. Electromyographic identification of additional mild myoclonus is a new finding whose significance is discussed. Highlights: ET onset involved upper limbs and at inclusion, 28% of the patients exhibited involvement of an additional body region.ET impacted quality of life for all patients.Girls and patients affected for >5 years reported worse emotional outcomes.Mild myoclonic jerks were identified on 7/17 polymyographic recordings.

Myoclonus and dystonia in cerebrotendinous xanthomatosis.

BACKGROUND: Cerebrotendinous xanthomatosis (CTX) is an inherited neurometabolic disorder. The main neurological manifestations of the disease are pyramidal syndrome, ataxia, peripheral neuropathy, cognitive impairment, epilepsy, and psychiatric disturbances. Myoclonic dystonia has been reported on in the setting of various neurometabolic diseases. Anecdotal reports describe movement disorders associated with CTX, but no dystonia with myoclonic events. METHODS: We collected clinical, biochemical, electrophysiological, neuroradiological, and genetic data of 6 patients with myoclonus and mild dystonia associated with CTX. From a systematic literature review, we analyzed 31 patients with movement disorders secondary to CTX. RESULTS: Our 6 patients presented distal myoclonus with mild dystonia of the upper limbs. Myoclonus was of subcortical origin, based on neurophysiological recordings, and differed from oromandibular myoclonus previously described in CTX patients. CONCLUSIONS: These results expand the phenotype of CTX and suggest that myoclonus and/or dystonia are underdiagnosed. In keeping with our findings, tremors previously observed in CTX patients might actually correspond to myoclonic events. We hypothesize that a dysfunction of the dentate nuclei-basal ganglia pathway may be involved.

Neurochemokines: a menage a trois providing new insights on the functions of chemokines in the central nervous system.

Recent observations suggest that besides their role in the immune system, chemokines have important functions in the brain. There is a great line of evidence to suggest that chemokines are a unique class of neurotransmitters/neuromodulators, which regulate many biological aspects as diverse as neurodevelopment, neuroinflammation and synaptic transmission. In physiopathological conditions, many chemokines are synthesized in activated astrocytes and microglial cells, suggesting their involvement in brain defense mechanisms. However, when evoking chemokine functions in the nervous system, it is important to make a distinction between resting conditions and various pathological states including inflammatory diseases, autoimmune or neurodegenerative disorders in which chemokine functions have been extensively studied. We illustrate here the emergent concept of the neuromodulatory/neurotransmitter activities of neurochemokines and their potential role as a regulatory alarm system and as a group of messenger molecules for the crosstalk between neurons and cells from their surrounding microenvironment. In this deliberately challenging review, we provide novel hypotheses on the role of these subtle messenger molecules in brain functions leading to the evidence that previous dogmas concerning chemokines should be reconsidered.

Dystonic tremor caused by mutation of the glucose transporter gene GLUT1.

Glucose transporter 1 deficiency syndrome (GLUT1-DS) is due to heterozygous mutation of the glucose transporter type 1 gene (GLUT1/SLC2A1). GLUT1-DS is characterized by movement disorders, including paroxysmal exercise-induced dystonia (PED), as well as seizures, mental retardation and hypoglycorrhachia. Tremor was recently shown to be part of the phenotype, but its clinical and electrophysiological features have not yet been described in detail, and GLUT1 tremor reports are rare. We describe two patients, a young woman and her mother, who were referred to us for tremor. We also systematically review published cases of GLUT1-DS with tremor (14 cases, including ours), focusing on clinical features. In most cases (10/14), the tremor, which involved the limbs and voice, fulfilled clinical criteria for dystonic tremor (DT), occurring in body areas affected by dystonia. Tremor was the only permanent symptom in 2 cases. Recordings, reported here for the first time, showed an irregular 6- to 8.5-Hz tremor compatible with DT in our two patients. These findings show that tremor, and particularly DT, may be a presenting symptom of GLUT1-DS. Patients who present with dystonic tremor, with or without mental retardation, seizures, movement disorders and/or a family history, should therefore be screened for GLUT1-DS.

Tremor-like subcortical myoclonus in STXBP1 encephalopathy.

The phenotypic spectrum of STXBP1-related encephalopathy ranges from infantile epileptic encephalopathy to intellectual disability with nonsyndromic or absent epilepsy. Although being frequently reported, the tremor associated with STXBP1 has not been fully characterized to date. The aim of our study was to describe it. We recruited patients with intellectual disability due to STXBP1 variants, regardless of their epileptic phenotype, who had tremor at examination and who underwent neurophysiological testing including polymyographic registration of upper limbs muscles activity at rest, during posture maintenance and action. Six patients met the inclusion criteria over four years. Clinically, all had a postural and action distal tremor increased by emotions. Neurophysiological recordings showed a specific myoclonus pattern and were highly suggestive of a subcortical generator. The tremor-like observed in STXBP1 encephalopathy is due to a subcortical pseudo-rhythmic myoclonus.

Myoclonus dystonia plus syndrome due to a novel 7q21 microdeletion.

Myoclonus dystonia (M-D) is a rare genetic movement disorder characterized by a combination of myoclonic jerks and dystonia. It is usually due to mutations in the SGCE gene. We report on a patient with a typical M-D syndrome, but also short stature, microcephaly, and mental retardation. Molecular analysis showed no mutations within the SGCE gene but a microdeletion encompassing the SGCE gene in chromosome region 7q21. Array-CGH analysis showed that the deletion spanned approximately 1.88 Mb. We suggest that M-D plus patients with mental retardation, microcephaly, dysmorphism, or short stature, all frequently associated disorders, should be screened for 7q21 microdeletion. By examining previously published cases of mental retardation associated with pure 7q21 deletions, we identified two distinct regions of respectively 455 and 496 kb that are critical for mental retardation and growth retardation. Among the genes located within these regions, LOC253012, also known as HEPACAM2, is a good candidate for both mental retardation and microcephaly.

Dissociation in reactive and proactive inhibitory control in Myoclonus dystonia.

Myoclonus-dystonia (MD) is a syndrome characterized by myoclonus of subcortical origin and dystonia, frequently associated with psychiatric comorbidities. The motor and psychiatric phenotypes of this syndrome likely result from cortico-striato-thamalo-cerebellar-cortical pathway dysfunction. We hypothesized that reactive and proactive inhibitory control may be altered in these patients. Using the Stop Signal Task, we assessed reactive and proactive inhibitory control in MD patients with (n = 12) and without (n = 21) deep brain stimulation of the globus pallidus interna and compared their performance to matched healthy controls (n = 24). Reactive inhibition was considered as the ability to stop an already initiated action and measured using the stop signal reaction time. Proactive inhibition was assessed through the influence of several consecutive GO or STOP trials on decreased response time or inhibitory process facilitation. The proactive inhibition was solely impaired in unoperated MD patients. Patients with deep brain stimulation showed impairment in reactive inhibition, independent of presence of obsessive-compulsive disorders. This impairment in reactive inhibitory control correlated with intrinsic severity of myoclonus (i.e. pre-operative score). The results point to a dissociation in reactive and proactive inhibitory control in MD patients with and without deep brain stimulation of the globus pallidus interna.

Myoclonus-dystonia: an update.

Our knowledge of the clinical, neurophysiological, and genetic aspects of myoclonus-dystonia (M-D) has improved markedly in the recent years. Basic research has provided new insights into the complex dysfunctions involved in the pathogenesis of M-D. On the basis of a comprehensive literature search, this review summarizes current knowledge on M-D, with a focus on recent findings. We also propose modified diagnostic criteria and recommendations for clinical management.

Predominant cortical dysfunction in Guadeloupean parkinsonism.

Atypical parkinsonism is extremely frequent in Guadeloupe and may have an environmental cause. One-half of the patients with this tauopathy have dopa-resistant parkinsonism, tremor, subcortical dementia and abnormal eye movements suggestive of progressive supranuclear palsy (PSP). They also have hallucinations, dysautonomia, which are not characteristic of PSP. Furthermore, the oculomotor abnormalities and the tremor, which is jerky, differ from what is observed in classical PSP patients. We therefore undertook an electrophysiological study to characterize these features in greater detail. Nine representative Guadeloupean PSP-like (Gd-PSP) patients were selected for electro-oculographic recordings of horizontal eye movements [visually guided saccades (VGS), antisaccades (AS) and smooth pursuit], clinical evaluation of vertical saccade velocity and electrophysiological analysis of abnormal limb movements [electromyographic polygraphy, EEG jerk-locked-back-averaging (JLBA) and long-loop C-reflex]. Vertical saccade velocity was reduced in five patients. The velocity of horizontal VGS was normal, although the latencies were increased and horizontal smooth pursuit (HSP) was mostly saccadic. The AS error rate was above 70% in most patients. Myoclonus was detected in 89% of the Gd-PSP patients. It was mainly small amplitude rest and action myoclonus in the upper limbs, characterized by short arrhythmic 24-76 ms bursts and was of cortical origin, as confirmed by JLBA in five patients. In conclusion, Gd-PSP patients have cortical myoclonus and cortical oculomotor impairments, but only minor signs of brainstem oculomotor dysfunction, suggesting that cortical dysfunction predominates over brainstem impairments. This electrophysiological study, added to previous clinical, neuropsychological and neuroradiological studies, has enriched the characterization of Guadeloupean atypical parkinsonism, which thus appears to be a new clinical entity.

KIF1C Variants Are Associated with Hypomyelination, Ataxia, Tremor, and Dystonia in Fraternal Twins.

Background: KIF1C (Kinesin Family Member 1C) variants have been associated with hereditary spastic paraplegia and spastic ataxia. Case report: We report fraternal twins presenting with cerebellar ataxia and dystonic tremor. Their brain MRI showed a hypomyelinating leukoencephalopathy. Whole exome sequencing identified a homozygous KIF1C variant in both patients. Discussion: KIF1C variants can manifest as a complex movement disorder with cerebellar ataxia and dystonic tremor. KIF1C variants may also cause a hypomyelinating leukoencephalopathy.

Cortical excitability in DYT-11 positive myoclonus dystonia.

Myoclonus-dystonia (M-D) is an autosomal dominant movement disorder caused by mutations in the epsilon-sarcoglycan gene (DYT11). We explore pathophysiological characteristics of M-D with the hypothesis that they may be different from those of sporadic or genetic dystonia. We compared five carriers of the DYT11 gene mutation and 10 healthy controls. Using transcranial magnetic stimulation, we measured parameters assessing cortical membrane excitability (active motor threshold, aMT) and synaptic activity (short interval, sICI) and afferent (AI) intracortical inhibitions and their interaction. aMT was significantly higher in the DYT11 gene carriers than in normal subjects. The others parameters (sICI, AI and their interaction) were not different between the two groups. In DYT11 gene carriers cortical membrane excitability was impaired while parameters assessing cortical synaptic activity were normal. Opposite results have been obtained in focal sporadic and generalized DYT1 dystonias.

Dopaminergic deficit is not the rule in orthostatic tremor.

Involvement of the dopaminergic system in orthostatic tremor is controversial. The aim of this study was to detect possible dopaminergic denervation in primary orthostatic tremor (OT). Twelve consecutive patients with a firm diagnosis of primary orthostatic tremor were compared with age-matched normal controls. All the patients had a neurological examination, surface polymyography, and quantification of striatal dopamine transporters with (123)I-FP-CIT SPECT imaging. There was no significant difference in (123)I-FP-CIT SPECT findings between controls and patients with OT. Longstanding primary orthostatic tremor is not necessarily associated with (123)I-FP-CIT SPECT abnormalities, as 8 of our patients had more than a 10-year history of OT. Primary orthostatic tremor without dopaminergic denervation remains a valid entity, although representing only a subtype of high-frequency OT. A new role may emerge for (123)I-FP-CIT SPECT in distinguishing between patients whose symptoms will be restricted to OT throughout the disease course and patients at an increased risk of developing PD. (c) 2008 Movement Disorder Society.