Changes in cerebellar output abnormally modulate cortical myoclonus sensorimotor hyperexcitability.

Cortical myoclonus is produced by abnormal neuronal discharges within the sensorimotor cortex, as demonstrated by electrophysiology. Our hypothesis is that the loss of cerebellar inhibitory control over the motor cortex, via cerebello-thalamo-cortical connections, could induce the increased sensorimotor cortical excitability that eventually causes cortical myoclonus. To explore this hypothesis, in the present study we applied anodal transcranial direct current stimulation over the cerebellum of patients affected by cortical myoclonus and healthy controls and assessed its effect on sensorimotor cortex excitability. We expected that anodal cerebellar transcranial direct current stimulation would increase the inhibitory cerebellar drive to the motor cortex and therefore reduce the sensorimotor cortex hyperexcitability observed in cortical myoclonus. Ten patients affected by cortical myoclonus of various aetiology and 10 aged-matched healthy control subjects were included in the study. All participants underwent somatosensory evoked potentials, long-latency reflexes and short-interval intracortical inhibition recording at baseline and immediately after 20 min session of cerebellar anodal transcranial direct current stimulation. In patients, myoclonus was recorded by the means of surface EMG before and after the cerebellar stimulation. Anodal cerebellar transcranial direct current stimulation did not change the above variables in healthy controls, while it significantly increased the amplitude of somatosensory evoked potential cortical components, long-latency reflexes and decreased short-interval intracortical inhibition in patients; alongside, a trend towards worsening of the myoclonus after the cerebellar stimulation was observed. Interestingly, when dividing patients in those with and without giant somatosensory evoked potentials, the increment of the somatosensory evoked potential cortical components was observed mainly in those with giant potentials. Our data showed that anodal cerebellar transcranial direct current stimulation facilitates-and does not inhibit-sensorimotor cortex excitability in cortical myoclonus syndromes. This paradoxical response might be due to an abnormal homeostatic plasticity within the sensorimotor cortex, driven by dysfunctional cerebello-thalamo-cortical input to the motor cortex. We suggest that the cerebellum is implicated in the pathophysiology of cortical myoclonus and that these results could open the way to new forms of treatment or treatment targets.

The natural history of progressive myoclonus ataxia.

Progressive myoclonus ataxia (PMA) is a rare clinical syndrome characterized by the presence of progressive myoclonus and ataxia, and can be accompanied by mild cognitive impairment and infrequent epileptic seizures. This is the first study to describe the natural history of PMA and identify clinical, electrophysiological, and genetic features explaining the variability in disease progression. A Dutch cohort of consecutive patients meeting the criteria of the refined definition of PMA was included. The current phenotype was assessed during in-person consultation by movement disorders experts, and retrospective data was collected to describe disease presentation and progression, including brain imaging and therapy efficacy. Extensive genetic and electrophysiological tests were performed. The presence of cortical hyperexcitability was determined, by either the identification of a cortical correlate of myoclonic jerks with simultaneous electromyography-electroencephalography or a giant somatosensory evoked potential. We included 34 patients with PMA with a median disease duration of 15 years and a clear progressive course in most patients (76%). A molecular etiology was identified in 82% patients: ATM, CAMTA1, DHDDS, EBF3, GOSR2, ITPR1, KCNC3, NUS1, POLR1A, PRKCG, SEMA6B, SPTBN2, TPP1, ZMYND11, and a 12p13.32 deletion. The natural history is a rather homogenous onset of ataxia in the first two years of life followed by myoclonus in the first 5 years of life. Main accompanying neurological dysfunctions included cognitive impairment (62%), epilepsy (38%), autism spectrum disorder (27%), and behavioral problems (18%). Disease progression showed large variability ranging from an epilepsy free PMA phenotype (62%) to evolution towards a progressive myoclonus epilepsy (PME) phenotype (18%): the existence of a PMA-PME spectrum. Cortical hyperexcitability could be tested in 17 patients, and was present in 11 patients and supported cortical myoclonus. Interestingly, post-hoc analysis showed that an absence of cortical hyperexcitability, suggesting non-cortical myoclonus, was associated with the PMA-end of the spectrum with no epilepsy and milder myoclonus, independent of disease duration. An association between the underlying genetic defects and progression on the PMA-PME spectrum was observed. By describing the natural history of the largest cohort of published patients with PMA so far, we see a homogeneous onset with variable disease progression, in which phenotypic evolution to PME occurs in the minority. Genetic and electrophysiological features may be of prognostic value, especially the determination of cortical hyperexcitability. Furthermore, the identification of cortical and non-cortical myoclonus in PMA helps us gain insight in the underlying pathophysiology of myoclonus.

Substantiating the Short Burst Duration in Cortical Myoclonus.

BACKGROUND: Myoclonus is characterized by involuntary, shock-like movements, of which cortical (CM) and non-cortical myoclonus (NCM) are most common. Electrophysiology can help differentiate between these subtypes; however, the diagnostic value of several features is largely unknown. OBJECTIVE: This study aims to determine the diagnostic value of the burst duration in distinguishing CM and NCM. METHODS: We manually identified the burst duration of 8 patients with CM, confirmed by electromyography-electroencephalography registration or somatosensory-evoked potentials, and 19 patients with NCM, suspected due to a myoclonus-dystonia phenotype (MYC/DYT-SGCE positive and negative). RESULTS: The sensitivity and specificity were calculated to assess the diagnostic value. The burst duration of CM (31.1 ms) was significantly shorter than that of NCM (56.7 ms), with a sensitivity of 100% and a specificity of 89.5% at a threshold of 45.0 ms. A minimum of 10 randomly selected bursts were sufficient for reliable diagnostic accuracy. CONCLUSION: The burst duration seems a valuable supportive diagnostic criterion for distinguishing CM and NCM. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Differential diagnosis of familial adult myoclonic epilepsy.

OBJECTIVE: Familial adult myoclonic epilepsy (FAME) is an under-recognized disorder characterized by cortical myoclonus, generalized tonic-clonic seizures, and additional clinical symptoms, which vary depending on the FAME subtype. FAME is caused by pentanucleotide repeat expansions of intronic TTTCA/TTTTA in different genes. FAME should be distinguished from a range of differential diagnoses. METHODS: The differential diagnoses and frequent presentations leading to misdiagnosis of FAME were investigated from the available literature and reported based on an expert opinion survey. RESULTS: The phenotypic features of FAME, including generalized tonic-clonic and myoclonic seizures, are also seen in other epilepsy syndromes, such as juvenile myoclonic epilepsy, with a resultant risk of misdiagnosis and lack of identification of the underlying cause. Cortical myoclonus may mimic essential tremor or drug-induced tremor. In younger individuals, the differential diagnosis includes progressive myoclonus epilepsies (PMEs), such as Unverricht-Lundborg disease, whereas, in adulthood, late-onset variants of PMEs, such as sialidoses, myoclonus epilepsy, and ataxia due to potassium channel pathogenic variants should be considered. PMEs may also be suggested by cognitive impairment, cerebellar signs, or psychiatric disorders. Electroencephalography (EEG) may show similarities to other idiopathic generalized epilepsies or PMEs, with generalized spike-wave activity. Signs of cortical hyperexcitability may be seen, such as an increased amplitude of somatosensory evoked potentials or enhanced cortical reflex to sensory stimuli, together with the neurophysiological pattern of the movement disorder. SIGNIFICANCE: Recognition of FAME will inform prognostic and genetic counseling and diagnosis of the insidious progression, which may occur in older individuals who show mild cognitive deterioration. Distinguishing FAME from other disorders in individuals or families with this constellation of symptoms is essential to allow the identification of underlying etiology.

Familial adult myoclonus epilepsy: Neuroimaging and neuropathological findings.

Familial adult myoclonus epilepsy (FAME) is characterized by cortical myoclonus and often epileptic seizures, but the pathophysiology of this condition remains uncertain. Here, we review the neuroimaging and neuropathological findings in FAME. Imaging findings, including functional magnetic resonance imaging, are in line with a cortical origin of involuntary tremulous movements (cortical myoclonic tremor) and indicate a complex pattern of cerebellar functional connectivity. Scarce neuropathological reports, mainly from a single family, provide evidence of morphological changes in the Purkinje cells. Cerebellar changes seem to be part of the syndrome, in at least some FAME pedigrees. Cortical hyperexcitability in FAME, resulting in the cardinal clinical symptoms, might be the result of decreased cortical inhibition via the cerebellothalamocortical loop. The pathological findings might share some similarities with other pentanucleotide repeat disorders. The relation with genetic findings in FAME needs to be elucidated.

A Biomarker for Benign Adult Familial Myoclonus Epilepsy: High-Frequency Activities in Giant Somatosensory Evoked Potentials.

BACKGROUND: Benign adult familial myoclonus epilepsy (BAFME) is one of the diseases that cause cortical myoclonus (CM) with giant somatosensory evoked potentials (SEPs). There are no useful diagnostic biomarkers differentiating BAFME from other CM diseases. OBJECTIVE: To establish reliable biomarkers including high-frequency oscillations (HFOs) with giant SEPs for the diagnosis of BAFME. METHODS: This retrospective case study included 49 consecutive CM patients (16 BAFME and 33 other CM patients) who exhibited giant P25 or N35 SEPs. SEPs were processed by a band-pass filter of 400-1000 Hz to analyze HFOs. Clinical and SEP findings were compared between (1) BAFME and other CM groups and (2) patients with presence and absence of P25-HFOs (HFOs superimposed on giant P25). The diagnostic power of each factor for BAFME was calculated. RESULTS: All 16 BAFME patients showed SEP P25-HFOs with significantly higher occurrence (P < 0.0001) compared with that of other CM groups. The presence of P25-HFOs significantly correlated with a BAFME diagnosis (P < 0.0001) and high SEP P25 and N35 amplitudes (P = 0.01 and P < 0.0001, respectively). BAFME was reliably diagnosed using P25-HFOs with high sensitivity (100%), specificity (87.9%), positive predictive value (80%), and negative predictive value (100%), demonstrating its superiority as a diagnostic factor compared to other factors. CONCLUSIONS: P25-HFOs with giant SEPs is a potential biomarker for BAFME diagnosis. P25-HFOs may reflect cortical hyperexcitability partly due to paroxysmal depolarizing shifts in epileptic neuronal activities and higher degrees of rhythmic tremulousness than those in ordinary CM. © 2021 International Parkinson and Movement Disorder Society.

Unravelling the enigma of cortical tremor and other forms of cortical myoclonus.

Cortical tremor is a fine rhythmic oscillation involving distal upper limbs, linked to increased sensorimotor cortex excitability, as seen in cortical myoclonus. Cortical tremor is the hallmark feature of autosomal dominant familial cortical myoclonic tremor and epilepsy (FCMTE), a syndrome not yet officially recognized and characterized by clinical and genetic heterogeneity. Non-coding repeat expansions in different genes have been recently recognized to play an essential role in its pathogenesis. Cortical tremor is considered a rhythmic variant of cortical myoclonus and is part of the 'spectrum of cortical myoclonus', i.e. a wide range of clinical motor phenomena, from reflex myoclonus to myoclonic epilepsy, caused by abnormal sensorimotor cortical discharges. The aim of this update is to provide a detailed analysis of the mechanisms defining cortical tremor, as seen in FCMTE. After reviewing the clinical and genetic features of FCMTE, we discuss the possible mechanisms generating the distinct elements of the cortical myoclonus spectrum, and how cortical tremor fits into it. We propose that the spectrum is due to the evolution from a spatially limited focus of excitability to recruitment of more complex mechanisms capable of sustaining repetitive activity, overcoming inhibitory mechanisms that restrict excitatory bursts, and engaging wide areas of cortex. Finally, we provide evidence for a possible common denominator of the elements of the spectrum, i.e. the cerebellum, and discuss its role in FCMTE, according to recent genetic findings.

Progressive myoclonus ataxia: Time for a new definition?

BACKGROUND: The clinical demarcation of the syndrome progressive myoclonus ataxia is unclear, leading to a lack of recognition and difficult differentiation from other neurological syndromes. OBJECTIVES: The objective of this study was to apply a refined definition of progressive myoclonus ataxia and describe the clinical characteristics in patients with progressive myoclonus ataxia and with isolated cortical myoclonus. METHODS: A retro- and prospective analysis was performed in our tertiary referral center between 1994 and 2014. Inclusion criteria for progressive myoclonus ataxia patients were the presence of myoclonus and ataxia with or without infrequent (all types, treatment responsive) epileptic seizures. Inclusion criteria for isolated cortical myoclonus was the presence of isolated cortical myoclonus. Clinical and electrophysiological characteristics data were systematically scored. RESULTS: A total of 14 progressive myoclonus ataxia patients (males, 7; females, 7), median age 14.5 years, and 8 isolated cortical myoclonus patients (males, 2; females, 6), median age 23.5 years, were identified. In 93% of the progressive myoclonus ataxia patients, ataxia started first (median 2 years) followed by myoclonus (4 years) and finally infrequent epilepsy (9.3 years), with a progressive course in 93%. In 64% of the progressive myoclonus ataxia patients, a genetic underlying etiology was identified, including 3 not earlier reported causative progressive myoclonus ataxia genes. In isolated cortical myoclonus patients, myoclonus started at (median) 12 years with progression over time in 63% and a single epileptic seizure in 1 patient. No genetic causes were identified. CONCLUSION: Using a refined definition, we could create a rather homogenous progressive myoclonus ataxia group. Patients with isolated cortical myoclonus have a different course and do not appear to evolve in progressive myoclonus ataxia. The refined progressive myoclonus ataxia definition is a successful first step toward creating a separate syndrome for both clinical practice and future genetic research. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Effect of repetitive transcranial magnetic stimulation on action myoclonus: A pilot study in patients with EPM1.

OBJECTIVE: The objective of this study was to explore the short-term effects of repetitive transcranial magnetic stimulation (rTMS) on action myoclonus. METHODS: Nine patients with Unverricht-Lundborg (EPM1) progressive myoclonus epilepsy type underwent two series of 500 stimuli at 0.3Hz through round coil twice a day for five consecutive days. Clinical and neurophysiological examinations were performed two hours before starting the first rTMS session and two hours after the end of the last rTMS session. RESULTS: Eight patients completed the protocol; one discontinued because of a transient increase in spontaneous jerks. The unified myoclonus rating scale indicated a 25% reduction in posttreatment myoclonus with action score associated with an increase in the cortical motor threshold and lengthening of the cortical silent period (CSP). The decrease in the myoclonus with action scores correlated with the prolongation of CSP. CONCLUSIONS: Repetitive transcranial magnetic stimulation can be safely used in patients with EPM1, improves action myoclonus, and partially restores deficient cortical inhibition.

Epilepsia partialis continua after an anterior circulation ischaemic stroke.

BACKGROUND AND PURPOSE: Although cerebrovascular disorders are the main cause of epilepsia partialis continua (EPC) in adulthood, the frequency of EPC after stroke is unknown. The aim was to prospectively ascertain its frequency 1 year after an ischaemic stroke. METHODS: This was a prospective study of consecutive acute anterior circulation ischaemic stroke patients, previously independent, with an admission National Institutes of Health Stroke Scale score ≥4, an acute ischaemic lesion on imaging and no previous epileptic seizures. During admission patients received standardized diagnostic and medical care and were submitted to a neurophysiological evaluation protocol. One year after stroke, patients were re-evaluated by an epilepsy expert neurologist and performed a video-electroencephalogram with electromyography co-registration whenever myoclonus was observed during neurological examination for jerk-locked back averaging analysis (JLBA). EPC was defined as continuously repeated fragments of epileptic seizures, with preserved consciousness, lasting at least 1 h, and representing locally restricted epileptic activity. RESULTS: In all, 151 acute anterior circulation stroke patients were consecutively included and prospectively evaluated, but 23 died in the first year. One year after stroke, from 127 patients alive, 117 (92.1%) underwent clinical and neurophysiological evaluation. In two (1.7%) patients, EPC diagnosis was made both by clinical and electroencephalographic criteria, namely JLBA. Both patients had a history of remote symptomatic seizures and one of them acute symptomatic seizures and non-convulsive status epilepticus criteria during the first 7 days after stroke. CONCLUSIONS: Despite its low frequency, the high stroke incidence makes post-stroke EPC relevant. This study draws attention to this recognizable condition with therapeutic and eventually prognostic implications.