Potential Benefit of Channel Activators in Loss-of-Function Primary Potassium Channelopathies Causing Heredoataxia.

Potassium channels (KCN) are transmembrane complexes that regulate the resting membrane potential and the duration of action potentials in cells. The opening of KCN brings about an efflux of K+ ions that induces cell repolarization after depolarization, returns the transmembrane potential to its resting state, and enables for continuous spiking ability. The aim of this work was to assess the role of KCN dysfunction in the pathogenesis of hereditary ataxias and the mechanisms of action of KCN opening agents (KCO). In consequence, a review of the ad hoc medical literature was performed. Among hereditary KCN diseases causing ataxia, mutated Kv3.3, Kv4.3, and Kv1.1 channels provoke spinocerebellar ataxia (SCA) type 13, SCA19/22, and episodic ataxia type 1 (EA1), respectively. The K+ efflux was found to be reduced in experimental models of these diseases, resulting in abnormally prolonged depolarization and incomplete repolarization, thereby interfering with repetitive discharges in the cells. Hence, substances able to promote normal spiking activity in the cerebellum could provide symptomatic benefit. Although drugs used in clinical practice do not activate Kv3.3 or Kv4.3 directly, available KCO probably could ameliorate ataxic symptoms in SCA13 and SCA19/22, as verified with acetazolamide in EA1, and retigabine in a mouse model of hypokalemic periodic paralysis. To summarize, ataxia could possibly be improved by non-specific KCO in SCA13 and SCA19/22. The identification of new specific KCO agents will undoubtedly constitute a promising therapeutic strategy for these diseases.

Neuromuscular Ultrasound Findings of Myokymia in a Young Woman With Generalized Anti-LGI-1 and Anti-Caspr2 Antibodies Negative Isaac Syndrome.

ABSTRACT: Isaac syndrome is one of the rare peripheral nerve hyperexcitability (PNH) syndromes, which manifests with gross fasciculations, muscle undulation, twitching, and cramps, with or without autonomic and sensory symptoms. The diagnosis relies on characteristic electromyogram findings and the presence of anti-leucine-rich glial inactivated 1 and anti-contactin-associated protein 2 antibodies in the serum. Here, we report the case of a 21-year-old woman, who presented with extremities and tongue myokymia whose electromyogram findings were compatible with PNH, albeit seronegative for antibodies. Neuromuscular ultrasound was performed showing high-frequency rotatory, to-and-fro, high-amplitude movement of superficial and deep muscle fascicles, more prominent in the proximal than distal muscles. Neuromuscular ultrasound may be a useful adjunct in the diagnosis of PNH.

Generalized myokymia, or neuromyotonia, or both in dogs with or without spinocerebellar ataxia.

BACKGROUND: KCNJ10 and CAPN1 variants cause "spinocerebellar" ataxia in dogs, but their association with generalized myokymia and neuromyotonia remains unclear. OBJECTIVE: To investigate the association between KCNJ10 and CAPN1 and myokymia or neuromyotonia, with or without concurrent spinocerebellar ataxia. ANIMALS: Thirty-three client-owned dogs with spinocerebellar ataxia, myokymia neuromytonia, or a combination of these signs. METHODS: Genetic analysis of a cohort of dogs clinically diagnosed with spinocerebellar ataxia, myokymia or neuromyotonia. KCNJ10 c.627C>G and CAPN1 c.344G>A variants and the coding sequence of KCNA1, KCNA2, KCNA6, KCNJ10 and HINT1 were sequenced using DNA extracted from blood samples. RESULTS: Twenty-four Jack Russell terriers, 1 Jack Russell terrier cross, 1 Dachshund and 1 mixed breed with spinocerebellar ataxia were biallelic (homozygous) for the KCNJ10 c.627C>G variant. Twenty-one of those dogs had myokymia, neuromyotonia, or both. One Parson Russell terrier with spinocerebellar ataxia alone was biallelic for the CAPN1 c.344G>A variant. Neither variant was found in 1 Jack Russell terrier with ataxia alone, nor in 3 Jack Russell terriers and 1 Yorkshire terrier with myokymia and neuromyotonia alone. No other causal variants were found in the coding sequence of the investigated candidate genes in these latter 5 dogs. CONCLUSION: The KCNJ10 c.627C>G variant, or rarely the CAPN1 c.344G>A variant, was confirmed to be the causal variant of spinocerebellar ataxia. We also report the presence of the KCNJ10 c.627C>G variant in the Dachshund breed. In dogs with myokymia and neuromyotonia alone the reported gene variants were not found. Other genetic or immune-mediated causes should be investigated to explain the clinical signs of these cases.

Severe and rare neurological manifestations following COVID-19 infection in children: A Malaysian tertiary centre experience.

INTRODUCTION: Since the emergence of COVID-19, we have experienced potent variants and sub-variants of the virus with non-specific neurological manifestations. We observed a surge of the Omicron variant of COVID-19 patients with neurological manifestations where less cases of multisystem inflammatory syndrome in children (MIS-C) were reported. This article describes our experience of children with severe and rare neurological manifestations following COVID-19 infection. METHODS: This is a retrospective observational case series of patients under 18 years old who fulfilled the WHO COVID-19 case definition and were referred to our paediatric neurology unit at Hospital Tunku Azizah Kuala Lumpur. Their demographic data, neurological symptoms, laboratory and supporting investigations, neuroimaging, treatment and outcomes were collected and analysed. RESULTS: There were eleven patients with neurological manifestations who fulfilled the WHO COVID-19 case definition. Nine patients presented with seizures and/or encephalopathy, one patient with eye opsoclonus and another patient with persistent limbs myokymia. Based on the history, clinical, electrophysiological and radiological findings, two of them had febrile infection-related epilepsy syndrome, two had acute disseminated encephalomyelitis, two had acute necrotising encephalopathy of childhood, one each had hemiconvulsion-hemiplegia-epilepsy syndrome, acute encephalopathy with bilateral striatal necrosis, hemi-acute encephalopathy with biphasic seizures and reduced diffusion, infection-associated opsoclonus and myokymia. CONCLUSIONS: This case series highlighted a wide spectrum of neurological manifestations of COVID-19 infection. Early recognition and prompt investigations are important to provide appropriate interventions. It is essential that these investigations should take place in a timely fashion and COVID-19 quarantine period should not hinder the confirmation of various presenting clinical syndromes.

An activator of voltage-gated K+ channels Kv1.1 as a therapeutic candidate for episodic ataxia type 1.

Loss-of-function mutations in the KCNA1(Kv1.1) gene cause episodic ataxia type 1 (EA1), a neurological disease characterized by cerebellar dysfunction, ataxic attacks, persistent myokymia with painful cramps in skeletal muscles, and epilepsy. Precision medicine for EA1 treatment is currently unfeasible, as no drug that can enhance the activity of Kv1.1-containing channels and offset the functional defects caused by KCNA1 mutations has been clinically approved. Here, we uncovered that niflumic acid (NFA), a currently prescribed analgesic and anti-inflammatory drug with an excellent safety profile in the clinic, potentiates the activity of Kv1.1 channels. NFA increased Kv1.1 current amplitudes by enhancing the channel open probability, causing a hyperpolarizing shift in the voltage dependence of both channel opening and gating charge movement, slowing the OFF-gating current decay. NFA exerted similar actions on both homomeric Kv1.2 and heteromeric Kv1.1/Kv1.2 channels, which are formed in most brain structures. We show that through its potentiating action, NFA mitigated the EA1 mutation-induced functional defects in Kv1.1 and restored cerebellar synaptic transmission, Purkinje cell availability, and precision of firing. In addition, NFA ameliorated the motor performance of a knock-in mouse model of EA1 and restored the neuromuscular transmission and climbing ability in Shaker (Kv1.1) mutant Drosophila melanogaster flies (Sh5). By virtue of its multiple actions, NFA has strong potential as an efficacious single-molecule-based therapeutic agent for EA1 and serves as a valuable model for drug discovery.

Basket to Purkinje Cell Inhibitory Ephaptic Coupling Is Abolished in Episodic Ataxia Type 1.

Dominantly inherited missense mutations of the KCNA1 gene, which encodes the KV1.1 potassium channel subunit, cause Episodic Ataxia type 1 (EA1). Although the cerebellar incoordination is thought to arise from abnormal Purkinje cell output, the underlying functional deficit remains unclear. Here we examine synaptic and non-synaptic inhibition of Purkinje cells by cerebellar basket cells in an adult mouse model of EA1. The synaptic function of basket cell terminals was unaffected, despite their intense enrichment for KV1.1-containing channels. In turn, the phase response curve quantifying the influence of basket cell input on Purkine cell output was maintained. However, ultra-fast non-synaptic ephaptic coupling, which occurs in the cerebellar 'pinceau' formation surrounding the axon initial segment of Purkinje cells, was profoundly reduced in EA1 mice in comparison with their wild type littermates. The altered temporal profile of basket cell inhibition of Purkinje cells underlines the importance of Kv1.1 channels for this form of signalling, and may contribute to the clinical phenotype of EA1.

[Clinical and neuroelectrophysiological characteristics of primary peripheral nerve hyperexcitability syndrome].

Objective: To investigate the clinical and neuroelectrophysiological characteristics of patients with primary peripheral nerve hyperexcitability syndrome (PNHS). Methods: The clinical data of 20 patients who were diagnosed with PNHS in Beijing Tiantan Hospital from April 2016 to January 2023 were retrospectively collected. All patients underwent neuroelectrophysiological examinations. Clinical and electrophysiological characteristics were compared between the antibody positive and antibody negative groups, according to serum and cerebrospinal fluid anti-contactin-associated protein-like 2 (CASPR2) and/or anti-leucine-rich glioma-inactivated protein 1 (LGI-1) antibodies. Results: There were 12 males and 8 females, with a mean age of (44.0±17.2) years and the disease course of [M (Q1, Q3)] 2.3 (1.1, 11.5) months. Motor symptoms included fasciculations, myokymia, muscle pain, cramps, and stiffness. These symptoms were commonly seen in the lower limbs (17 patients), followed by upper limbs (11 patients), face (11 patients) and trunk (9 patients). Nineteen (19/20) patients had sensory abnormalities and/or autonomic dysfunction, 13 patients had central nervous system involvement, and 5 patients had concomitant lung cancer or thymic lesions. The characteristic spontaneous potentials on needle electromyography (EMG) were myokymia potential (19 patients), fasciculation potential (12 patients), spastic potential (3 patients), neuromyotonic potential (1 patients), etc, which were commonly seen in the lower limb muscles, especially the gastrocnemius muscle(12 patients). After-discharge potential was found in 8 patients, and 7 were in the tibial nerve. Seven patients had positive serum anti-CASPR2 antibodies, and 3 of them had concomitant anti-LGI1 antibodies. And 1 patient had positive serum anti-LGI1 antibody alone. Compared with patients in the antibody negative group (n=12), the patients who had anti-VGKC complex antibodies (n=8) had a shorter course of disease [M (Q1, Q3): 1.8 (1, 2) months vs 9.5 (3.3, 20.3) months, P=0.012], higher incidence of after-discharge potential (6/8 vs 2/12, P=0.019). The immunotherapy regimen (multi-dru, single-drug, no immunotherapy: 6, 2, 0 patients) in antibody-positive patients was different from the antibody-negative group (3, 6, 3 patients, U=21.00, P=0.023). Conclusions: The symptoms of motor nerve hyperexcitation, characteristic EMG spontaneous potentials and after-discharge potentials in PNHS patients are most commonly seen in the lower limbs. Attention should be paid to concomitant sensory and autonomic nerve hyperexcitation. PNHS patients with positive serum anti-CASPR2 antibodies may require immunotherapy with multiple drugs.

Novel Genetic Variants Expand the Functional, Molecular, and Pathological Diversity of KCNA1 Channelopathy.

The KCNA1 gene encodes Kv1.1 voltage-gated potassium channel α subunits, which are crucial for maintaining healthy neuronal firing and preventing hyperexcitability. Mutations in the KCNA1 gene can cause several neurological diseases and symptoms, such as episodic ataxia type 1 (EA1) and epilepsy, which may occur alone or in combination, making it challenging to establish simple genotype-phenotype correlations. Previous analyses of human KCNA1 variants have shown that epilepsy-linked mutations tend to cluster in regions critical for the channel's pore, whereas EA1-associated mutations are evenly distributed across the length of the protein. In this review, we examine 17 recently discovered pathogenic or likely pathogenic KCNA1 variants to gain new insights into the molecular genetic basis of KCNA1 channelopathy. We provide the first systematic breakdown of disease rates for KCNA1 variants in different protein domains, uncovering potential location biases that influence genotype-phenotype correlations. Our examination of the new mutations strengthens the proposed link between the pore region and epilepsy and reveals new connections between epilepsy-related variants, genetic modifiers, and respiratory dysfunction. Additionally, the new variants include the first two gain-of-function mutations ever discovered for KCNA1, the first frameshift mutation, and the first mutations located in the cytoplasmic N-terminal domain, broadening the functional and molecular scope of KCNA1 channelopathy. Moreover, the recently identified variants highlight emerging links between KCNA1 and musculoskeletal abnormalities and nystagmus, conditions not typically associated with KCNA1. These findings improve our understanding of KCNA1 channelopathy and promise to enhance personalized diagnosis and treatment for individuals with KCNA1-linked disorders.

A case report of lumbosacral plexopathy in a patient with a history of sacral chordoma and radiotherapy: Will the detection of myokymia on the EMG help to solve the case?1.

BACKGROUND: When a patient with a prior history of malignancy and radiotherapy develops progressive weakness as a presentation of plexus involvement, the differential diagnosis usually rests between radiation-induced plexopathy and invasion from recurrent tumor. The presence of myokymic discharges is helpful in differentiating radiation-induced from neoplastic plexopathy. OBJECTIVE: To present a case report of a patient with chordoma, a locally aggressive tumor, who was diagnosed with recurrent tumor accompanied by the occurrence of myokymia in needle electromyographic examination. METHOD: A 55-year-old male patient with a history of chordoma and radiotherapy presented to our outpatient clinic with complaints of foot drop, and impaired walking for two months. His latest magnetic resonance imaging (MRI) which was performed three months earlier did not show recurrence. Upon electromyographic evaluation, myokymia, the pathognomic electromyography abnormal wave for radiation plexopathy was detected supporting a diagnosis of radiation plexitis rather than recurrent neoplastic invasion. One month later he presented with more severe pain and was re-evaluated by an MRI, on which a mass was detected indicating relapse. CONCLUSION: With this case report, we would like to emphasize that the behaviour of the tumor should be considered and imaging should be repeated when tumors display aggressive or recurrent behaviour.

Myokymia in a Patient with Chronic Inflammatory Demyelinating Polyradiculoneuropathy.

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an acquired, immune-mediated neuropathy affecting peripheral nerves and nerve roots. It is characterized by symmetric weakness involving both proximal and distal muscles; it can be relapsing-remitting or progressive in course. The clinical manifestations of CIDP are various and may present with atypical features, like myokymia, tremor, or tremor-like phenomena, which may mislead the clinician in diagnosis.

Episodic ataxia type 2 (EA2) with interictal myokymia and focal dystonia.

Episodic ataxia type 1 and 2 (EA1 and EA2) are the most well-described of the episodic ataxias. They are autosomal dominantly inherited early-onset diseases characterized by attacks of cerebellar dysfunction. EA1 is clinically characterized by short episodes of ataxia with interictal myokymia, whereas EA2 is characterized by longer-lasting recurrent ataxia, slurred speech, and interictal nystagmus. We report on a patient with EA2 with interictal focal dystonia and also interictal myokymia, which is hitherto not reported as an interictal feature associated to EA2. The patient carries a previously described heterozygous pathogenic de novo frameshift variant in the CACNA1A gene, establishing the diagnosis of EA2. She had symptom onset at age 13 and from age 48 she developed interictal myokymia and focal dystonia as illustrated in Supplemental Movie S1. We conclude that interictal myokymia and focal dystonia may be interictal features associated to EA2 caused by the cerebellar pathophysiology of EA2. Episodes of ataxia were successfully treated with acetazolamide in low dose, whereas the interictal features were unresponsive to acetazolamide.

Facial involvement in multiple sclerosis.

BACKGROUND: Multiple sclerosis (MS) can present with facial symptoms and signs, such as facial palsy, myokymia, and hemifacial spasm. Considering the importance of early diagnosis, treatment, and exclusion of causes other than MS, we aimed to assess the prevalence of these disorders in patients with MS. METHODS: MS patients who were referred to the Isfahan MS clinic from March 2021 to March 2022 were observed for facial presentations of the disease. A checklist of patients' baseline characteristics and disease features were then completed through patient interview and medical files. RESULTS: Of the total of 2260 MS patients who were assessed, 3.27% had facial palsy, 1.28% had myokymia, and 0.84% presented with hemifacial spasm. The mean age of facial symptom onset was 30.74, 29.07, and 31.37 years, respectively. No relationship was found between the type of facial presentation and factors such as age, gender, subtype of MS, affected side of face, and time of presentation. CONCLUSION: On the grounds that facial disorders can be the first presentation of MS, patients with atypical features of other common facial diseases such as Bell's palsy should therefore be carefully assessed and followed for any clues pertaining to the diagnosis of MS.

A reverse genetics and genomics approach to gene paralog function and disease: Myokymia and the juxtaparanode.

The leucine-rich glioma-inactivated (LGI) family consists of four highly conserved paralogous genes, LGI1-4, that are highly expressed in mammalian central and/or peripheral nervous systems. LGI1 antibodies are detected in subjects with autoimmune limbic encephalitis and peripheral nerve hyperexcitability syndromes (PNHSs) such as Isaacs and Morvan syndromes. Pathogenic variations of LGI1 and LGI4 are associated with neurological disorders as disease traits including familial temporal lobe epilepsy and neurogenic arthrogryposis multiplex congenita 1 with myelin defects, respectively. No human disease has been reported associated with either LGI2 or LGI3. We implemented exome sequencing and family-based genomics to identify individuals with deleterious variants in LGI3 and utilized GeneMatcher to connect practitioners and researchers worldwide to investigate the clinical and electrophysiological phenotype in affected subjects. We also generated Lgi3-null mice and performed peripheral nerve dissection and immunohistochemistry to examine the juxtaparanode LGI3 microarchitecture. As a result, we identified 16 individuals from eight unrelated families with loss-of-function (LoF) bi-allelic variants in LGI3. Deep phenotypic characterization showed LGI3 LoF causes a potentially clinically recognizable PNHS trait characterized by global developmental delay, intellectual disability, distal deformities with diminished reflexes, visible facial myokymia, and distinctive electromyographic features suggestive of motor nerve instability. Lgi3-null mice showed reduced and mis-localized Kv1 channel complexes in myelinated peripheral axons. Our data demonstrate bi-allelic LoF variants in LGI3 cause a clinically distinguishable disease trait of PNHS, most likely caused by disturbed Kv1 channel distribution in the absence of LGI3.

Morvan's syndrome Presenting with Psychiatric Manifestations - A Case Report and Review of the Literature.

The term "la chorιe fibrillare" was used by the French physician Augustine Marie Morvan to describe a syndrome showing hyperactivity features involving the central, autonomic, and peripheral nervous system. The central hyperactivity symptoms are confusion, behavioral problems, hallucinations, myoclonus, and insomnia; the autonomic hyperactivity symptoms are hyperhidrosis and variations in blood pressure; and peripheral hyperexcitability is characterized by painful cramps, myokymia, and neuromyotonia. Here, we present a case that has typical features of Morvan's syndrome and provides a brief description based on available literature.

Clinical Reasoning: A 73-Year-Old Woman With Episodic Dysarthria and Horizontal Binocular Diplopia.

A 73-year-old woman presented with transient episodes of dysarthria and horizontal diplopia. She had stereotactic radiosurgery 18 years prior for a retroclival meningioma. Neurologic examination was notable for right-sided tongue deviation, tongue fasciculations, and intermittent impaired abduction of the right eye. MRI ruled out recurrence or progression of the retroclival meningioma. EEG failed to reveal electrographic seizures. EMG showed spontaneous depolarizations in bursts that sounded like "marching soldiers" in the right hemitongue, consistent with myokymia. Focal myokymia is an unusual EMG finding that is usually seen in demyelinating disorders, after radiation, or in neoplastic/inflammatory conditions. The clinical presentation and EMG findings were most consistent with delayed radiation-induced myokymia. Similar cases of transient dysarthria and tongue myokymia from radiation have been infrequently reported in the literature; however, this case uniquely exhibited additional episodes of transient horizontal diplopia, which was possibly from ocular myokymia or neuromyotonia. Although there are limited data, sodium channel inhibitors (e.g., carbamazepine, oxcarbazepine, and lacosamide) have shown some success to provide symptomatic relief, most likely secondary to their ability to inhibit underlying peripheral nerve hyperexcitability. Our patient was started on lacosamide 50 mg twice a day with a notable decrease in symptom frequency. This case illustrates the importance of detailed clinical and electrodiagnostic studies in making the diagnosis of delayed radiation-induced myokymia with episodic dysarthria and provides guidance on potential therapeutics.