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.

Acetazolamide-Induced Periorbital Myokymia: A Case Report

Acetazolamide, a carbonic anhydrase inhibitor, is primarily used in the treatment of glaucoma, due to its role in decreasing intraocular pressure by lowering the production of aqueous humor. Additionally, by lowering cerebrospinal fluid (CSF) production, it is also used in the treatment of raised intracranial pressure. Drug-induced myokymia has rarely been reported, with known triggers being clozapine, gabapentin and flunarizine, and topiramate. Acetazolamide-induced myokymia itself has only been reported once before, to the best of our knowledge, and the exact mechanism behind this occurrence remains unknown. We, therefore, report a rare case of periorbital myokymia induced by the use of acetazolamide in a patient diagnosed with idiopathic intracranial hypertension. The nature of her symptoms was significant, as they caused her considerable distress, and subsided almost immediately upon discontinuation of the drug.

Rituximab Was Effective in Relieving Symptoms of Isaacs Syndrome: A Case Report

We presented a 23-year-old patient who had experienced neuromyotonia in his left leg. Although he tested negative for anti-LGI1 and anti-CASPR2 antibodies, we diagnosed him with Isaacs syndrome due to myokymic discharges on electromyography and symptoms being relieved by intravenous methylprednisolone (IVMP) and intravenous immunoglobulin (IVIg). IVMP, IVIg, plasma exchange, or cyclosporine treatment did not provide a long-term response; however, rituximab showed long-term improvement. Rituximab should be considered early in the treatment of patients with antibody-negative Isaacs syndrome who are responsive to immunotherapy, including IVMP, IVIg, and plasma exchange, and have long-term symptoms that are hard to control.

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.

Pseudo-pheochromocytoma due to obstructive sleep apnea: a case report

SUMMARY

Obstructive sleep apnea (OSA) is a condition of intermittent nocturnal upper airway obstruction. OSA increases sympathetic drive which may result in clinical and biochemical features suggestive of pheochromocytoma. We present the case of a 65-year-old male with a 2.9-cm left adrenal incidentaloma on CT, hypertension, symptoms of headache, anxiety and diaphoresis, and persistently elevated 24-h urine norepinephrine (initially 818 nmol/day (89-470)) and normetanephrine (initially 11.2 µmol/day (0.6-2.7)). He was started on prazosin and underwent left adrenalectomy. Pathology revealed an adrenal corticoadenoma with no evidence of pheochromocytoma. Over the next 2 years, urine norepinephrine and normetanephrine remained significantly elevated with no MIBG avid disease. Years later, he was diagnosed with severe OSA and treated with continuous positive airway pressure. Urine testing done once OSA was well controlled revealed complete normalization of urine norepinephrine and normetanephrine with substantial symptom improvement. It was concluded that the patient never had a pheochromocytoma but rather an adrenal adenoma with biochemistry and symptoms suggestive of pheochromocytoma due to untreated severe OSA. Pseudo-pheochromocytoma is a rare presentation of OSA and should be considered on the differential of elevated urine catecholamines and metanephrines in the right clinical setting.

LEARNING POINTS

Obstructive sleep apnea (OSA) is a common condition among adults. OSA may rarely present as pseudo-pheochromocytoma with symptoms of pallor, palpitations, perspiration, headache, or anxiety. OSA should be considered on the differential of elevated urine catecholamines and metanephrines, especially in patients with negative metaiodobenzylguanidine (MIBG) scan results.

Post-Irradiation Facial Neuromyotonia/Myokymia: A Hemifacial Spasm Mimic

Background:

Hemifacial spasm is diagnosed on a clinical base, with certain atypical features alerting the physician for mimics.

Phenomenology shown:

Hemifacial neuromyotonia/myokymia characterized by tonic hemifacial contraction followed by multifocal undulating hemifacial twitches.

Educational value:

These features are a red flag for (post-irradiation) facial neuromyotonia/myokymia which generally responds well to low dose carbamazepine.

Video Presentation of Myokymia in a Snakebite

Patients with snakebites have highly variable presentations, and delayed diagnosis may lead to unfavorable outcomes. Here, we describe the case of a snakebite in a 23-year-old male who presented with myokymias. On management with mechanical ventilation and anti-snake venom, the patient improved and was discharged. The presence of myokymias may be an early clue to diagnosis and the need for mechanical ventilation in a patient with a snakebite.

Eribulin Mesylate-related Multifocal Demyelinating Neuropathy with Myokymia in a Breast Cancer Patient

We herein report a 48-year-old woman receiving eribulin mesylate for breast cancer who presented with gait disorder, distal limb paresthesia, and weakness progressing monthly. A nerve conduction study indicated demyelination with multifocal conduction block. Considering the immune-mediated pathology of her condition, she was administered intravenous immunoglobulin. Her neurological symptoms improved promptly after intravenous immunoglobulin therapy and eribulin withdrawal. Furthermore, the limb myokymia seen at the time of admission disappeared. Her symptoms continued to improve without additional treatment. We conclude that eribulin was a rare cause of demyelinating neuropathy with multifocal conduction block derived from immune-mediated pathology.

International veterinary canine dyskinesia task force ECVN consensus statement: Terminology and classification

Movement disorders are a heterogeneous group of clinical syndromes in humans and animals characterized by involuntary movements without changes in consciousness. Canine movement disorders broadly include tremors, peripheral nerve hyperexcitability disorders, paroxysmal dyskinesia, and dystonia. Of these, canine paroxysmal dyskinesias remain one of the more difficult to identify and characterize in dogs. Canine paroxysmal dyskinesias include an array of movement disorders in which there is a recurrent episode of abnormal, involuntary, movement. In this consensus statement, we recommend standard terminology for describing the various movement disorders with an emphasis on paroxysmal dyskinesia, as well as a preliminary classification and clinical approach to reporting cases. In the clinical approach to movement disorders, we recommend categorizing movements into hyperkinetic vs hypokinetic, paroxysmal vs persistent, exercise‐induced vs not related to exercise, using a detailed description of movements using the recommended terminology presented here, differentiating movement disorders vs other differential diagnoses, and then finally, determining whether the paroxysmal dyskinesia is due to either inherited or acquired etiologies. This consensus statement represents a starting point for consistent reporting of clinical descriptions and terminology associated with canine movement disorders, with additional focus on paroxysmal dyskinesia. With consistent reporting and identification of additional genetic mutations responsible for these disorders, our understanding of the phenotype, genotype, and pathophysiology will continue to develop and inform further modification of these recommendations.

Quantitative analysis of myokymic discharges in radiation versus nonradiation cases

INTRODUCTION

Myokymic discharges are classically associated with nerve injury from prior radiation but may occur in other neuromuscular disorders. Using quantitative analysis we aimed to identify the spectrum of conditions in which myokymic discharges are present and determine if there are electrophysiological features that distinguish postradiation from nonradiation causes of myokymia.

METHODS

We reviewed the clinical history of all patients examined in our electromyography labs with myokymic discharges recorded from June 2017 to February 2020. Quantitative analysis of each myokymic discharge was performed using a custom MATLAB script, assessing features such as burst frequency, spikes per burst, and burst regularity.

RESULTS

Eighty-eight distinct myokymic discharges (70 patients) were analyzed: 51 postradiation recordings from 35 patients and 37 recordings from 35 nonradiation patients. The diagnostic spectrum of nonradiation cases was diverse, with common causes being median neuropathy (n = 8), cervical (n = 7), and lumbar (n = 5) radiculopathy, and motor neuron disease (n = 5). On quantitative analysis, postradiation myokymia had an increased burst-to-silence ratio (median, 0.29; nonradiation, 0.08) and greater peak number (median, 15; nonradiation, 7). Except for one patient with hereditary peripheral nerve hyperexcitability, all patients who had two or more muscles demonstrating myokymic discharges belonged to postradiation group.

CONCLUSIONS

Myokymic discharges can be seen in diverse neuromuscular conditions; most common in our cohort was chronic median neuropathy. Postradiation myokymia appears to have distinguishing morphological features when quantitatively analyzed compared with nonradiation cases.

Musculoskeletal Features without Ataxia Associated with a Novel de novo Mutation in KCNA1 Impairing the Voltage Sensitivity of Kv1.1 Channel

The KCNA1 gene encodes the α subunit of the voltage-gated Kv1.1 potassium channel that critically regulates neuronal excitability in the central and peripheral nervous systems. Mutations in KCNA1 have been classically associated with episodic ataxia type 1 (EA1), a movement disorder triggered by physical and emotional stress. Additional features variably reported in recent years include epilepsy, myokymia, migraine, paroxysmal dyskinesia, hyperthermia, hypomagnesemia, and cataplexy. Interestingly, a few individuals with neuromyotonia, either isolated or associated with skeletal deformities, have been reported carrying variants in the S2–S3 transmembrane segments of Kv1.1 channels in the absence of any other symptoms. Here, we have identified by whole-exome sequencing a novel de novo variant, T268K, in KCNA1 in a boy displaying recurrent episodes of neuromyotonia, muscle hypertrophy, and skeletal deformities. Through functional analysis in heterologous cells and structural modeling, we show that the mutation, located at the extracellular end of the S3 helix, causes deleterious effects, disrupting Kv1.1 function by altering the voltage dependence of activation and kinetics of deactivation, likely due to abnormal interactions with the voltage sensor in the S4 segment. Our study supports previous evidence suggesting that specific residues within the S2 and S3 segments of Kv1.1 result in a distinctive phenotype with predominant musculoskeletal presentation.

Paroxysmal Symptoms in Multiple Sclerosis-A Review of the Literature

Paroxysmal symptoms are well-recognized manifestations of multiple sclerosis (MS). These are characterized by multiple, brief, sudden onset, and stereotyped episodes. They manifest as motor, sensory, visual, brainstem, and autonomic symptoms. When occurring in the setting of an established MS, the diagnosis is relatively straightforward. Conversely, the diagnosis is significantly more challenging when they occur as the initial manifestation of MS. The aim of this review is to summarize the various forms of paroxysmal symptoms reported in MS, with emphasis on the clinical features, radiological findings and treatment options.

One Bite, Two Patients: Disparate Clinical Courses Following Simultaneous Crotalus oreganus abyssus Envenomation

A number of crotaline species have been associated with neurotoxic envenomation in North America. One clinical sign that can occur is myokymia: fine, involuntary, wave-like muscle movements occurring at regular intervals. We report an unusual scenario in which a single snakebite resulted in simultaneous envenomation of 2 patients. Both developed myokymia, with 1 having respiratory compromise. One patient also developed a hypersensitivity reaction to antivenom. Envenomation by the Grand Canyon rattlesnake, Crotalus oreganus abyssus, can produce significant neurotoxicity and resultant respiratory compromise. Antivenom may be helpful but can produce hypersensitivity reactions.

Facial myokymia in inherited peripheral nerve hyperexcitability syndrome

Peripheral nerve hyperexcitability syndrome comprises a heterogeneous group of diseases, clinically characterised by myokymia, fasciculation, muscle cramps and stiffness. The causes are either immune mediated or non-immune mediated. Non-immune-mediated forms are mostly genetic, relating to two main genes: KCNQ2 and KCNA1 Patients with KCNQ2 gene mutations typically present with epileptic encephalopathy, benign familial neonatal seizures and myokymia, though occasionally with purely peripheral nerve hyperexcitability. We report a woman with marked facial myokymia and distal upper limb contractures whose mother also had subtle facial myokymia; both had the c.G620A (p.R207Q) variant in the KCNQ2 gene. Patients with familial myokymia and peripheral nerve hyperexcitability syndrome should be investigated for KCNQ2 variants. This autosomal dominant condition may respond to antiepileptic medications acting at potassium channels.

Will Tonic Water Stop My Eyelid Twitching?

Eyelid myokymia, commonly referred to as “eyelid twitching”, is a common, benign condition that resolves in most individuals within hours to days; however, chronic cases can persist for several weeks to months, prompting the search for home remedies that may reduce the frequency or duration of symptoms. In this article, we discuss the proposed pathophysiologic mechanism and safety concerns surrounding tonic water as a treatment for eyelid myokymia.

Morvan's syndrome with anti contactin associated protein like 2 - voltage gated potassium channel antibody presenting with syndrome of inappropriate antidiuretic hormone secretion

Morvan's syndrome is a rare autoimmune disorder characterized by triad of peripheral nerve hyperexcitability, autonomic dysfunction, and central nervous system symptoms. Antibodies against contactin-associated protein-like 2 (CASPR2), a subtype of voltage-gated potassium channel (VGKC) complex, are found in a significant proportion of patients with Morvan's syndrome and are thought to play a key role in peripheral as well as central clinical manifestations. We report a patient of Morvan's syndrome with positive CASPR2–anti-VGKC antibody having syndrome of inappropriate antidiuretic hormone as a cause of persistent hyponatremia.

Neuromyotonia in a horse

This article describes the clinical and electromyographic findings of neuromyotonia in a 19‐month‐old male crossbred Quarter Horse that presented with stiffness and muscle asymmetry in the hind limbs as well as sacrococcygeal, paravertebral, and gluteal myokymia. An electromyographic study showed spontaneous continuous muscle fiber activity with high‐frequency discharges, fibrillations, positive sharp waves, fasciculation potentials, and complex repetitive discharges. Histological examination of the gluteal muscle showed a mixed neurogenic and myopathic pattern. The findings are consistent with neuromyotonia.

Identification of a New de Novo Mutation Underlying Regressive Episodic Ataxia Type I

Episodic ataxia type 1 (EA1), a Shaker-like K⁺channelopathy, is a consequence of genetic anomalies in the KCNA1 gene that lead to dysfunctions in the voltage-gated K⁺ channel Kv1. 1. Generally, KCNA1 mutations are inherited in an autosomal dominant manner. Here we report the clinical phenotype of an EA1 patient characterized by ataxia attacks that decrease in frequency with age, and eventually leading to therapy discontinuation. A new de novo mutation (c.932G>A) that changed a highly conserved glycine residue into an aspartate (p.G311D) was identified by using targeted next-generation sequencing. The conserved glycine is located in the S4–S5 linker, a crucial domain controlling Kv1.1 channel gating. In silico analyses predicted the mutation deleterious. Heterologous expression of the mutant (Kv1.1-G311D) channels resulted in remarkably decreased amplitudes of measured current, confirming the identified variant is pathogenic. Collectively, these findings corroborate the notion that EA1 also results from de novo variants and point out that regardless of the mutation-induced deleterious loss of Kv1.1 channel function the ataxia phenotype may improve spontaneously.

Eyelid Myokymia with Concomitant Cerebral Tumour: A Case Report

Eyelid myokymia is a localised movement disorder of the orbicularis oculi muscle with involuntary, fine, continuous, and undulating contractions. Although this entity is thought to be peripheral nerve origin, it rarely occurs with an intracranial lesion. The authors report a case of eyelid myokymia with concomitant cerebral tumour. A 52-year-old woman had a 6-month history of left eyelid myokymia accompanied by upper eyelid ptosis and lower eyelid reverse ptosis. Magnetic resonance imaging showed a solid mass measuring 20 × 25 × 20 mm in the temporal lobe of the cerebral cortex, showing isointense on T1-weighted and hyperintense on T2-weighted images. The clinical diagnosis was cerebral astrocytoma.

Isaacs' syndrome in a patient with dermatomyositis: case report and review of the literature

This is a case report of Isaacs' syndrome in dermatomyositis. The patient presented with proximal muscle weakness, rash, elevated muscle enzyme, myopathic electromyograph and typical muscle biopsy. Ultimately he developed typical symptoms of Isaacs' syndrome which is an autoimmune channelopathy from voltage gated potassium channel antibody (anti-VGKC) leading to dysfunction of axonal discharge at neuromuscular junctions. It shares some similar characteristics with dermatomyositis such as autoimmunity, its association with malignancy and the response to treatment.

Hybanthus calceolaria poisoning in cattle

Hybanthus calceolaria, also known as "papaconha" or "ipepacuanha," is a herbaceous plant found in northeastern Brazil, which is often implicated by farmers as the cause of neurological signs in livestock grazing. Several poisoning outbreaks associated with the ingestion of this plant were observed in cattle in the municipalities of Colônia de Gurguéia in the state of Piauí and Sirinhaém in the state of Pernambuco, Brazil. The main clinical signs were ataxia, recumbency, and myokymia. No significant lesions were observed during necropsy or on histological examination. The disease was experimentally reproduced by the administration of 2 daily doses of 40 g/kg/body weight of the fresh green plant containing fruits. The plants without fruits were nontoxic, which is in accordance with the farmers' information, as it was stated that the poisoning only occurs when the plant is fruiting.

Examination and clinical care of the patient with neuropathy

Examination of a patient with peripheral neuropathy starts with careful questioning of the patient about the history of symptoms and signs and of a possible familial disorder. Several steps are required during examination of the patient with peripheral neuropathy: first the pattern of neuropathy and site of lesions should be determined: roots, nerve trunks, focal, multifocal, length-dependent generalized polyneuropathy, the type of nerve fibers predominantly affected, the association with trophic changes and autonomic dysfunction, the course of the disease ranging from acute inflammatory polyneuritis or fulminant multifocal neuropathy to an extremely slow progression as in Charcot-Marie-Tooth syndromes. At the end of this first contact with the patient, the neurologist must decide which investigations seem necessary and their timing including electrophysiological tests, imaging, CSF examination, blood tests, nerve and muscle biopsy, DNA testing, etc. In some cases, life-threatening manifestations, including weakness of respiratory muscles or swallowing difficulty, or autonomic dysfunction, require urgent therapeutic decisions.

Ten Years' Follow-Up of a Family With Myokymia and Muscle Cramps Without Ataxia

We report 10 years' follow-up of the previously described family with a novel mutation of the KCNA1 gene. The family consisted of 3 affected boys (first seen at ages 3, 11, and 12) and their affected mother and asymptomatic father and sister. They clinically presented with diffuse myokymia, muscle cramps, and lower limb spasticity without ataxia, but episodic ataxia developed later during adolescence and early adulthood. Long-term follow-ups of families with known KCNA1 gene mutation are rarely mentioned in the literature. Treatment with carbamazepine, 600 to 800 mg daily resulted in cessation of muscle cramps and marked improvement of lower leg symptoms. In the youngest child, after 2 years carbamazepine had to be changed to oxcarbazepine because of side effects. Carbamazepine and oxcarbazepine are both effective in treatment of symptoms related to KCNA1 gene mutation. Symptoms will reoccur if treatment is stopped and there is variability of symptom severity between family members.