Myokymia, neuromyotonia, dermatomyositis, and voltage-gated K+ channel antibodies

An Unusual Presentation of Dermatomyositis With Muscle Hypertrophy

Peripheral nerve hyperexcitability is a rare disorder characterized by spontaneous motor unit activity. Although peripheral nerve hyperexcitability is seen in multiple immune-mediated neurological conditions, an association with dermatomyositis has rarely been reported. We present a 65-year-old woman with serological and muscle biopsy features of dermatomyositis who also developed marked muscle hypertrophy, stiffness, and delayed relaxation along with electrodiagnostic features of peripheral nerve hyperexcitability such as that seen in Isaacs syndrome.

Eyelid myokymia caused by a trigeminal schwannoma as determined by the trigeminal-evoked blink reflex

A 57-year-old man had trigeminal schwannoma in Meckel's cave with eyelid myokymia only. The evaluation of the trigeminal-evoked blink reflex was useful for confirming eyelid myokymia and contributed to surgical decision-making. In patients with persistent eyelid myokymia, neurophysiological and imaging evaluations may be useful for determining the underlying pathophysiology.

The Ophthalmic Side Effects of Topiramate: A Review

Topiramate (TPM) is a sulfonamide drug with multiple modes of action. It inhibits carbonic anhydrase, blocks sodium channels, enhances potassium channels, and stimulates postsynaptic gamma-aminobutyric acid (GABA) receptors. Pharmacists Joe Gardocki and Bruce Maryanoff synthesized TPM for the first time in 1979. The FDA did not approve it for medical use in the US until 1996. Around 2004, it was authorized for the prevention of migraine headaches.

TPM, like any medication, has several side effects. Common aftermaths include weight loss, diarrhea, dizziness, sleepiness, fatigue, and coordination issues. Some people may experience mental health issues like memory problems, confusion, and speech or language difficulties. The most well-known ocular side effects of TPM are choroidal effusion syndrome, angle-closure glaucoma, and myopic shift. Aside from these, other ophthalmic adverse effects may arise in some people, including retinal problems, uveitis, visual field defects, myokymia, and neuro-ophthalmology complications. If such complications are not identified and treated promptly, they can be severe and vision-threatening, potentially leading to permanent blindness.

TPM's application as a standalone and adjunctive therapy has increased over time. In 2019, more than 10 million prescriptions of TPM were issued. Due to its extensive use, medical professionals and patients must be aware of its potential repercussions, especially ophthalmic issues. The current review paper likewise makes a step in this direction. This article's primary purpose is to educate readers by providing a comprehensive assessment of the research on TPM's ocular side effects. All the information has been collected via a thorough search of the Google Search Engine and PubMed.

Neuromuscular junction disorders beyond myasthenia gravis

PURPOSE OF REVIEW

To give an overview of the recent data on three autoimmune neuromuscular junction disorders with the recent Food Drug Administration (FDA) approval of amifampridine [3,4-Diaminopyridine (3,4-DAP) and 3,4-diaminopyridine phosphate (3,4-DAPP) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS).

RECENT FINDINGS

In LEMS, the most important recent development is the introduction of FDA approved amifampridine for the symptomatic treatment. Randomized controlled studies showed an extremely effective improvement with amifampridine with daily dose of ≤ 80 mg with minimal side reactions. The next important development is in the electrodiagnostic criteria. Now 10 s exercise and an incremental response ≥ 60% either after 10 s exercise or at the high-rate stimulation in the repetitive nerve stimulation test are recommended as the standard tests.In 2016, myasthenia-gravis Lambert-Eaton overlap syndrome (MLOS) was coined as new syndrome for patients with myasthenia gravis and LEMS combined symptoms in same patients.In Isaacs syndrome, voltage gated calcium channel antibody order is no longer recommended because of low specificity for immunotherapy responsive disorders. Instead, ' leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated like-2 (CASPR2) autoantibody tests' are recommended.

SUMMARY

In LEMS, amifampridine (3,4 DAP and 3,4-DAPP) is approved by the FDA as an effective symptomatic treatment. MLOS is coined as new syndrome recently. In Isaacs syndrome, LGI1 and CASPR2 antibody tests are recommended.

Topiramate-Induced Persistent Eyelid Myokymia

Background. Topiramate (TPM) is a psychotropic drug, which is used mainly as an antiepileptic drug and now over the years is used for a wider range of indications, including migraine prophylaxis and binge eating disorders. Although ocular side effects of Topiramate have been frequently reported, neuroophthalmologic manifestations such as myokymia are rarely reported. Case Presentation. This case report presents a case of a 47-year-old woman who had begun TPM for binge eating problem. She developed unilateral long standing lower eyelid twitching, which progressed to upper eyelid and eyebrow at the same side. The patient was not a smoker or excessive alcohol or caffeine abuser. Increasing the resting time and changing life style made no significant changes in her eyelid twitching. There was no definite evidence by neuroimaging and clinical or laboratory evaluations causing eyelid myokymia. The symptoms resolved with discontinuation of TPM. Conclusion. Although eyelid myokymia is a benign and self-limited condition, it sometimes becomes a source of distress in chronic long standing cases. Physicians should be aware of the neuroophthalmologic side effects of this drug.

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.

Understanding autoimmunity: The ion channel perspective

Ion channels are integral membrane proteins that orchestrate the passage of ions across the cell membrane and thus regulate various key physiological processes of the living system. The stringently regulated expression and function of these channels hold a pivotal role in the development and execution of various cellular functions. Malfunction of these channels results in debilitating diseases collectively termed channelopathies. In this review, we highlight the role of these proteins in the immune system with special emphasis on the development of autoimmunity. The role of ion channels in various autoimmune diseases is also listed out. This comprehensive review summarizes the ion channels that could be used as molecular targets in the development of new therapeutics against autoimmune disorders.

Corticomotoneuronal function and hyperexcitability in acquired neuromyotonia

Acquired neuromyotonia encompasses a group of inflammatory disorders characterized by symptoms reflecting peripheral nerve hyperexcitability, which may be clinically confused in the early stages with amyotrophic lateral sclerosis. Despite a clear peripheral nerve focus, it remains unclear whether the ectopic activity in acquired neuromyotonia receives a central contribution. To clarify whether cortical hyperexcitability contributes to development of clinical features of acquired neuromyotonia, the present study investigated whether threshold tracking transcranial magnetic stimulation could detect cortical hyperexcitability in acquired neuromyotonia, and whether this technique could differentiate acquired neuromyotonia from amyotrophic lateral sclerosis. Cortical excitability studies were undertaken in 18 patients with acquired neuromyotonia and 104 patients with amyotrophic lateral sclerosis, with results compared to 62 normal controls. Short-interval intracortical inhibition in patients with acquired neuromyotonia was significantly different when compared to patients with amyotrophic lateral sclerosis (averaged short interval intracortical inhibition acquired neuromyotonia 11.3 ± 1.9%; amyotrophic lateral sclerosis 2.6 ± 0.9%, P < 0.001). In addition, the motor evoked potential amplitudes (acquired neuromyotonia 21.0 ± 3.1%; amyotrophic lateral sclerosis 38.1 ± 2.2%, P < 0.0001), intracortical facilitation (acquired neuromyotonia −0.9 ± 1.3%; amyotrophic lateral sclerosis −2.3 ± 0.6%, P < 0.0001), resting motor thresholds (acquired neuromyotonia 62.2 ± 1.6%; amyotrophic lateral sclerosis 57.2 ± 0.9%, P < 0.05) and cortical silent period durations (acquired neuromyotonia 212.8 ± 6.9 ms; amyotrophic lateral sclerosis 181.1 ± 4.3 ms, P < 0.0001) were significantly different between patients with acquired neuromyotonia and amyotrophic lateral sclerosis. Threshold tracking transcranial magnetic stimulation established corticomotoneuronal integrity in acquired neuromyotonia, arguing against a contribution of central processes to the development of nerve hyperexcitability in acquired neuromyotonia.

Myokymia and neuromyotonia in 37 Jack Russell terriers

The clinical and clinicopathological characteristics, treatment and outcome of vermicular muscle contractions (myokymia) and generalized muscle stiffness (neuromyotonia) in 37 Jack Russell terriers were evaluated retrospectively. Thirty dogs were affected by both disorders, whereas seven were presented with myokymia and never developed neuromyotonia. Clinical signs started at the mean age of 8 months. Except for signs of myokymia and neuromyotonia, clinical and neurological examination was normal in all dogs. Thirty dogs demonstrated typical signs of hereditary ataxia. Changes in serum chemistry included increased creatine kinase, aspartate aminotransferase and alanine aminotransferase concentrations. Electromyographic abnormalities, especially in muscles showing macroscopically visible myokymia, consisted of semirhythmic bursts of doublet, triplet, or multiplet discharges of a single motor unit. The amplitudes varied between 80 μV and 1 mV and occurred with an interburst frequency between 10 and 40 Hz and an intraburst frequency between 150 and 280 Hz. Most dogs were treated with a sodium channel blocker with variable results. Seven dogs died (most likely because of hyperthermia) or were euthanased during a neuromyotonic attack; 15 dogs were euthanased due to worsening of clinical signs, or lack of or no long-lasting effect of medication, and three were euthanased for unknown or unrelated reasons. Nine dogs were lost to follow-up and three were still alive 5-10.5 years after the start of clinical signs. In conclusion, young Jack Russell terriers with myokymia and neuromyotonia should undergo a complete blood and electrophysiological examination. Long-term prognosis is not favourable.

Myokymia and neuromyotonia in a cat

A 6-year-old spayed female domestic shorthair cat was examined because of a 2-week history of rhythmic muscle movements. Physical examination revealed thoracic limb rigidity, contracture of the carpi, generalized muscle atrophy, and rhythmic rippling of the muscles of all 4 limbs. Results of a CBC and serum biochemistry profile were unremarkable other than high creatine kinase activity. Electromyography revealed unique high-frequency discharges, including rhythmic bursts of single motor unit potentials appearing as doublets (myokymia) and more prolonged bursts of nonrhythmic motor unit potentials with characteristic waning amplitudes (neuromyotonia). Histologic examination of muscle biopsy specimens revealed noninflammatory necrotizing myopathy with regeneration. The cat did not respond to treatment with carbamazepine or prednisone but improved rapidly after treatment with phenytoin was initiated. Six months after initial examination, electromyography revealed a substantial decrease in the amount of spontaneous activity in previously affected muscles. However, the myokymic and neuromyotonic discharges were still present, albeit with a substantial decrease in frequency.

The neurobiology of antiepileptic drugs for the treatment of nonepileptic conditions

Antiepileptic drugs (AEDs) are commonly prescribed for nonepileptic conditions, including migraine headache, chronic neuropathic pain, mood disorders, schizophrenia and various neuromuscular syndromes. In many of these conditions, as in epilepsy, the drugs act by modifying the excitability of nerve (or muscle) through effects on voltage-gated sodium and calcium channels or by promoting inhibition mediated by gamma-aminobutyric acid (GABA) A receptors. In neuropathic pain, chronic nerve injury is associated with the redistribution and altered subunit compositions of sodium and calcium channels that predispose neurons in sensory pathways to fire spontaneously or at inappropriately high frequencies, often from ectopic sites. AEDs may counteract this abnormal activity by selectively affecting pain-specific firing; for example, many AEDs suppress high-frequency action potentials by blocking voltage-activated sodium channels in a use-dependent fashion. Alternatively, AEDs may specifically target pathological channels; for example, gabapentin is a ligand of alpha2delta voltage-activated calcium channel subunits that are overexpressed in sensory neurons after nerve injury. Emerging evidence suggests that effects on signaling pathways that regulate neuronal plasticity and survival may be a factor in the delayed clinical efficacy of AEDs in some neuropsychiatric conditions, including bipolar affective disorder.