Neuromyotonia, peripheral neuropathy and myasthenia gravis

Systematic Review of the Clinical Characteristics and Management of Isaac Syndrome

OBJECTIVES

Isaac syndrome (IS) is a condition characterized by peripheral nerve hyperexcitability caused by voltage-gated potassium channel (VGKC)-complex antibodies. Muscle twitching, stiffness, hypertrophy, and dysautonomic characteristics, such as hyperhidrosis, are common manifestations. The syndrome can be autoimmune or paraneoplastic, with thymoma being a common cause of paraneoplastic IS. Furthermore, this condition could be handed down from one generation to another. However, there is limited information regarding outcomes, relapses, associated syndromes, associated malignancies (other than thymoma), and treatment options. Despite its rarity, there remains a need for effective management strategies for patients with IS. To address this gap, we conducted a systematic review to summarize the most common and effective treatments of IS in immunomodulatory agents and symptomatic medications, as well as to describe outcomes, relapses, and associated malignancies. Altogether, this review serves to guide clinical practice recommendations for IS and highlight areas for further research.

METHODS

We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol to conduct a systematic review of cases reposted through the PubMed and Google Scholar databases. The terms "Isaac Syndrome" and "Acquired Neuromyotonia" were used. The Joanna Briggs Institute's critical appraisal tool was used to evaluate the quality of the included studies.

RESULTS

We identified 61 case reports and 4 case series, comprising a total of 70 patients with IS (mean age at onset: 42.5 ± 18 years, and 69% were males). Fourteen cases reported relapses. Thymoma was the most common malignancy associated with IS, followed by lymphoma. Among various serum antibodies, voltage-gated potassium channel-complex antibodies were the most reported antibodies elevated in IS (reported in 38 patients and elevated in 21 patients [55.2%]), followed by acetylcholine ganglionic receptor antibodies, which were reported in 30% of patients (n = 21) and were elevated in 5 cases. The most common electromyography findings were myokymic discharges (n = 22), followed by fasciculations (n = 21) and neuromyotonia (n = 19). For treatment, combining anticonvulsants such as carbamazepine with immunotherapy therapy showed the best results in controlling the symptoms. Among immunotherapy therapies, the combination of plasma exchange plus intravenous high-dose steroids achieved the best results in the acute treatment of IS ([n = 6], with improvement noted in 83.3% [n = 5] of cases). Among the symptomatic treatments with anticonvulsants, carbamazepine was the most efficacious anticonvulsant in treatment of IS, with an average effective dosing of 480 mg/day (carbamazepine was used in 32.3% of acute treatment strategies [n = 23], with improvement noted in 73.9% [n = 17] of cases).

CONCLUSIONS

IS a rare neuromuscular syndrome that tends to affect middle-aged men. These patients should be screened for thymoma and other malignancies such as lymphomas. The management of IS symptoms can be challenging, but based on our review, the combination of multiple immunosuppressives such as IV steroids and plasmapheresis with anticonvulsants such as carbamazepine seems to achieve the best results.

Myasthenia Gravis-An Analysis of Multimodal Evoked Potentials

INTRODUCTION

The aim of this study is a comprehensive analysis of the parameters of exogenous evoked potentials (visual, brainstem auditory, and somatosensory) in patients with myasthenia gravis (MG), a prototype of both neuromuscular junction disease and autoimmune disease. The study also seeks to isolate electrophysiological changes that may indicate disorders within the central and/or peripheral nervous system.

METHODS

A total of forty-two consecutive patients with myasthenia gravis (24 women, 18 men) were included in the study. All of the patients underwent EP examination. MR images were also analyzed.

RESULTS

In the group of MG patients, the latency of P100 (113.9 ± 13.9; p < 0.0001) VEP, wave III (3.92 ± 0.29; p = 0.015), wave V (5.93 ± 0.32; <0.0001), interlatency III-V (2.00 ± 0.12; p < 0.0001), interlatency I-V (4.20 ± 0.28; p < 0.001) BAEP, and all components of SEP (N9, P10, N13, P16, N20, P22) were significantly longer. Mean wave I and V amplitude BAEP were relatively lower.

CONCLUSIONS

The results of the study suggest the presence of disturbances in the bioelectric activities of the central and peripheral nervous system in MG patients.

A systematic review of paraneoplastic syndromes associated with thymoma: Treatment modalities, recurrence, and outcomes in resected cases

OBJECTIVE

Paraneoplastic syndromes associated with thymomas remain incompletely understood. The objective was to examine the association between surgically resected thymomas and paraneoplastic syndromes over the past half century.

METHODS

A primary PubMed/MEDLINE search was used to identify published articles describing paraneoplastic syndromes associated with thymomas from 1960 to 2019. A secondary search identified additional articles referenced in the articles found in the primary search. Kaplan-Meier and log-rank test were used for time-to-event data analyses.

RESULTS

From 407 articles describing 507 patients, 123 different paraneoplastic syndromes were associated with thymoma. The 5 most common paraneoplastic syndromes were myasthenia gravis, pure red cell aplasia, lichen planus, Good syndrome, and limbic encephalitis. Complete or partial resolution of paraneoplastic syndrome symptoms after surgery was noted in 76% of patients, of whom 21% had a relapse or new paraneoplastic syndrome onset after surgery. The most common adjunctive therapy associated with resolution of paraneoplastic syndrome was corticosteroids (30%). For all patients after surgery, thymoma recurrence was observed in 17% of cases, whereas recurrence of paraneoplastic syndrome was observed in 34% of cases, and both were observed in approximately 11% of cases. The 5- and 10-year overall survivals were 78% and 66%, respectively. Improved overall survival was associated with patients who had total resolution from paraneoplastic syndrome.

CONCLUSIONS

A comprehensive assessment of publications over the past half century suggests that a multimodal treatment approach that includes surgical resection of thymomas is able to achieve paraneoplastic syndrome resolution in a majority of patients. Onset of new paraneoplastic syndromes after surgery is associated with the recurrence of the first paraneoplastic syndrome, and resolution of paraneoplastic syndrome is associated with improved overall survival.

Paraneoplastic Isaacs' syndrome: a case series and review of the literature

OBJECTIVE

Isaacs' syndrome is a rare disease resulting from hyperexcitability of peripheral nerves causing continuous muscle fiber activity characterized by muscle twitching and stiffness at rest and delayed muscle relaxation after voluntary contraction. Our objective was to discuss the relationship of Isaacs' syndrome to paraneoplastic syndromes as reported in the available literature and in 3 patients evaluated at our academic medical center.

METHODS

We review the literature on Isaacs' syndrome and describe 3 patients in whom Isaacs' syndrome heralded underlying malignancy or benign neoplasm, including their presenting symptoms, electrophysiologic findings, and laboratory and pathology results.

RESULTS

In all 3 cases, clinical and electrodiagnostic testing was suggestive of Isaacs' syndrome. Two patients tested positive, and one was negative for voltage-gated potassium channel antibodies. Two of the patients developed malignant tumors, that is, one was diagnosed with metastatic thymoma and one with lymphoplasmacytic lymphoma, ranging from 6 months to 1 year after the diagnosis of Isaacs' syndrome. One patient was diagnosed with a spinal cord hemangioblastoma 5 years after he was diagnosed with Isaacs' syndrome.

CONCLUSIONS

Our case series highlights the association of Isaacs' syndrome with a variety of neoplasms both malignant and benign. Our report also underscores the fact that Isaacs' syndrome may be diagnosed several years before a neoplasm is discovered. In our cases, Isaacs' syndrome overlapped with other neuromuscular disorders, that is, myasthenia gravis in a patient with thymoma and chronic inflammatory demyelinating polyneuropathy in a patient with lymphoplasmacytic lymphoma with paraproteinemia. To our knowledge, this is the first report of an association between Isaacs' syndrome with lymphoplasmacytic lymphoma and a spinal cord hemangioblastoma.

Plasma exchange as a therapeutic option in patients with neurologic symptoms due to antibodies to voltage-gated potassium channels: a report of five cases and review of the literature

Antibodies to voltage-gated potassium channels (VGKC) are associated with acquired neuromyotonia, limbic encephalitis, and Morvan's syndrome. The antibodies are often not associated with malignancy and have shown good clinical response to immunomodulatory therapies. A record review identified five patients with laboratory evidence of antibodies to VGKC who underwent plasma exchange (PE) as part of their immunosuppressive therapy for neurologic disease. Four of the patients presented with limbic encephalitis and one with neuromyotonia. Symptoms included memory impairment, seizures, and personality changes. All PE were 1.0 volume and were performed on an every-other-day schedule. Replacement fluid was 5% normal serum albumin except when a bleeding risk was identified and then fresh frozen plasma was added. Four of five patients were also receiving concurrent immunosuppressive therapy including corticosteroids. Of the five patients treated with PE, three had sustained improvement in symptoms for 6-17 months following PE. Two patients did not have signs of improvement at a limited follow-up. One patient had recurrence of her symptoms, which responded to additional PE. These cases, as well as the reports in the literature, suggest that PE could be a useful adjunctive therapy for patients with VGKC antibodies and neurologic symptoms.

Neuromyotonia

Neuromyotonia is a rare condition of spontaneous and continuous muscle fibre activity of peripheral nerve origin. It represents the more severe phenotype of peripheral nerve hyperexcitability, and when acquired is often associated with antibodies to voltage-gated potassium channels. There are no specific published electromyographic or clinical diagnostic criteria for this disorder. This review highlights the classical clinical, electrophysiological and immunological features of this disorder from what is currently known in the literature to date, and also from the author's own patients' studies. Neuromyotonia is best classified as a moderately severe disorder of peripheral nerve hyperexcitability, with electromyographic features of spontaneous, continuous, irregularly occurring doublet, or multiplet single motor unit (or partial motor unit) discharges, firing at a high intraburst frequency (30-300Hz). Invariably, patients develop persistent muscle contraction, often worse following exercise. About 40% of patients with acquired neuromyotonia will have detectable voltage-gated potassium-channel antibodies. Clinical, electrophysiological and immunological measurements are important in defining the phenotype of neuromyotonia, and other, milder forms of peripheral nerve hyperexcitability.

Current therapies for neuromuscular manifestations of paraneoplastic syndromes

The neuromuscular manifestations of paraneoplastic disorders result in diverse syndromes that may also occur in patients without cancer. In general, treatment of these disorders is the same whether or not there is an underlying malignancy. However, when the disorder is believed to be paraneoplastic, the main concern should be prompt detection and treatment of the tumor, as this has been shown to offer the best chance for neurologic stabilization or improvement. The paraneoplastic neuromuscular disorders can be divided into two main categories: those that are directly mediated by antibodies and those that are believed to result from other immune-mediated mechanisms, including cytotoxic T-cell responses with or without association with specific antibodies. For disorders in which the antibodies are pathogenic, therapy is aimed at removing the antibodies. For the other disorders, adjuvant therapies are for the most part empiric and include a variety of immunosuppressant and immunomodulatory agents.

Unusual neurophysiological and immunological findings in myasthenia gravis: a case report

We describe the case of a male patient with ocular myasthenia gravis who developed a diabetic neuropathy similar to chronic inflammatory demyelinating polyradiculoneuropathy associated with transient generalized 'myokymic' discharges and distal weakness. He had antibodies against acetylcholine receptor and GQ1b ganglioside, but not anti-voltage-gated K(+) channel antibodies. Serial electrophysiological and immunological findings showed that diabetes was involved in the immune-mediated mechanism of peripheral neuropathy. We hypothesize that the concomitant appearance of distal motor weakness and decreased compound muscle action potentials upon repetitive nerve stimulation, together with increased distal motor latency and generalized peripheral nerve hyperexcitability, were all related to transient serum positivity to anti-GQ1b antibodies.

Acquired neuromyotonia in association with systemic lupus erythematosus

Acquired neuromyotonia (NMT) is a rare condition resulting from a dysfunction of motor nerves. Current literature suggests acquired NMT is an antibody-mediated channelopathy. We present a case of acquired NMT in a patient with systemic lupus erythematosus. This association has not been previously reported.

Remote neurologic manifestations of cancer

Paraneoplastic disorders may affect any part of the central or peripheral nervous systems. Although relatively uncommon, these disorders are a significant cause of neurologic morbidity for cancer patients. At least some paraneoplastic syndromes are believed to be caused by an autoimmune reaction against shared tumor-neural antigens. This article summarizes the clinical features of paraneoplastic disorders, the current evidence for autoimmunity, and guidelines for diagnosis and treatment.

Acquired neuromyotonia and peripheral neuropathy in a patient with Hodgkin's disease

Acquired neuromyotonia is characterized by hyperexcitability of motor nerves resulting in continuous muscle fiber activity. It occurs most often as a paraneoplastic syndrome in patients with cancers of the immune system. Antibodies against voltage-gated potassium channels (VGKCs) have been detected in some patients. Peripheral neuropathy is sometimes present. We report on a patient with Hodgkin's lymphoma in complete remission who developed paresthesias followed by neuromyotonia with bulbar involvement. Peripheral sensorimotor neuropathy was diagnosed electrophysiologically and evidence of axonal degeneration and demyelination was detected by sural nerve biopsy. The patient's complaints, including dysarthria, improved after carbamazepine treatment.

Neuromyotonia: autoimmune pathogenesis and response to immune modulating therapy

BACKGROUND

Neuromyotonia (NMT) has been postulated to be an autoimmune channelopathy, probably by affecting voltage gated potassium channels (VGKC) leading to excitation and abnormal discharges [Sinha et al., Lancet 338 (1991) 75].

OBJECTIVE

To report three patients with NMT who had other associated immune-mediated conditions, i.e., myasthenia gravis, thymoma and various types of peripheral neuropathies. One patient had peripheral neuropathy and involvement of pre- and post-synaptic neuromuscular junction.

RESULTS

All three patients had evidence of polyneuropathy and neuromyotonic discharges on electrodiagnostic studies. Elevated acetylcholine receptor antibodies were noted in all patients and malignant thymoma was found in two patients with metastasis. All three patients showed moderate to marked response to plasma exchange.

CONCLUSIONS

These findings strongly suggest a humoral autoimmune pathogenesis of NMT, probably by K(+) channel involvement, affecting acetylcholine quantal release and postsynaptic membrane. Clinicians should be aware of this association of immune-mediated conditions in NMT patients and marked improvement with plasma exchange.

Acquired neuromyotonia: a new autoantibody-mediated neuronal potassium channelopathy

Neuromyotonia (Isaacs syndrome) is a rare and heterogenous syndrome of continuous motor unit activity of peripheral nerve origin that manifests as various combinations of muscle stiffness, cramps, twitching, weakness, and delayed muscle relaxation. Although neuromyotonia may accompany an assortment of inherited diseases, most cases are acquired. The observation that the acquired form is often associated with an autoimmune disorder, and the demonstration that some cases improve after plasma exchange, has led to a search for an immune-mediated etiology. This review summarizes the recent immunological and electrophysiological evidence that autoantibodies to voltage-gated potassium channels produce the peripheral motor nerve hyperexcitability that characterizes neuromyotonia and thus establishes acquired neuromyotonia as an autoantibody-mediated disorder. In the nervous system, ion channels and neurotransmitter receptors that function as ligand-gated ion channels seem to be favored targets for autoantibody attack, and neuromyotonia can now be added to the growing list of autoimmune channelopathies.

Morvan's fibrillary chorea: a paraneoplastic manifestation of thymoma

Morvan's fibrillary chorea is a rare disease characterised by symptoms which include neuromyotonia, cramping, weakness, pruritus, hyperhidrosis, insomnia, and delirium. The first case of Morvan's fibrillary chorea to be associated with clinical manifestations of myasthenia gravis with thymoma, psoriasis, and atopic dermatitis is reported. Muscle histopathology disclosed chronic denervation and myopathic changes and in vitro electrophysiology demonstrated both presynaptic and postsynaptic defects in neuromuscular transmission. Serum antibodies to acetylcholine receptors, titin, N-type calcium channels, and voltage gated potassium channels were detected. Plasmapheresis, thymectomy, and long term immunosuppression induced a dramatic resolution of symptoms. The association of thymoma with other autoimmune disorders and autoantibodies, and prolonged and sustained remission with chronic immunosuppression, place Morvan's fibrillary chorea on the range of neurological diseases arising as a paraneoplastic complication of cortical thymomas.