Clinical evaluation of plasma exchange and high dose intravenous immunoglobulin in a patient with Isaacs' syndrome

Effectiveness of therapeutic plasma exchange in case of rare neurological disorder Isaacs syndrome

Isaacs syndrome is a disease characterized by nerve hyperexcitability and pseudomyotonia and treated with immunomodulatory and symptomatic therapy approaches. Here, we report a case of anti-(leucine-rich glioma-inactivated 1) antibody-positive patient diagnosed as Isaacs syndrome and accomplished a nearly complete response to only four sessions of therapeutic plasma exchange (TPE). Our experience suggests that TPE along with other immunomodulatory agents may be beneficial and well-tolerated approach in patient with Isaacs syndrome.

Autoimmune neuromyotonia

PURPOSE OF REVIEW

Autoimmune neuromyotonia encompasses a group of rare immune-mediated neurological disorders frequently associated with anti-contactin-associated protein-like 2 (CASPR2) antibodies and featuring clinical and electrical signs of peripheral nerve hyperexcitability (PNH). We aim to summarize the current knowledge on immune-mediated neuromyotonia, focusing on clinical presentations, pathophysiology, and management.

RECENT FINDINGS

Neuromyotonia is a major feature of several autoimmune neurological syndromes characterized by PNH with or without central neurological system involvement. Experimental and clinical evidence suggest that anti-CASPR2 antibodies are directly pathogenic in autoimmune neuromyotonia patients.

SUMMARY

Neuromyotonia, a form of PNH, is a major feature in several syndromes associated with anti-CASPR2 antibodies, including cramp-fasciculation syndrome, Isaacs syndrome, Morvan syndrome, and autoimmune limbic encephalitis. Diagnosis relies on the identification of motor, sensory, and autonomic signs of PNH along with other neurological symptoms, anti-CASPR2 antibody-positivity, and of characteristic electroneuromyographic abnormalities. Paraneoplastic associations with thymoma are possible, especially in Morvan syndrome. Patients usually respond to immune-active treatments, including steroids, intravenous immunoglobulins, plasma exchanges, and rituximab.

Current Treatment Options for Peripheral Nerve Hyperexcitability Syndromes

PURPOSE OF REVIEW

Peripheral nerve hyperexcitability (PNH) syndromes are divided into primary and secondary groups based on the presence or absence of demonstrable peripheral nerve disease. In this review, we systematically evaluate the evidence for current therapies and supportive managements based on autoimmune, paraneoplastic, and genetic components in pathophysiology reported in the literature.

RECENT FINDINGS

Current therapy options are based on symptomatic management as well as focusing the underlying immune/genetic/paraneoplastic pathology by immunosuppressants, chemotherapy, and surgery. Further research is desired to provide treatment options geared specifically towards addressing PNH. Supportive care can also be an area for future research.

Endoscopic treatment for esophageal varices complicated by Isaacs' syndrome involving difficulty with conventional sedation

A 54-year-old male consulted a local doctor with a chief complaint of systemic convulsions and muscle stiffness and was diagnosed with Isaacs' syndrome based on positive findings for antibodies against voltage-gated potassium channels in 2009. He subsequently experienced repeated hematemesis in 2013, at which time he was taken to our hospital by ambulance. Emergent endoscopy revealed esophageal varices with spurting bleeding. The bleeding was stopped with urgent endoscopic variceal ligation. Three days later, the patient developed sudden dyspnea with stridor during inspiration under sedation with an intravenous injection of low-dose flunitrazepam prior to receiving additional treatment and was aroused with intravenous flumazenil, after which his dyspnea immediately improved. Dyspnea may be induced by muscle cramps associated with Isaacs' syndrome exacerbated by sedation. Endoscopic variceal ligation was performed safely using multiple ligation devices in an awake state following pre-medication with hydroxyzine, without sudden dyspnea. Endoscopists should be cautious of the use of sedatives in patients with diseases associated with muscle twitching or stiffness, as in the current case. In addition, it is necessary to administer endoscopic treatment in an awake state or under conscious sedation in patients with a high risk of dyspnea.

Chronic pain as a manifestation of potassium channel-complex autoimmunity

OBJECTIVE

Autoantibodies targeting voltage-gated potassium channel (VGKC) complexes cause a spectrum of neuronal hyperexcitability disorders. We investigated pain as a manifestation of VGKC-complex autoimmunity.

METHODS

We reviewed the prevalence and characteristics of pain in VGKC-complex-immunoglobulin G (IgG)-seropositive patients in 25 months of comprehensive service testing for neural autoantibodies, subtyped positive sera for LGI1-IgG and CASPR2-IgG specificities, and reviewed pain prevalence in autoimmune control patients.

RESULTS

VGKC-complex-IgG was identified in 1,992 patients of 54,853 tested (4%). Of 316 evaluated neurologically at Mayo Clinic, 159 (50%) had pain, in isolation (28%) or with accompanying neurologic manifestations (72%), and not attributable to alternative cause. Pain was subacute in onset, chronic in course, neuropathic, nociceptive, regional, or diffuse and sometimes attributed to fibromyalgia (6%) or psychogenic cause (13%). Most patients had normal peripheral nervous system function, measured by neuropathy impairment scores and nerve conduction. Evidence of neuronal hyperexcitability (hyperhidrosis, quantitative heat-pain hyperalgesia, or electromyographic excitability) was 25-fold more common in pain patients. Pain management required multiple medications in 70% (narcotics, 30%); 13 of 16 patients reported pain relief with immunotherapy. Pain was significantly associated with CASPR2-IgG-positivity (16% positive with pain, 7% without pain; p = 0.014) but not with LGI1-IgG. Less than 10% of 167 patients with neural autoantibodies other than VGKC-complex-IgG reported pain.

CONCLUSIONS

Chronic idiopathic pain is a syndromic manifestation of VGKC-complex autoimmunity. Hyperexcitability of nociceptive pathways is implicated. CASPR2-IgG significantly associates with pain, but in most patients the antigenic VGKC-complex molecule remains to be determined. VGKC-complex autoimmunity represents an important new direction for pain research and therapy.

[Intravenous IgG for treatment of neuromuscular diseases]

BACKGROUND

Highly purified IgG administered intravenously (IVIG) is used to treat many neurological diseases.

MATERIAL AND METHODS

This review is based on articles identified through a search in PubMed and the authors' knowledge and experience within the field.

RESULTS

The effect of IVIG has been best documented in the treatment of acute and chronic inflammatory demyelinating polyradiculoneuropathy, multifocal motor neuropathy and acute exacerbation of myasthenia gravis. Some smaller studies support explorative IVIG treatment in other neurological diseases such as Lambert-Eaton myasthenic syndrome, paraproteinemic neuropathy, neuropathy caused by vasculitis, inflammatory myopathies and stiff-person syndrome.

INTERPRETATION

IVIG affects the immune system in different ways. Documentation for the effect of such treatment in most neurological diseases remains sparse.

Management of paraneoplastic neurological syndromes: report of an EFNS Task Force

Paraneoplastic neurological syndromes (PNS) are remote effects of cancer on the nervous system. An overview of the management of classical PNS, i.e. paraneoplastic limbic encephalitis, subacute sensory neuronopathy, paraneoplastic cerebellar degeneration, paraneoplastic opsoclonus-myoclonus, Lambert-Eaton myasthenic syndrome and paraneoplastic peripheral nerve hyperexcitability is given. Myasthenia gravis and paraproteinemic neuropathies are not included in this report. No evidence-based recommendations were possible, but good practice points were agreed by consensus. Urgent investigation is indicated, especially in central nervous system (CNS) syndromes, to allow tumour therapy to be started early and prevent progressive neuronal death and irreversible disability. Onconeural antibodies are of great importance in the investigation of PNS and can be used to focus tumour search. PDG-PET is useful if the initial radiological tumour screen is negative. Early detection and treatment of the tumour is the approach that seems to offer the greatest chance for PNS stabilization. Immune therapy usually has no or modest effect on the CNS syndromes, whereas such therapy is beneficial for PNS affecting the neuromuscular junction. Symptomatic therapy should be offered to all patients with PNS.

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.

Mechanism of action of voltage-gated K+ channel antibodies in acquired neuromyotonia

Acquired neuromyotonia (ANM) is associated with antibodies to voltage-gated K+ channels (VGKCs). ANM sera reduce the number of K+ currents in neuronal cell lines, but it is not clear how the antibodies act. Here, we show by using the NB-1 cell line that the reduction in K+ currents by IgG is independent of added complement. IgG Fc and Fab fragments from ANM sera had no effect, but three of four ANM F(ab')2 fragments significantly reduced K+ currents. Thus, cross-linking of the channels by divalent antibodies is likely to be an important mechanism in reducing K+ currents.

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.

Isaacs' syndrome as a potassium channelopathy of the nerve

Isaacs' syndrome (acquired neuromyotonia) is an antibody-mediated potassium channel disorder (channelopathy). The target channel proteins of the antigens are voltage-gated potassium channels (VGKCs), especially dendrotoxin-sensitive fast potassium channels. The suppression of voltage-gated outward K(+) current by antibodies induces hyperexcitability of the peripheral nerve. Patch clamp studies show that antibodies may not directly block the kinetics of VGKCs but may decrease channel density. Electrophysiological, pharmacological, and immunological findings indicate that the site of origin of spontaneous discharges is principally in the distal portion of the motor nerve and/or within the terminal arborization. The spectrum of potassium channelopathies is expanding. The existence of antibodies against VGKCs should be considered in patients who present with generalized nerve hyperexcitability of undetermined etiology.

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.

Successful immunoglobulin treatment in a patient with neuromyotonia

Neuromyotonia is characterized by spontaneous and continuous muscle fibre activity leading to muscle cramps, pseudomyotonia, myokymia and weakness. Electromyographic recordings show typical findings. An auto-immune mechanism has been suggested in at least a subset of patients. Various therapies have been tried with different outcome. A patient with neuromyotonia responding well to high-dose immunoglobulin treatment is presented.

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.

Ion channels in presynaptic nerve terminals and control of transmitter release

The primary function of the presynaptic nerve terminal is to release transmitter quanta and thus activate the postsynaptic target cell. In almost every step leading to the release of transmitter quanta, there is a substantial involvement of ion channels. In this review, the multitude of ion channels in the presynaptic terminal are surveyed. There are at least 12 different major categories of ion channels representing several tens of different ion channel types; the number of different ion channel molecules at presynaptic nerve terminals is many hundreds. We describe the different ion channel molecules at the surface membrane and inside the nerve terminal in the context of their possible role in the process of transmitter release. Frequently, a number of different ion channel molecules, with the same basic function, are present at the same nerve terminal. This is especially evident in the cases of calcium channels and potassium channels. This abundance of ion channels allows for a physiological and pharmacological fine tuning of the process of transmitter release and thus of synaptic transmission.

Reversible F-wave hyperexcitability associated with antibodies to potassium channels in Isaacs' syndrome

We report a case of Isaacs' syndrome showing F-wave hyperexcitability which was reversible after either epidural block or plasmapheresis. A 14-year-old girl with progressive muscle cramp and myokymia in the legs showed high amplitude, long duration, polyphasic F-waves after either tibial nerve or peroneal nerve stimulation. Potassium current of PC-12 cell membrane was suppressed by her serum, IgM of which strongly reacted with proteins of approximately 50 kDa of the lysates of a PC-12 cell line. After an epidural nerve block with 1 per cent lidocaine 10 ml, the myokymia temporally improved, during which time the hyperexcitable F-waves became normalized. We treated her with double filtration plasmapheresis, which resulted in remarkable improvement of myokymia; simultaneously, the abnormal F-waves showed a decrease in amplitude, duration, and in the number of phases. We concluded that there was hyperexcitability of the proximal site of motor fibers in our patient, and possible immune mechanisms gave rise to the myokymia and unusual F-wave features.

Intravenous immunoglobulin preparation increases myoplasmic calcium concentration by activating the dihydropyridine-ryanodine receptor complex

A human intravenous immunoglobulin preparation (IVIg) released Ca2+ from the sarcoplasmic reticulum of cultured human skeletal muscle cells in a dose-dependent manner. Blocking the dihydropyridine-ryanodine receptor complex abrogated the IVIg-mediated Ca2+ response, whereas inhibition of the voltage-operated Na+-channels or acetylcholine receptors did not. This effect of IVIg was not mediated by its main component, the IgG molecules, and differed between preparations from different manufacturers. Heating destroyed the activity. Data shows that an unidentified serum protein present in IVIg can influence human muscle cells by an effect on the dihydropyridine receptor. This phenomenon may be important in interpreting the (side) effects of IVIg in neuromuscular diseases.

Peripartum management of a patient with Isaacs' syndrome

PURPOSE

To describe the peripartum management of a patient with Isaacs' syndrome with specific reference to the anaesthetic implications of the disease process. Associated medical problems included obesity, pregnancy induced hypertension and a difficult airway.

CLINICAL FEATURES

This 30-yr-old gravida V para 0 woman presented to the anaesthesia consultation clinic at 37-wk gestation to discuss pain relief options for labour and delivery. She had a history of Isaacs' syndrome (a peripheral motor neuron disorder), congenital heart disease (ASD and VSD), treated Hashimotos thyroiditis, obesity and a family history of haemachromatosis. On the day of consultation, she was hypertensive and peripheral oedema was noted. Her urine showed trace protein. Four days later, she presented to the labour suite and her cervix was 9 cm dilated. An epidural anaesthetic was given without difficulty and she had an uneventful labour and delivery course. There were no subsequent neurological complications.

CONCLUSION

Isaacs' syndrome is an extremely rare peripheral motor neuron disorder. This patient was successfully managed with epidural analgesia for labour and delivered a healthy child with no congenital anomalies.