Repetitive Nerve Stimulation Test Research Articles

Abnormal sympathetic hyper-reactivity in patients with myasthenia gravis: A prospective study

IntroductionPatients with myasthenia gravis, especially those in crises, are not infrequently observed to demonstrate wide fluctuation in heart rate and blood pressure. ObjectiveThis study was conducted to assess autonomic function in patients with myasthenia gravis. MethodsPatients with myasthenia gravis diagnosed on the basis of typical clinical details, edrophonium or neostigmine test, decremental response on repetitive nerve stimulation testing and anti acetyl choline receptor antibody testing, were compared with age and gender matched controls. Apart from detailed clinical evaluation, all subjects underwent tests of autonomic function, viz. heart rate and blood pressure response on orthostatic tests and isometric handgrip test, Valsalva maneuver, R–R interval variation (RRIV) and the sympathetic skin response (SSR). Results were compared with those in the control group using repeated measures ANOVA and the paired t-test. ResultsSixty-four patients (27 males, 37 females) with a mean age of 40.5±17years) with myasthenia gravis of an average 3±4years duration, and 241 normal controls were enrolled. On the orthostatic tests, patients showed rise in heart rate, systolic and diastolic blood pressure, as did controls, however, the rate and the duration of rise was significantly higher than in the controls (p<0.01). Similar difference between patients and controls, in rate of rise of these parameters was observed on the isometric hand grip test. No significant difference was observed between the two groups on tests of parasympathetic function (Valsalva ratio, RRIV). These effects could also partially be due to pyridostigmine, which all patients were receiving. ConclusionThis study suggests sympathetic hyper-reactivity in patients with myasthenia gravis, which could be responsible for serious hemodynamic instability in patients in crisis.

Riluzole blocks human muscle acetylcholine receptors

Riluzole, the only drug available against amyotrophic lateral sclerosis (ALS), has recently been shown to block muscle ACh receptors (AChRs), raising concerns about possible negative side-effects on neuromuscular transmission in treated patients. In this work we studied riluzole's impact on the function of muscle AChRs in vitro and on neuromuscular transmission in ALS patients, using electrophysiological techniques. Human recombinant AChRs composed of α(1)β(1)δ subunits plus the γ or ε subunit (γ- or ε-AChR) were expressed in HEK cells or Xenopus oocytes. In both preparations, riluzole at 0.5 μm, a clinically relevant concentration, reversibly reduced the amplitude and accelerated the decay of ACh-evoked current if applied before coapplication with ACh. The action on γ-AChRs was more potent and faster than on ε-AChRs. In HEK outside-out patches, riluzole-induced block of macroscopic ACh-evoked current gradually developed during the initial milliseconds of ACh presence. Single channel recordings in HEK cells and in human myotubes from ALS patients showed that riluzole prolongs channel closed time, but has no effect on channel conductance and open duration. Finally, compound muscle action potentials (CMAPs) evoked by nerve stimulation in ALS patients remained unaltered after a 1 week suspension of riluzole treatment. These data indicate that riluzole, while apparently safe with regard to synaptic transmission, may affect the function of AChRs expressed in denervated muscle fibres of ALS patients, with biological consequences that remain to be investigated.

Contralateral Weakness Following Botulinum Toxin for Post-Stroke Spasticity (P04.091)

Objective: We present two patients receiving Botulinum Toxin-A for post-stroke spasticity who developed isolated contralateral limb weakness. Background Botulinum toxin (BoNT) is considered safe and effective in the treatment of post-stroke spasticity. Randomized controlled trials have shown that BoNT is effective in reducing muscle tone and improving disability in the areas of pain, personal hygiene, dressing, and limb position. Adverse effects have generally been mild, including weakness of injected and neighboring muscles. These two cases illustrate an unusual adverse effect of BoNT with its pathophysiology supported by electrodiagnostic testing. Design/Methods: Two patients received high doses of botulinum toxin-Type A (OnabotulinumtoxinA) with large dilution volumes and injection of proximal upper extremity muscles. Both patients developed isolated weakness of the contralateral limb. Following this adverse event both patients underwent electrodiagnostic testing of the affected limb, including repetitive nerve stimulation and EMG. Results: Repetitive nerve stimulation testing of motor nerves in the limb contralateral to the injections demonstrated a decrement of 23% and 16%, respectively. EMG revealed spontaneous activity and small polyphasic units with reduced recruitment in affected muscles. These findings are consistent with severe blockade of the neuromuscular junction. Both patients subsequently improved. Conclusions: This adverse effect of botulinum toxin, with weakness involving only the contralateral upper extremity, suggests diffusion of toxin through tissue planes from proximal upper extremity muscles, across the midline, to contralateral muscles. High doses of botulinum toxin, high volume dilutions, and injection of proximal upper extremity muscles appear to be risk factors for this important adverse effect. Disclosure: Dr. Thomas has nothing to disclose. Dr. Simpson has received personal compensation for activities with NeurogesX, Eli Lilly, Astra Zeneca, Newron, Allergan, Pfizer, Endo, Covidien, Astellas, Ipsen, Gilead, Merz and GlaxoSmithKline. Dr. Simpson has received research support from NeurogesX, Pfizer, Eli Lilly, and Allergan.

Subacute progressive ophthalmoplegia associated with dermatomyositis

Dermatomyositis is a systemic autoimmune disorder that primarily affects the skin and skeletal muscle in the extremities, and is characterized by weakness of the proximal groups of limb muscles. Extraocular muscle involvement is a very rare manifestation of dermatomyositis [5, 8]. We herein report a patient who manifested dermatomyositis with subacute progressive ophthalmoplegia. The patient was a 53-year-old Japanese male who presented with myalgia and difficulty in climbing stairs. He developed progressive diplopia with eyelid edema and ocular pain 2 weeks after presentation, followed by difficulties in raising his arms. No autoimmune, endocrinopathy, or malignant diseases were observed. The physical examination revealed the presence of Gottron’s papules on the dorsal surface of the hands, and a neurological examination showed symmetrical weakness of the proximal muscles, including the upper limbs muscles, and bilateral ophthalmoplegia with total limitations of eye movements (Fig. 1). There was no weakness of the facial muscles or bulbar palsy. Laboratory tests revealed an increased creatine kinase (CK) level (10,808 U/l; normal range, 25–190). There was no abnormal thyroid function or serum autoantibody, including antinuclear antibody, anti-acetylcholine receptor antibody, and anti-thyroid antibodies. No malignant tumors, including thymoma or thymic hyperplasia, were observed using whole-body CT and PET imaging. Intravenous edrophonium had no effect on the ophthalmoplegia. The repetitive nerve stimulation test was normal. The muscle biopsy at the left vastus medialis muscle revealed inflammatory myopathic changes, which showed the invasion of mononuclear cells into the interfascicular septae and within the fascicles, perifascicular atrophy, and variations in the muscle fiber size. An immunohistochemical analysis showed the mononuclear cells to be CD4and CD8-positive lymphocytes. Ragged red fiber or cytochrome c oxidase-negative fibers were absent. The patient was treated with 60 mg/day oral prednisolone. His ocular impairment, weakness of the proximal muscles, and elevated CK values became markedly improved 1 month after the steroid therapy. Orbital magnetic resonance imaging (MRI) scans revealed an increased thickness of the extraocular muscles on T1-weighted images (Fig. 2a) and high-intensity signals of the extraocular muscles on fat-suppressed T2-weighted images (Fig. 2c), which were both improved after the steroid therapy (Fig. 2b, d). No myositis-associated autoantibodies, including anti Jo-1, PM-Scl-100, PL-7, PL-12, EJ, OJ, KS, M2, Ku (p70/80), SRP, Rib-P antibodies and the antimitochondrial antibody of M2 subtype, were detectable in the serum. Previous reports have suggested that the ophthalmoplegia observed in inflammatory myopathies is caused by the S. Kono (&) T. Bunai T. Konishi K. Shirakawa H. Miyajima First Department of Medicine, Hamamatsu University School of Medicine, 1-20-1, Handayama, Hamamatsu 431-3192, Japan e-mail: satokono@hama-med.ac.jp

A Case of Lambert-Eaton Myasthenic Syndrome with Small-Cell Lung Cancer and Transient Increase in Anti-Acetylcholine-Receptor-Binding Antibody Titer

BackgroundLambert-Eaton myasthenic syndrome (LEMS) is a presynaptic neuromuscular junction disorder that is most frequently associated with small-cell lung cancer (SCLC). The titers of antibodies against voltage-gated calcium channels are frequently increased in LEMS, but only rarely is titer of anti-acetylcholine-receptor-binding antibodies (AChR-abs) increased.Case ReportA 57-year-old male was admitted to our hospital due to dry mouth and eyes and progressive proximal limb weakness of 2 months duration. The results of a repetitive nerve stimulation test disclosed all criteria for the electrophysiological LEMS pattern, and the patient's AChR-abs titer was 0.587 nmol/L. At a follow-up performed 5 years after successful treatment of SCLC and LEMS, his AChR-abs titer had decreased to 0.001 nmol/L.ConclusionsWe suggest that this was a case of transient pseudopositivity of AChR-abs in SCLC with LEMS.

Limb-Girdle Myasthenia Gravis in a 10-Year-Old Girl

A 10-year-old girl presented with progressive proximal limb muscle weakness without facial, ocular, or bulbar muscle involvement. There was no fatigability or diurnal fluctuation in symptoms. Her weakness worsened with febrile illnesses and recovered with accruing disabilities over a few weeks. Serum creatine kinase levels and muscle biopsy were normal. A significant decrement on repetitive nerve stimulation test and positive response to therapeutic neostigmine challenge test confirmed the diagnosis of limb-girdle myasthenia. She responded well to corticosteroids and thymectomy, demonstrating a likely autoimmune etiology. This case highlights the long-term fluctuations in a case of myasthenia gravis and the need for a high index of suspicion for myasthenia in children presenting with unexplained muscle weakness, even in the absence of typical features such as fatigability, diurnal fluctuation, and oculobulbar weakness.

Clinical value of low-frequency repetitive nerve stimulation in myasthenia gravis

To explore the value of low-frequency repetitive nerve stimulation (RNS) in the diagnosis of myasthenia gravis (MG). A total of 436 MG patients admitted during the period of July 2008 and August 2010 and undergoing the repetitive nerve stimulation test were reviewed retrospectively. We analyzed the positive rates of RNS in MG patients and compared the abnormalities in different nerves including facial, accessory, axillary and ulnar nerves. Among them, 73.85% had abnormal recordings on low-frequency RNS test. The highest abnormality was in facial nerves (82.30%), then axillary nerves (52.17%) and the lowest in ulnar nerves (27.64%). The positive rates of RNS in ocular MG were significant lower than those in general MG patients. And there were no significant statistical differences of RNS abnormal rates in types IIa, IIb, III and IV MG patients with 89.66%, 82.56%, 91.67% and 83.33%, respectively. In ocular MG, 16.34% patients were positive in RNS test under the stimulation of accessory, axillary and ulnar nerves. And 79.50% patients with general MG had two or more nerves with abnormal results. The low-frequency RNS test is of great value in the diagnosis of MG. And it shows a higher sensitivity in general MG patients than that in ocular ones. The stimulation of facial and axillary nerves increases the positive rates of RNS in MG patients.

Anatomical variation of the vertebral artery clinically mimicking myasthenia gravis

Cranial nerve palsy, most commonly trigeminal, abducens, or facial, caused by compression of an ectatic or elongated intracranial artery is a well-known phenomenon. Symptoms of brain stem compression by an abnormal artery have rarely been reported (Tomasello et al. Neurosurgery 56(suppl 1):117-124, 2005). The authors present a 59-year-old woman with intermittent ptosis of the right eye, diplopia and swallowing disturbances, enhanced after physical effort, implying myasthenia gravis. Typical diagnostic procedures, e.g. repetitive nerve stimulation tests, acetylcholine receptor antibodies level were within normal limit. Neurogenic changes from the orbicularis oculi muscle were found in EMG. MRI and angio-CT revealed anatomical variation of the vertebral artery (elongated and arcuate route), causing intermittent signs of brain stem lesion. We point out the similarity of the clinical symptoms of myasthenia gravis and vascular brain stem compression by abnormal vertebral artery. The two diseases require completely different therapeutic proceedings.

Repetitive Nerve Stimulation Test in Amyotrophic Lateral Sclerosis with Predominant Oropharyngeal Manifestations

Background and PurposeAmyotrophic lateral sclerosis (ALS) patients display easy fatigability and abnormal decrements on repetitive nerve stimulation (RNS) test of clinically involved limb muscles, which can result in ALS being misdiagnosed as myasthenia gravis. We retrospectively analyzed the RNS tests of ten ALS patients with only or predominant oropharyngeal symptoms without ocular or facial weakness.MethodsRNS tests were performed on the abductor digiti quinti, flexor carpi ulnaris, orbicularis oculi (OO), nasalis and trapezius muscles at low-rate stimulation frequencies of 3 and 5-Hz. Decrements greater than 10% of the compound muscle action potential amplitude on the fifth stimulation compared to the first was regarded as abnormal.ResultsSix patients complained of muscular fatigue or diurnal fluctuation. Among the ten patients, three exhibited abnormal decrements during low-rate stimulation in the facial muscles but not in the limb muscles, two exhibited abnormal decrements in the OO and nasalis muscles, and one exhibited abnormal decrements in the OO muscle.ConclusionsThese findings show that the facial muscles may be involved in some early oropharyngeal forms of ALS, although facial weakness may not be clinically evident. We confirm herein that abnormal decrement of facial muscles to RNS test cannot make a definite diagnose for myasthenia gravis.

Seropositive Myasthenia Gravis Associated with Small-Cell Lung Carcinoma

BackgroundLambert-Eaton myasthenic syndrome is well known to be a classical paraneoplastic syndrome of small cell lung carcinoma (SCLC). Three cases of seronegative myasthenia gravis (MG) and SCLC were previously reported.Case ReportA 65-year-old man developed a severe progressive respiratory failure with clinical features of MG. Tests showed a decremental response in the repetitive nerve stimulation test, abnormal single-fiber electromyography, and positive acetylcholine receptor antibody. SCLC was confirmed by the lung biopsy.ConclusionsThis case represents the first case of seropositive MG and SCLC.

Comparison of Clinical Manifestations between Patients with Ocular Myasthenia Gravis and Generalized Myasthenia Gravis

PurposeTo compare the clinical manifestations between patients with ocular myasthenia gravis and those with generalized myasthenia gravis (MG).MethodsThe medical records of 71 patients diagnosed with MG between January 1995 and December 2007 were reviewed. Demographics, sensitivities of diagnostic methods, the presence of systemic autoimmune diseases, ophthalmic complications caused by MG, and treatments were evaluated and compared.ResultsFourteen patients (20%) were diagnosed with ocular MG and 57 patients (80%) with generalized MG. Sensitivities of anti-acetylcholine receptor antibody and repetitive nerve stimulation tests were significantly higher in the generalized MG group (84%, 89%) compared to those in the ocular MG group (50%, 54%) (p = 0.011, p = 0.008). The sensitivity of the neostigmine test was the highest in both groups (98% of generalized MG, 79% of ocular MG), and the difference between the two groups was borderline significant (p = 0.058). The most common symptoms were ptosis and diplopia, and both groups presented with pain, blurred vision, and tearing. Systemic autoimmune disease was more prominent in the generalized MG group (21%) than in the ocular MG group (14%), and steroid therapy was used more frequently in the generalized MG group (82%) than in the ocular MG group (57%). Ophthalmic complications associated with long-term steroid treatment were more profound in the generalized MG (30%) compared to those of the ocular MG (21%).ConclusionsThe generalized MG group was associated with higher sensitivities to diagnostic tests, more systemic steroid use, higher ophthalmic complications caused by systemic autoimmune disease, and long-term steroid treatment compared to those of the ocular MG group.

A 75‐YEAR‐OLD CAUCASIAN MAN WITH UNUSUAL PRESENTATION OF MYASTHENIA GRAVIS

A 75‐YEAR‐OLD CAUCASIAN MAN WITH UNUSUAL PRESENTATION OF MYASTHENIA GRAVIS

Central and peripheral autonomic failure in cold-induced sweating syndrome type 1

Cold-induced sweating syndrome type 1 (CISS1) is a rare disorder characterized by profuse sweating in a cold environment, determined by mutations in cytokine receptor–like factor 1 ( CRLF1 ).1 Its pathogenesis is not fully understood. It has been demonstrated in vitro that CRLF1 may be involved in inducing differentiation from a noradrenergic to a cholinergic transmitter phenotype. During development, catecholaminergic and cholinergic neurotransmission is required for the induction of secretory function, whereas cholinergic transmission becomes crucial for the maintenance of the secretory responsiveness.2 The abnormal sweat response in CISS1 could be also related to alterations in temperature signals acting on hypothalamus and preoptic areas.1 We report clinical, molecular, skin biopsy, and temperature monitoring data of an Italian boy with CISS1. ### Case report. A 16-year-old boy had come to our observation at 1 year of age. His parents were healthy and unrelated. A brother, with facial dysmorphisms and hypotonia, had died at age 3 months from bronchopulmonary infection. Our patient was hypotonic at birth and experienced severe feeding difficulties. He had elongated face, high-arched palate, weak cry, large pinnae, short hands, tapering fingers, clinodactyly, and reduced tendon reflexes. Concentric needle EMG, nerve conduction velocity (NCV) studies (ulnar, median, peroneal, tibial, and sural nerves), and repetitive nerve stimulation testing excluded a …

A Case of Paramyotonia Congenita Without Periodic Paralysis

Paramyotonia congenita (PC), first described in 1886 by Eulenberg, is characterized by cold and exercise-induced muscle stiffness and intermittent flaccid paresis not necessarily related to cold or myotonia. Several authors segregated a pure form of PC, which has no periodic paralysis, even after cold exposure. The existence of this phenotype has been debated in the literature. We describe electrophysiological and molecular genetic features of a patient with PC who had no history of periodic paralysis. Immersion in cold water or potassium load could not induce clinical paralysis. However, repetitive nerve stimulation and exercise test demonstrated a drop in compound muscle action potential amplitude. Genetic analysis revealed the substitution of valine for glycine on the human skeletal muscle sodium channel (SCN4A) gene. The G1306V mutation is rare in the classic form of PC, and moreover might be the first in pure paramyotonia.

Pseudo-Internuclear Ophthalmoplegia as a Sign of Overlapping Myasthenia Gravis in a Patient with 'Intractable' Hypothyroidism

We describe a 52-year-old man with a history of increasing fatigability and gait disturbances that were first attributed to hypothyroidism. On examination, he had bilateral pseudo-internuclear ophthalmoplegia with weakness of adduction and abducting nystagmus. Convergence was also impaired and he showed proximal weakness of the limb. Intravenous edrophonium almost completely abolished the nystagmus and adducting muscle weakness, and improved the strength of proximal muscles groups. The clinical response to the administration of edrophonium, the presence of AChR binding antibodes and the repetitive nerve stimulation test findings indicated that the patient had pseudo-internuclear ophthalmoplegia as a manifestation of generalized myasthenia gravis. Whereas hypothyroidism was effectively controlled with levothyroxine, his subsequent response to thymectomy, prednisolone and cholinesterase inhibitors confirmed the diagnosis of generalized myasthenia gravis.

Clinical and Electrophysiological Characteristics of Larynx in Myasthenia Gravis

We investigated the clinical and electrophysiological characteristics of the larynx in patients with myasthenia gravis (MG). Thirty-two cases of MG were analyzed. The laryngeal behaviors and characteristics of laryngeal electromyography were evaluated, and voice assessment and repetitive nerve stimulation (RNS) tests were conducted. The initial symptoms of patients were ptosis and/or diplopia in 28, dysphagia and slurred speech in 3, and limb weakness in 1. Only 8 patients had slight hoarseness and vocal fatigue, and 4 patients had positive laryngeal signs. When compared with normal subjects, the patients with MG had worse results on the acoustic analysis of shimmer, their normalized noise energy was greater, and the harmonics-to-noise ratio and maximum phonation time were significantly lower. The RNS findings were positive in 28 patients and negative in 4 patients. The average (+/-SD) amplitude decrement was 31.9% +/- 19.1%. The mean number of involved laryngeal muscles was 2.22 +/- 1.35. Cricothyroid muscles were involved in 26 cases, thyroarytenoid muscles were involved in 14 cases, posterior cricoarytenoid muscles were involved in 6 cases, and lateral cricoarytenoid muscles were involved in 2 cases. Although few patients presented with laryngeal symptoms as their initial symptoms, most patients with MG exhibited asymmetry and abnormal findings on laryngeal electromyography. The RNS test for laryngeal muscles is a more sensitive indicator for the diagnosis of MG, especially in the cricothyroid muscle.

3,4‐Diaminopyridine is more effective than placebo in a randomized, double‐blind, cross‐over drug study in LEMS

The purpose of this study was to investigate the clinical and electrophysiological efficacy of 3,4-diaminopyridine (DAP) in patients with Lambert-Eaton myasthenic syndrome (LEMS) in a randomized, double-blind, cross-over drug trial. The diagnosis of LEMS was made based on the combination of fluctuating muscle weakness, diminished or absent reflexes, and more than 60% increment of the compound muscle action potential (CMAP) amplitude after brief exercise or 50-HZ stimulation on a repetitive nerve stimulation (RNS) test. Evaluations were done at baseline, with placebo, and with 3,4-DAP (up to 75-80 mg/day). Assignment of placebo or 3,4-DAP was done in a double-blinded manner. Measurements included subjective symptoms score, objective clinical measurements [LEMS classification, muscle strength score, quantitative myasthenia gravis (QMG) score] and RNS test and single-fiber electromyography (SFEMG). The differences between placebo and baseline values (placebo change) were compared with the differences between 3,4-DAP and baseline or placebo values (DAP change). Seven patients with LEMS (QMG score >9) participated in the study. One patient had major side-effects with 3,4-DAP and withdrew from the study. Statistically significant efficacy was noted with DAP change (N = 13) compared with placebo change (N = 7) according to the subjective symptoms score (P = 0.01), LEMS classification (P < 0.001), muscle strength score (P < 0.006), QMG score (P = 0.02), and CMAP (P = 0.03). For long-term treatment, 2 patients preferred 3,4-DAP, 1 chose guanidine hydrochloride, 1 preferred pyridostigmine, and 2 chose no treatment. A randomized, double-blind, cross-over drug trial of 3,4-DAP showed significant efficacy over placebo in patients with LEMS. As a long-term treatment, however, not all patients preferred this drug.

Electrophysiological diagnosis and patterns of response to treatment of botulism with neuromuscular respiratory failure

In this study we describe the electrophysiological findings in botulism patients with neuromuscular respiratory failure from major botulism outbreaks in Thailand. High-rate repetitive nerve stimulation testing (RNST) of the abductor digiti minimi (ADM) muscle of 17 botulism patients with neuromuscular respiratory failure showed mostly incremental responses, especially in response to >20-HZ stimulation. In the most severe stage of neuromuscular respiratory failure, RNST failed to elicit a compound muscle action potential (CMAP) of the ADM muscle. In the moderately severe stage, the initial CMAPs were of very low amplitude, and a 3-HZ RNST elicited incremental or decremental responses. A 10-HZ RNST elicited mainly decremental responses. In the early recovery stage, the initial CMAP amplitudes of the ADM muscle improved, with initially low amplitudes and an incremental response to 3- and 10-HZ RNSTs. Improved electrophysiological patterns of the ADM muscle correlated with improved respiratory muscle function. Incremental responses to 20-HZ RNST were most useful for diagnosis. The initial electrodiagnostic sign of recovery following treatment of neuromuscular respiratory failure was an increased CMAP amplitude and an incremental response to 10-20-HZ RNST. Muscle Nerve 40: 271-278, 2009.

Electrophysiological studies in a mouse model of Schwartz–Jampel syndrome demonstrate muscle fiber hyperactivity of peripheral nerve origin

Schwartz-Jampel syndrome (SJS) is an autosomal-recessive condition characterized by muscle stiffness and chondrodysplasia. It is due to loss-of-function hypomorphic mutations in the HSPG2 gene that encodes for perlecan, a proteoglycan secreted into the basement membrane. The origin of muscle stiffness in SJS is debated. To resolve this issue, we performed an electrophysiological investigation of an SJS mouse model with a missense mutation in the HSPG2 gene. Compound muscle action potential amplitudes, distal motor latencies, repetitive nerve stimulation tests, and sensory nerve conduction velocities of SJS mice were normal. On electromyography (EMG), neuromyotonic discharges, that is, bursts of motor unit action potentials firing at high rates (120-300 HZ), were constantly observed in SJS mice in all muscles, except in the diaphragm. Neuromyotonic discharges were not influenced by general anesthesia and disappeared with curare administration. They persisted after complete motor nerve section, terminating only with Wallerian degeneration. These results demonstrate that perlecan deficiency in SJS provokes a neuromyotonic syndrome. The findings further suggest a distal axonal localization of the generator of neuromyotonic discharges. SJS should now be considered as an inherited disorder with peripheral nerve hyperexcitability.

22. Hemoglobin concentration changes induced by transcranial magnetic stimulation (TMS) over the primary motor area

The aim of this study was to elucidate the correlation between excitation–contraction coupling time (ECCT) of the masseter and the bite force in myasthenia gravis (MG). Compound muscle action potentials (CMAPs) of the masseter and movement-related potentials (MRPs) using an accelerometer placed on the chin were simultaneously recorded after trigeminal nerve stimulation by a monopolar needle electrode inserted into the mandibular notch. The ECCT was defined as the difference in onset latencies between CMAP and MRP. The repetitive nerve stimulation test (RNS) was also performed in the same masseter before the ECCT recording. The bite force was measured using a pressure-sensitive sheet immediately after the ECCT recording. Successive examinations of RNS/ECCT and the bite force measurements were performed in 18 patients with MG. We calculated percent difference of the bite force to estimate the inter-trial differences of the bite force in each subject. The ECCT was significantly correlated with the percent difference of the bite force (p = 0.02). On the other hand, the percent difference of the bite force did not show any significant relationship with either the decrement in RNS or CMAP amplitude of the masseter. Our results suggest that dysfunction of E–C coupling may contribute to the muscle weakness in MG.