Electrophysiological evaluation of the neuromuscular junction: a brief review / Avaliação eletrofisiológica da junção neuromuscular: breve revisão

Abstract The nerve terminal and muscle membrane compose the neuromuscular junction. After opening the voltage-gated calcium channels, action potentials from the motor axons provoke a cascade for the acetylcholine release from synaptic vesicles to the synaptic cleft, where it binds to its receptor at the muscle membrane for depolarization. Low amplitude compound muscle action potential typically presents in presynaptic disorders, increasing by more than 100% after a 10-second effort in the Lambert-Eaton myasthenic syndrome and less in botulism. Needle electromyography may show myopathic motor unit action potentials and morphological instability ("jiggle") due to impulse blocking. Low-frequency repetitive nerve stimulation (RNS) is helpful in postsynaptic disorders, such as myasthenia gravis and most congenital myasthenic syndromes, where the number of functioning acetylcholine receptors is reduced. Low-frequency RNS with a decrement >10% is abnormal when comparing the 4th to the first compound muscle action potential amplitude. High-frequency RNS is helpful in presynaptic disorders like Lambert-Eaton myasthenic syndrome, botulism, and some rare congenital myasthenic syndromes. The high-frequency RNS releases more calcium, increasing the acetylcholine with a compound muscle action potential increment. Concentric needle records apparent single-fiber action potentials (spikes). A voluntary activation measures the jitter between spikes from two endplates. An electrical activation measures the jitter of one spike (one endplate). The jitter is the most sensitive test for detecting a neuromuscular junction dysfunction. Most neuromuscular junction disorders are responsive to treatment.

Resumo O nervo terminal e a membrana muscular compõem a junção neuromuscular. Após a abertura dos canais de cálcio dependentes de voltagem, os potenciais de ação do axônio motor provocam uma cascata de eventos que libera acetilcolina das vesículas para a fenda sináptica, ligando-se ao receptor na membrana muscular para despolarização. O potencial de ação muscular composto de baixa amplitude ocorre nas desordens pré-sinápticas, aumentando em mais de 100% após esforço de 10 segundos na síndrome miastênica de Lambert-Eaton e menos no botulismo. A eletromiografia pode mostrar potenciais de ação da unidade motora miopáticos e instabilidade morfológica ("jiggle") devido ao bloqueio do impulso. Estimulação nervosa repetitiva (ENR) de baixa frequência é útil nos distúrbios pós-sinápticos, como miastenia gravis e a maioria das síndromes miastênicas congênitas, quando há número reduzido de receptores de acetilcolina funcionantes. ENR de baixa frequência com decremento >10% é anormal comparando-se à amplitude do quarto com o primeiro potencial de ação muscular composto. ENR de alta frequência é útil nas doenças pré-sinápticas, como síndrome miastênica de Lambert-Eaton, botulismo e algumas síndromes miastênicas congênitas raras. ENR de alta frequência libera mais cálcio, aumenta acetilcolina, resultando em incremento do potencial de ação muscular composto. O eletrodo de agulha concêntrico registra potenciais de ação aparente de fibra única (PAAFU). Ativação voluntária mede jitter entre dois PAAFUs (duas junções neuromusculares). Ativação elétrica mede jitter de um PAAFU (uma junção neuromuscular). Jitter é o teste mais sensível para detectar disfunção de junção neuromuscular. A maioria dos distúrbios juncionais é responsiva ao tratamento.

Diagnostic accuracy and clinical utility of bed side tests versus laboratory tests in the diagnosis of ocular myasthenia

Purpose: To assess the diagnostic accuracy of forced eyelid closure test (FECT), ice pack test (IPT), repetitive nerve stimulation test (RNS), and acetylcholine receptor (AchR) antibody test in patients with suspected ocular myasthenia. To assess the clinical utility of AchR antibody test in predicting disease progression. Methods: Retrospective cohort study of patients diagnosed with ocular myasthenia at a South?Indian neuro?ophthalmology tertiary eye clinic. Baseline characteristics; ocular myasthenia symptoms; results of FECT, IPT, RNS, and AchR antibody test; and progression time to generalized myasthenia (GM) over 36 months from the time of diagnosis were recorded and analyzed using receiver operator curve analysis, multiple logistic regression, and Kaplan朚eier survival analysis. Results: FECT had a sensitivity of 96.7% (95% CI: 88.5�.6) and a specificity of 75% (95% CI: 34.9�.8). Combination of FECT and IPT, using the positivity of at least one test, increased the sensitivity to 98.3% (95% CI: 91�0), reducing the specificity to 50% (95% CI: 15.7�.3), whereas using the positivity of both tests, we obtained a sensitivity of 71.7% (95% CI: 58.6�.5) and a specificity of 100% (95% CI: 63.1�0). In the subset of patients with double negative RNS and AchR antibodies, the positive predictive value of combined FECT and IPT (double positive) was 100%. Patients who developed GM were more likely to have a positive AchR antibody test result (P = 0.001). Conclusion: Combined FECT and IPT (double positive) has high diagnostic accuracy even among patients with normal RNS and negative AchR antibodies. Despite low sensitivity, AchR?antibody test has a significant predictive value in disease progression.

Repetitive Nerve Stimulation in Amyotrophic Lateral Sclerosis / 中华医学杂志(英文版)

<p><b>Background</b>Nowadays, it is widely known that decremental responses in low-frequency repetitive nerve stimulation (LF-RNS) are frequently observed in patients with amyotrophic lateral sclerosis (ALS). The pathological mechanism of this phenomenon remains unknown. This study aimed to illuminate the features of RNS in Chinese patients with ALS.</p><p><b>Methods</b>Clinical and electrophysiological data of 146 probable and definite ALS patients who underwent RNS were retrospectively enrolled and analyzed. LF-RNS (3 Hz) was performed in trapezius, deltoid, abductor digiti minimi (ADM), quadriceps femoris, and tibialis anterior. High-frequency RNS (HF-RNS, 10 Hz) was performed only in ADM. The two-sample t-test and Chi-squared test were used for statistical analysis.</p><p><b>Results</b>Decremental responses to LF-RNS (≥10%) in at least one muscle were detected in 83 (56.8%) of the cases and were most commonly seen in trapezius and deltoid. The incidence of decremental response was higher in patients with upper limb onset. Incremental responses to HF-RNS (≥60%) in ADM were observed in 6 (5.6%) of the cases. In 106 muscles with decremental response, 62 (57.4%) muscles had a continuous decremental pattern, more than a U-shape pattern (37 cases, 34.3%). Nineteen cases showed definite decrements in LF-RNS tests in trapezius, while no abnormalities were found in the electromyography and neurological examination of the sternocleidomastoid muscle, supplied by the accessory nerve as well.</p><p><b>Conclusions</b>Decremental responses in the RNS are commonly observed in ALS patients. The findings regarding the trapezius indicated that some ALS onsets could be initiated by a "dying back" process, with destruction of neuromuscular junctions (NMJs) before motor neurons. Incremental responses in the ADM implied damage of the NMJs involved both the post and presynaptic membranes.</p>

Repetitive Nerve Stimulation in MuSK-Antibody-Positive Myasthenia Gravis

BACKGROUND AND PURPOSE: Responses to repetitive nerve stimulation (RNS) in patients with muscle-specific tyrosine kinase (MuSK) antibody (Ab)-positive myasthenia gravis (MG) vary depending on the muscles tested. We analyzed the RNS responses of limb and facial muscles in MuSK-Ab-positive and acetylcholine receptor (AChR)-Ab-negative MG (MuSK MG) and MuSK-Ab-negative and AChR-Ab-negative [double-seronegative (DSN)] MG patients. METHODS: We retrospectively compared RNS responses between 45 MuSK MG and 29 DSN MG. RNS was applied to the abductor digiti minimi, flexor carpi ulnaris, trapezius, orbicularis oculi, and nasalis muscles. RESULTS: Abnormal RNS responses in limb muscles were observed in 22.2 and 58.6% of MuSK MG and DSN MG patients, respectively, with abnormal facial responses observed in 77.8 and 65.5%, and abnormal responses observed in any of the five muscles in 86.7 and 72.4%. Abnormal RNS responses in the abductor digiti minimi or flexor carpi ulnaris were less frequent in MuSK MG (8.9 and 15.6%, respectively) than in DSN MG (37.9 and 55.2%), whereas the findings for other muscles were not significantly different between the groups. Abnormal facial responses but normal limb responses were independently associated with MuSK MG (odds ratio=5.224, 95% confidence interval=1.300–20.990). CONCLUSIONS: Abnormal RNS responses primarily in facial muscles without involvement of limb muscles were more pronounced in MuSK MG than in DSN MG. RNS of both facial and limb muscles in AChR-Ab-negative MG can increase the test sensitivity and aid in early suspicion of MuSK MG.

Diagnostic value of low-frequency repetitive nerve stimulation in patients with ocular myasthenia gravis / 中国基层医药

Objective To investigate the diagnostic value of low-frequency repetitive nerve stimulation (RNS) in patients with ocular myasthenia gravis(MG).Methods The clinical data of the low-frequency RNS of 54 in-patients with ocular MG were analyzed.Results The positive rate of low-frequency RNS was 53.7％ in 54 patients.The abnormal rate of the facial nerve and the proximal limb nerve was significantly higher than that of low limb distal nerve.The differences were statistically significant(x2 =6.783,P =0.009;x2 =4.167,P =0.041).In all the examined nerves,the abnormal rate of right facial nerve was the highest(46.3％),and the lowest on the ulnar nerve(11.1％).The abnormal rate was statistically significant in all these nerves (x2 =21.995,P =0.001).Conclusion Low-frequency RNS plays an important role in the diagnosis of ocular MG,and the facial nerve should be the first choice in this examination.

Repetitive nerve stimulation in amyotrophic lateral sclerosis / 西安交通大学学报(医学版)

ABSTRACT:Objective To evaluate the features and related factors of decremental response in amyotrophic lateral sclerosis (ALS)patients to low-frequency repetitive nerve stimulation (RNS)in proximal nerves.Methods We performed RNS studies in proximal axillary and accessory nerves with recording in deltoid and trapezius mus-cle respectively in 87 ALS patients.Decremental compound muscle action potential (CMAP)and related factors were analyzed prospectively,and abnormal group of decremental response in ALS patients was compared with 39 pa-tients with myasthenia gravis.Results ① Abnormal decremental responses were found in 43.7% and 49.4% of ALS patients with deltoid and trapezius muscle recording respectively.They were found more frequent in trapezius muscle than those of deltoid muscle.② There was no relationship of decremental response with gender,age,onset or course of disease,ALSFRS-r scores,or rate of disease progression in ALS patients.③ There was significant rela-tionship between decremental response and fluctuating muscle weakness.Decremental responses decreased more ob-viously in ALS patients with fluctuating muscle weakness than in those with nonfluctuating muscle weakness.④ Dec-remental responses were greater in patients with myasthenia gravis than that in ALS patients.Conclusion Decre-mental response with proximal muscle recording is not an uncommon feature in ALS patients;therefore,it should not be treated as a criterium to rule out ALS.Abnormal decremental response of trapezius muscle is found more fre-quent than that of deltoid muscle.Decremental response range in patients with myasthenia gravis is significantly lar-ger than that in ALS patients.One should be more careful when diagnosing ALS patients with fluctuating muscle weakness and abnormal decremental response.

A Patient with Coexisting Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome

BACKGROUND: The coexistence of myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) is very rare and remains controversial. CASE REPORT: A 48-year-old woman initially presented with noticeable right ptosis and intermittent diplopia. She then developed fluctuating proximal limb weakness and difficulty in swallowing. The serum titer of anti-acetylcholine-receptor antibody was elevated and the edrophonium (Tensilon) test was positive. However, repetitive nerve stimulation revealed abnormalities typical of LEMS. The patient exhibited a good response to treatment with anticholinesterase inhibitors and steroids, and long-term evaluation disclosed that she presented with the clinical, electrophysiological, and immunological characteristics of both diseases. CONCLUSIONS: The reported clinical and electrophysiological features suggest that this patient was a very rare case of combined MG and LEMS.

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

BACKGROUND AND PURPOSE: Amyotrophic 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. METHODS: RNS 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. RESULTS: Six 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. CONCLUSIONS: These 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.

Non-paraneoplastic Lambert-Eaton myasthenic syndrome: a brief review of 10 cases / Síndrome miastênica de Lambert-Eaton não paraneoplásica: uma breve revisão de dez casos

Lambert-Eaton myasthenic syndrome (LEMS) is an immune-mediated disorder of the presynaptic neuromuscular transmission, which more frequently occurs as the remote effect of a neoplasm, in the paraneoplastic form (P-LEMS), or in a non-paraneoplastic form (NP-LEMS); but few studies describe the clinical features of NP-LEMS. We analyzed the clinical manifestations, laboratory findings, electrophysiological studies, and treatment responses in ten Brazilian patients suffering from NP-LEMS. The mean age was 41.5 years. More often neurological findings were hyporeflexia or areflexia with a post-exercise improvement. Treatment response occurred with pyridostigmine, guanidine, prednisone, azathioprine, and cyclosporine; but not response was observed after intravenous immunoglobulin and plasma exchange. Age at onset, clinical manifestations, and electrophysiological abnormalities can help more in the diagnosis than serum antibodies; the symptomatic treatment with pyridostigmine was effective; and the immunosuppressive treatment with prednisone, azathioprine, or cyclosporine was more beneficial than plasma exchange or intravenous immunoglobulin treatment.

A síndrome miastênica de Lambert-Eaton (LEMS) é uma desordem imunomediada da transmissão neuromuscular pré-sinaptica, que mais frequentemente ocorre como efeito à distância de uma neoplasia, na forma paraneoplásica (P-LEMS), ou na forma não paraneoplásica (NP-LEMS); porém poucos estudos têm descrito as características da NP-LEMS. Nós analisamos as manifestações clínicas, laboratoriais, eletrofisiológicas, e resposta ao tratamento em dez pacientes brasileiros com NP-LEMS. A idade média foi de 41,5 anos. A manifestação neurológica mais freqüente foi hiporeflexia ou arreflexia com melhora após o exercício. A resposta ao tratamento ocorreu com piridostigmina, guanidina, prednisona, azatioprina, e ciclosporina; mas não com imunoglobulina intravenosa e plasmaférese. A idade de início, manifestações clínicas e eletrofisiológicas ajudaram mais no diagnóstico do que os anticorpos séricos; o tratamento sintomático com piridostigmina foi efetivo; e o tratamento imunossupressor com prednisona, azatioprina, ou ciclosporina beneficiou mais do que a plasmaférese ou a imunoglobulina intravenosa.

Iatrogenic Botulism After Intramuscular Injection of Botulinum Toxin Type A

Botulinum toxin type A (BTA) is widely used for both medical treatment and cosmetic purposes. A 46-year-old woman presented with progressive generalized weakness and dysphagia. The patient had injected BTA into her both of her calves by herself for cosmetic purposes. Repetitive nerve stimulation of the right facial nerve demonstrated reduced compound muscle action potential amplitudes of the orbicularis oculi and nasalis muscles, and a reduced response to low-frequency, repetitive stimulation. The possibility of iatrogenic botulism should be considered when using BTA.

Electrophysiological Changes in Lambert-Eaton Myasthenic Syndrome With Intravenous Immunoglobulin Therapy

No abstract available.

Modulation of Human Somatosensory Cortical Excitability by Repetitive Peripheral Nerve Stimulation

OBJECTIVE: To investigate whether the somatosensory cortical excitability could be modulated by repetitive electrical stimulation (RES) on the tibial nerve at human ankle joint. METHOD: The subjects were 10 healthy volunteers. The study was composed of 3 sessions: first session, baseline evaluation; second session, RES with a intensity for proprioceptive stimulation on tibial nerve at the right ankle for 3 different duration of 30 minutes, 1 hour, and 2 hours; third session, repeat of baseline evaluation after RES (post- RES evaluation). The baseline evaluation include somatosensory evoked potential study with stimulation of right tibial nerve and compound muscle action potential (CMAPs) of tibial nerve recorded at abductor hallucis and H reflex. The amplitude of each study were measured and compared between baseline evaluation and post-RES evaluation using Kruscal-Wallis test. RESULT: There was no significant change in amplitudes of SSEP, CMAP and H reflex between baseline evaluation and post-RES evaluation of 30 minutes, 1 hour and 2 hours. CONCLUSION: This study suggests that chronic repetitive proprioceptive afferent nerve stimulations could not modulate primary somatosensory cortex in healthy subjects. However, we could not rule out the limitations of sensitivity of somatosensory evoked potential study.

A comparative study of single fiber electromyography and repetitive nerve stimulation of the same extensor digitorum communis muscle in patients with myasthenia gravis / 中华物理医学与康复杂志

Objective To investigate the possible causes of the different diagnostic sensitivity of voluntary single fiber electromyography (SFEMG) and repetitive nerve stimulation(RNS) in patients with myasthenia gravis (MG). Methods The voluntary SFEMG and RNS at low rates were recorded successively from the same extensor digitorum communis (EDC) muscle on the same day in 67 patients with MG. Results The diagnostic sensitivity of SFEMG and RNS was 92.5% and 50.7%, respectively, with the former statistically significantly higher than the later. The percentage of decrement of RNS was positively correlated with 3 SFEMG parameters, i.e. the mean jitter, percentage of abnormal pairs of potential and percentage of impulse blocking. Among the 34 cases with significant decrement on RNS, 2 had no impulse blocking and the maximum decrement reached 62%, while 33 cases with normal RNS had up to 58% of impulse blocking. Conclusion The voluntary SFEMG was more sensitive than RNS in diagnosing MG even in the same muscle. The blocking phenomenon observed in voluntary SFEMG was not completely corresponding to the decrement in RNS.The possible explanations were partly because that RNS recorded the total muscle fibers response in surface of the muscle and SFEMG examined the increasing or blocking at individual motor end-plates, and partly because that the voluntary SFEMG and RNS might explored endplates belonging to different motor units.

Electrophysiologic Responses of Neuromuscular Junction by High Dose of Botulinum Toxin A Injection: Local and Distant Effects

OBJECTIVE: The purpose of this study was to measure the local and distant effects of BTX-A of different dosage through the electrophysiologic study. METHOD: Sixteen Sprague-Dawley rats were used and divided into four groups by the dosage of BTX-A (Botox , Allergan Co.): 2, 4, 6, 8 U for each of the four rats. BTX-A was injected into tibialis anterior (TA) muscles. Slow rate (3 Hz) and fast rate (20 Hz) repetitive nerve stimulation test (RNST) was performed before and after BTX-A injection. The schedule of postinjection was as follows: 2 days after the injection, every seven days till 10 weeks postinjection, once a month for 4 months. RESULTS: In the fast rate RNST of the treated TA muscle, dose-dependent increments were seen on the 2nd day postin jection and thereafter dose-dependent decrements appeared and weakened over the course of time. In the slow rate RNST of the treated TA, dose-dependent decrements were observed through ten weeks postinjection in all groups. In the fast rate RNST of the untreated TA, incremental responses were produced in all groups in a dose-dependent manner. In the slow rate RNST of the untreated TA, there were no changes. CONCLUSION: The BTX-A injection causes local paralysis in the treated muscles and presynaptic dysfunction of the neuro muscular junction in the distant untreated muscles in a dosedependent manner. This study could not be differentiated between neuromuscular dysfunction, myopathy or neuropathy through these RNST studies.

Diagnostic Sensitivity of Several Muscles in Repetitive Nerve Stimulation Test for Myasthenia Gravis / 영남의대학술지

BACKGROUND: This study was undertaken to evaluate the diagnostic sensitivity of several muscles in repetitive nerve stimulation test (RNST) for myasthenia gravis (MG) patients. MATERIALS AND METHODS: The study population consisted of 39 MG patients classified by modified Ossermann's classification. Using Stalberg's method, RNST was systematically performed in facial (orbicularis oculi and nasalis) and upper extremity (flexor carpi ulnaris, abductor digiti quinti and anconeus) muscles. RESULTS: The significant electrodecremental response of RNST were noted in orbicularis oculi (58.9%), nasalis (51.3%), flexor carpi ulnaris (42%), anconeus (41%) and abductor digiti quinti muscles (27%). Among the 3 muscles of upper extremity (abductor digiti quinti, flexor carpi ulnaris and anconeus), the positive electrodecremental response of anconeus muscles was significantly higher than other two muscles (p<0.05) in type IIa, IIb and there were no statistical differences of the positive electrodecremental response between orbicularis oculi and nasalis muscles. The facial muscles showed more prominent decremental responses than upper extremity muscles in type I MG(p<0.05). In type IIa MG patients, there were no significant statistical differences between facial and upper extremity muscles but significant statistical differences among upper extremity muscles. In type IIb MG patients, there were no significant statistical differences in all tested muscles in spite of the increased positive electrodecremental response of RNST. CONCLUSION: On the basis of this study, RNST would be initially performed for the orbicularis or nasalis in type I MG and for the anconeus in type IIa or IIb MG.

Clinical Significance of Axonal Stimulation Single Fiber Electromyography in Patients with Myasthenia Gravis

BACKGROUND: The axonal stimulation single fiber electromyography (S-SFEMG) is a relatively new electrophysio-logical technique and has several advantages over conventional voluntarily activated single fiber electromyography (V-SFEMG). This study was performed in patients with myasthenia gravis (MG) in order to analyze their neuromuscular transmission defects and thus to verify the usefulness of the S-SFEMG technique. METHODS: In 44 patients with MG, S-SFEMG was performed on the extensor digitorum communis muscle. The repetitive nerve stimulation test (RNST) on orbicularis oculi, trapezius, flexor carpi ulnaris, and abductor digiti quinti muscles was also performed at the same time. The results of the RNS and S-SFEMG were then analysed in detail. RESULTS: The S-SFEMG was found abnormal in 84.1%, while RNST was found abnormal in 75.0% of the patients tested. The normal S-SFEMG result was observed exclusively among 7 ocular type MG patients. The mean of the mean consecutive difference (MCD) value, % of fibers with blocking and % of fibers with abnormal jitter, was more increased in patients with generalized type MG than those with ocular type MG. This difference was statistically significant (P<0.01) in all 3 variables. CONCLUSIONS The S-SFEMG is a highly sensitive and useful diagnostic tool in MG. Although it demands more strict technical consideration than V-SFEMG, it is less time-consuming and applicable to uncooperative patients including children. Our study shows S-SFEMG to be especially useful in patients with ocular type MG whose RNST results do not show definite decremen-tal responses.

Re-evaluation of Repetitive Nerve Stimulation Test in Myasthenia Gravis and Myasthenic Syndrome

BACKGROUND: The repetitive nerve stimulation (RNS) test is a useful tool in the evaluation of neuromuscular transmission disorders. In our laboratory, we frequently use Oh's method, which tests 5 kinds of muscles (flexor carpi ulnaris (FCU), abductor digiti quinti (ADQ), orbicularis oculi, nasalis and trapezius) with 3 kinds of low rate stimulation (LRS) and high rate stimulation (HRS). This method has the advantage of high sensitivity, but is time consuming and painful to patients. So, we tried to reestablish the stage of RNS to overcome this problem and to create a useful test. METHODS: We analyzed RNS data from 369 patients, retrospectively. The number of patients with myasthenia gravis (MG) was 357 and the number with myasthenic syndrome was 12. We compared the sensitivity of individual muscle as well as individual stimulation rate. And we analyzed the results of MG and myasthenic syndrome to verify the usefulness of HRS. RESULTS: The sensitivity of RNS (LRS) was 69.7% in MG (generalized symptom 86.4%, only ocular symptom 40.3%). The sensitivity was higher with 3 pps and 5 pps than with 2 pps, while the exclusion of 2 pps did not affect the sensitivity. We found only 3 cases (1.0%) with post-tetanic exhaustion (PTE) in MG patients with negative results on LRS. The distributions of resting CMAP and post-exercise CMAP were different between MG and myasthenic syndrome. In most cases of myasthenic syndrome, the resting CMAP of ADQ and FCU was below 4.0 mV and post-exercise CMAP of ADQ and FCU was above 50%. CONCLUSIONS: LRS may be done with only 3 and 5 pps, and HRS of the ulnar nerve was helpful only if there was a suspicion of myasthenic syndrome (resting CMAP50%, in ADQ & FCU) or a borderline decremental response in LRS.

Comparison between the Electric and Magnetic Stimulations for a Repetitive Nerve Stimulation Test

The low rate repetitive nerve stimulation test(RST) using the electric stimulation has been known the best procedure among the electroliagnostic evaluations for the neuromuscular transmission. However, the electric stimulation often causes a considerable discomfort and pain during the procedure. On the contrary, the magnetic stimulation is much easier and less painful in activating to activate the deep seated nerves. The purpose of this study was to compare the effect of repetitive magnetic and electric stimulation for the induction of compound muscle action potentials(CMAP) of abductor digiti quinti and deltoid muscles in 25 healthy subjects. The results were showed there were no significant differences in the amplitudes of CMAP of axillary and ulnar nerves between the magnetic and electric stimulations. And there were no significant differences in the decremental ratio of CMAP between the magnetic and electric stimulations. The magnetic stimulations were less painful for the subjects than electric stimulations in both proximal and distal muscles. In conclusion, the magnetic stimulation proved to be a useful method for repetitive nerve stimulations in the diagnosis of neuromuscular disease.

Correlations between electrophysiological parameters of repetitive nerve stimulation and single fiber electromyography tests in myasthenia gravis

BACKGROUND AND PURPOSE: For diagnosis of acquired autoimmune myasthenia gravis (MG), single fiber electromyography (SFEMG) is known to be much more sensitive than repetitive nerve stimulation test (RNST) in demonstrating the electrophysiological defects of neuromuscular transmission. Neuromuscular blocking in SFEMG is presumed to have the same physiologic basis with decremental response in RNST. The authors performed the study to know the correlations between the electrophysiological parameters of the RNST (decremental response) and the SFEMG (jitter and blocking) and to understand the basic physiological mechanisms in MG. METHODS: In 28 patients with definite MG (12 : ocular MG, 16 : generalized MG), RNST and SFEMG tests were done in orbicularis oculi and abductor digiti quinti and in extensor digitorum communis, respectively. The correlations between several factors, such as maximum decremental response (%) in RNST, mean value of mean consecutive differences (MCD's) (?sec) and blocking pairs (%) were analyzed. RESULTS: In 12 ocular MG patients, RNST and SFEMG abnormalities were found in 4 (33.3%) and in 10 (83.3%), respectively. In 16 generalized MG patients, abnormal decremental responses were found in 13 (81.3%) and increased jitters in 15 (93.8%). SFEMG showed significant correlations between blockings and mean MCD's (R=0.54, p<0.01). When the correlation between RNST and SFEMG was analyzed, increased percentage of blockings in extensor digitorum communis were correlated with maximum degree of decremental responses in abductor digiti quinti or orbicularis oculi (R=0.60, p<0.001). The degree of mean MCD's was poorly correlated with maximum decremental responses (R=0.23, p=0.229). But the correlation became significant (R=0.43, p<0.05) by analyzing mean MCD's and maximum decremental responses only from abductor digiti quinti, reflecting that blockings have similar electrophysiological meanings with increased mean MCD's. CONCLUSION: The good correlation between decremental response in RNST and blocking or mean MCD's in SFEMG was found. Therefore the authors concluded that the parameters of the RNST and the SFEMG show similar electrophysiologic phenomena of the abnormal neuromuscular transmission in MG.