Trigeminal nerve repetitive stimulation in myasthenia gravis

The aim of this study was to evaluate the utility of repetitive nerve stimulation (RNS) of the trigeminal nerve in assessing patients with myasthenia gravis (MG). In 26 normal controls and 21 patients with myasthenia gravis (MG), 2-Hz repetitive stimulation of the trigeminal nerve was performed using a monopolar needle for percutaneous nerve stimulation and recording over the surface of the masseter. In the MG patients, repetitive stimulation of the ulnar, spinal accessory, and facial nerves was also performed. The mean percent decrement in the compound muscle action potential (CMAP) amplitude among the different nerves at rest were: ulnar, 4.3%; spinal accessory, 10.1%; facial, 14%; and trigeminal, 17.3%. The facial nerve demonstrated abnormal decrement in 57% of all patients, compared with the spinal accessory (48%), trigeminal (43%), and ulnar (20%) nerves. All patients tolerated trigeminal RNS better than or as well as facial RNS. The study demonstrates that trigeminal RNS is a safe, reliable, efficient, and well-tolerated technique that provides another cranial nerve-muscle combination that can be used to supplement repetitive stimulation of other limb or cranial nerves in the evaluation of patients with bulbar or generalized MG.     

Radial nerve repetitive stimulation in myasthenia gravis

The purpose of this study was to compare the diagnostic yield of repetitive radial nerve stimulation (RNS) while recording from extensor indicis proprius (EIP) to other commonly used muscle-nerve combinations in patients with myasthenia gravis (MG). Radial RNS with recording from EIP was performed in 20 controls and 20 patients with MG. It revealed an abnormal decrement at rest in 35% of patients compared to 11% with ulnar nerve stimulation, 64% with spinal accessory nerve stimulation, and 74% with facial nerve stimulation. Radial-EIP RNS is a reliable technique in the evaluation of MG and appears more sensitive than ulnar nerve RNS.     

The accessory nerve repetitive nerve stimulation test: a valuable second-line test in myasthenia gravis

The diagnostic usefulness of the accessory nerve repetitive nerve stimulation (RNS) test was evaluated in 100 patients with myasthenia gravis (MG). The test was easy to perform and reliable at the low rates of stimulation. A higher diagnostic sensitivity was found in the accessory nerve RNS test than in the ulnar nerve RNS test on either the abductor digiti quinti or flexor carpi ulnaris muscles, especially in mild generalized MG. Diagnostic sensitivity was significantly increased when RNS test results for three muscles were combined, especially in mild generalized MG and sero-positive MG. In a small number of cases only the ulnar or accessory nerve RNS test was abnormal. There was a good correlation between electrophysiological and clinical severity of MG in the accessory nerve RNS test Thus, we conclude that the accessory nerve RNS test is a valuable second-line test and its greatest usefulness is in cases of mild generalized MG.     

Electrodiagnostic evaluation of patients with myasthenia gravis and related disorders

The technique of repetitive nerve stimulation was developed as a means of confirming a diagnosis of MG. The application of this test in the clinical evaluation of patients with muscle weakness has identified other disorders of neuromuscular transmission such as LEMS, infantile botulism, and several forms of congenital myasthenia. Repetitive nerve stimulation to several different nerves, before and after exercising the muscles, usually permits identification of disorders of neuromuscular transmission more readily than very detailed study of one muscle. There are other useful electrodiagnostic tests, but in most cases, repetitive nerve stimulation of weak muscles will permit the identification of a disorder of neuromuscular transmission.     

Is the stimulation frequency of the repetitive nerve stimulation test that you choose appropriate?

The repetitive nerve stimulation test (RNST) has been a useful method in the diagnosis of myasthenia gravis (MG). In clinical practice, a short train of repetitive stimulation is usually given at 3 Hz. Although it was documented that lower stimulation frequencies could offer a greater sensitivity, no study has been done to testify the most sensitive stimulation frequency for RNST. To find out an optimal stimulation frequency, we performed RNST at 0.5, 1, 3, 5, 7, 10, 15 and 20 Hz in 15 MG patients and 5 healthy subjects. The results showed that the decremental response was most often seen at 7 Hz rather than at 3 Hz. To augment the sensitivity in the diagnosis of MG, RNST should be performed stimulation not only at 3Hz but also at other frequencies, preferably 7 Hz.     

肋间神经重复电刺激在激素冲击治疗重症肌无力中的应用

目的探讨肋间神经重复电刺激(IRNS)和膈神经重复电刺激(PRNS)对激素冲击治疗时重症肌无力(MG)患者呼吸受累的预测价值.方法治疗开始前3天内检测36例MG患者PRNS和IRNS,同时观察用力肺活量(FVC)、MG临床评分、治疗中临床呼吸症状变化.结果大剂量激素治疗后2～13天14例(40%)患者出现呼吸功能受累或原有呼吸困难加重,呼吸功能恶化患者与未恶化患者相比,上述参数及MG临床类型均有明显差异.Lo-gistic回归分析显示3Hz及5Hz的IRNS双侧波幅衰减均值超过30%时比不超过时发生呼吸困难或原有呼吸困难加重的相对危险度均为19.523.结论治疗中呼吸功能受累与上述指标及MG临床分型均有关系,IRNS可以预测是否发生呼吸功能恶化.     

Sensitivity of repetitive facial-nerve stimulation in patients with myasthenia gravis

Repetitive stimulation of the facial nerve is commonly performed in cases of suspected myasthenia gravis (MG) because bulbar weakness is often present, but the most sensitive facial muscle is unknown. We compared the sensitivity of repetitive nerve stimulation (RNS) to the frontalis and nasalis muscles in 244 patients with suspected MG. We found no difference in sensitivity of RNS when recording from these muscles in both ocular and generalized MG. In addition, we confirmed the low sensitivity of RNS for ocular (18%) or generalized (47%) MG. The specificity of facial RNS for both muscles was 100% and, in certain circumstances, may obviate the need for further diagnostic testing.     

Stimulated single-fiber electromyography in Lambert-Eaton myasthenic syndrome.

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission. Electrodiagnosis is confirmed by an increase in compound muscle action potential amplitude during high-frequency repetitive nerve stimulation or following brief exercise. We describe the results of stimulated single-fiber electromyography in 4 patients with disorders of neuromuscular transmission: LEMS (2), LEMS/myasthenia gravis (MG) overlap (1), and MG (1). Stimulated SFEMG was performed in the extensor digitorum communis muscle with axonal intramuscular suprathreshold stimulation at low and high rates. In all 4 patients, a rate dependence of jitter was found. In LEMS and LEMS/MG, jitter and blocking improved with high stimulation rates, as compared with the opposite effect in MG. We conclude that stimulated SFEMG is a valuable technique in the diagnosis of LEMS.     

Low-dose tacrolimus for intractable myasthenia gravis

We treated two patients suffering from intractable myasthenia gravis (MG) with low-dose tacrolimus plus prednisolone. Both patients showed significant improvement of myasthenic signs, accompanied by suppressed serum anti-acetylcholine receptor antibody, waning in compound muscle action potential by repetitive nerve stimulation and IL-2 production by peripheral blood mononuclear cells. Low-dose tacrolimus plus prednisolone is a promising therapeutic regimen for intractable MG.     

Decrement pattern in Lambert-Eaton myasthenic syndrome is different from myasthenia gravis

The decrement pattern at low rates of repetitive nerve stimulation in myasthenia gravis (MG) is characterized by a decrease of compound muscle action potential size within the first 4-5 responses. With subsequent stimuli, compound muscle action potential size either increases or does not change. Following an observation that the pattern of decrement might be different in patients with Lambert-Eaton myasthenic syndrome (LEMS), we retrospectively studied traces from eight LEMS patients and 14 patients with seropositive generalized MG, calculating decrement percent from first to fourth and from first to ninth compound muscle action potential. In the LEMS patients, compound muscle action potential amplitude decreased progressively from first to ninth stimulus at 2, 3 or 5Hz in all traces but one. In contrast, MG patients demonstrated the expected improvement after the initial decrement in all traces except one. In the evaluation of patients suspected of having myasthenia gravis, the finding of progressive decrement pattern at low rates of repetitive nerve stimulation may alert the electromyographer to the possibility of Lambert-Eaton syndrome and prompt the performance of further electrodiagnostic tests.     

伴自发电位重症肌无力的临床及电生理特点

目的探究伴自发电位重症肌无力患者的临床及电生理特点。方法收集重症肌无力住院患者共90例,均行重复神经电刺激、针电极肌电图检查,其中6例出现自发电位,回顾性分析6例病例临床及电生理特点。结果 6例患者均确诊为全身型重症肌无力,其中胸腺瘤合并率为3/6。乙酰胆碱受体抗体均阳性且多数滴度较高,其他重症肌无力抗体均阴性。针电极肌电图可见自发电位,均伴运动单位时限缩窄,重复神经电刺激均见低频波幅递减、高频未见递增。结论本研究揭示了全身型重症肌无力患者的一种少见电生理表现,即以正锐波及纤颤电位为主的自发电位,可为严重神经肌肉接头异常所致。     

Repetitive phrenic nerve stimulation in myasthenia gravis.

OBJECTIVE: In patients with MG it may be difficult to determine whether respiratory insufficiency is due to a defect in neuromuscular transmission. We therefore studied the clinical value of repetitive electrical stimulation of the phrenic nerve. METHODS: Repetitive phrenic nerve stimulation at 3 Hz was performed in 25 patients with MG. We recorded from the ipsilateral hemidiaphragm with surface electrodes before and after exercising the diaphragm for 10 and 90 seconds. The percent decrement of the negative peak (NP) area between the first and the fifth or sixth diaphragmatic compound muscle action potential (DCMAP) was analyzed and results compared with those from 10 healthy individuals. RESULTS: The mean +/- standard deviation percent change of the NP area in healthy individuals was -2.1 +/- 4.2%, with a normal cutoff of > or = 11%. Twelve patients (48%) had an abnormal decrement of DCMAP--9 had a decrement when the diaphragm was rested, 3 only after fatiguing of the diaphragm. The mean percent change in the 12 patients was 20% at rest, -18% after 10 seconds of exercise, and -23% after 90 seconds of exercise-a pattern consistent with MG. Repetitive stimulation of the accessory nerve with recording of the trapezius CMAP (TCMAP) was abnormal in nine patients (36%). The three patients with abnormal decrement of the DCMAP despite normal TCMAP had symptoms of dyspnea. CONCLUSIONS: Repetitive phrenic nerve stimulation studies are a promising tool in the diagnosis of respiratory muscle weakness in MG and should be part of electrophysiologic studies in patients with undiagnosed respiratory failure.     

Contrast of time courses of changes in muscular potentials to prolonged stimulation at 5 Hz in rat medial gastrocnemius and soleus muscles

Time courses of changes in muscular potentials to repetitive stimulation at 5 Hz for 10 min were compared between rat medial gastrocnemius (MG) and soleus (SOL) muscles. Stimuli were applied to a sciatic nerve near the entrance of the MG and lateral gastrocnemius (LG) muscles and its exit segment from the LG to the SOL muscles. Muscular potentials were generally evoked in the form of a biphasic wave at the MG muscle and were always of a simple biphasic pattern at the SOL muscle. It was found that, due to prolonged stimulation, muscular potentials were rapidly and notably reduced in the MG muscle, whereas they were gradually facilitated in the SOL muscle. This contrast was similar to differences in the time course of changes in muscular potentials under these conditions in the MG muscle of dystrophic and littermate normal mice.     

Is exercise necessary with repetitive nerve stimulation in evaluating patients with suspected myasthenia gravis?

We retrospectively evaluated the effect of exercise on the degree of decrement in ulnar, spinal accessory, and facial repetitive nerve stimulation (RNS) in 179 patients with myasthenia gravis (MG) to assess whether exercise increases the diagnostic yield of identifying significant decrements. The mean worsening of decrement following exercise was 1.9% (ulnar nerve), 1.9% (spinal accessory nerve), and 1.3% (facial nerve). Abnormal (> or =10%) decrement solely following exercise occurred in the ulnar nerve in 7% of patients, accessory nerve in 5%, and facial nerve in 7%. When analyzed according to Myasthenia Gravis Foundation of America class of disease, the likelihood of producing > or =10% decrement only after exercise was greatest in class I MG with facial RNS and in class II and III generalized MG with ulnar and spinal accessory RNS. In all other disease stages, the likelihood of producing > or =10% decrement only after exercise was < or =7%. This study suggests that exercise increases the yield of diagnosis of MG by RNS in only a small percent of patients. Therefore, in most patients with suspected MG, RNS at rest is sufficient and the additional time required for prolonged postexercise RNS may be better spent in examining other muscle-nerve combinations.     

Comparison of diagnosis value for new onset myasthenia gravis by many clinical auxiliary examinations

BACKGROUND: The clinical values of neostigmine test, clinical electrophysiologic study and acetylcholine receptor antibody detection in diagnosing myasthenia gravis (MG) found newly are unclear in China. OBJECTIVE: To investigate the reference value of common clinical diagnosis parameters in correctly diagnosing untreated MG found newly. DESIGN: Retrospective case analysis. SETTING: Department of Neurology, Beijing Hospital, Ministry of Health. PARTICIPANTS: Totally 156 outpatients with MG admitted to Department of Neurology, Beijing Hospital, Ministry of Health between January 1999 and December 2002. The involved patients, 72 males and 84 females, were aged 2–79 years. They were classified according to Osserman's criteria: ⅡA 72，ⅡB 76, Ⅲ 3 and Ⅳ 5. They were all subjected to being inquired of disease history, neostigmine test, and acetylcholine receptor antibody detection, met the diagnosis criteria of Neuroimmunology Committee of China, and confirmed by clinical electrophysiologic detections; Informed consents were obtained from all the involved subjects. METHODS: ①After admission, every patient was intramuscularly injected with 1.5 mg neostigmine; If the patient was a child, the injection dose was decreased according to his/her age. If his/her score of any observation index after injection was improved ≥ 50% as compared with before injection , his positive index was set as positive. Positive neostigmine test was set if there was one positive index. ②Repetitive nerve stimulation and single fiber electromyography were performed with Dantec Keypoint electromyogram (EMG) apparatus. ③Acetylcholine receptor antibody was detected by ELISA method. MAIN OUTCOME MEASURES: Clinical absolute and relative scores of MG, acetylcholine receptor antibody level, and repetitive nerve stimulation and single fiber electromyography examination results. RESULTS: The positive rates of neostigmine test, repetitive nerve stimulation and single fiber electromyography examination for MG were 86.5%, 82.6%, and 69.2%, respectively, and the positive rate of acetylcholine receptor antibody was 78.8%. CONCLUSION: Standardized neostigmine test has the highest sensitivity to diagnose MG.     

Repetitive hypoglossal nerve stimulation in myasthenia gravis.

OBJECTIVES: To assess the diagnostic efficacy of repetitive nerve stimulation (RNS) of the hypoglossal nerve in patients with myasthenia gravis (MG) and bulbar symptoms (dysphagia, dysarthria). METHODS: Twenty patients with MG and 25 normal controls had RNS of the hypoglossal nerve. All patients also had single fibre electromyography (SFEMG) of the orbicularis oculi and RNS with recordings of the nasalis, trapezius and abductor pollicis brevis muscles. RESULTS: All patients had positive SFEMG studies. Nine patients with bulbar symptoms had positive hypoglossal RNS, including 3 with negative RNS recordings in other muscles. Eleven patients with no bulbar symptoms showed negative hypoglossal RNS, including two with positive RNS recordings from other muscles. CONCLUSIONS: Abnormal RNS of the hypoglossal nerve correlates well with bulbar dysfunction and further characterises the extent of neuromuscular transmission defect in MG patients.     

Mechanisms of fatigue in normal intercostal muscle and muscle from patients with myasthenia gravis

Fatigue mechanisms in normal intercostal muscle and muscle from patients with myasthenia gravis (MG) were evaluated by monitoring the compound muscle action potential (CMAP) and tetanic tension responses to repetitive nerve or muscle stimulation in vitro. When fatigue was induced by nerve stimulation at 30 Hz for 0.5 s every 2.5 s, about half of the original tension decreased after 30 min in normal muscle and 5 min in MG muscle. Analysis of the changes in area of CMAPs and tension indicated that impairment of neuromuscular transmission, muscle membrane excitation, and excitation-contraction (E-C) coupling and contractility accounted for 40%, 29%, and 31% of fatigue in normal muscle, and 83%, 0%, and 17% of fatigue in MG muscle. When fatigue was induced by muscle stimulation at 30 Hz, tension declined by a quarter after 30 min in normal muscle, but by a half after 17 min in MG muscle. Impairment of muscle membrane excitation and E-C coupling and contractility accounted for 58% and 42% of fatigue in normal muscle, and 22% and 78% of fatigue in MG muscle. Thus, fatigue of normal muscle is caused by impairment of at least four processes, and enhanced fatigue of MG muscle is caused by greater impairment of neuromuscular transmission, E-C coupling, and contractility. © 1993 John Wiley & Sons, Inc.     

Peroneal nerve repetitive nerve stimulation test: Its value in diagnosis of myasthenia gravis and Lambert–Eaton myasthenic syndrome

We have developed a repetitive nerve stimulation (RNS) technique for the peroneal nerve. Normal limits for the decremental responses for the anterior tibialis and extensor digitorum brevis muscles are 6–21% at the low rate of stimulation and 44–70% at the high rate of stimulation. These values exceed the normal limits for other commonly tested muscles. This may be due to the lower safety factor for neuromuscular transmission for the anterior tibialis and extensor digitorum brevis muscles. We present 4 cases in which the peroneal nerve RNS test was crucial for the diagnosis of the limb-girdle form of MG or LEMS. Thus, we conclude that, in a small number of patients with neuromuscular transmission disorders, the peroneal nerve RNS test is needed for confirmation of disease. © 1995 John Wiley & Sons, Inc.     

Muscle strength and fatigue in patients with generalized myasthenia gravis

Myasthenia gravis (MG) is characterized by fatigue and fluctuating muscle weakness resulting from impaired neuromuscular transmission (NMT). The objective of this study was to quantify, by direct measurement of muscle force, the strength and fatigue of patients with MG. A maximal voluntary isometric contraction protocol of shoulder abductors was used in conjunction with conventional fatigue and disease‐severity instruments. Results from patients with (D‐MG) and without (ND‐MG) decrement on repetitive nerve stimulation (RNS) of the spinal accessory and axillary nerves were compared with healthy controls. Patients with MG reported greater fatigue than controls. Muscle strength was lowest in the D‐MG group, followed by the ND‐MG group and controls. Normalized shoulder abduction fatigue and recovery values did not differ between the D‐MG and ND‐MG groups or controls. The RNS decrement appears to relate best to disease severity and muscle weakness but not to objective measures of fatigue in this population. Muscle Nerve, 2009     

Diagnostic sensitivity of the laboratory tests in myasthenia gravis.

The diagnostic sensitivity of three laboratory tests [serum antiacetylcholine receptor antibody (AChR-ab) assay, the repetitive nerve stimulation (RNS) test, and, the single fiber EMG (SFEMG)] for myasthenia gravis (MG) was compared in 120 patients. In all cases, at least one of the tests was abnormal. SFEMG was the most sensitive test, being abnormal in 92% of cases, followed by the RNS test (77%) and the AChR-ab assay (73%). SFEMG was abnormal in all cases with negative AChR-ab and RNS tests, in 97% of cases with negative AChR-ab assay, in 89% of cases with negative RNS test, and in 89% of cases with mild MG. We conclude that one of these three tests is abnormal in all cases of MG, and that the SFEMG is most sensitive in the diagnosis of MG.