Muscle strength and fatigue in newly diagnosed patients with myasthenia gravis

Introduction: Dynamometry is increasingly used as an objective measurement of muscle strength in neurological diseases. No study has applied dynamometry in untreated newly diagnosed patients with myasthenia gravis (MG). Methods: Isometric muscle strength at the shoulder, knee, and ankle was determined in 21 MG patients before and after initial anti‐myasthenic treatment. Isometric strength was compared with MG evaluation scales. Results: Muscle strength was reduced for knee extensors and shoulder abductors but normal for ankle extensors. Isometric muscle strength did not correlate significantly with manual muscle testing (MG Composite). Dynamometry revealed improved muscle strength of up to 50% (median 17%; range ‐1.8–49.8) despite no change in the MG Composite score. Conclusions: Dynamometry appears to be a more sensitive method of identifying changes in limb strength than MG evaluation scales. This supports the use of dynamometry in MG patients, especially for evaluation of the effect of anti‐myasthenic treatment. Muscle Nerve 54 : 709–714, 2016     

New strategy for improving the diagnostic sensitivity of repetitive nerve stimulation in myasthenia gravis

Introduction: The diagnostic sensitivity of repetitive nerve stimulation (RNS) in patients with myasthenia gravis (MG) varies as a function of the number of muscles or the choice of muscles studied. Methods: By exploring 12 muscles bilaterally, we evaluated the global sensitivity of RNS at rest, the sensitivity in different clinical forms, and the sensitivity of different combinations of muscles studied. Results: The global sensitivity of RNS was 82%, and specificity was 100%. The sensitivity in the MG subgroups was as follows: ocular (O) = 67%; oculobulbar (OB) = 86%; and generalized (G) = 89%. The most sensitive muscles were the anconeus in group O, orbicularis oculi (OO) or nasalis in group OB, and the trapezius in group G. Maximum sensitivity was obtained by exploring OO, trapezius, and anconeus bilaterally. Conclusions: We recommend bilateral exploration of at least 3 muscles, a facial muscle, trapezius, and anconeus. Muscle Nerve 55 : 532–538, 2017     

重症肌无力患者低频重复神经电刺激的特点

目的研究重症肌无力(myasthenia gravis,MG)患者低频重复神经电刺激(repetitive nerve stimulation,RNS)的特点。方法回顾性分析1995-2010年作者医院住院的275例MG患者的低频RNS检查资料。结果 275例患者中RNS检查结果异常216例,异常率为78.55%。其中Ⅰ型RNS异常率最低(48.91%),且与其他临床分型异常率之间存在统计学差异(P<0.05)。刺激腋神经RNS异常率最高(58.68%),面神经次之(56.18%),尺神经最低(18.88%)。在眼轮匝肌和三角肌进行记录时所测得的RNS异常率高于在小指展肌所测(P<0.01)。结论 MG患者RNS异常率与临床分型及检测部位有关。Ⅰ型患者RNS异常率低于其余各分型,于近端肌肉记录时所测的RNS异常率明显高于在远端肌肉所测。     

Single fiber EMG and repetitive stimulation of the same muscle in myasthenia gravis

We performed RNS and SFEMG studies of the same muscle in 46 patients with myasthenia gravis. Maximum decrement to 3–5-Hz stimulation before and after maximum voluntary exercise, percentage of action potential pairs with increased jitter and blocking, and mean MCD in each study were compared. A significant decrement (> 10% decrease in CMAP area or amplitude between the first and fourth response) was never found without increased jitter and impulse blocking on SFEMG. Increased jitter, blocking, and mean MCD were each correlated with maximum decrement (r > 0.61, P < 0.0001). We conclude that decrement to RNS and impulse blocking on SFEMG result from the same physiologic phenomenon, and that SFEMG is more sensitive at detecting disordered neuromuscular transmission given its ability to detect impulse blocking at levels below the resolution of RNS and increased neuromuscular jitter when there is not blocking. © 1994 John Wiley & Sons, Inc.     

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.     

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.     

AAEM case report #3: myasthenia gravis.

Reported here are the electrodiagnostic findings in a patient with myasthenia gravis who had dysarthria, dysphagia, and dyspnea. The use of repetitive nerve stimulation and single fiber electromyography studies for the evaluation of patients suspected of myasthenia gravis is reviewed.     

重症肌无力的电生理研究

目的探讨重症肌无力（ＭＧ）患者的电生理特征及其诊断价值。方法应用针极肌电图（ＥＭＧ），重复神经电刺激（ＲＮＳ）和激发重复神经电刺激（ＡＲＮＳ）方法，对４７例ＭＧ患者的肌肉和神经肌肉传递功能进行研究。结果部分患者的肌肉见到病理自发电位及短小动作电位，具近端肌分布特征。ＡＲＮＳ阳性率（９０．６％）较ＲＮＳ阳性率（８３．０％）高。Ⅰ型患者肢体肌群存在多项电生理异常。结论适当、综合应用电生理检测技术有助于ＭＧ的早期诊断     

Tongue force in patients with myasthenia gravis

OBJECTIVES: The aim was to study tongue force in patients with bulbar myasthenia gravis and compare it with that of patients with ocular myasthenia gravis, patients in clinical remission who previously suffered from bulbar myasthenia gravis, and healthy subjects. MATERIAL AND METHODS: Tongue force was measured with a tongue force transducer in cranial and lateral directions, which coincide with the directions in which the tongue exerts force during swallowing, speech, and mastication. RESULTS: Tongue force in lateral direction was significantly decreased in patients with bulbar myasthenia gravis. In addition, our findings suggest an incomplete recovery of lateral tongue force in the patients of the remission group. CONCLUSION: Our tongue force measurements may be useful for longitudinal evaluation of therapy in individual patients and also in studies of therapy efficacy in matched groups of patients if the influence of factors such as age, dental state, and sex is taken into account.     

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.     

Correlation of C3 level with severity of generalized myasthenia gravis

Acute exacerbation of generalized myasthenia gravis (GMG) can cause swallowing impairment, respiratory failure, or death. It is important to identify immunological factors that might be regarded reliably as an index of the patient's clinical condition, response to treatment, and measure of certain immune aberrations of MG. In this study we investigated correlations between complement component C3, acetylcholine receptor antibody (AChRab) titer, and clinical severity of GMG. AChRab titer and C3 concentration were determined by radioimmunoassay and nephelometry, respectively. The clinical severity of GMG was assessed by the quantitative MG score (QMGS) according to Besinger and colleagues. Our findings indicate that the C3 level correlates with clinical severity of AChRab‐positive GMG. Muscle Nerve, 2009     

Lifetime course of myasthenia gravis

Between 1940 and 2000 a total of 1976 patients with myasthenia gravis (MG) were studied. Diagnosis was made by improvement in weakness after anticholinesterase medication. The historical developments in diagnosis and treatment of MG are reviewed. We analyzed the clinical course of MG as influenced by age, gender, thymectomy, thymomectomy, and the presence of antibodies to acetylcholine receptors (AChR). The clinical course of MG was significantly influenced by age and gender, and these need special attention in managing patients. The most severe level of weakness and high mortality occurred during the first 1 to 2 years of the disease, after which many patients experienced improvement. For treating MG patients the usefulness of thymectomy remains to be proven, and novel drugs need to be developed to increase the number as well as normal functioning of the AChRs and other components of the neuromuscular system.     

Decremental response of the nasalis and hypothenar muscles in myasthenia gravis

Repetitive nerve stimulation (RNS) is a standard diagnostic procedure in myasthenia gravis (MG). Although RNS sensitivity is highest in weak muscles, RNS is easier to perform in distal muscles that are often not affected. Twenty-five patients with MG were assessed to compare the sensitivity of RNS of the nasalis muscle to that of the hypothenar muscles. Abnormal decrement was found in hypothenar muscles in 9 patients (36%) and in the nasalis muscle in 13 patients (52%). RNS of the nasalis muscle appeared more useful to detect abnormal neuromuscular transmission in patients with oculobulbar MG (5 of 5) than hypothenar RNS (1 of 5). In patients with generalized MG, hypothenar muscles had a similar yield of abnormal RNS tests.     

High-temperature repetitive nerve stimulation in myasthenia gravis

High temperature enhances the decrement on repetitive nerve stimulation (RNS) in patients with myasthenia gravis (MG). However, the limit of this phenomenon at high temperature is unknown. Three-hertz ulnar RNS was performed in 7 patients with MG at a skin temperature of 32°C and then with the hand in a 44°C water bath. At 32°C, the mean decrement preactivation was 5% (range, 0–24%); after 1 min of exercise, the mean decrement reached a maximum of 11% (range, 1–34%) 2 min postactivation. At a hand temperature of 42°C, the mean decrement preactivation was 17% (range, 0–65%); after exercise, the mean decrement reached a maximum of 29% (range, 5–74%) 1 min postactivation. In 3 subjects, RNS was normal at 32°C, but a definite decrement developed with heating. These findings demonstrate that very high temperature can improve the sensitivity of ulnar RNS for postsynaptic neuromuscular transmission defects. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1414–1418, 1998