Single fiber EMG in the frontalis muscle in ocular myasthenia: specificity and sensitivity.

Patients (n = 41) with isolated weakness of the eyelids or extraocular muscles, who had been referred for single fiber electromyography (SFEMG), were followed up after 4 to 24 months, At follow-up the patients were classified as "definite ocular myasthenia gravis" (MG), "definite other diagnosis," or "no definite diagnosis" on the basis of the completed investigations and subsequent course. The original SFEMG findings in the frontalis muscle were then reviewed. The specificity and sensitivity of SFEMG for "definite ocular MG" could be maximized by using as criteria for abnormality greater than 8/20 pairs with jitter greater than 45 microseconds, or a mean jitter of 20 pairs of greater than 50 microseconds. Patients with abnormal SFEMG according to these criteria have MG, and are likely to require treatment in the immediate future. Patients who have normal SFEMG according to these criteria (and no other demonstrated disorder) may have MG, but it is so mild that they are unlikely to require treatment. Two patients whose final diagnosis was progressive external ophthalmoplegia had normal SFEMG according to these criteria.     

Myotonic dystrophy type 1 coexisting with myasthenia gravis and thymoma

Myotonic dystrophy type 1 (DM1) is an autosomal-dominant multisystemic disorder that may rarely be associated with benign and malignant neoplasms. Cases of both thymoma and myasthenia gravis in association with DM1 are extremely rare. A literature review revealed only three prior reports. We present a 51-year-old man with a family history of DM1 and fluctuating diplopia and ptosis, who was found to have acetylcholine receptor-binding antibodies, thymoma, and a clinical presentation compatible with ocular myasthenia gravis as well as positive genetic testing for DM1. Needle electromyographic (EMG) study demonstrated diffuse runs of myotonic discharges in multiple muscles, consistent with the diagnosis of DM1. Single-fiber EMG showed both increased jitter and blocking. Due to somatic instability, which has been shown previously in DM1, the myotonin protein kinase (DMPK) gene appears to act as a tumor suppressor. Therefore, abnormal CTG repeat expansions in the gene could lead to the development of thymoma and myasthenia gravis.     

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.     

Multiple innervation of muscle fibers in myasthenia gravis

Single fiber EMG recordings from patients with myasthenia gravis obtained during axonal microstimulation revealed an occasional bimodal distribution of response latencies. This phenomenon could be dependent on stimulus strength, however, in a way different from that in the axon reflex. It is suggested to be due to dual neuromuscular junctions (NMJs) supplied by two different motor neurons. Some cases of bimodal jitter were not dependent on stimulus strength and are assumed to be due to dual innervation by the same neuron. The phenomenon could only be demonstrated at abnormal NMJs with partial impulse blocking. It is suggested to reflect multiple reinnervation of muscle fibers that had undergone functional or structural denervation in the course of the immune attack against the original NMJ. This study suggests that the coexisting NMJs from the same or different motor neurons may be functional at the same time.© 1995 John Wiley &Sons, Inc.     

Single-fiber electromyography of masseter muscle in myasthenia gravis

Jitter after axonal microstimulation in the masseter muscle was studied in 30 consecutive patients (12 women) with myasthenia gravis (MG). Patients' mean age was 42.3 (12-75), median disease duration was 3 months (1-72), and onset was ocular (15 cases), oculobulbar (7), bulbar (6), or generalized (2). There were 23 newly-diagnosed patients. Nine cases developed purely ocular MG and 21 cases developed generalized MG. In the latter group, five subjects had a rapidly progressive course and 16 subjects had stable or well-controlled disease (MGFA grade 2-3). Six patients did not have circulating anti-acetylcholine receptor antibodies. Masseter single-fiber electromyography (SFEMG) was abnormal in 6 of 9 ocular MG patients and in all generalized cases (overall sensitivity 27 of 30 cases or 90%; confidence interval 79.3%-100.0% at P = 0.95). Masseter should be considered for SFEMG in diagnosis of MG, especially in cases with bulbar onset.     

Myasthenia gravis presenting as weakness after magnesium administration

We studied a patient with no prior history of neuromuscular disease who became virtually quadriplegic after parenteral magnesium administration for preeclampsia. The serum magnesium concentration was 3.0 mEq/L, which is usually well tolerated. The magnesium was stopped and she recovered over a few days. While she was weak, 2-Hz repetitive stimulation revealed a decrement without significant facilitation at rapid rates or after exercise, suggesting postsynaptic neuromuscular blockade. After her strength returned, repetitive stimulation was normal, but single fiber EMG revealed increased jitter and blocking. Her acetylcholine receptor antibody level was markedly elevated. Although paralysis after magnesium administration has been described in patients with known myasthenia gravis, it has not previously been reported to be the initial or only manifestation of the disease. Patients who are unusually sensitive to the neuromuscular effects of magnesium should be suspected of having an underlying disorder of neuromuscular transmission.     

AChR抗体阳性重症肌无力合并舌肌萎缩2例报道并文献分析

目的 探讨重症肌无力(MG)患者合并舌肌萎缩的发病特点及机制。方法 分析武汉同济医院神经内科住院部2例乙酰胆碱受体(AChR)抗体阳性MG患者合并舌肌萎缩的临床资料,检索MG合并舌肌萎缩的文献报道,总结此类疾病的特点、萎缩机制、治疗方法及预后。结果 在临床上MG合并舌肌萎缩并不多见,大多数患者伴有血清肌肉特异性酪氨酸肌酶(MuSK)抗体阳性,伴AChR抗体阳性者较为罕见,肌肉萎缩的发病机制具体不详; 该类患者除发病时间较长外,通常提示更严重的病情、更差的治疗反应、更不良的预后。结论 MG舌肌萎缩临床少见,严重影响着患者的言语、咀嚼和吞咽等功能,除病程较长外,其肌肉萎缩机制暂不清楚,有待临床进一步探索,以改善此类患者预后和生活质量。     

Myasthenia gravis treated with ciclosporin

Six patients (4 females, 2 males) with generalized myasthenia gravis (MG) have been treated in an open study with ciclosporin (5-10 mg/kg/day), originally for 28 weeks. The age of the patients ranged from 16-61 years and the duration of symptoms from 5-30 years. Four of the patients had been thymectomized. Ciclosporin was added to prednisolone in 5 of the patients. Three of these had in addition previously used azathioprine without satisfactory improvement. The efficacy was measured by scoring the degree of muscle weakness on clinical examination and by scoring of the patients' personal assessment of their fatigability and muscle strength. In 5 patients there was a moderate to marked improvement in muscle strength and fatigueability on ciclosporin therapy. In one patient the effect was slight to moderate. The degree of improvement was similar in the one patient who received ciclosporin alone and in those also using prednisolone. The levels of anti ACh-r antibodies decreased in 3 patients, increased in 2, and were unchanged in one patient. Side effects known to occur on ciclosporin therapy were noticed, but they were tolerable in all patients. An increase in serum creatinine (mean 10%) and decrease in creatinine clearance (mean 21%) were seen in all patients. The treatment with ciclosporin has been continued in all 6 patients, but the dosage has been reduced to 5 mg/kg/day. Deterioration 3-4 weeks after discontinuation of ciclosporin was seen in one case, but resumption of therapy resulted in improvement as before. The total treatment period is now 24-34 months (March, 1987).(ABSTRACT TRUNCATED AT 250 WORDS)     

Myasthenia gravis and premature ovarian failure

We describe a patient who developed seropositive myasthenia gravis 16 years after she was diagnosed with autoimmune premature ovarian failure with antibodies to the receptor for follicle-stimulating hormone (FSH). Although thymectomy led to improvement of her myasthenic symptoms, menses did not resume. Such combined seropositivity for antibodies to acetylcholine and ovarian hormone receptors in a patient with myasthenia gravis and premature ovarian failure may reflect common disease mechanisms, although the precise pathogenesis of these disorders remains ill-defined.     

Single-fiber electromyography in limb and facial muscles in muscle-specific kinase antibody and acetylcholine receptor antibody myasthenia gravis

We examined the findings from single-fiber electromyography in extensor digitorum communis (EDC) and orbicularis oculi (OOc) in 13 myasthenia gravis (MG) patients with muscle-specific kinase antibodies (MuSK-MG) and 12 MG patients with acetylcholine receptor antibodies (AChR-MG) with similar clinical scores. More than 70% of AChR-MG patients had abnormal jitter in both EDC and OOc, but the majority of MuSK-MG patients had normal jitter in EDC despite abnormal jitter in OOc. These findings demonstrate clear differences between the neurophysiology of MuSK-MG and AChR-MG.     

Surrogate therapeutic outcome measures in patients with myasthenia gravis

Treatment of acquired myasthenia gravis (MG) with immunotherapies successfully relieves symptoms and improves strength as documented by the Quantitative Myasthenia Gravis Score for disease severity (QMGS). Neuromuscular function, as demonstrated by the surrogate measures of repetitive nerve stimulation (RNS) and single-fiber electromyography (SFEMG), is sensitive for diagnosis and staging disease severity. This study of 51 patients treated with immunomodulation confirmed that RNS and SFEMG are useful to stage disease severity, but found that clinical measures such as the QMGS are more sensitive to change than electrophysiological parameters. The presence of blocking on SFEMG did predict responsiveness to intravenous immunoglobulin (IVIG) treatment, providing clinicians with an objective, reliable, quantitative measure to help determine which patients will benefit from this costly treatment.     

Myasthenia gravis Lambert‐Eaton overlap syndrome

Introduction: To assess whether a myasthenia gravis (MG) Lambert‐Eaton overlap syndrome (MLOS) exists. Methods: Case reports that met the universally accepted diagnostic criteria for MG and Lambert‐Eaton myasthenic syndrome (LEMS) were sought through a PubMed search. Fifty‐five possible cases of MLOS were identified. Results: Thirty‐nine cases met the diagnostic criteria for MG and LEMS. Analysis of clinical features showed that these patients have common MG and LEMS symptoms: oculo‐bulbar paresis and good response to anti‐cholinesterase for MG and limb weakness and decreased or absent reflexes for LEMS. All had the classical LEMS pattern in the repetitive nerve stimulation test: low compound muscle action potential amplitude and incremental response > 60% with brief exercise or at high rate of stimulation. Eight patients had combined positive acetylcholine receptor antibody (AChR‐ab) or muscle‐specific kinase‐ab and voltage‐gated calcium channel‐ ab tests. Conclusions: A myasthenia gravis Lambert‐Eaton overlap syndrome (MLOS) does exist. Muscle Nerve 53 : 20–26, 2016     

Myasthenia gravis associated with etanercept therapy

Etanercept is an antagonist of tumor necrosis factor alpha that was developed to treat rheumatoid arthritis. In this report we present a patient who developed myasthenia gravis while taking etanercept and had resolution of symptoms after stopping it. This is the first report of this potential side effect and is of additional interest, because etanercept has been proposed as a treatment for myasthenia gravis. Muscle Nerve, 2009     

Single-fiber electromyography in experimental autoimmune myasthenia gravis

The sensitivity of stimulated single-fiber electromyography in the detection of early abnormalities in neuromuscular transmission in experimental autoimmune myasthenia gravis (EAMG) was tested. Increased jitter and blocking were seen up to 3 weeks before clinical illness or decrement developed. Stimulation at 10 Hz appeared more sensitive in detection of abnormalities than stimulation at 3 or 5 Hz. Jitter values did not correlate with anti-Torpedo acetylcholine receptor (AChR), nor with anti-rat AChR antibody titer. No correlation was found between jitter and AChR loss or AChR-antibody complexes in muscle. It is concluded that, in addition to AChR loss and the presence of AChR-antibody complexes, other factors must determine the neuromuscular dysfunction in EAMG and possibly myasthenia gravis.     

Adverse effect of verapamil in myasthenia gravis.

Verapamil, a class IV anti-arrhythmic drug that blocks voltage-dependent calcium channels in cardiac and smooth muscle, also has effects on presynaptic and postsynaptic voltage-dependent calcium channels at the neuromuscular junction. In a postoperative patient with pre-existent myasthenia gravis, oral verapamil caused a marked exacerbation in myasthenic weakness.     

重症肌无力患者Jitter值及肌纤维密度测定研究

运用单纤维肌电图（SFEMG）技术对49例重症肌无力（MG）患者和35例正常人进行了Jitter值、肌纤维密度（FD）值测定，同时结合低频重复电刺激（IFRNS）、烟碱型乙酰胆碱受体抗体（nAchRab）测定作了对比研究。结果显示:MG患者的Jitter明显增宽（P＜0.01）;SFEMG检出MG比LFRNS与nAchRab测定阳性率高（P＜0.05），而且发现临床尚未出现肌无力症状的肌肉中也存在潜在的神经肌肉传递障碍;MG患者FD值无明显增高（P＞0.05）。从而提示，Jitter测定对诊断MG是一项敏感性较高的电生理技术，FD测定可作为区分MG患者与其它神经肌肉疾病患者Jitter异常的一个良好指标。     

Responses of intercostal muscle biopsies from normal subjects and patients with myasthenia gravis

In order to evaluate the mechanisms of weakness in muscles of patients with myasthenia gravis (MG), intercostal muscle biopsies were obtained from 9 normal subjects and 6 MG patients, and the compound muscle action potential (AP) and tension responses to nerve and muscle stimulation, and contracture responses on exposure to caffeine, were monitored in vitro. In normal muscle, on stimulation of the nerve or muscle at 30 to 100 Hz, the AP responses showed decrement in amplitude, one-third of which was attributable to failure of neuromuscular transmission and two-thirds to failure of muscle membrane excitation. On stimulation at 1 to 5 Hz, the AP responses showed very little decrement, while the contractile responses showed significant fade in tension, due to failure of E-C coupling or contractility. In muscle from patients with generalized MG, stimulation of the nerve at all frequencies (1 to 100 Hz) caused much greater decrement in APs and fade in tension responses than in normal muscle, due mainly to failure of neuromuscular transmission. However, at 100 Hz, 40% of the decrement in APs was due to failure of muscle membrane excitation, and at 1 to 5 Hz, 40% of the fade in tension was due to failure of E-C coupling or contractility, as in normal muscle. On direct stimulation the contraction and half-relaxation times were slower and the tetanic tension was smaller than in normal muscle, especially in the MG patient with thymoma. Caffeine-induced contractures were smaller in MG muscle than in normal muscle. These results indicate that while the weakness of MG muscle is due mainly to failure of neuromuscular transmission, it is also partly due to reduced E-C coupling or contractility.     

Acquired rippling muscle disease with myasthenia gravis

Rippling muscle disease (RMD) is a rare disorder that occurs in both familial and sporadic forms. Seven patients have previously been reported with myasthenia gravis and sporadic RMD. There have been conflicting reports of the electrophysiological characteristics of rippling muscles in this acquired form. Another such patient is reported, and the clinical, electrophysiological, and laboratory features of this disorder are described. In addition, this patient had alopecia areata and recurrent metastatic thymoma, years after resection of a benign thymoma. This report emphasizes the clinical manifestations of RMD in association with myasthenia gravis (RMD-MG), and its distinctive features, in this and previously reported patients.     

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.