Difference in distribution of muscle weakness between myasthenia gravis and the Lambert-Eaton myasthenic syndrome

BACKGROUND: Myasthenia gravis and the Lambert-Eaton myasthenic syndrome (LEMS) may have a similar distribution of muscle weakness. Deciding on a diagnosis of myasthenia gravis or LEMS on clinical grounds may therefore be difficult. OBJECTIVE: To compare the localisation of initial muscle weakness and the distribution of weakness at the time of maximum severity in patients with myasthenia gravis and LEMS. SUBJECTS: 101 patients with myasthenia gravis and 38 patients with LEMS. RESULTS: In myasthenia gravis, initial weakness involved extraocular muscles in 59%, bulbar muscles in 29%, and limb muscles in 12% of the patients. In LEMS no patient had ocular weakness, 5% had bulbar weakness, and 95% had weakness of the limbs as the first symptom (p < 0.001). At the point of maximum severity, weakness in myasthenia gravis was purely ocular in 25%, oculobulbar in 5%, restricted to the limbs in 2%, and present in both oculobulbar muscles and limbs in 68%. At this point, none of the LEMS patients had weakness restricted to extraocular or bulbar muscles (p = 0.002). The legs were affected in all LEMS patients, whereas in 12 patients with generalised myasthenia gravis limb weakness was restricted to the arms (p = 0.024). CONCLUSIONS: In a patient suspected to have a myasthenic syndrome whose first symptom is ocular weakness, LEMS is virtually excluded. Limb weakness confined to the arms is only found in generalised myasthenia gravis and not in LEMS. Muscle weakness in myasthenia gravis tends to develop in a craniocaudal direction, and in the opposite direction in LEMS.     

Effect of diazepam on muscle weakness in a model of myasthenia gravis in rats

Summary Rats chronically received -bungarotoxin which caused a reduction of nicotinic acetylcholine receptors and weakness, especially of lip muscles. It was found that diazepam (0.75 – 2mg kg^–1, s.c), after a 15 min period of excitation and increased lip weakness, caused sedation and some improvement of the lip. Even after 5mg kg^–1 diazepam, muscle function was not markedly affected and breathing appeared normal. It is concluded that sedation in rats by diazepam does not entail aggravation of the muscle weakness caused by a partial neuromuscular block.     

Muscle weakness and functional disability in patients with myasthenia gravis

Introduction: Muscle weakness and functional disability have not been evaluated in a population-based study of patients with myasthenia gravis (MG). Methods: All patients with MG in a well-defined catchment area were identified in the Danish National Patient Registry. Of the 175 eligible patients, 90 participated and were studied using MG-specific scales, isometric dynamometry, and functional tests. Fifty age- and sex-matched subjects served as controls. Results: Muscle strength was reduced by 13%, 21%, and 12% for shoulder abduction, knee extension, and ankle extension, respectively (P < 0.05). Chair stand and 400-meter walking were impaired by 24% and 23%, respectively (P < 0.05). Muscle strength and functional performances were related to MG-specific scales. Discussion: MG patients have moderately reduced isometric muscle strength and impaired physical performance. Muscle weakness and functional tests relate closely to MG-specific scales, suggesting that dynamometry and functional tests can be used to monitor MG patients and as efficacy parameters in clinical trials. Muscle Nerve 59 :218–223, 2019     

Perineurial cell ensheathement of muscle fibers: a new syndrome of fatigable muscle weakness mimicking myasthenia gravis

Many newly discovered pathological and physiological variants of neuromuscular junction function have been identified. We report a case of a myasthenia gravis-like syndrome with onset of ptosis at age six years and eventual evaluation for peripheral weakness twenty years later. Subsequent muscle biopsy showed a previously unreported finding of perineurial cell ensheathement of the muscle fibers. We suggest that the ensheathement of the muscle cells by perineurial cells may alter the microenvironment interfering with neuromuscular transmission.     

Neurogenic muscle atrophy in myasthenia gravis

Two cases of severe myasthenia gravis are described, with histological findings. Both cases showed severe neurogenic atrophy of the muscles of the tongue, with fatty pseudohypertrophy and a remarkable proliferation of terminal nerve fibres. Similar, but less severe, changes were present in other bulbar muscles. The findings are in keeping with the view that functional interruption at the neuromuscular junctions results first in failure to transmit the contractile impulse, and at a later stage in denervation atrophy. Terminal proliferation of axons is regarded as an attempt, on the part of motor fibres, to compensate for the breakdown of normal neuromuscular interaction.     

Late onset generalized myasthenia gravis presenting with facial weakness and bulbar signs without extraocular muscle involvement

Bilateral facial palsy is a common sign of autoimmune myasthenia gravis (MG). However, facial muscle weakness without clinical signs of extraocular muscle (EOM) involvement is extremely rare. We describe a late onset generalized MG presenting with facial weakness and bulbar signs without EOM deficits. The diagnosis was based on neurophysiological assessment and positive acetylcholine receptor antibody titer. Thymoma was excluded. The clinical response to corticosteroids, pyridostigmine and intravenous immunoglobulin was complete. EOM weakness was never observed during a 3-year follow-up, also during a later exacerbation of MG.     

Musk-antibody positive myasthenia gravis presenting with isolated neck extensor weakness

Dropped head sign is characterized by the gradual forward sagging of the head due to weakness of neck extensor muscles. This may be a prominent sign of several neuromuscular disorders and may be an isolated feature of myasthenia gravis (MG). We describe a patient with isolated neck extensor weakness, eletrophysiological findings suggesting myasthenia gravis and positive MuSK antibodies. This case supports that finding anti-MuSK antibodies may be extremely helpful in dropped head patients and negative acetylcholine receptor antibodies especially if needle EMG does not reveal myopathic or neurogenic patterns.     

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.     

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.     

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.     

重症肌无力的舌肌萎缩

重症肌无力(MG)为一种由抗体介导的、累及神经肌肉接头的自身免疫性疾病,由于患者血清中存在抗乙酰胆碱受体(AChR)抗体,使神经肌肉接头的突触后膜上的受体遭到破坏,导致神经肌肉传递障碍.但研究发现,全身型MG患者中只有80%存在AChR抗体阳性,即AChR抗体阳性MG(以下称为AChR-MG),其余20%血清AChR抗体呈阴性.     

Heterogeneity of immunopathological features of AChR/MuSK autoantibody-negative myasthenia gravis

We compared B cells and germinal centers in thymus from myasthenia gravis (MG) patients either with anti-acetylcholine receptor (AChR) autoantibodies or with neither anti-muscle-specific tyrosine kinase (MuSK) nor anti-AChR (seronegative MG: SN-MG). The numbers and frequencies of total and germinal center B cells varied in the SN-MG thymi, some of which were normal/atrophic. Others were clearly hyperplastic, their B cell parameters overlapping with those in AChR-positive MG, which implicates the thymus in pathogenesis. Indeed, some SN-MG patients apparently benefited from thymectomy, which should be considered a management option.