Ephedrine for myasthenia gravis, neonatal myasthenia and the congenital myasthenic syndromes

Myasthenia gravis-Pathophysiology, diagnosis, and treatment

Myasthenia gravis (MG) is an autoimmune disease characterized by dysfunction of the neuromuscular junction resulting in skeletal muscle weakness. It is equally prevalent in males and females, but debuts at a younger age in females and at an older age in males. Ptosis, diplopia, facial bulbar weakness, and limb weakness are the most common symptoms. MG can be classified based on the presence of serum autoantibodies. Acetylcholine receptor (AChR) antibodies are found in 80%-85% of patients, muscle-specific kinase (MuSK) antibodies in 5%-8%, and <1% may have low-density lipoprotein receptor-related protein 4 (Lrp4) antibodies. Approximately 10% of patients are seronegative for antibodies binding the known disease-related antigens. In patients with AChR MG, 10%-20% have a thymoma, which is usually detected at the onset of the disease. Important differences between clinical presentation, treatment responsiveness, and disease mechanisms have been observed between these different serologic MG classes. Besides the typical clinical features and serologic testing, the diagnosis can be established with additional tests, including repetitive nerve stimulation, single fiber EMG, and the ice pack test. Treatment options for MG consist of symptomatic treatment (such as pyridostigmine), immunosuppressive treatment, or thymectomy. Despite the treatment with symptomatic drugs, steroid-sparing immunosuppressants, intravenous immunoglobulins, plasmapheresis, and thymectomy, a large proportion of patients remain chronically dependent on corticosteroids (CS). In the past decade, the number of treatment options for MG has considerably increased. Advances in the understanding of the pathophysiology have led to new treatment options targeting B or T cells, the complement cascade, the neonatal Fc receptor or cytokines. In the future, these new treatments are likely to reduce the chronic use of CS, diminish side effects, and decrease the number of patients with refractory disease.

Pharmacological Treatments for Congenital Myasthenic Syndromes Caused by COLQ Mutations

BACKGROUND

Congenital myasthenic syndromes (CMS) refer to a series of inherited disorders caused by defects in various proteins. Mutation in the collagen-like tail subunit of asymmetric acetylcholinesterase (COLQ) is the second-most common cause of CMS. However, data on pharmacological treatments are limited.

OBJECTIVE

In this study, we reviewed related reports to determine the most appropriate pharmacological strategy for CMS caused by COLQ mutations. A literature review and meta-analysis were also performed. PubMed, MEDLINE, Web of Science, and Cochrane Library databases were searched to identify studies published in English before July 22, 2022.

RESULTS

A total of 42 studies including 164 patients with CMS due to 72 different COLQ mutations were selected for evaluation. Most studies were case reports, and none were randomized clinical trials. Our meta-analysis revealed evidence that β-adrenergic agonists, including salbutamol and ephedrine, can be used as first-line pharmacological treatments for CMS patients with COLQ mutations, as 98.7% of patients (74/75) treated with β-adrenergic agonists showed positive effects. In addition, AChEIs should be avoided in CMS patients with COLQ mutations, as 90.5% (105/116) of patients treated with AChEIs showed either no or negative effects.

CONCLUSION

(1) β-adrenergic agonist therapy is the first pharmacological strategy for treating CMS with COLQ mutations. (2) AChEIs should be avoided in patients with CMS with COLQ mutations.

Novel LG1 Mutations in Agrin Causing Congenital Myasthenia Syndrome

The patient had suffered from both proximal and distal limb weakness since her early childhood, without the involvement of ocular or respiratory muscles. Repetitive nerve stimulation (RNS) at 3 Hz showed significant decrement in the area and amplitude of the compound muscle action potential (CMAP) on the right abductor digiti minimi (26%) and trapezius (17%). Whole-exon sequencing revealed two novel heterozygous mutations (p.Q1406Rfs*29 and p.R1521H) in the LG1 domain of agrin, which were deemed likely pathogenic for congenital myasthenic syndromes (CMS) according to a bioinformatics analysis. The patient showed remarkable improvement after treatment with salbutamol. This case expanded the mutation spectrum of AGRN.

Current Treatment of Myasthenia Gravis

Myasthenia gravis (MG) is the most extensively studied antibody-mediated disease in humans. Substantial progress has been made in the treatment of MG in the last century, resulting in a change of its natural course from a disease with poor prognosis with a high mortality rate in the early 20th century to a treatable condition with a large proportion of patients attaining very good disease control. This review summarizes the current treatment options for MG, including non-immunosuppressive and immunosuppressive treatments, as well as thymectomy and targeted immunomodulatory drugs.

Targeted therapies for congenital myasthenic syndromes: systematic review and steps towards a treatabolome

Despite recent scientific advances, most rare genetic diseases — including most neuromuscular diseases — do not currently have curative gene-based therapies available. However, in some cases, such as vitamin, cofactor or enzyme deficiencies, channelopathies and disorders of the neuromuscular junction, a confirmed genetic diagnosis provides guidance on treatment, with drugs available that may significantly alter the disease course, improve functional ability and extend life expectancy. Nevertheless, many treatable patients remain undiagnosed or do not receive treatment even after genetic diagnosis. The growth of computer-aided genetic analysis systems that enable clinicians to diagnose their undiagnosed patients has not yet been matched by genetics-based decision-support systems for treatment guidance. Generating a ‘treatabolome’ of treatable variants and the evidence for the treatment has the potential to increase treatment rates for treatable conditions. Here, we use the congenital myasthenic syndromes (CMS), a group of clinically and genetically heterogeneous but frequently treatable neuromuscular conditions, to illustrate the steps in the creation of a treatabolome for rare inherited diseases. We perform a systematic review of the evidence for pharmacological treatment of each CMS type, gathering evidence from 207 studies of over 1000 patients and stratifying by genetic defect, as treatment varies depending on the underlying cause. We assess the strength and quality of the evidence and create a dataset that provides the foundation for a computer-aided system to enable clinicians to gain easier access to information about treatable variants and the evidence they need to consider.

Passive transfer models of myasthenia gravis with muscle-specific kinase antibodies

Myasthenia gravis (MG) with antibodies to muscle-specific kinase (MuSK) is characterized by fluctuating fatigable weakness. In MuSK MG, involvement of bulbar muscles, neck, and shoulder and respiratory weakness are more prominent than in acetylcholine receptor (AChR) MG. MuSK autoantibodies are mainly of the IgG4 subclass, and as such are unable to activate complement, have low affinity for Fc receptors, and are functionally monovalent. Therefore, the pathogenicity of IgG4 MuSK autoantibodies was initially questioned. A broad collection of in vitro active immunization and passive transfer models has been developed that have shed light on the pathogenicity of MuSK autoantibodies. Passive transfer studies with purified IgG4 from MuSK MG patients confirmed that IgG4 is sufficient to reproduce clear clinical, electrophysiological, and histological signs of myasthenia. In vitro experiments revealed that MuSK IgG4 autoantibodies preferably bind the first Ig-like domain of MuSK, correlate with disease severity, and interfere with the association between MuSK and low-density lipoprotein receptor-related protein 4 and collagen Q. Some patients have additional IgG1 MuSK autoantibodies, but their role in the disease is unclear. Altogether, this provides a rationale for epitope-specific or IgG4-specific treatment strategies for MuSK MG and emphasizes the importance of the development of different experimental models.

Aggregated N-of-1 trials for unlicensed medicines for small populations: an assessment of a trial with ephedrine for myasthenia gravis

Background

Inexpensive medicines with a long history of use may currently be prescribed off-label for rare indications. Reimbursement is at the discretion of health insurance companies, and may be unpredictable. The example addressed was ephedrine as add-on treatment for myasthenia gravis. Stakeholders from academia, a patient organization, the Dutch National Health Care Institute (NHCI) and Dutch Medicines Evaluation Board (MEB) advised on the trial design. The NHCI and MEB agreed to provide scientific advice on the suitability of the evidence generated by the trial, for regulatory decisions. This paper describes the feasibility of the trial and the utility of its aggregated results.

Results

The trialists experienced the trial as feasible. Retrospective interviews showed that the trial as performed was acceptable to patients. The treatment effect in the primary outcome measure, muscle strength, was statistically significant when inferred to the population level, though the effect size was modest. Secondary outcomes were statistically significant in a preplanned, fixed effects analysis within the four patients. The NHCI advised that it could potentially make reimbursement decisions based on the Fitting Evidence framework, should the trialists decide to apply for reimbursement. The MEB advised that for a licensing decision, the N-of-1 design is a last-resort option for demonstrating treatment benefit in a rare disease. N-of-1 trials alone do not provide enough evidence on potential risk. The MEB found the current trial inconclusive. It suggested doing a 2-armed trial of longer duration, possibly with a different outcome measure (postponement of corticosteroid use). It suggested engaging a consultancy or commercial sponsor, should the trialists decide to seek market authorization of the drug.

Conclusions

In theory, evidence from aggregated N-of-1 trials is suitable for use in licensing and reimbursement decisions. The current example illustrates differences in interpretation of N-of-1 results by health authorities. In the era of personalized medicine, consensus is required on the interpretation of data from study designs geared to small groups. Demonstrating effectiveness of inexpensive medicines in small populations may require involvement of non-commercial parties, to preserve affordability.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0636-y) contains supplementary material, which is available to authorized users.

Ephedrine as add-on therapy for patients with myasthenia gravis: protocol for a series of randomised, placebo-controlled n-of-1 trials

INTRODUCTION

Myasthenia gravis (MG), a rare neuromuscular disease, is often initially treated using acetylcholinesterase inhibitors. Patients who do not respond adequately depend on the use of corticosteroids or other immunosuppressive medication, but these may have serious side effects. Clinical observations suggest that ephedrine can diminish, postpone or even prevent the need for immunosuppressive therapy when added to acetylcholinesterase inhibitors or low-dose prednisone. In the Netherlands, ephedrine is not licensed for MG nor is reimbursement guaranteed. MG is a rare condition, and ephedrine might be indicated only in a subset of patients. Thus, randomised controlled trials comparing large groups are difficult to conduct. We, therefore, aim to aggregate data from a small series of n-of-1 trials (also known as single patient trials) to assess the effect of ephedrine as add-on treatment for MG.

METHODS AND ANALYSIS

Single-centre, placebo-controlled, double-blind, randomised, multiple crossover n-of-1 studies in 4 adult patients with generalised MG who show inadequate improvement on pyridostigmine and/or immunosuppressive drugs. Each n-of-1 trial has 3 cycles of two 5-day intervention periods.

TREATMENT

25 mg ephedrine or placebo, twice daily.

MAIN OUTCOME MEASURE

Quantitative Myasthenia Gravis (QMG) test.

STATISTICAL ANALYSIS

fixed effects linear model for QMG for all patients combined.

SECONDARY OUTCOME MEASURES

Clinical: effects on MG-Composite and MG-Activities of Daily Living (MG-ADL) scales; QMG at individual level; adverse events. Acceptability of trial design: number of patients eligible and enrolled; number of treatment cycles completed; patients' and caregivers' experiences.

ETHICS AND DISSEMINATION

This study was approved by the Medical Ethics Committee of Leiden University Medical Center, No. P14.108. Results of the trial will be reported in a peer-reviewed publication. Regulatory stakeholders will comment on the suitability of the trial for market authorisation and reimbursement purposes.

TRIAL REGISTRATION NUMBER

This study is registered under EudraCT number 2014-001355-23, protocol no. 40960, V.1.0, registration date 27 March 2014.