Longstanding and Refractory Anti-Muscle Specific Tyrosine Kinase Antibody-Associated Myasthenia Gravis (Anti-MuSK-MG) in a Child Successfully Treated with Rituximab

Rituximab treatment in myasthenia gravis

Myasthenia gravis (MG) is a chronic autoimmune disease mediated by antibodies against post-synaptic proteins of the neuromuscular junction. Up to 10%-30% of patients are refractory to conventional treatments. For these patients, rituximab has been used off-label in the recent decades. Rituximab is a monoclonal antibody against the CD20 protein that leads to B cell depletion and to the synthesis of new antibody-secreting plasma cells. Although rituximab was created to treat B-cell lymphoma, its use has widely increased to treat autoimmune diseases. In MG, the benefit of rituximab treatment in MuSK-positive patients seems clear, but a high variability in the results of observational studies and even clinical trials has been reported for AChR-positive patients. Moreover, few evidence has been reported in seronegative MG and juvenile MG and some questions about regimen of administration or monitoring strategies, remains open. In this review, we intend to revise the available literature on this topic and resume the current evidence of effectiveness of Rituximab in MG, with special attention to results on every MG subtype, as well as the administration protocols, monitoring strategies and safety profile of the drug.

Rituximab in juvenile myasthenia gravis-an international cohort study and literature review

Juvenile myasthenia gravis (JMG) is a rare, antibody-mediated disorder of the neuromuscular junction. Treatment strategies in JMG are largely informed by adult MG treatments as the pathophysiology is similar. Rituximab is increasingly considered as a treatment option in refractory JMG but has not yet been systematically investigated in this patient group We conducted a retrospective study from five international centres with expertise in paediatric myasthenia. 10 JMG patients treated with rituximab were identified. Following rituximab treatment all patients had a reduction in JMG-related hospital admissions. At 24 month follow up, 6 patients (60%) had achieved complete stable remission or pharmacological remission and 7 patients were able to reduce immunomodulatory treatment(s). The main side-effect was infusion-related reactions (30%) which resolved in all patients with symptomatic treatment. We compared our cohort to previously reported JMG cases treated with rituximab and noted similar response rates but a slightly higher side-effect profile. Rituximab is a safe and effective treatment option in moderate to severe JMG and most patients have an improvement in MG symptoms post treatment.

Rituximab Therapy in the Treatment of Juvenile Myasthenia Gravis: The French Experience

OBJECTIVE

Corticosteroids are the first-line immunosuppressants in the management of juvenile myasthenia gravis despite their adverse effects. The place of new immunosuppressive therapies is not clearly defined by the last international consensus held in March 2019, due to the lack of clinical trials. The aim of this study is to describe the use of rituximab, its efficacy and safety in 8 main pediatric centers of the French neuromuscular reference network in order to propose a new place in the therapeutic strategy of juvenile myasthenia gravis.

METHOD

We conducted a retrospective multicenter study from January 1, 2009 to April 30, 2020, including a large cohort of children with myasthenia gravis in 8 main French pediatric reference centers of the Filnemus network. The type of myasthenia, the different lines of immunosuppressive treatment and the clinical course of the patients were collected. To evaluate the efficacy of rituximab, we studied the clinical course of patients on immunosuppressive therapy. Outcome was defined as the clinical and therapeutic status of patients at the last visit: stable without immunosuppressants, stable with immunosuppressants or unstable.

RESULTS

We included 74 patients: 18 children with ocular form and 56 children with generalized form. Of the 37 patients who required immunosuppressive therapy, 27 were treated with rituximab. Patients treated with rituximab had a better outcome than patients treated with conventional immunosuppressants (p = 0.006). The use of rituximab as a first-line immunosuppressant showed a better efficacy with a discontinuation of immunosuppressants in 75% of patients (vs. 25%, p=0.04) and resulted cortisone sparing (42% vs. 92%, p=0.03) compared with rituximab treatment as a second or third-line immunosuppression. Rituximab was well tolerated; no adverse effect was observed.

CONCLUSION

The use of rituximab has increased in France over the last 10 years as first line immunosuppressant. This study suggests a good tolerability and efficacy of rituximab in juvenile myasthenia gravis. Early use appears to improve outcomes and facilitate cortisone-sparing in antibody-positive generalized juvenile myasthenia.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that for children with MG rituximab is effective and well tolerated.

Immunopathology of Autoimmune Myasthenia Gravis: Implications for Improved Testing Algorithms and Treatment Strategies

Myasthenia gravis (MG) is a heterogeneous condition, characterized by autoantibodies (Abs) that target functionally important structures within neuromuscular junctions (NMJ), thus affecting nerve-to-muscle transmission. MG patients are more often now subgrouped based on the profile of serum autoantibodies, which segregate with clinical presentation, immunopathology, and their response to therapies. The serological testing plays an essential role in confirming MG diagnosis and guiding disease management, although a small percentage of MG patients remain negative for antibodies. With the advancements in new highly effective pathophysiologically-specific immunotherapeutic options, it has become increasingly important to identify the specific Abs responsible for the pathogenicity in individual MG patients. There are several new assays and protocols being developed for the improved detection of Abs in MG patients. This review focuses on the divergent immunopathological mechanisms in MG, and discusses their relevance to improved diagnostic and treatment. We propose a comprehensive "reflex testing," algorithm for the presence of MG autoantibodies, and foresee that in the near future, the convenience and specificity of novel assays will permit the clinicians to consider them into routine systematic testing, thus stimulating laboratories to make these tests available. Moreover, adopting treatment driven testing algorithms will be crucial to identify subgroups of patients potentially benefiting from novel immunotherapies for MG.

Management of Juvenile Myasthenia Gravis

Juvenile Myasthenia Gravis (JMG) is a rare disorder, defined as myasthenia gravis in children younger than 18 years of age. While clinical phenotypes are similar to adults, there are a number of caveats that influence management: broader differential diagnoses; higher rates of spontaneous remission; and the need to initiate appropriate treatment early, to avoid the long-term physical and psychosocial morbidity. Current practice is taken from treatment guidelines for adult MG or individual experience, with considerable variability seen across centers. We discuss our approach to treating JMG, in a large specialist JMG service, and review currently available evidence and highlight potential areas for future research. First-line treatment of generalized JMG is symptomatic management with pyridostigmine, but early use of immunosuppression, where good control is not achieved is important. Oral prednisolone is used as first-line immunosuppression with appropriate prevention and monitoring of side effects. Second-line therapies including azathioprine and mycophenolate may be considered where there is: no response to steroids, inability to wean to a reasonable minimum effective dose or if side-effects are intolerable. Management of ocular JMG is similar, but requires close involvement of ophthalmology in young children to prevent amblyopia. Muscle-specific tyrosine kinase (MuSK)-JMG show a poorer response to pyridostigmine and anecdotal evidence suggests that rituximab should be considered as second-line immunosuppression. Thymectomy is indicated in any patient with a thymoma, and consideration should be given in acetylcholine receptor (AChR) positive JMG allowing time for spontaneous remission. The benefit is less clear in ocular JMG and is not advised in MuSK-JMG. Children experiencing a myasthenic crisis require urgent hospital admission with access to the intensive care unit. PLEX is preferred over IVIG due to rapid onset of action, but this needs to be balanced with feasibility in very young children. Key questions remain in the management of JMG: when to initiate both first- and second-line treatments, choosing between steroid-sparing agents, and determining the optimal dose and treatment duration. We feel that given the rarity of this disease, the establishment of national registries and collaboration across groups will be needed to address these issues and facilitate future drug trials in JMG.