Response of patients with refractory myasthenia gravis to rituximab: a retrospective study

Clinical characteristics of refractory myasthenia gravis patients

BACKGROUND

A subset of myasthenia gravis (MG) patients is refractory to standard therapies. Identifying the characteristics of this population is essential as newer treatment strategies emerge that may be more effective in this group.

OBJECTIVE

The aim of our study is to describe the clinical features of refractory MG patients and compare them to those of non-refractory patients.

METHODS

A retrospective chart review was completed of 128 MG patients referred to a tertiary neuromuscular clinic from 2003 to 2011. Patients were classified as refractory or non-refractory based on predefined criteria, and clinical features were compared.

RESULTS

Nineteen out of 128 patients were classified as refractory (14.8 percent). Compared to the non-refractory patients, the refractory patients were more likely to be younger at onset, female, thymomatous, and MuSK-antibody positive.

CONCLUSION

Refractory MG patients represent a small but distinct group for whom exploring newer therapeutic approaches and immunopathologic differences is warranted.

Myasthenia gravis: Five new things

Myasthenia gravis (MG) is the most common autoimmune disease affecting neuromuscular junction transmission. MG is characterized by muscle weakness that worsens with activity and fluctuates over the course of the day. Involvement of respiratory musculature can lead to life-threatening crisis requiring intensive care unit care. Antibody testing is positive in most patients with MG. Treatment of MG includes short-term symptomatic treatment, chronic immunosuppression, surgical intervention, and immunomodulatory therapies for severe disease or crisis. We review advances in 5 areas relevant to diagnosis and management of MG: the role of IV immunoglobulin vs plasmapharesis in myasthenic crisis and severe disease; the clinical characterization of patients with antibodies to muscle-specific tyrosine kinase receptors; old and new investigational treatments; management of MG in pregnancy; and new confirmatory diagnostic tests.

Management challenges in muscle-specific tyrosine kinase myasthenia gravis

Myasthenia gravis with antibodies to muscle-specific tyrosine kinase (MuSK-MG) is generally considered a severe disease because of the associated weakness distribution with prevalent involvement of bulbar muscles and a rapidly progressive course and early respiratory crises. Its treatment can be unrewarding, owing to poor response to acetylcholinesterase inhibitors in most patients, disease relapses in spite of high-dose immunosuppression, and development of permanent bulbar weakness. High-dose prednisone plus plasma exchange is the recommended approach for treating rapidly progressive bulbar weakness. In the disease management, oral steroids proved effective, plasma exchange produced marked, albeit short-term, improvement, while conventional immunosuppressants were comparatively less effective. Rituximab is a promising treatment for refractory MuSK-MG; in uncontrolled studies, nearly all treated patients achieved significant improvement with substantial decrease of medication. It is yet to be clarified whether the early use of rituximab could prevent the permanent bulbar weakness, which constitutes a relevant disability in these patients.

Paraneoplastic syndromes of the neuromuscular junction: therapeutic options in myasthenia gravis, lambert-eaton myasthenic syndrome, and neuromyotonia

OPINION STATEMENT

Myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS) and neuromyotonia are neuromuscular transmission disorders occurring with or without associated malignancy. Due to the common antibody-mediated pathophysiology, immunosuppression has an important role in the treatment of each of these disorders. Symptomatic treatment is more variable. Pyridostigmine is first-line treatment in generalized MG. Response seems to be better in patients with acetylcholine receptor (AChR) antibodies than in patients with antibodies against muscle-specific tyrosine kinase (MuSK). Pyridostigmine can be sufficient in mild MG, although most patients need additional immunosuppressive therapy. If so, prednisolone is efficient in the majority of the patients, with a relatively early onset of clinical effect. High drug dosage and treatment duration should be limited as much as possible because of serious corticosteroid-related side effects. As long-term treatment is needed in most patients for sustainable remission, adding non-steroid immunosuppressive drugs should be considered. Their therapeutic response is usually delayed and often takes a period of several months. In the meantime, corticosteroids are continued and doses are tapered down over a period of several months. There are no trials comparing different immunosuppressive drugs. Choice is mainly based on the clinician's familiarity with certain drugs and their side effects, combined with patients' characteristics. Most commonly used is azathioprine. Alternatively, tacrolimus, cyclosporine A, mycophenolate mofetil or rituximab can be used. The use of cyclophosphamide is limited to refractory cases, due to serious side effects. Plasma exchange and intravenous immunoglobulin induce rapid but temporary improvement, and are reserved for severe disease exacerbations because of high costs of treatment. It is recommended that computed tomography (CT) of the thorax is performed in every AChR-positive MG patient, and that patients are referred for thymectomy in case of thymoma. In patients without thymoma, thymectomy can be considered as well, especially in younger, AChR-positive patients with severe disease. However, definite proof of benefit is lacking and an international randomized trial to clarify this topic is currently ongoing. When LEMS is suspected, always search for malignancy, especially small cell lung carcinoma with continued screening up to two years. In paraneoplastic LEMS, cancer treatment usually results in clinical improvement of the myasthenic symptoms. 3,4-Diaminopyridine is first-line symptomatic treatment in LEMS. It is usually well tolerated and effective. When immunosuppressive therapy is needed, the same considerations apply to LEMS as described for MG. Peripheral nerve hyperexcitability in neuromyotonia can be treated with anticonvulsant drugs such as phenytoin, valproic acid or carbamazepine. When response in insufficient, start prednisolone in mild disease and consider the addition of azathioprine. Plasma exchange or intravenous immunoglobulin is indicated in severe neuromyotonia and in patients with neuromyotonia combined with central nervous system symptoms, a clinical picture known as Morvan's syndrome.

Monoclonal antibodies in neuroinflammatory diseases

INTRODUCTION

Monoclonal antibodies (mAbs) represent an emerging and rapidly growing field of therapy in neuroinflammatory diseases. Adhesion molecule blockade by natalizumab represents the first approved mAb therapy in neurology, approved for therapy of highly active multiple sclerosis (MS). Removal of immune cells by anti-CD52 mAb alemtuzumab or anti-CD20 mAb rituximab are other prime examples with existing positive Phase II and Phase III trials. MS clearly represents the neuroinflammatory disease entity with the largest body of evidence. However, some of these approaches are currently investigated or translated for use in other, rare neuroinflammatory diseases, such as neuromyelitis optica (NMO), inflammatory neuropathies and (neuro)-muscular disorders.

AREAS COVERED

This review will highlight the most relevant therapeutic approaches involving mAbs in the field of neuroinflammatory diseases as published in peer-reviewed journals and presented on international meetings.

EXPERT OPINION

There is continuously growing evidence on the therapeutic relevance of mAbs in neuroinflammatory disorders. In MS meanwhile several studies have provided evidence for efficacy: In addition to natalizumab, approved in 2006, several other candidates are under development, the most eminent examples with the most advanced study programs being anti-CD52 alemtuzumab, anti-CD20 principles and anti-CD25 daclizumab. Other intriguing candidates are anti-IL-17 strategies, and interference with the complement pathway, partly also developed for other neuroinflammatory disorders.

Rituximab in severe seronegative juvenile myasthenia gravis: review of the literature

Myasthenia gravis is an autoimmune neuromuscular disorder caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction. A wide range of symptomatic therapy with acetylcholinesterase inhibitors and immunotherapy such as corticosteroids, azathioprine, cyclosporine, mycophenolate mofetil, plasmapheresis, and intravenous immunoglobulin has been used in the treatment of myasthenia gravis, with variable responses. However, most modalities of treatment involve delayed onset of action. We describe a child with severe, life-threatening seronegative myasthenia gravis who repeatedly failed extubation and responded dramatically to rituximab. She achieved complete and sustained remission for more than 9 months, with gradual reduction in steroid dose without any side effects. Advances in the treatment of myasthenia gravis have reduced mortality and morbidity and improved the quality of life in these patients.