Prolonged improvement after rituximab: two cases of resistant muscle-specific receptor tyrosine kinase + myasthenia gravis

Long-Term Remission With Low-Dose Rituximab in Myasthenia Gravis: A Retrospective Study

OBJETIVE

Rituximab (RTX) is a therapeutic option, for patients with myasthenia gravis (MG) not responding to conventional immunosuppressive treatment. In this cohort, we evaluated long-term efficacy of RTX in the treatment of refractory generalized MG.

METHODS

A retrospective study was performed in adult patients with refractory generalized MG and at least 24 months of follow-up, between January/2015 and October/2021. The Myasthenia Gravis Status and Treatment Intensity Score was used to assess outcomes, and CD19/CD20+ B-cell counts were monitored.

RESULTS

Sixteen patients with MG (8 antiacetylcholine receptor+ and 8 muscle-specific antikinase+; mean age 45.5 ± 16.2 years) treated with low-dose RTX protocols were included. CD19/CD20 levels remained undetectable 12 months after induction, and no new relapses were observed during follow-up.

CONCLUSIONS

Low-dose RTX infusions were sufficient to achieve undetectable CD19/20 cell counts and sustained clinical remission. In low and middle-income countries, the impact of low-dose RTX therapy represents a paradigm shift in decision-making for long-term treatment.

Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study

BACKGROUND

B-cell targeted therapy with rituximab has shown durable response in treating refractory myasthenia gravis (MG). This study compares the response to rituximab between patients with acetylcholine receptor autoantibody positive (AChR+) and muscle-specific kinase autoantibody positive (MuSK+) MG.

METHODS

This retrospective study included 33 patients with either AChR+ or MuSK+ MG who were treated with rituximab from 05/31/2003 to 05/31/2017. Pretreatment and post-treatment immunotherapy regimens, clinical symptoms, and examination findings were evaluated.

RESULTS

Median MGFA Class of II at baseline improved to an asymptomatic median classification at 12-months and last follow-up (p-values <.001) post-rituximab. Improvement in MGFA class was not significantly different between the groups. Twenty-one patients achieved clinical remission (12/17 AChR+, 9/16 MuSK+) with time to remission of 441.4 ± 336.6 days for AChR+ versus 230 ± 180.8 days for MuSK+ patients (p-value 0.049). The mean prednisone dosage requirement decreased significantly in both groups post-rituximab. AChR+ patients required more hospitalizations for exacerbation post-rituximab (p-value 0.046).

CONCLUSION

Rituximab treatment response is observed in both AChR+ and MuSK+ patients supporting the role of B cell depletion in the management of MG. While there was no significant difference between these groups in terms of clinical improvement, symptom-free state, and prednisone burden, MuSK+ MG patients may experience greater benefits, including earlier time to remission, fewer exacerbations and hospitalizations post-treatment.

Agrin and LRP4 antibodies as new biomarkers of myasthenia gravis

Myasthenia gravis (MG) is a common disorder that affects the neuromuscular junction. It is caused by antibodies against acetylcholine receptor and muscle-specific tyrosine kinase; however, some MG patients do not have antibodies against either of the proteins. Recent studies have revealed antibodies against agrin and its receptor LRP4-both critical for neuromuscular junction formation and maintenance-in MG patients from various populations. Results from experimental autoimmune MG animal models indicate that anti-LRP4 antibodies are causal to MG. Clinical studies have begun to reveal the significance of the new biomarkers. With their identification, MG appears to be a complex disease entity that can be classified into different subtypes with different etiology, each with unique symptoms. Future systematic studies of large cohorts of well-diagnosed MG patients are needed to determine whether each subtype of patients would respond to different therapeutic strategies. Results should contribute to the goal of precision medicine for MG patients. Anti-agrin and anti-LRP4 antibodies are also detectable in some patients with amyotrophic lateral sclerosis or Lou Gehrig's disease; however, whether they are a cause or response to the disorder remains unclear.

Mechanisms underlying B cell immune dysregulation and autoantibody production in MuSK myasthenia gravis

Pathogenic autoantibodies to muscle-specific tyrosine kinase (MuSK) can be found in patients with myasthenia gravis (MG) who do not have detectable antibodies to the acetylcholine receptor. Although the autoantibody-mediated pathology is well understood, much remains to be learned about the cellular immunology that contributes to autoantibody production. To that end, our laboratory has investigated particular components associated with the cellular immunopathology of MuSK MG. First, we found that B cell tolerance defects contribute to the abnormal development of the naive repertoire, which indicates that dysregulation occurs before the production of autoantibodies. Second, both the naive and antigen-experienced memory B cell repertoire, which we examined through the application of high-throughput adaptive immune receptor repertoire sequencing, include abnormalities not found in healthy controls. This highlights a broad immune dysregulation. Third, using complementary approaches, including production of human monoclonal antibodies, we determined that circulating plasmablasts directly contribute to the production of MuSK-specific autoantibodies in patients experiencing relapse following B cell depletion therapy. These collective findings contribute to defining a mechanistic model that describes MuSK MG immunopathogenesis.

Rituximab as treatment for anti-MuSK myasthenia gravis: Multicenter blinded prospective review

OBJECTIVE

To evaluate the efficacy of rituximab in treatment of anti-muscle-specific kinase (MuSK) myasthenia gravis (MG).

METHODS

This was a multicenter, blinded, prospective review, comparing anti-MuSK-positive patients with MG treated with rituximab to those not treated with rituximab. The primary clinical endpoint was the Myasthenia Gravis Status and Treatment Intensity (MGSTI), a novel outcome that combines the Myasthenia Gravis Foundation of America (MGFA) postintervention status (PIS) and the number and dosages of other immunosuppressant therapies used. A priori, an MGSTI of level ≤2 was used to define a favorable outcome. Secondary outcomes included modified MGFA PIS of minimal manifestations or better, mean/median prednisone dose, and mean/median doses of other immunosuppressant drugs.

RESULTS

Seventy-seven of 119 patients with anti-MuSK MG evaluated between January 1, 2005, and January 1, 2015, at 10 neuromuscular centers were selected for analysis after review of limited clinical data by a blinded expert panel. An additional 22 patients were excluded due to insufficient follow-up. Baseline characteristics were similar between the rituximab-treated patients (n = 24) and the controls (n = 31). Median follow-up duration was >3.5 years. At last visit, 58% (14/24) of rituximab-treated patients reached the primary outcome compared to 16% (5/31) of controls (p = 0.002). Number needed to treat for the primary outcome is 2.4. At last visit, 29% of rituximab-treated patients were taking prednisone (mean dose 4.5 mg/day) compared to 74% of controls (mean dose 13 mg/day) (p = 0.001 and p = 0.005).

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that for patients with anti-MuSK MG, rituximab increased the probability of a favorable outcome.

[A case of refractory generalized myasthenia gravis with anti-acetylcholine receptor antibodies treated with rituximab]

We report a case of a 57-year-old woman with thymoma-associated generalized myasthenia gravis (MG) showing severe bulbar and respiratory symptoms, moderate weakness of the neck muscles, and mild weakness of extremity muscles. Corticosteroid treatment with various types of immunosuppressive agents, such as cyclosporine, tacrolimus, and azathioprine, did not improve her symptoms. Plasma exchange transiently improved her symptoms, and she was required to undergo plasmapheresis every 4 weeks. At first, cyclophosphamide pulse therapy was administered, which improved her symptoms transiently. Thereafter, rituximab (RTX) was administered. Six months after RTX administration, respiratory distress and dysphagia improved gradually, and reduction in the dosage of corticosteroids from 30 mg/day to 10 mg/day did not result in symptom deterioration. Therefore, the interval between successive plasmapheresis treatments was increased from 4 to 9 weeks 19 months after the first RTX administration. During a 26-month period from the first administration of RTX, the number of CD20+ B cells in peripheral blood decreased and remained at 0% to 26% of that before RTX treatment. The titer of anti-acetylcholine receptor antibodies did not change during the first course of treatment (0.6-0.9 nmol/l). The clinical symptom worsened with the increase of the number of CD20+ B cells in peripheral blood in the 27 month after 1st RTX administration. Therefore, RTX was administered a second time, after which the patient's clinical symptoms again improved gradually. The titer of anti-acetylcholine receptor antibodies came to be stable with 0.5-0.7 nmol and low level during the 2nd course. Corticosteroids could be discontinued in the 16th month. The findings suggest that RTX can be one of the choices for pharmacological therapy in patients with intractable MG accompanied by the presence of anti-acetylcholine receptor antibodies.

Current and future immunotherapy targets in autoimmune neurology

Randomized controlled treatment trials of autoimmune neurologic disorders are generally lacking and data pertaining to treatment are mostly derived from expert opinion, large case series, and anecdotal reports. The treatment of autoimmune neurologic disorders comprises oncologic therapy (where appropriate) and immunotherapy. In this chapter, we first describe the standard acute and chronic immunotherapies and provide a practical overview of their use in the clinic (mechanisms of action, dosing, monitoring, and side effects). Novel approaches to treatment of autoimmune neurologic disorders, through new drug discovery or repurposing, are dependent on improved mechanistic understanding of immunopathology. Such approaches, with emphasis on monoclonal antibodies, are discussed using the paradigm of three autoimmune neurologic disorders whose immunopathogenesis is better understood, specifically myasthenia gravis, neuromyelitis optica, and chronic inflammatory demyelinating polyradiculoneuropathy. It is important to realize that the treatment strategy and management plan must be individualized for each patient. In general these are influenced by the following: clinical severity, antibody type, presence or absence of cancer, and prior treatment response, if known.

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.

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.

Autoimmune polyendocrine syndrome type 1: Utility of KCNRG autoantibodies as a marker of active pulmonary disease and successful treatment with rituximab

Autoimmune polyendocrine syndrome type 1 (APS-1), also known as Autoimmune Polyendocrinopathy Candidiasis and Ectodermal Dysplasia (APECD) is a disorder caused by mutations in the autoimmune regulator (AIRE) gene. In some APS-1 patients, significant pulmonary disease is observed. Autoantibodies directed against the potassium channel regulatory protein (KCNRG), found in epithelial cells of terminal bronchioles, have been suggested as a marker for pulmonary disease in APS-1 patients. We report two patients with APS-1; one with and one without lung disease. Patient 1 had multiple admissions for pneumonia and respiratory insufficiency, required non-invasive ventilation, and had findings of bronchiectasis on thoracic imaging and significant lymphocytic infiltrates of the airways on lung biopsy. To verify the autoimmune cause of pulmonary symptoms APS-1 patients, both were tested in a blinded manner for the presence of autoantibodies to KCNRG in serum. We found that only Patient 1 had autoantibodies present. Additionally, Patient 1 had progressive disease despite treatment with several immunomodulating agents, including corticosteroids, azathioprine, and mycophenolate. Patient 1 had a lung biopsy performed which was consistent with B cell lymphocytic aggregates. Rituximab treatment was initiated with apparent good response. This report illustrates the practical use of KCNRG autoantibodies to identify APS-1 patients with pulmonary risk and the successful use of the monoclonal antibody, Rituximab, to treat pulmonary disease in APS-1 patients.