- Email: [email protected]
Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study
Journal of the Neurological Sciences 411 (2020) 116690
Contents lists available at ScienceDirect
Journal of the Neurological Sciences journal homepage: www.elsevier.com/locate/jns
Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study
T
Tess Litchmana,1, Bhaskar Roya,1, Aditya Kumara, Aditi Sharmaa, Valentine Njikeb, Richard J. Nowaka,⁎ a b
Yale School of Medicine, Department of Neurology, New Haven, CT, USA Griffin Hospital-Derby, Yale University Prevention Research Center, Derby, CT, USA
ARTICLE INFO
ABSTRACT
Keywords: Myasthenia gravis Rituximab Immunotherapy B cell depletion
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.
1. Introduction Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction, leading to muscular weakness and fatigue. Antibodies to the acetylcholine receptor (AChR) are detected in up to 80% of patients, with up to 40% of patients who lack antibodies to AChR having antibodies to muscle-specific kinase (MuSK) [1–3]. Treatment typically includes symptom management with acetylcholinesterase inhibitors as well as immunotherapy, including agents such as corticosteroids, azathioprine, cyclosporine, mycophenolate mofetil, plasma exchange (PLEX), and intravenous immunoglobulin (IVIg) [4–6]. Thymectomy, with or without thymoma, has also been shown to be beneficial in the treatment of generalized AChR+ MG [7]. Response to immunomodulatory therapies in myasthenia gravis (MG)
can be variable. A subset of MG patients remains refractory to conventional agents [8]. B-cell targeted therapy with rituximab has shown durable response in treating refractory MG. The benefits of rituximab in MG have been reported by several groups [9–18]. Treatment of MG with rituximab has been shown to result in sustained clinical improvement, as well as allowing for tapering and discontinuing of other immunotherapies [9,19]. A recent phase 2 clinical trial of rituximab in AChR+ MG (BeatMG Study) demonstrated a favorable safety profile, however, met the primary futility outcome at 52-weeks suggesting that there would be a low probability of achieving the prespecified steroid sparing effect difference in a similar mildly symptomatic cohort on concomitant immunotherapy [20,21]. This study was not limited to refractory disease or powered to assess efficacy. A multicenter blinded, prospective review of MuSK+ MG demonstrated better clinical
Corresponding author at: Yale University School of Medicine, Department of Neurology, Division of Neuromuscular Medicine, Program in Clinical & Translational Neuromuscular Research (CTNR), PO Box 208018, New Haven, CT 06520, USA. E-mail address: [email protected] (R.J. Nowak). 1 These authors contributed equally ⁎
https://doi.org/10.1016/j.jns.2020.116690 Received 24 July 2019; Received in revised form 20 December 2019; Accepted 17 January 2020 Available online 18 January 2020 0022-510X/ © 2020 Elsevier B.V. All rights reserved.
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
outcomes with rituximab as compared with other treatment regimens [22]. MG patients are typically treated similarly regardless of their serotype [15]. Several studies have suggested that MuSK+ patients have a more severe form of the disease and may be more resistant to established treatments than AChR+ MG patients [8,23,24,25,26]. Additionally, several small studies have suggested that MuSK+ MG patients tend to respond better to rituximab and have prolonged better clinical outcomes compared to AChR+ MG patients [10,15,26–32]. A 2017 systematic review of rituximab treatment in MG demonstrated clinical status improvement in both AChR+ and MuSK+ groups with less relapses in MuSK+ MG post-rituximab compared to AChR+ MG3. Additional studies are needed to investigate and further characterize the differential response to rituximab treatments between AChR+ and MuSK+ patients with long-term follow-up. We report our experience with rituximab in 33 patients with generalized MG, 17 with AChR+ MG and 16 with MuSK+ MG, who had an average follow-up of approximately 5 years. We analyzed the difference in treatment response between the AChR+ and MuSK+ MG.
immunoglobulin (IVIg). The number of administered rituximab treatment cycles, time since last treatment cycle, time to relapse, time to remission and post-relapse treatments were also reviewed. The Myasthenia Gravis Foundation of America (MGFA) clinical classification criteria [33] and post-intervention status (PIS) were used to assign clinical state 12 months after completion of the initial set of rituximab cycles and at last visit. We defined “improved clinical status” when Complete Stable Remission (CSR), Minimal Manifestations (MM), and/ or Improved (I) PIS change was achieved. Remission was defined as when the patient achieved “asymptomatic” status based on the MGFA classification and had not relapsed for 12 months. Exacerbation was defined as when a patient had clinically deteriorated based on a worsened MGFA class. Rescue therapy was defined as the need for the addition of an immunotherapy (IVIg or PLEX) during a disease exacerbation. This was quantified via chart review by noting for each disease exacerbation which treatments were used. Maintenance therapy was defined as regularly scheduled immunotherapy treatments (IVIg or PLEX). These were quantified via chart review of regularly scheduled treatments for the patient. Concomitant use of other immunosuppressive agents and their daily dose was also reviewed.
2. Methods 2.1. Patients
2.2. Rituximab
This retrospective study included patients with generalized MG requiring rituximab therapy and followed for a minimum of 12 months after completion of the initial set of rituximab treatment cycles (Table 1). We identified 33 patients followed in the Yale Myasthenia Gravis Clinic, New Haven, Connecticut from May 31, 2003 to May 31, 2017. This study was approved by the institutional review board of Yale University as part of an observational study examining the treatment and disease course of MG. All patients provided written informed consent. Rituximab was administered in cases when the immunotherapy dosage could not be lowered without clinical relapse, adequate clinical control could not be achieved, and/or patients experienced severe adverse effects due to the current immunosuppressive therapy. Pretreatment and post-treatment immunotherapy regimens, clinical symptoms, and examination findings were evaluated. These included prednisone (which is the standard first-line agent), plasma exchange (PLEX), azathioprine, mycophenolate mofetil, and intravenous
Patients were treated with an initial 2- to 4- cycle regimen, except for two patients who only received 1 cycle. Because no established infusion protocol for rituximab use in MG currently exists, the MG clinic used a standard protocol adopted from the non-Hodgkin lymphoma regimen of 4 weekly infusions of 375 mg/m2. One cycle is defined as 1 infusion per week for 4 consecutive weeks. The interval between cycles was 6 months. The number of rituximab treatment cycles or intervals between cycles was not dictated by B-cell counts but rather based on clinical improvement and patient toleration of tapering or withdrawal of other immunotherapies (i.e. corticosteroids). 2.3. Statistical analysis Statistical analysis was performed using R version 1.4.3. Descriptive statistics are represented as mean ± standard deviation if not specified otherwise. Wilcoxon-signed rank tests for paired analysis, and Mann-
Table 1 Demographics and baseline characteristics. All patients (n = 33)
AChR (n = 17)
MuSK (n = 16)
p-Value
Demographics: Age at onset, mean (SD) Female, n (%) Worst MGFA classification, median (range) Thymoma, n (%) Duration of disease in days before rituximab, mean (SD) Length of follow-up in days, mean (SD)
35.9 (15.6) 24 (72%) III (II-V) 7 (21%) 1579.4 ± 2423.8 1861.5 (953.4)
33 (25) 10 (58%) III (II-V) 7 (46%) 1169.2 ± 762.6 1196.1 (743.9)
34.8 (14.9) 14 (87%) III (II-V) 0 (0%) 2025.9 ± 3391.1 1718.6 (1143.1)
0.70 0.12 0.19 0.06 0.33 0.41
Current and previous treatment: Patients on prednisone when starting rituximab, n (%) Prednisone dose in mg/day, mean (SD) Patients on maintenance IVIg and/or PLEX, n (%) Use of oral steroid sparing agents, n (%)a Patients with previous rescue therapy with IVIg and/or PLEX, n (%) Previous thymectomy, n (%) Time from thymectomy to 1st cycle of rituximab, mean (SD)
29 (87%) 39.1 (23.9) 15 (46%) 17 (51%) 29 (87.9%) 20 (61%) 940.6 (1096.9)
16 (94%) 46.8 (20.8) 4 (24%) 9 (53%) 16 (94%) 15 (88%) 730.6 (589.3)
13 (81%) 30.9 (24.9) 11(69%) 9 (56%) 13 (81.3%) 5 (31%) 1675.5 (2094.7)
0.26 0.06 0.02 0.86 >0.9 <0.01 0.44
Disease exacerbation pre-rituximab: Number of exacerbations, mean (SD)
1.7 (2.9)
2.6 (2.7)
0.8 (0.9)
0.06
Rituximab therapy: Number of rituximab cycles, mean (SD)
3.1 (1.3)
3.1 (0.9)
3.1 (1.7)
>0.9
a Azathioprine (6 AChR+, 4 MuSK+); mycophenolate mofetil (3 AChR+, 4 MuSK+); cyclosporine (1 MuSK+). IVIg, intravenous immunoglobulin; PLEX, plasma exchange.
2
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Whitney U test for unpaired analysis were used for non-parametric data. Paired or unpaired t-test was used for parametric data as applicable. χ2 test or Fisher's exact test were used for nominal data as applicable. Kaplan-Meier survival curves were generated with log-rank test to study the duration of response to rituximab. Significance was defined as p-value of <0.05. 3. Results Thirty-three patients were identified (17 AChR+, 16 MuSK+; mean age 35.9 ± 15.6 years; 24 women and 9 men) with a mean follow-up of 1861 ± 953.4 days. Twenty-seven patients (87.9%) were receiving prednisone before initiating rituximab therapy. The mean number of induction rituximab cycles received was 3.1 ± 1.3. The AChR+ and MuSK+ groups were well matched overall. There were no significant differences between the AChR+ and MuSK+ groups in terms of age at onset of disease, gender, length of follow-up, or number of rituximab cycles received. Key differences noted were that the number of patients receiving either IVIg or PLEX maintenance therapy prior to rituximab was higher in the MuSK+ group (4/17 in AChR+ vs. 11/16 in MuSK+, p-value 0.02) and the number of patients undergoing thymectomy was higher in the AChR+ group (15/17 in AChR+ vs. 5/16 in MuSK+, p-value <.01) (Table 1). The median baseline MGFA Clinical Class was II for the entire group, which improved to asymptomatic (0) both at 12-months and last follow-up (p-values <.01) after rituximab treatment (Table 1, Fig. 1). The median MFGA Clinical Class for AChR+ patients improved from a baseline of II to asymptomatic (0) at 12-months (p-value <.01) and at last visit (p-value <.01) after rituximab treatment. Similarly, MuSK+ patients improved from a median baseline class of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01) (Fig. 1). MM or better PIS was attained at 12-months in 10 (58.8%) AChR+ patients and 11 (68.8%) MuSK+ patients, respectively (p-value 0.72). At last follow-up MM or better PIS was attained in 11 (64.7%) and 12 (75%) of AChR+ and MuSK+ patient respectively. Twenty-one patients achieved clinical remission (12 AChR+, 9 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) (Fig. 2, Table 2). Overall, the MuSK+ group required a shorter period of time to achieve remission, as defined by MGFA class of asymptomatic without any relapse for 12 months. The mean prednisone dose requirement decreased in both groups following rituximab treatment (AChR+: baseline 46.8 ± 20.8 mg/day, 12-months 11.8 ± 15.3 mg/day, last follow-up 17.9 ± 15.6; MuSK+: baseline 30.9 ± 24.9 mg/day, 12-months 9.5 ± 8.7 mg/day, last follow-up 2.8 ± 3.8 mg/day). While this was significant within groups
Fig. 2. Time to remission between AChR+ (n = 9) and MuSK+ (n = 12) patients post-rituximab (days since start of first rituximab infusion). Comparison data shown is only for those that achieved clinical remission.
(p-value <.01), there was no significant difference between the two groups (baseline p-value 0.057, 12-months p-value 1, last follow-up pvalue 0.75) (Tables 1, 2, 3). There was also no significant difference between the groups in terms of ability to taper off prednisone completely or to reduce the daily dose of prednisone ≤10 mg (p-values 0.69 and 0.49 respectively). The length of time required to taper off prednisone completely or ≤10 mg/day post-rituximab also did not defer significantly between the groups (p-values 0.4 and 0.08 respectively) (Table 2). The most commonly used steroid sparing agents in our cohort were azathioprine (AZA) and mycophenolate mofetil (MMF). Only one patient in the MuSK+ group was on cyclosporine only before rituximab infusion. Overall use of steroid sparing agents was significantly reduced following rituximab treatment [18 patients at baseline, 8 patients at 12months (p-value 0.02), and 5 patients at last follow-up (p-value 0.002)]; however, this did not reach statistical significance when AChR+ and MuSK+ groups were considered separately. There was no significant difference between the groups in terms of successful reduction of concomitant use of steroid sparing agents (Tables 2, 3). Sixteen (48.5%) patients relapsed after rituximab therapy (Table 2). The relapse rate was 58.8% and 37.5% for AChR+ and MuSK+ patients respectively (p-value 0.22). There was no significant difference in time to relapse between AChR+ and MuSK+ patients (p-value 0.09) (Fig. 3A). However, when the cohort was restricted to patients who received ≥3 rituximab cycles, MuSK+ patients relapsed later than
Fig. 1. MGFA clinical class at baseline, 12-months, and at last visit for AChR+ and MuSK+ patients. (A) The median MGFA clinical class for AChR+ patients improved from a baseline of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01) post-rituximab. (B) Similarly, MuSK+ patients improved from a median baseline MGFA clinical class of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01). 3
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Table 2 Outcome measures post-rituximab therapy. AChR (n = 17)
MuSK (n = 16)
p-Value
Clinical outcome: MM or better at 12 months, n (%) MM or better at last visit, n (%) Patients with clinical remission,a n (%) Days to remission, mean (SD) Patients with relapse, n (%) Days to relapse, mean (SD)
10 (58.8%) 11(65%) 12 (70.6%) 441.4 (336.6) 10 (58.8%) 824.1 ± 479.3
11 (68.8%) 12 (75%) 9 (56.3%) 230 (180.8) 6 (37.5%) 1529 ± 1338.4
0.72 0.71 0.39 0.049 0.22 0.09
Steroid-sparing effect: Prednisone dose at 12-months in mg/day, mean (SD) Prednisone dose at last visit in mg/day, mean (SD) Able to taper prednisone to ≤10 mg/day, n (%) Time to ≤10 mg/day in days, mean (SD) Able to taper prednisone completely, n (%) Time to taper prednisone completely in days, mean (SD)
11.8 (15.3) 17.9 (15.63) 14 (82%) 361.9 (232.8) 12 (70%) 811.4 ± 395.6
9.5 (8.7) 2.8 (3.8) 13 (81%) 219.1 (152.0) 9 (56%) 712.4 ± 395.6
1 0.75 0.49 0.08 0.69 0.4
Disease exacerbation: Number of exacerbations, mean (SD) Number of patients hospitalized for exacerbations, n (%)
1.7 (1.2) 5 (29%)
1.4 (1.1) 0 (0%)
0.42 0.045
Steroid sparing agents: Use of oral steroid sparing agents, n (%)
3 (18%)
2 (12.5%)
>0.9
Maintenance therapy: Number of patients requiring maintenance therapy with IVIg and/or PLEX, n (%) Total number of IVIg and/or PLEX treatment cycles, Mean (SD)
6 (35.3%) 9.8 (31.8)
6 (43.8%) 9.1 (19.8)
1 0.77
Rescue therapy: Number of patients requiring rescue therapy with IVIg and/or PLEX, n (%) Total number of IVIg and/or PLEX treatment cycles, Mean (SD)
7 (41.2%) 0.7 (1.1)
3 (18.8%) 0.5 (1.1)
0.26 0.27
a
Clinical remission was defined as when the patient achieved “asymptomatic” status based on the MGFA classification and had not relapsed for 12 months.
Table 3 Comparison of treatment burden between the AChR+ and MuSK+ groups. AChR
MuSK
Pre-rituximab
Post-rituximab
p-Value
Pre-rituximab
Post-rituximab
p-Value
46.8 (20.8)
11.6 (14.7) 17.9 ± 15.6
<0.01 <0.01
30.9 (24.9)
5.9 (8.0) 2.3 ± 3.8
<0.01 <0.01
Steroid-sparing agent use: Azathioprine Mycophenolate mofetil Cyclosporine
6 3 0
3 0 0
0.43 0.22 NA
4 4 1
2 0 0
0.65 0.10 NA
Maintenance IVIg and PLEX: Number of patients on main-tenance IVIg and PLEX treatments Total number of maintenance IVIg and PLEX treatments, n (SD)
4 22.3 (61.3)
6 9.8 (31.9)
0.71 0.29
11 21.7 (27.2)
6 9.1 (19.8)
0.16 0.21
Rescue IVIg and PLEX: Number of patients on rescue IVIg and PLEX treatments Total number of rescue IVIg and PLEX treatments, n (SD)
16 2.1 (1.2)
7 0.7(1.1)
<0.01 <0.01
13 2.1 (2)
3 0.5 (1.1)
<0.01 0.02
Prednisone use: Prednisone dose (pre-rituximab and 1 year) Prednisone dose (last visit)
AChR+ patients (p-value 0.03) (Fig. 3B). AChR+ patients had more MG-related hospitalizations as compared to MuSK+ patients during the entire follow-up period (p-value 0.045) (Table 2). We examined the effect of rituximab treatment on the total burden of IVIg and PLEX required as maintenance therapy and there was no statistically significant reduction compared to pre-rituximab in either the AChR+ or MuSK+ group (p-value 0.29 and 0.21 respectively). Similarly, the number of patients requiring maintenance IVIg or PLEX was not significantly different in either group post-rituximab therapy compared to pre-rituximab (p-values 0.71 and 0.16 respectively). There was also no difference between the AChR+ and MuSK+ groups in terms of total number of maintenance therapy requirement post-rituximab infusion (p-value 0.77). Less number of patients required IVIg or PLEX as rescue therapy following rituximab in both groups (p-values <.01). Similarly, number of rescue therapy required either with IVIg or PLEX reduced significantly in both AChR+ and MuSK+ patients post-rituximab therapy
(p-value <.01 and 0.02 respectively). However, there was no significant difference between groups in terms of number of patients requiring rescue therapy or the total number of rescue therapy events required post-rituximab (p-values 0.26 and 0.27 respectively) (Tables 2, 3). Twenty patients had undergone thymectomy (60.6%), of whom 7 (21.1%) had a thymoma (Table 1). All patients with a thymoma were AChR+. While the thymoma subgroup received more rituximab cycles (3.6 ± 0.9 vs. 2.5 ± 0.8, p-value 0.03), there were no significant differences found between the thymoma vs non-thymoma groups in terms of above mentioned clinical outcomes. All patients in the study tolerated rituximab treatment without severe adverse side effects identified per chart review. 4. Discussion Targeted immunotherapies demonstrate great potential for a subset 4
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Fig. 3. (A) Time to relapse between all AChR+ and MuSK+ patients post-rituximab. (B) Time to relapse between AChR+ and MuSK+ patients who received ≥3 cycles of rituximab. All patients are included in this analysis. Time reflects days since start of first rituximab infusion.
of MG patients who are refractory to or have adverse effects from conventional immunosuppressive treatments. Depletion of B cells with rituximab, with its established precedence in other autoimmune disorders such as rheumatoid arthritis [34–36], has availed itself as an appealing next-line option. In this retrospective analysis of 33 patients with refractory AChR+ or MuSK+ MG and extended follow-up, a long-lasting clinical benefit was again observed following rituximab therapy [19]. These results support the findings from previous studies demonstrating the benefit of rituximab in managing refractory MG [9,10,37–39]. Additionally, our findings add valuable insights regarding whether B-cell depletion therapy should be maintained or utilized as an induction regimen. It also informs us as to the expected rate of relapse after achieving remission following completion of an induction regimen. The overall relapse rate in our entire cohort was 48.5%, occurring approximately 2.7 years after treatment (992 ± 783.9 days). While the relapse rate was similar to those previously reported [10,40], the duration of disease stability was longer in our cohort. Prednisone burden was also successfully reduced in both groups. While concomitant steroid sparing agent use was reduced among the whole cohort, statistical significance was not achieved when groups were considered separately, which may be related to small sample size with between group analysis. There were some trends suggesting that the MuSK+ group may experience greater benefit with rituximab, specifically a faster time to remission and a longer time to relapse, which is further supported by more frequent MG-related hospitalizations and need for rescue therapy in the AChR+ group. Despite interesting observations, this report is limited by the retrospective nature of our study, varied baseline immunotherapy regimens and number of rituximab treatment cycles. Unfortunately, it does not adequately address the question of differential response to rituximab between AChR+ and MuSK+ patients or whether antibody status is a predictor of response or durability. In our healthcare system rituximab use is mostly restricted to the outpatient setting. While our study included patients with refractory generalized disease, in the attempt to stabilize patients prior to start of infusions, the majority of the patients were categorized as mild-moderate in severity (based on MGFA class) at the time of rituximab initiation. This may have resulted in a scale floor effect masking any possible difference between groups. Due to the MGFA classification only being a gross measure of disease severity, true burden of disease differences could not be assessed as other outcomes were not available for analysis, such as MG Activities of Daily Living (MG-ADL) or Quantitative MG (QMG) scores. While there is strong evidence that AChR+ and MuSK+ MG are
distinct disease entities with unique immunopathologic mechanisms [41–43], dramatic clinical differences were not noted with anti-CD20 therapy. B-cell depletion appears to benefit both groups of patients. As a clearer picture emerges regarding pathogenic B-cell populations and whether these return upon B-cell recovery, the application of targeted therapy can be better tailored to each patient. Despite the results from the BeatMG Study, a phase 2 trial of only AChR+ patients, the scientific rationale for B-cell depletion in MG is established based on the totality of published data and experience with CD20-targeted therapy. Further insights from BeatMG Study subgroup analyses and an ongoing placebo-controlled trial of rituximab in new onset generalized MG will aid in better understanding where B-cell depletion therapy might best fit the overall treatment paradigm [44]. Nonetheless, we must further consider whether anti-CD19 as opposed to anti-CD20 may be more effective or durable. The primary objective of B-cell depletion is the elimination of autoantibody producing cells. In the case of anti-CD20 therapy this goal is partially achieved by preventing the formation of new plasma cells from their precursors. As CD20 is generally not expressed on the majority of autoantibody-producing cells, specifically plasma cells and plasmablasts, this is one potential disadvantage of an anti-CD20 treatment approach. On the other hand, anti-CD19 therapy depletes both plasmablasts and plasma cells due to the expression of CD19 on these cells, and thus these agents may potentially be more effective at eliminating production of pathogenic autoantibodies. However, this assumption needs to be tested in a clinical setting, and whether this translates into additional or differential clinical benefit between AChR+ and MuSK+ MG beyond that seen with anti-CD20 therapeutics remains to be seen. 5. Conclusions Rituximab therapy is a reasonable option for both AChR+ and MuSK+ generalized MG patients, especially those with difficult to control disease. While MuSK+ MG patients may experience greater benefits, a significant differential response between groups was not observed in our retrospective study. B-cell targeted therapy continues to be a rational strategy in the MG treatment paradigm. Further investigations are warranted to explore how B-cell depletion therapy is best applied to achieve improved outcomes which are both meaningful and sustained in our patients. Funding None. 5
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Declaration of Competing Interest
[21] R.J. Nowak, BeatMG: Phase II Trial of Rituximab In Myasthenia Gravis, ClinicalTrials.gov, (2018) (Identifier: NCT02110706). [22] M.K. Hehir, L.D. Hobson-Webb, M. Benatar, et al., Rituximab as treatment for antiMuSK myasthenia gravis: Multicenter blinded prospective review, Neurology. 89 (10) (2017) 1069–1077. [23] F. Deymeer, O. Gungor-Tuncer, V. Yilmaz, et al., Clinical comparison of anti-MuSKvs anti-AChR-positive and seronegative myasthenia gravis, Neurology. 68 (8) (2007) 609–611. [24] S.J. Oh, M.B. Morgan, L. Lu, et al., Different characteristic phenotypes according to antibody in myasthenia gravis, J. Clin. Neuromuscul. Dis. 14 (2) (2012) 57–65. [25] A. Nikolic, P. Djukic, I. Basta, et al., The predictive value of the presence of different antibodies and thymus pathology to the clinical outcome in patients with generalized myasthenia gravis, Clin. Neurol. Neurosurg. 115 (4) (2013) 432–437. [26] A. Evoli, P.A. Tonali, L. Padua, et al., Clinical correlates with anti-MuSK antibodies in generalized seronegative myasthenia gravis, Brain. 126 (10) (2003) 2304–2311. [27] I. Illa, J.A. Diaz-Manera, C. Juarez, et al., “Seronegative” myasthenia gravis and antiMuSK positive antibodies: description of Spanish series, Med. Clin. 125 (3) (2005) 100–102. [28] D.B. Sanders, K. El-Salem, J.M. Massey, J. McConville, A. Vincent, Clinical aspects of MuSK antibody positive seronegative MG, Neurology. 60 (12) (2003) 1978–1980. [29] D.E. Stickler, J.M. Massey, D.B. Sanders, MuSK-antibody positive myasthenia gravis: clinical and electrodiagnostic patterns, Clin. Neurophysiol. 116 (9) (2005) 2065–2068. [30] A. Vincent, M.I. Leite, Neuromuscular junction autoimmune disease: muscle specific kinase antibodies and treatments for myasthenia gravis, Curr. Opin. Neurol. 18 (5) (2005) 519–525. [31] A. Vincent, J. Bowen, J. Newsom-Davis, J. McConville, Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets, Lancet Neurol. 2 (2) (2003) 99–106. [32] L. Zhou, J. McConville, V. Chaudhry, et al., Clinical comparison of muscle-specific tyrosine kinase (MuSK) antibody-positive and -negative myasthenic patients, Muscle Nerve 30 (1) (2004) 55–60. [33] A. Jaretzki 3rd, R.J. Barohn, R.M. Ernstoff, et al., Myasthenia gravis: recommendations for clinical research standards. Task force of the medical scientific advisory board of the myasthenia gravis foundation of america, Neurology. 55 (1) (2000) 16–23. [34] M.C. Dalakas, B cells as therapeutic targets in autoimmune neurological disorders, Nat. Clin. Pract. Neurol. 4 (10) (2008) 557–567. [35] T. Dorner, D. Isenberg, D. Jayne, H. Wiendl, D. Zillikens, G. Burmester, Current status on B-cell depletion therapy in autoimmune diseases other than rheumatoid arthritis, Autoimmun. Rev. 9 (2) (2009) 82–89. [36] J.C. Edwards, L. Szczepanski, J. Szechinski, et al., Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis, N. Engl. J. Med. 350 (25) (2004) 2572–2581. [37] S. Blum, D. Gillis, H. Brown, et al., Use and monitoring of low dose rituximab in myasthenia gravis, J. Neurol. Neurosurg. Psychiatry 82 (6) (2011) 659–663. [38] B. Keung, K.R. Robeson, D.B. DiCapua, et al., Long-term benefit of rituximab in MuSK autoantibody myasthenia gravis patients, J. Neurol. Neurosurg. Psychiatry 84 (12) (2013) 1407–1409. [39] F. Chan, A. Swayne, D. Gillis, et al., Long-term follow-up of patients with myasthenia gravis treated with low-dose rituximab, J. Neurol. Neurosurg. Psychiatry 90 (8) (2019) 955–956. [40] E. Cortés-Vicente, R. Rojas-Garcia, J. Díaz-Manera, et al., The impact of rituximab infusion protocol on the long-term outcome in anti-MuSK myasthenia gravis, Ann. Clin. Transl. Neurol. 5 (6) (2018) 710–716. [41] A. Rødgaard, F.C. Nielsen, R. Djurup, F. Somnier, S. Gammeltoft, Acetylcholine receptor antibody in myasthenia gravis: predominance of IgG subclasses 1 and 3, Clin. Exp. Immunol. 67 (1) (1987) 82–88. [42] E.H. Niks, Y. van Leeuwen, M.I. Leite, et al., Clinical fluctuations in MuSK myasthenia gravis are related to antigen-specific IgG4 instead of IgG1, J. Neuroimmunol. 195 (1–2) (2008) 151–156. [43] I. Koneczny, J. Cossins, P. Waters, D. Beeson, A. Vincent, MuSK myasthenia gravis IgG4 disrupts the interaction of LRP4 with MuSK but both IgG4 and IgG1-3 can disperse preformed agrin-independent AChR clusters, PLoS ONE 8 (11) (2013) e80695. [44] F. Piehl, A Study Evaluating the Safety and Efficacy of Rituximab in Patients With Myasthenia Gravis (Rinomax), ClinicalTrials.gov, (2019) (Identifier: NCT02950155).
Richard J. Nowak reports no conflicts directly related to this work. Dr. Nowak has received research support from the National Institutes of Health (NIH), Genentech, Alexion Pharmaceuticals, Ra Pharmaceuticals, Myasthenia Gravis Foundation of America, Momenta, and Grifols. He has served as consultant/advisor for Alexion Pharmaceuticals, CSL Behring, Grifols, Ra Pharmaceuticals, Roivant, and Momenta. Bhaskar Roy reports no conflicts directly related to this work. Dr. Roy has served as consultant/advisor for Alexion Pharmaceuticals. All other authors report no conflicts related to his work. References [1] W. Hoch, J. McConville, S. Helms, J. Newsom-Davis, A. Melms, A. Vincent, Autoantibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies, Nat. Med. 7 (3) (2001) 365–368. [2] J.J. Verschuuren, M.G. Huijbers, J.J. Plomp, et al., Pathophysiology of myasthenia gravis with antibodies to the acetylcholine receptor, muscle-specific kinase and lowdensity lipoprotein receptor-related protein 4, Autoimmun. Rev. 12 (9) (2013) 918–923. [3] R. Tandan, M.K. Hehir 2nd, W. Waheed, D.B. Howard, Rituximab treatment of myasthenia gravis: a systematic review, Muscle Nerve 56 (2) (2017) 185–196. [4] B.M. Conti-Fine, M. Milani, H.J. Kaminski, Myasthenia gravis: past, present, and future, J. Clin. Invest. 116 (11) (2006) 2843–2854. [5] R. Gold, C. Schneider-Gold, Current and future standards in treatment of myasthenia gravis, Neurotherapeutics 5 (4) (2008) 535–541. [6] S. Sathasivam, Steroids and immunosuppressant drugs in myasthenia gravis, Nat. Clin. Pract. Neurol. 4 (6) (2008) 317–327. [7] G.I. Wolfe, H.J. Kaminski, I.B. Aban, et al., Randomized trial of thymectomy in myasthenia gravis, N. Engl. J. Med. 375 (6) (2016) 511–522. [8] J. Suh, J.M. Goldstein, R.J. Nowak, Clinical characteristics of refractory myasthenia gravis patients, Yale J. Biol. Med 86 (2) (2013) 255–260. [9] R.J. Nowak, D.B. Dicapua, N. Zebardast, J.M. Goldstein, Response of patients with refractory myasthenia gravis to rituximab: a retrospective study, Ther. Adv. Neurol. Disord. 4 (5) (2011) 259–266. [10] J. Diaz-Manera, E. Martinez-Hernandez, L. Querol, et al., Long-lasting treatment effect of rituximab in MuSK myasthenia, Neurology. 78 (3) (2012) 189–193. [11] N. Zebardast, H.S. Patwa, S.P. Novella, J.M. Goldstein, Rituximab in the management of refractory myasthenia gravis, Muscle Nerve 41 (3) (2010) 375–378. [12] P. Burusnukul, T.D. Brennan, E.J. Cupler, Prolonged improvement after rituximab: two cases of resistant muscle-specific receptor tyrosine kinase + myasthenia gravis, J. Clin. Neuromuscul. Dis. 12 (2) (2010) 85–87. [13] C. Lebrun, V. Bourg, N. Tieulie, P. Thomas, Successful treatment of refractory generalized myasthenia gravis with rituximab, Eur. J. Neurol. 16 (2) (2009) 246–250. [14] K. Stieglbauer, R. Topakian, V. Schaffer, F.T. Aichner, Rituximab for myasthenia gravis: three case reports and review of the literature, J. Neurol. Sci. 280 (1–2) (2009) 120–122. [15] I. Illa, J. Diaz-Manera, R. Rojas-Garcia, et al., Sustained response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients, J. Neuroimmunol. 201–202 (2008) 90–94. [16] W.S. Baek, A. Bashey, G.L. Sheean, Complete remission induced by rituximab in refractory, seronegative, muscle-specific, kinase-positive myasthenia gravis, J. Neurol. Neurosurg. Psychiatry 78 (7) (2007) 771. [17] M. Thakre, J. Inshasi, M. Marashi, Rituximab in refractory MuSK antibody myasthenia gravis, J. Neurol. 254 (7) (2007) 968–969. [18] B. Hain, K. Jordan, M. Deschauer, S. Zierz, Successful treatment of MuSK antibodypositive myasthenia gravis with rituximab, Muscle Nerve 33 (4) (2006) 575–580. [19] K.R. Robeson, A. Kumar, B. Keung, et al., Durability of the rituximab response in acetylcholine receptor autoantibody-positive myasthenia gravis, JAMA Neurol. 74 (1) (2017) 60–66. [20] R.J. Nowak, et al., B cell targeted treatment in myasthenia gravis (BeatMG): a phase 2 trial of rituximab in myasthenia gravis, Neurology 90 (2018) e2182–e2194.
6
Contents lists available at ScienceDirect
Journal of the Neurological Sciences journal homepage: www.elsevier.com/locate/jns
Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study
T
Tess Litchmana,1, Bhaskar Roya,1, Aditya Kumara, Aditi Sharmaa, Valentine Njikeb, Richard J. Nowaka,⁎ a b
Yale School of Medicine, Department of Neurology, New Haven, CT, USA Griffin Hospital-Derby, Yale University Prevention Research Center, Derby, CT, USA
ARTICLE INFO
ABSTRACT
Keywords: Myasthenia gravis Rituximab Immunotherapy B cell depletion
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.
1. Introduction Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction, leading to muscular weakness and fatigue. Antibodies to the acetylcholine receptor (AChR) are detected in up to 80% of patients, with up to 40% of patients who lack antibodies to AChR having antibodies to muscle-specific kinase (MuSK) [1–3]. Treatment typically includes symptom management with acetylcholinesterase inhibitors as well as immunotherapy, including agents such as corticosteroids, azathioprine, cyclosporine, mycophenolate mofetil, plasma exchange (PLEX), and intravenous immunoglobulin (IVIg) [4–6]. Thymectomy, with or without thymoma, has also been shown to be beneficial in the treatment of generalized AChR+ MG [7]. Response to immunomodulatory therapies in myasthenia gravis (MG)
can be variable. A subset of MG patients remains refractory to conventional agents [8]. B-cell targeted therapy with rituximab has shown durable response in treating refractory MG. The benefits of rituximab in MG have been reported by several groups [9–18]. Treatment of MG with rituximab has been shown to result in sustained clinical improvement, as well as allowing for tapering and discontinuing of other immunotherapies [9,19]. A recent phase 2 clinical trial of rituximab in AChR+ MG (BeatMG Study) demonstrated a favorable safety profile, however, met the primary futility outcome at 52-weeks suggesting that there would be a low probability of achieving the prespecified steroid sparing effect difference in a similar mildly symptomatic cohort on concomitant immunotherapy [20,21]. This study was not limited to refractory disease or powered to assess efficacy. A multicenter blinded, prospective review of MuSK+ MG demonstrated better clinical
Corresponding author at: Yale University School of Medicine, Department of Neurology, Division of Neuromuscular Medicine, Program in Clinical & Translational Neuromuscular Research (CTNR), PO Box 208018, New Haven, CT 06520, USA. E-mail address: [email protected] (R.J. Nowak). 1 These authors contributed equally ⁎
https://doi.org/10.1016/j.jns.2020.116690 Received 24 July 2019; Received in revised form 20 December 2019; Accepted 17 January 2020 Available online 18 January 2020 0022-510X/ © 2020 Elsevier B.V. All rights reserved.
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
outcomes with rituximab as compared with other treatment regimens [22]. MG patients are typically treated similarly regardless of their serotype [15]. Several studies have suggested that MuSK+ patients have a more severe form of the disease and may be more resistant to established treatments than AChR+ MG patients [8,23,24,25,26]. Additionally, several small studies have suggested that MuSK+ MG patients tend to respond better to rituximab and have prolonged better clinical outcomes compared to AChR+ MG patients [10,15,26–32]. A 2017 systematic review of rituximab treatment in MG demonstrated clinical status improvement in both AChR+ and MuSK+ groups with less relapses in MuSK+ MG post-rituximab compared to AChR+ MG3. Additional studies are needed to investigate and further characterize the differential response to rituximab treatments between AChR+ and MuSK+ patients with long-term follow-up. We report our experience with rituximab in 33 patients with generalized MG, 17 with AChR+ MG and 16 with MuSK+ MG, who had an average follow-up of approximately 5 years. We analyzed the difference in treatment response between the AChR+ and MuSK+ MG.
immunoglobulin (IVIg). The number of administered rituximab treatment cycles, time since last treatment cycle, time to relapse, time to remission and post-relapse treatments were also reviewed. The Myasthenia Gravis Foundation of America (MGFA) clinical classification criteria [33] and post-intervention status (PIS) were used to assign clinical state 12 months after completion of the initial set of rituximab cycles and at last visit. We defined “improved clinical status” when Complete Stable Remission (CSR), Minimal Manifestations (MM), and/ or Improved (I) PIS change was achieved. Remission was defined as when the patient achieved “asymptomatic” status based on the MGFA classification and had not relapsed for 12 months. Exacerbation was defined as when a patient had clinically deteriorated based on a worsened MGFA class. Rescue therapy was defined as the need for the addition of an immunotherapy (IVIg or PLEX) during a disease exacerbation. This was quantified via chart review by noting for each disease exacerbation which treatments were used. Maintenance therapy was defined as regularly scheduled immunotherapy treatments (IVIg or PLEX). These were quantified via chart review of regularly scheduled treatments for the patient. Concomitant use of other immunosuppressive agents and their daily dose was also reviewed.
2. Methods 2.1. Patients
2.2. Rituximab
This retrospective study included patients with generalized MG requiring rituximab therapy and followed for a minimum of 12 months after completion of the initial set of rituximab treatment cycles (Table 1). We identified 33 patients followed in the Yale Myasthenia Gravis Clinic, New Haven, Connecticut from May 31, 2003 to May 31, 2017. This study was approved by the institutional review board of Yale University as part of an observational study examining the treatment and disease course of MG. All patients provided written informed consent. Rituximab was administered in cases when the immunotherapy dosage could not be lowered without clinical relapse, adequate clinical control could not be achieved, and/or patients experienced severe adverse effects due to the current immunosuppressive therapy. Pretreatment and post-treatment immunotherapy regimens, clinical symptoms, and examination findings were evaluated. These included prednisone (which is the standard first-line agent), plasma exchange (PLEX), azathioprine, mycophenolate mofetil, and intravenous
Patients were treated with an initial 2- to 4- cycle regimen, except for two patients who only received 1 cycle. Because no established infusion protocol for rituximab use in MG currently exists, the MG clinic used a standard protocol adopted from the non-Hodgkin lymphoma regimen of 4 weekly infusions of 375 mg/m2. One cycle is defined as 1 infusion per week for 4 consecutive weeks. The interval between cycles was 6 months. The number of rituximab treatment cycles or intervals between cycles was not dictated by B-cell counts but rather based on clinical improvement and patient toleration of tapering or withdrawal of other immunotherapies (i.e. corticosteroids). 2.3. Statistical analysis Statistical analysis was performed using R version 1.4.3. Descriptive statistics are represented as mean ± standard deviation if not specified otherwise. Wilcoxon-signed rank tests for paired analysis, and Mann-
Table 1 Demographics and baseline characteristics. All patients (n = 33)
AChR (n = 17)
MuSK (n = 16)
p-Value
Demographics: Age at onset, mean (SD) Female, n (%) Worst MGFA classification, median (range) Thymoma, n (%) Duration of disease in days before rituximab, mean (SD) Length of follow-up in days, mean (SD)
35.9 (15.6) 24 (72%) III (II-V) 7 (21%) 1579.4 ± 2423.8 1861.5 (953.4)
33 (25) 10 (58%) III (II-V) 7 (46%) 1169.2 ± 762.6 1196.1 (743.9)
34.8 (14.9) 14 (87%) III (II-V) 0 (0%) 2025.9 ± 3391.1 1718.6 (1143.1)
0.70 0.12 0.19 0.06 0.33 0.41
Current and previous treatment: Patients on prednisone when starting rituximab, n (%) Prednisone dose in mg/day, mean (SD) Patients on maintenance IVIg and/or PLEX, n (%) Use of oral steroid sparing agents, n (%)a Patients with previous rescue therapy with IVIg and/or PLEX, n (%) Previous thymectomy, n (%) Time from thymectomy to 1st cycle of rituximab, mean (SD)
29 (87%) 39.1 (23.9) 15 (46%) 17 (51%) 29 (87.9%) 20 (61%) 940.6 (1096.9)
16 (94%) 46.8 (20.8) 4 (24%) 9 (53%) 16 (94%) 15 (88%) 730.6 (589.3)
13 (81%) 30.9 (24.9) 11(69%) 9 (56%) 13 (81.3%) 5 (31%) 1675.5 (2094.7)
0.26 0.06 0.02 0.86 >0.9 <0.01 0.44
Disease exacerbation pre-rituximab: Number of exacerbations, mean (SD)
1.7 (2.9)
2.6 (2.7)
0.8 (0.9)
0.06
Rituximab therapy: Number of rituximab cycles, mean (SD)
3.1 (1.3)
3.1 (0.9)
3.1 (1.7)
>0.9
a Azathioprine (6 AChR+, 4 MuSK+); mycophenolate mofetil (3 AChR+, 4 MuSK+); cyclosporine (1 MuSK+). IVIg, intravenous immunoglobulin; PLEX, plasma exchange.
2
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Whitney U test for unpaired analysis were used for non-parametric data. Paired or unpaired t-test was used for parametric data as applicable. χ2 test or Fisher's exact test were used for nominal data as applicable. Kaplan-Meier survival curves were generated with log-rank test to study the duration of response to rituximab. Significance was defined as p-value of <0.05. 3. Results Thirty-three patients were identified (17 AChR+, 16 MuSK+; mean age 35.9 ± 15.6 years; 24 women and 9 men) with a mean follow-up of 1861 ± 953.4 days. Twenty-seven patients (87.9%) were receiving prednisone before initiating rituximab therapy. The mean number of induction rituximab cycles received was 3.1 ± 1.3. The AChR+ and MuSK+ groups were well matched overall. There were no significant differences between the AChR+ and MuSK+ groups in terms of age at onset of disease, gender, length of follow-up, or number of rituximab cycles received. Key differences noted were that the number of patients receiving either IVIg or PLEX maintenance therapy prior to rituximab was higher in the MuSK+ group (4/17 in AChR+ vs. 11/16 in MuSK+, p-value 0.02) and the number of patients undergoing thymectomy was higher in the AChR+ group (15/17 in AChR+ vs. 5/16 in MuSK+, p-value <.01) (Table 1). The median baseline MGFA Clinical Class was II for the entire group, which improved to asymptomatic (0) both at 12-months and last follow-up (p-values <.01) after rituximab treatment (Table 1, Fig. 1). The median MFGA Clinical Class for AChR+ patients improved from a baseline of II to asymptomatic (0) at 12-months (p-value <.01) and at last visit (p-value <.01) after rituximab treatment. Similarly, MuSK+ patients improved from a median baseline class of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01) (Fig. 1). MM or better PIS was attained at 12-months in 10 (58.8%) AChR+ patients and 11 (68.8%) MuSK+ patients, respectively (p-value 0.72). At last follow-up MM or better PIS was attained in 11 (64.7%) and 12 (75%) of AChR+ and MuSK+ patient respectively. Twenty-one patients achieved clinical remission (12 AChR+, 9 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) (Fig. 2, Table 2). Overall, the MuSK+ group required a shorter period of time to achieve remission, as defined by MGFA class of asymptomatic without any relapse for 12 months. The mean prednisone dose requirement decreased in both groups following rituximab treatment (AChR+: baseline 46.8 ± 20.8 mg/day, 12-months 11.8 ± 15.3 mg/day, last follow-up 17.9 ± 15.6; MuSK+: baseline 30.9 ± 24.9 mg/day, 12-months 9.5 ± 8.7 mg/day, last follow-up 2.8 ± 3.8 mg/day). While this was significant within groups
Fig. 2. Time to remission between AChR+ (n = 9) and MuSK+ (n = 12) patients post-rituximab (days since start of first rituximab infusion). Comparison data shown is only for those that achieved clinical remission.
(p-value <.01), there was no significant difference between the two groups (baseline p-value 0.057, 12-months p-value 1, last follow-up pvalue 0.75) (Tables 1, 2, 3). There was also no significant difference between the groups in terms of ability to taper off prednisone completely or to reduce the daily dose of prednisone ≤10 mg (p-values 0.69 and 0.49 respectively). The length of time required to taper off prednisone completely or ≤10 mg/day post-rituximab also did not defer significantly between the groups (p-values 0.4 and 0.08 respectively) (Table 2). The most commonly used steroid sparing agents in our cohort were azathioprine (AZA) and mycophenolate mofetil (MMF). Only one patient in the MuSK+ group was on cyclosporine only before rituximab infusion. Overall use of steroid sparing agents was significantly reduced following rituximab treatment [18 patients at baseline, 8 patients at 12months (p-value 0.02), and 5 patients at last follow-up (p-value 0.002)]; however, this did not reach statistical significance when AChR+ and MuSK+ groups were considered separately. There was no significant difference between the groups in terms of successful reduction of concomitant use of steroid sparing agents (Tables 2, 3). Sixteen (48.5%) patients relapsed after rituximab therapy (Table 2). The relapse rate was 58.8% and 37.5% for AChR+ and MuSK+ patients respectively (p-value 0.22). There was no significant difference in time to relapse between AChR+ and MuSK+ patients (p-value 0.09) (Fig. 3A). However, when the cohort was restricted to patients who received ≥3 rituximab cycles, MuSK+ patients relapsed later than
Fig. 1. MGFA clinical class at baseline, 12-months, and at last visit for AChR+ and MuSK+ patients. (A) The median MGFA clinical class for AChR+ patients improved from a baseline of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01) post-rituximab. (B) Similarly, MuSK+ patients improved from a median baseline MGFA clinical class of II to asymptomatic (0) at 12-months (p-value <.01) and at last follow-up visit (p-value <.01). 3
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Table 2 Outcome measures post-rituximab therapy. AChR (n = 17)
MuSK (n = 16)
p-Value
Clinical outcome: MM or better at 12 months, n (%) MM or better at last visit, n (%) Patients with clinical remission,a n (%) Days to remission, mean (SD) Patients with relapse, n (%) Days to relapse, mean (SD)
10 (58.8%) 11(65%) 12 (70.6%) 441.4 (336.6) 10 (58.8%) 824.1 ± 479.3
11 (68.8%) 12 (75%) 9 (56.3%) 230 (180.8) 6 (37.5%) 1529 ± 1338.4
0.72 0.71 0.39 0.049 0.22 0.09
Steroid-sparing effect: Prednisone dose at 12-months in mg/day, mean (SD) Prednisone dose at last visit in mg/day, mean (SD) Able to taper prednisone to ≤10 mg/day, n (%) Time to ≤10 mg/day in days, mean (SD) Able to taper prednisone completely, n (%) Time to taper prednisone completely in days, mean (SD)
11.8 (15.3) 17.9 (15.63) 14 (82%) 361.9 (232.8) 12 (70%) 811.4 ± 395.6
9.5 (8.7) 2.8 (3.8) 13 (81%) 219.1 (152.0) 9 (56%) 712.4 ± 395.6
1 0.75 0.49 0.08 0.69 0.4
Disease exacerbation: Number of exacerbations, mean (SD) Number of patients hospitalized for exacerbations, n (%)
1.7 (1.2) 5 (29%)
1.4 (1.1) 0 (0%)
0.42 0.045
Steroid sparing agents: Use of oral steroid sparing agents, n (%)
3 (18%)
2 (12.5%)
>0.9
Maintenance therapy: Number of patients requiring maintenance therapy with IVIg and/or PLEX, n (%) Total number of IVIg and/or PLEX treatment cycles, Mean (SD)
6 (35.3%) 9.8 (31.8)
6 (43.8%) 9.1 (19.8)
1 0.77
Rescue therapy: Number of patients requiring rescue therapy with IVIg and/or PLEX, n (%) Total number of IVIg and/or PLEX treatment cycles, Mean (SD)
7 (41.2%) 0.7 (1.1)
3 (18.8%) 0.5 (1.1)
0.26 0.27
a
Clinical remission was defined as when the patient achieved “asymptomatic” status based on the MGFA classification and had not relapsed for 12 months.
Table 3 Comparison of treatment burden between the AChR+ and MuSK+ groups. AChR
MuSK
Pre-rituximab
Post-rituximab
p-Value
Pre-rituximab
Post-rituximab
p-Value
46.8 (20.8)
11.6 (14.7) 17.9 ± 15.6
<0.01 <0.01
30.9 (24.9)
5.9 (8.0) 2.3 ± 3.8
<0.01 <0.01
Steroid-sparing agent use: Azathioprine Mycophenolate mofetil Cyclosporine
6 3 0
3 0 0
0.43 0.22 NA
4 4 1
2 0 0
0.65 0.10 NA
Maintenance IVIg and PLEX: Number of patients on main-tenance IVIg and PLEX treatments Total number of maintenance IVIg and PLEX treatments, n (SD)
4 22.3 (61.3)
6 9.8 (31.9)
0.71 0.29
11 21.7 (27.2)
6 9.1 (19.8)
0.16 0.21
Rescue IVIg and PLEX: Number of patients on rescue IVIg and PLEX treatments Total number of rescue IVIg and PLEX treatments, n (SD)
16 2.1 (1.2)
7 0.7(1.1)
<0.01 <0.01
13 2.1 (2)
3 0.5 (1.1)
<0.01 0.02
Prednisone use: Prednisone dose (pre-rituximab and 1 year) Prednisone dose (last visit)
AChR+ patients (p-value 0.03) (Fig. 3B). AChR+ patients had more MG-related hospitalizations as compared to MuSK+ patients during the entire follow-up period (p-value 0.045) (Table 2). We examined the effect of rituximab treatment on the total burden of IVIg and PLEX required as maintenance therapy and there was no statistically significant reduction compared to pre-rituximab in either the AChR+ or MuSK+ group (p-value 0.29 and 0.21 respectively). Similarly, the number of patients requiring maintenance IVIg or PLEX was not significantly different in either group post-rituximab therapy compared to pre-rituximab (p-values 0.71 and 0.16 respectively). There was also no difference between the AChR+ and MuSK+ groups in terms of total number of maintenance therapy requirement post-rituximab infusion (p-value 0.77). Less number of patients required IVIg or PLEX as rescue therapy following rituximab in both groups (p-values <.01). Similarly, number of rescue therapy required either with IVIg or PLEX reduced significantly in both AChR+ and MuSK+ patients post-rituximab therapy
(p-value <.01 and 0.02 respectively). However, there was no significant difference between groups in terms of number of patients requiring rescue therapy or the total number of rescue therapy events required post-rituximab (p-values 0.26 and 0.27 respectively) (Tables 2, 3). Twenty patients had undergone thymectomy (60.6%), of whom 7 (21.1%) had a thymoma (Table 1). All patients with a thymoma were AChR+. While the thymoma subgroup received more rituximab cycles (3.6 ± 0.9 vs. 2.5 ± 0.8, p-value 0.03), there were no significant differences found between the thymoma vs non-thymoma groups in terms of above mentioned clinical outcomes. All patients in the study tolerated rituximab treatment without severe adverse side effects identified per chart review. 4. Discussion Targeted immunotherapies demonstrate great potential for a subset 4
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Fig. 3. (A) Time to relapse between all AChR+ and MuSK+ patients post-rituximab. (B) Time to relapse between AChR+ and MuSK+ patients who received ≥3 cycles of rituximab. All patients are included in this analysis. Time reflects days since start of first rituximab infusion.
of MG patients who are refractory to or have adverse effects from conventional immunosuppressive treatments. Depletion of B cells with rituximab, with its established precedence in other autoimmune disorders such as rheumatoid arthritis [34–36], has availed itself as an appealing next-line option. In this retrospective analysis of 33 patients with refractory AChR+ or MuSK+ MG and extended follow-up, a long-lasting clinical benefit was again observed following rituximab therapy [19]. These results support the findings from previous studies demonstrating the benefit of rituximab in managing refractory MG [9,10,37–39]. Additionally, our findings add valuable insights regarding whether B-cell depletion therapy should be maintained or utilized as an induction regimen. It also informs us as to the expected rate of relapse after achieving remission following completion of an induction regimen. The overall relapse rate in our entire cohort was 48.5%, occurring approximately 2.7 years after treatment (992 ± 783.9 days). While the relapse rate was similar to those previously reported [10,40], the duration of disease stability was longer in our cohort. Prednisone burden was also successfully reduced in both groups. While concomitant steroid sparing agent use was reduced among the whole cohort, statistical significance was not achieved when groups were considered separately, which may be related to small sample size with between group analysis. There were some trends suggesting that the MuSK+ group may experience greater benefit with rituximab, specifically a faster time to remission and a longer time to relapse, which is further supported by more frequent MG-related hospitalizations and need for rescue therapy in the AChR+ group. Despite interesting observations, this report is limited by the retrospective nature of our study, varied baseline immunotherapy regimens and number of rituximab treatment cycles. Unfortunately, it does not adequately address the question of differential response to rituximab between AChR+ and MuSK+ patients or whether antibody status is a predictor of response or durability. In our healthcare system rituximab use is mostly restricted to the outpatient setting. While our study included patients with refractory generalized disease, in the attempt to stabilize patients prior to start of infusions, the majority of the patients were categorized as mild-moderate in severity (based on MGFA class) at the time of rituximab initiation. This may have resulted in a scale floor effect masking any possible difference between groups. Due to the MGFA classification only being a gross measure of disease severity, true burden of disease differences could not be assessed as other outcomes were not available for analysis, such as MG Activities of Daily Living (MG-ADL) or Quantitative MG (QMG) scores. While there is strong evidence that AChR+ and MuSK+ MG are
distinct disease entities with unique immunopathologic mechanisms [41–43], dramatic clinical differences were not noted with anti-CD20 therapy. B-cell depletion appears to benefit both groups of patients. As a clearer picture emerges regarding pathogenic B-cell populations and whether these return upon B-cell recovery, the application of targeted therapy can be better tailored to each patient. Despite the results from the BeatMG Study, a phase 2 trial of only AChR+ patients, the scientific rationale for B-cell depletion in MG is established based on the totality of published data and experience with CD20-targeted therapy. Further insights from BeatMG Study subgroup analyses and an ongoing placebo-controlled trial of rituximab in new onset generalized MG will aid in better understanding where B-cell depletion therapy might best fit the overall treatment paradigm [44]. Nonetheless, we must further consider whether anti-CD19 as opposed to anti-CD20 may be more effective or durable. The primary objective of B-cell depletion is the elimination of autoantibody producing cells. In the case of anti-CD20 therapy this goal is partially achieved by preventing the formation of new plasma cells from their precursors. As CD20 is generally not expressed on the majority of autoantibody-producing cells, specifically plasma cells and plasmablasts, this is one potential disadvantage of an anti-CD20 treatment approach. On the other hand, anti-CD19 therapy depletes both plasmablasts and plasma cells due to the expression of CD19 on these cells, and thus these agents may potentially be more effective at eliminating production of pathogenic autoantibodies. However, this assumption needs to be tested in a clinical setting, and whether this translates into additional or differential clinical benefit between AChR+ and MuSK+ MG beyond that seen with anti-CD20 therapeutics remains to be seen. 5. Conclusions Rituximab therapy is a reasonable option for both AChR+ and MuSK+ generalized MG patients, especially those with difficult to control disease. While MuSK+ MG patients may experience greater benefits, a significant differential response between groups was not observed in our retrospective study. B-cell targeted therapy continues to be a rational strategy in the MG treatment paradigm. Further investigations are warranted to explore how B-cell depletion therapy is best applied to achieve improved outcomes which are both meaningful and sustained in our patients. Funding None. 5
Journal of the Neurological Sciences 411 (2020) 116690
T. Litchman, et al.
Declaration of Competing Interest
[21] R.J. Nowak, BeatMG: Phase II Trial of Rituximab In Myasthenia Gravis, ClinicalTrials.gov, (2018) (Identifier: NCT02110706). [22] M.K. Hehir, L.D. Hobson-Webb, M. Benatar, et al., Rituximab as treatment for antiMuSK myasthenia gravis: Multicenter blinded prospective review, Neurology. 89 (10) (2017) 1069–1077. [23] F. Deymeer, O. Gungor-Tuncer, V. Yilmaz, et al., Clinical comparison of anti-MuSKvs anti-AChR-positive and seronegative myasthenia gravis, Neurology. 68 (8) (2007) 609–611. [24] S.J. Oh, M.B. Morgan, L. Lu, et al., Different characteristic phenotypes according to antibody in myasthenia gravis, J. Clin. Neuromuscul. Dis. 14 (2) (2012) 57–65. [25] A. Nikolic, P. Djukic, I. Basta, et al., The predictive value of the presence of different antibodies and thymus pathology to the clinical outcome in patients with generalized myasthenia gravis, Clin. Neurol. Neurosurg. 115 (4) (2013) 432–437. [26] A. Evoli, P.A. Tonali, L. Padua, et al., Clinical correlates with anti-MuSK antibodies in generalized seronegative myasthenia gravis, Brain. 126 (10) (2003) 2304–2311. [27] I. Illa, J.A. Diaz-Manera, C. Juarez, et al., “Seronegative” myasthenia gravis and antiMuSK positive antibodies: description of Spanish series, Med. Clin. 125 (3) (2005) 100–102. [28] D.B. Sanders, K. El-Salem, J.M. Massey, J. McConville, A. Vincent, Clinical aspects of MuSK antibody positive seronegative MG, Neurology. 60 (12) (2003) 1978–1980. [29] D.E. Stickler, J.M. Massey, D.B. Sanders, MuSK-antibody positive myasthenia gravis: clinical and electrodiagnostic patterns, Clin. Neurophysiol. 116 (9) (2005) 2065–2068. [30] A. Vincent, M.I. Leite, Neuromuscular junction autoimmune disease: muscle specific kinase antibodies and treatments for myasthenia gravis, Curr. Opin. Neurol. 18 (5) (2005) 519–525. [31] A. Vincent, J. Bowen, J. Newsom-Davis, J. McConville, Seronegative generalised myasthenia gravis: clinical features, antibodies, and their targets, Lancet Neurol. 2 (2) (2003) 99–106. [32] L. Zhou, J. McConville, V. Chaudhry, et al., Clinical comparison of muscle-specific tyrosine kinase (MuSK) antibody-positive and -negative myasthenic patients, Muscle Nerve 30 (1) (2004) 55–60. [33] A. Jaretzki 3rd, R.J. Barohn, R.M. Ernstoff, et al., Myasthenia gravis: recommendations for clinical research standards. Task force of the medical scientific advisory board of the myasthenia gravis foundation of america, Neurology. 55 (1) (2000) 16–23. [34] M.C. Dalakas, B cells as therapeutic targets in autoimmune neurological disorders, Nat. Clin. Pract. Neurol. 4 (10) (2008) 557–567. [35] T. Dorner, D. Isenberg, D. Jayne, H. Wiendl, D. Zillikens, G. Burmester, Current status on B-cell depletion therapy in autoimmune diseases other than rheumatoid arthritis, Autoimmun. Rev. 9 (2) (2009) 82–89. [36] J.C. Edwards, L. Szczepanski, J. Szechinski, et al., Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis, N. Engl. J. Med. 350 (25) (2004) 2572–2581. [37] S. Blum, D. Gillis, H. Brown, et al., Use and monitoring of low dose rituximab in myasthenia gravis, J. Neurol. Neurosurg. Psychiatry 82 (6) (2011) 659–663. [38] B. Keung, K.R. Robeson, D.B. DiCapua, et al., Long-term benefit of rituximab in MuSK autoantibody myasthenia gravis patients, J. Neurol. Neurosurg. Psychiatry 84 (12) (2013) 1407–1409. [39] F. Chan, A. Swayne, D. Gillis, et al., Long-term follow-up of patients with myasthenia gravis treated with low-dose rituximab, J. Neurol. Neurosurg. Psychiatry 90 (8) (2019) 955–956. [40] E. Cortés-Vicente, R. Rojas-Garcia, J. Díaz-Manera, et al., The impact of rituximab infusion protocol on the long-term outcome in anti-MuSK myasthenia gravis, Ann. Clin. Transl. Neurol. 5 (6) (2018) 710–716. [41] A. Rødgaard, F.C. Nielsen, R. Djurup, F. Somnier, S. Gammeltoft, Acetylcholine receptor antibody in myasthenia gravis: predominance of IgG subclasses 1 and 3, Clin. Exp. Immunol. 67 (1) (1987) 82–88. [42] E.H. Niks, Y. van Leeuwen, M.I. Leite, et al., Clinical fluctuations in MuSK myasthenia gravis are related to antigen-specific IgG4 instead of IgG1, J. Neuroimmunol. 195 (1–2) (2008) 151–156. [43] I. Koneczny, J. Cossins, P. Waters, D. Beeson, A. Vincent, MuSK myasthenia gravis IgG4 disrupts the interaction of LRP4 with MuSK but both IgG4 and IgG1-3 can disperse preformed agrin-independent AChR clusters, PLoS ONE 8 (11) (2013) e80695. [44] F. Piehl, A Study Evaluating the Safety and Efficacy of Rituximab in Patients With Myasthenia Gravis (Rinomax), ClinicalTrials.gov, (2019) (Identifier: NCT02950155).
Richard J. Nowak reports no conflicts directly related to this work. Dr. Nowak has received research support from the National Institutes of Health (NIH), Genentech, Alexion Pharmaceuticals, Ra Pharmaceuticals, Myasthenia Gravis Foundation of America, Momenta, and Grifols. He has served as consultant/advisor for Alexion Pharmaceuticals, CSL Behring, Grifols, Ra Pharmaceuticals, Roivant, and Momenta. Bhaskar Roy reports no conflicts directly related to this work. Dr. Roy has served as consultant/advisor for Alexion Pharmaceuticals. All other authors report no conflicts related to his work. References [1] W. Hoch, J. McConville, S. Helms, J. Newsom-Davis, A. Melms, A. Vincent, Autoantibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies, Nat. Med. 7 (3) (2001) 365–368. [2] J.J. Verschuuren, M.G. Huijbers, J.J. Plomp, et al., Pathophysiology of myasthenia gravis with antibodies to the acetylcholine receptor, muscle-specific kinase and lowdensity lipoprotein receptor-related protein 4, Autoimmun. Rev. 12 (9) (2013) 918–923. [3] R. Tandan, M.K. Hehir 2nd, W. Waheed, D.B. Howard, Rituximab treatment of myasthenia gravis: a systematic review, Muscle Nerve 56 (2) (2017) 185–196. [4] B.M. Conti-Fine, M. Milani, H.J. Kaminski, Myasthenia gravis: past, present, and future, J. Clin. Invest. 116 (11) (2006) 2843–2854. [5] R. Gold, C. Schneider-Gold, Current and future standards in treatment of myasthenia gravis, Neurotherapeutics 5 (4) (2008) 535–541. [6] S. Sathasivam, Steroids and immunosuppressant drugs in myasthenia gravis, Nat. Clin. Pract. Neurol. 4 (6) (2008) 317–327. [7] G.I. Wolfe, H.J. Kaminski, I.B. Aban, et al., Randomized trial of thymectomy in myasthenia gravis, N. Engl. J. Med. 375 (6) (2016) 511–522. [8] J. Suh, J.M. Goldstein, R.J. Nowak, Clinical characteristics of refractory myasthenia gravis patients, Yale J. Biol. Med 86 (2) (2013) 255–260. [9] R.J. Nowak, D.B. Dicapua, N. Zebardast, J.M. Goldstein, Response of patients with refractory myasthenia gravis to rituximab: a retrospective study, Ther. Adv. Neurol. Disord. 4 (5) (2011) 259–266. [10] J. Diaz-Manera, E. Martinez-Hernandez, L. Querol, et al., Long-lasting treatment effect of rituximab in MuSK myasthenia, Neurology. 78 (3) (2012) 189–193. [11] N. Zebardast, H.S. Patwa, S.P. Novella, J.M. Goldstein, Rituximab in the management of refractory myasthenia gravis, Muscle Nerve 41 (3) (2010) 375–378. [12] P. Burusnukul, T.D. Brennan, E.J. Cupler, Prolonged improvement after rituximab: two cases of resistant muscle-specific receptor tyrosine kinase + myasthenia gravis, J. Clin. Neuromuscul. Dis. 12 (2) (2010) 85–87. [13] C. Lebrun, V. Bourg, N. Tieulie, P. Thomas, Successful treatment of refractory generalized myasthenia gravis with rituximab, Eur. J. Neurol. 16 (2) (2009) 246–250. [14] K. Stieglbauer, R. Topakian, V. Schaffer, F.T. Aichner, Rituximab for myasthenia gravis: three case reports and review of the literature, J. Neurol. Sci. 280 (1–2) (2009) 120–122. [15] I. Illa, J. Diaz-Manera, R. Rojas-Garcia, et al., Sustained response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients, J. Neuroimmunol. 201–202 (2008) 90–94. [16] W.S. Baek, A. Bashey, G.L. Sheean, Complete remission induced by rituximab in refractory, seronegative, muscle-specific, kinase-positive myasthenia gravis, J. Neurol. Neurosurg. Psychiatry 78 (7) (2007) 771. [17] M. Thakre, J. Inshasi, M. Marashi, Rituximab in refractory MuSK antibody myasthenia gravis, J. Neurol. 254 (7) (2007) 968–969. [18] B. Hain, K. Jordan, M. Deschauer, S. Zierz, Successful treatment of MuSK antibodypositive myasthenia gravis with rituximab, Muscle Nerve 33 (4) (2006) 575–580. [19] K.R. Robeson, A. Kumar, B. Keung, et al., Durability of the rituximab response in acetylcholine receptor autoantibody-positive myasthenia gravis, JAMA Neurol. 74 (1) (2017) 60–66. [20] R.J. Nowak, et al., B cell targeted treatment in myasthenia gravis (BeatMG): a phase 2 trial of rituximab in myasthenia gravis, Neurology 90 (2018) e2182–e2194.
6