RESEARCH ARTICLE Drug-refractory myasthenia gravis: Clinical characteristics, treatments, and outcome Elena Corte  s-Vicente1,2,3,4 , Rodrigo Alvarez-Velasco 1,2,3,4 , Francesc Pla-Junca4, 1,2,3,4 5,6 4,7,8,9 Ricard Rojas-Garcia , Carmen Paradas , Teresa Sevilla , Carlos Casasnovas4,10 , Marıa Teresa Go mez-Caravaca , Julio Pardo , Alba Ramos-Fransi13,2, Ana Lara Pelayo-Negro6,14, 11 12 Gerardo Gutie rrez-Gutie rrez15, Janina Turon-Sans1,2,3,4, Adolfo Lo  pez de Munain6,16, 17 Antonio Guerrero-Sola , Ivonne Jerico  , Marıa Asuncio 18  n Martın19, Marıa Dolores Mendoza20, Germa n Morıs , Beatriz Ve 21 lez-Go  mez , Tania Garcia-Sobrino12, Elba Pascual-Gon 5 ~ i1,2,3,4 , 1,2,3,4 1,2,3,4 1,2,3,4 David Reyes-Leiva , Isabel Illa & Eduard Gallardo 1 Neuromuscular Diseases Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain 2 Department of Medicine, Universitat Auto noma de Barcelona, Barcelona, Spain 3 Biomedical Research Institute Sant Pau (IIB Sant Pau), Barcelona, Spain 4 Centro de Investigacio n Biomedica en Red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III, Madrid, Spain 5 Neurology Department, Neuromuscular Disorders Unit, Instituto de Biomedicina de Sevilla, Hospital U. Virgen del Rocıo, CSIC, Universidad de Sevilla, Sevilla, Spain 6 Centro de Investigacio n Biomedica en Red de Enfermedades Neurodegenerativas (CIBERNED), Instituto de Salud Carlos III, Madrid, Spain 7 Neuromuscular Unit, Neurology Department, Hospital Universitari i Polit ecnic La Fe, Valencia, Spain 8 Department of Medicine, Universitat de Valencia, Valencia, Spain 9 Biomedical Research Institute La Fe (IIS La Fe), Valencia, Spain 10 Unitat de Neuromuscular, Neurology Department, Hospital Universitari de Bellvitge – IDIBELL, L’Hospitalet de Llobregat, Barcelona, Spain 11 Neurology Department, Hospital Universitario Reina Sofıa, Co rdoba, Spain 12 Neurology Department, Hospital Clınico, Santiago de Compostela, Spain 13 Neuromuscular Diseases Unit, Department of Neurology, Hospital Germans Trias i Pujol, Badalona, Barcelona, Spain 14 Service of Neurology, University Hospital “Marques de Valdecilla (IDIVAL)”, University of Cantabria (UC), Santander, Spain 15 Neuromuscular Diseases Unit, Department of Neurology, Hospital Universitario Infanta Sofıa, Universidad Europea de Madrid, San Sebasti an de los Reyes, Madrid, Spain 16 Neurology Department, Donostia University Hospital, University of the Basque Country, Neurosciences Area, Biodonostia Research Institute, San Sebastian, Spain 17 Neuromuscular Diseases Unit, Department of Neurology, Institute of Neurosciences, Hospital Universitario Clınico San Carlos, Madrid, Spain 18 Department of Neurology, Complejo Hospitalario de Navarra-IdisNA, Pamplona, Spain 19 Department of Neurology, Complejo Asistencial Hospitalario de Burgos, Burgos, Spain 20 Department of Neurology, Hospital Universitario de Gran Canaria Doctor Negrın, Las Palmas de Gran Canaria, Spain 21 Department of Neurology, Hospital Central de Asturias, Oviedo, Spain Correspondence Abstract Elena Cort es-Vicente, Neuromuscular Diseases Unit, Department of Neurology, Objective: To describe the clinical characteristics and outcomes in patients Hospital de la Santa Creu i Sant Pau, C/Pare with refractory myasthenia gravis (MG) and to determine the effectiveness and Claret 167, 08025 Barcelona, Spain. side effects of the drugs used for their treatment. Methods: This observational Tel: 0034 935565986; Fax: 0034 retrospective cross-sectional multicenter study was based on data from the 935565602; E-mail: ecortes@santpau.cat Spanish MG Registry (NMD-ES). Patients were considered refractory when their MG Foundation of America post-interventional status (MGFA-PIS) was Funding Information This work was funded by the Instituto de Salud Carlos III through unchanged or worse after corticosteroids and two or more other immunosup- the project PI19/01774 (cofunded by the pressive agents. Clinical and immunologic characteristics of drug-refractory European Union ERDF), PI I. Illa and E. patients, efficiency and toxicity of drugs used, and outcome (MGFA-PIS) at Gallardo. E. Cortes-Vicente was supported by end of follow-up were studied. Results: We included 990 patients from 15 hos- a Juan Rod es grant (JR19/00037) from the pitals. Eighty-four patients (68 of 842 anti-acetylcholine receptor [AChR], 5 of Fondo de Investigacio n en Salud, Instituto de 26 anti-muscle-specific tyrosine kinase [MusK], 10 of 120 seronegative, and 1 Salud Carlos III and co-funded by European of 2 double-seropositive patients) were drug refractory. Drug-refractory patients Union (ERDF/ESF, “A way to make Europe”/ “Investing in your future”), Ministry of were more frequently women (p < 0.0001), younger at onset (p < 0.0001), and  Health (Spain). R. Alvarez-Velasco was anti-MuSK positive (p = 0.037). Moreover, they more frequently presented a 122 ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. E. Cort es-Vicente et al. Drug-Refractory Myasthenia Gravis supported by grant SLT008/18/00207 from generalized form of the disease, bulbar symptoms, and life-threatening events the Health Research and Innovation Strategic (p < 0.0001; p = 0.018; and p = 0.002, respectively) than non-drug-refractory Plan (PERIS). The NMD-ES Project and F. Pla- patients. Mean follow-up was 9.8 years (SD 4.5). Twenty-four (50%) refractory Junca (data curator) are partially funded by n Biomedica en patients had side effects to one or more of the drugs. At the end of follow-up, the Centro de Investigacio Red de Enfsermedades Raras (CIBERER). 42.9% of drug-refractory patients (42.6% of anti-AChR, 100% of anti-MuSK, and 10% of seronegative patients) and 79.8% of non-drug-refractory patients Received: 22 October 2021; Revised: 9 (p < 0.0001) achieved remission or had minimal manifestations. Eighty percent December 2021; Accepted: 9 December of drug-refractory-seronegative patients did not respond to any drug tested. 2021 Interpretation: In this study, 8.5% of MG patients were drug-refractory. New more specific drugs are needed to treat drug-refractory MG patients. Annals of Clinical and Translational Neurology 2022; 9(2): 122–131 doi: 10.1002/acn3.51492 patients and they had more frequent clinical exacerba- Introduction tions. The authors noted that early onset was associated Myasthenia gravis (MG) is an autoimmune disorder with a higher risk of refractoriness.10 In both these stud- caused by antibodies that bind to post-synaptic proteins ies, however, the number of patients was small and the at the neuromuscular junction.1,2 The disease is immuno- definition of drug-refractory MG differed from the cur- logically diverse.3 Patients usually present antibodies rent definition. In view of the lack of data available against the acetylcholine receptor (AChR) or the muscle- regarding the efficacy and side effects of drugs used for specific tyrosine kinase (MuSK). However, around 15% of the treatment of drug-refractory MG, further studies on patients do not have these antibodies and are considered drug-refractory MG are required. seronegative.4 Moreover, MG is clinically heterogeneous, The aim of this study was to determine the clinical, and some of its clinical characteristics, such as the pres- immunological and therapeutic characteristics in patients ence of thymoma5 and early disease onset,6 have been with drug refractory MG. Data were extracted from the related to greater severity. nationwide neurologist-driven MG Registry in Spain.5,6,11 Therapeutic strategies developed in recent decades have greatly improved the outcome of MG patients, resulting Methods in significant decreases in mortality and morbidity. Stan- dard treatment of MG consists of acetylcholinesterase Data source: NMD-ES project inhibitors, immunosuppressive drugs, and/or thymec- tomy, but it is individualized according to the patient The MG registry is part of the Spanish Neuromuscular characteristics. In severe weakness cases or exacerbations, Diseases Registry (NMD-ES). It was founded in 2010 and immunomodulatory therapies are used.7 However, around designed in accordance with current Spanish law on 10–15% of patients are drug refractory. Since 2016, biomedical research and data protection. Patients patients are considered drug refractory when their MG included must have a confirmed diagnosis of MG based Foundation of America post-intervention status (MGFA- on clinical findings and supported by positive autoanti- PIS) is unchanged or worse after corticosteroids and at bodies and/or electrophysiological studies. Data are col- least two other immunosuppressive agents, used in ade- lected by neurologists with expertise in neuromuscular quate doses for an adequate duration, with persistent dis- disorders at University hospitals in Spain. The Registry abling symptoms or side effects, and based on an includes 60 MG-specific items concerning demographic, international experts consensus.8 Identifying the charac- clinical, immunologic, and therapeutic aspects. Follow-up teristics of drug-refractory MG patients could ultimately information is updated once a year or whenever a signifi- lead to help the development of new treatments for these cant clinical event occurs. The Registry is reviewed annu- patients. ally to safeguard the quality of the information. Data Few articles have specifically studied drug-refractory included at the Registry have been used in previous pub- MG characteristics and data remain scarce. One recent lished studies.5,6,11 study found 14.8% of MG patients were treatment refrac- tory. Refractory status was associated with early-onset, Patients and clinical evaluation female sex, presence of anti-MuSK antibodies and thy- moma.9 In another study, around 11% of patients were This is an observational retrospective cross-sectional found to be drug refractory. MG was more severe in these multicenter study. We selected all patients in the MG ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association 123 Drug-Refractory Myasthenia Gravis E. Cort es-Vicente et al. registry with onset of MG between 1 January 2000, and Standard protocol approvals and patient 31 December 2017. We excluded patients lost to follow- consents up and patients for whom relevant information was All participating centers obtained approval from their missing. Patients were considered drug refractory as corresponding ethics committees to participate in the defined by Sanders et al.8 Follow-up ended on the date NMD-ES Registry, and all patients signed an informed of death or at the end of the study (31 December consent form for use of their data for scientific purposes. 2019). The demographic and clinical variables analyzed were: sex, age at onset, AChR and MuSK antibody positivity, Data availability statement severity and distribution of muscle weakness according to The data that support the findings of this study are avail- the Myasthenia Gravis Foundation of America (MGFA) able upon request from the corresponding author. The clinical classification12 at onset and at maximal worsen- data are not publicly available due to privacy or ethical ing, frequency of life-threatening events (defined as restrictions. MGFA IVB and V) and myasthenic crises (MGFA V) at onset and at maximal worsening, generalization—defined as patients with a focal ocular form of the disease at onset Statistical analysis (MGFA I) but later generalized (MGFA II or higher), thy- A descriptive data analysis was performed. The frequen- moma defined by pathologic study in patients undergoing cies of symptoms are reported as percentages. Demo- thymectomy and by thoracic CT in the others, thymec- graphic characteristics are reported as means and SD. tomy, follow-up time defined as the difference between Differences in baseline characteristics between patient the follow-up deadline or date of death and the date of subgroups were evaluated using the chi-squared test to diagnosis, and clinical outcome according to the MGFA compare categorical variables, and Student’s t test to post-intervention status (MGFA-PIS)12 at the end of compare quantitative variables. A significant difference follow-up. We analyzed the following therapeutic vari- was defined as p < 0.05. Missing data were dropped ables for drug-refractory MG patients: immunosuppres- as they were <5% of the sample for the relevant vari- sive and immunomodulatory agents required and reason ables. Data analysis was carried out using the STATA for withdrawal classified as inefficacy, side effects, preg- 13 software for Windows (StataCorp LP, College nancy, or clinical improvement. The most effective drug Station, TX). was that which achieved the best MGFA-PIS status (im- proved or better). Results MG standard of care in Spain A total of 1168 patients of the 1619 included in the MG Registry at the time of the study had MG onset between The current Standard of care to treat MG in Spain 1 January 2000, and 31 December 2017. We excluded 178 includes: (1) acetylcholinesterase inhibitors as symp- patients because relevant information was missing. The tomatic therapy; (2) immunosuppressive drugs, being sample was therefore made up of 990 patients from 15 steroids the first-line immunosuppressive treatment, aza- hospitals. Mean age at onset was 57.2 years (SD 19.1), thioprine and mycophenolate mofetil as second line 52.2% were men, 842 (85.1%) were anti-AChR positive, immunosuppressors or steroid-sparing agents, and 26 (2.6%) were anti-MuSK positive, 120 (12.1%) had others (cyclosporine, tacrolimus, rituximab, methotrex- seronegative MG, and 2 (0.2%) were anti-AChR and anti- ate, and cyclophosphamide) in case of side effects or MuSK double-positive (Fig. 1). Thymoma was diagnosed lack of response; (3) thymectomy, performed in patients in 128 (13.2%) patients. with thymoma and also in patients younger than A total of 84 participants (8.5%) were drug-refractory. 65 years with anti-AChR antibodies and no thymoma; Their mean age at onset was 44.4 years (SD 18.0) and 75% and (4) immunomodulatory therapies (intravenous were women. Eighty-one percent had anti-AChR antibod- immunoglobulin and plasma exchange), predominantly ies, 6% had anti-MuSK antibodies, 1.2% had anti-AChR used in acute worsening or MG crisis. However, treat- and anti-MuSK antibodies, and 11.9% were seronegative ment is individualized according to the patient charac- (Fig. 1). Among drug-refractory patients, 18.3% had thy- teristics. Patients with anti-MuSK MG are treated with moma. A generalized MG was developed by 92.3% of the prednisone as first-line immunosuppressive agent, ritux- patients, 77.5% of them had a generalized MG already at imab if they do not respond favorably to prednisone, onset. The frequency of bulbar symptoms, life-threatening and plasma exchange as immunomodulatory therapy for events, and myasthenic crises was 47.5%, 13.8%, and 3.8%, exacerbacions.7 124 ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association E. Cort es-Vicente et al. Drug-Refractory Myasthenia Gravis Figure 1. Flowchart shows patients included in the study, immunological characteristics, number of drug-refractory patients and outcome. MG, myasthenia gravis; anti-AChR, anti-acetylcholine receptor; anti-MuSK, anti-muscle-specific tyrosine kinase; MM, minimal manifestations; I, improvement; U, unchanged; W, worsening. respectively, at onset, and 62.8%, 28.2%, and 11.5% at of 3.3 (min 2–max 6), and seronegative patients with a maximal worsening (Table 1). Clinical classification of mean of 2.3 (min 2–max 3). The most frequently used MGFA at onset and at maximal worsening by immunologi- immunosuppressive therapies for drug-refractory and cal subgroup is detailed in Table 2. non-drug-refractory MG patients are shown in Fig- Compared to non-drug-refractory patients, patients ure S1A. Drug-refractory patients needed intravenous with drug-refractory MG were more frequently women immunoglobulin (86.9% vs. 23.7%, p < 0.0001) and (p < 0.0001), younger at onset (p < 0.0001), and anti- plasma exchange (19% vs. 4.4%, p < 0.0001) more fre- MuSK positive (p = 0.0001). They also more frequently quently than non-drug-refractory patients at some point had generalized MG (p = 0.001 at onset and p < 0.0001 of the disease (Fig. S1B). Drug-refractory patients were at maximal worsening), bulbar symptoms (p = 0.018), more frequently thymectomized than non-drug-refractory and life-threatening events (p = 0.002) at maximal wors- patients (44.0% vs. 23.4%, p < 0.0001). At the last ening. Table 1 shows clinical data of drug-refractory and follow-up, complete stable remission was achieved in 1 of non-drug-refractory patients. the 37 thymectomized drug-refractory patients and phar- Drug-refractory patients were treated with a mean of macological remission was achieved in another. Eight 3.2 (minimum 2–maximum 6) other-than-prednisone patients had minimal manifestations, 7 improved, 18 were immunosuppressive agents. Anti-AChR-positive drug- unchanged, and 2 worsen. refractory patients were treated with a mean of 3.6 (min The drug that most improved MGFA-PIS status for 2–max 5 drugs), anti-MuSK-positive patients with a mean each patient is detailed in Figure 2. Anti-AChR MG ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association 125 Drug-Refractory Myasthenia Gravis E. Cort es-Vicente et al. Table 1. Clinical characteristics of drug-refractory and non-drug-refractory myasthenia gravis patients and statistical analysis results. Drug-refractory Non-drug-refractory MG (n = 84) MG (n = 906) p value Age at onset 44.4 (SD 18.0) 58.4 (SD 18.8) <0.0001 Age at onset >65 yo (%) 12 (14.3) 428 (47.2) <0.0001 Sex (female %) 63 (75) 410 (45.3) <0.0001 Antibodies (%) AChR 68 (81) AChR 774 (85.4) 0.037 MuSK 5 (6) MuSK 21 (2.3) AChR+MuSK 1 (1.2) AChR+MuSK 1 (0.1) Seronegative 10 (11.9) Seronegative 110 (12.1) Thymoma (%) 15/82 (18.3) 113/890 (12.7) 0.152 MGFA classification at onset (%) I 18 (21.4) 375 (41.4) II 29 (34.5) 317 (35.0) III 19 (22.6) 125 (13.8) <0.0001 IV 11 (13.1) 49 (5.4) V 3 (3.6) 22 (2.4) Unknown 4 (4.8) 18 (2.0) MGFA classification at maximal worsening (%) I 6 (7.1) 247 (27.3) II 13 (15.5) 260 (28.7) III 30 (35.7) 213 (23.5) <0.0001 IV 20 (23.8) 76 (8.4) V 9 (10.7) 61 (6.7) Unknown 6 (7.1) 49 (5.4) Generalized MG (onset/maximal worsening, %) 62/80 (77.5) 513/888 (57.8) <0.0001 72/78 (92.3) 610/857 (71.2) <0.0001 Bulbar symptoms (onset/maximal worsening, %) 38/80 (47.5) 345/888 (38.9) 0.130 49/78 (62.8) 419/857 (48.9) 0.018 Life-threatening events (onset/maximal worsening, %) 11/80 (13.8) 67/888 (7.5) 0.051 22/78 (28.2) 126/857 (14.7) 0.002 Myasthenic crisis (onset/maximal worsening, %) 3/80 (3.8) 22/888 (2.5) 0.492 9/78 (11.5) 61/857 (7.1) 0.156 MG, myasthenia gravis; MGFA, Myasthenia Gravis Foundation of America; AChR, acetylcholine receptor; MuSK, muscle-specific tyrosine kinase. patients improved with a variety of drugs, the most fre- Patients were followed for a mean of 9.8 years (SD quent being rituximab (15%) and tacrolimus (15%). 4.5). At the end of follow-up, fewer drug-refractory Thirty-two percent of patients did not respond to any of patients achieved remission or had minimal manifesta- the drugs administered. Anti-MuSK patients mainly tions than non-drug-refractory patients (42.9% vs. 79.8%, responded favorably to rituximab (80%). The only patient p < 0.0001) (Fig. S2A). After breaking down the sample with both anti-AChR- and anti-MuSK-positive antibodies based on immunological subtype, we found that 42.6% of also responded favorably to rituximab. Eighty percent of anti-AChR-positive MG patients achieved remission or seronegative MG patients did not respond to any drug had minimal manifestations at the end of follow-up. This tested. MGFA-PIS status was achieved in 10% of seronegative Forty-two patients (50%) presented side effects that patients and 100% of anti-MuSK-positive patients led to drug withdrawal; 24 of them (28.6%) with 1 (Fig. S2B). drug, 11 patients (13.1%) with 2 drugs, 5 patients (6%) with 3 drugs, and 2 patients (2.4%) with 4 drugs. Aza- Discussion thioprine and mycophenolate mofetil were usually with- drawn because of inefficacy rather than because of side In our series, 8.5% of patients with MG were drug- effects. However, in the case of cyclosporine and tacroli- refractory despite the numerous therapeutic options mus, withdrawal because of inefficacy and withdrawal available. These patients were more likely to be female, because of side effects were both main reasons, and in to present early-age at onset, and to have anti-MuSK similar frequencies. The most frequent side effects for antibodies. We also observed that drug-refractory MG each immunosuppressor are detailed in Table 3. patients had more severe forms of the disease than 126 ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association E. Cort es-Vicente et al. Drug-Refractory Myasthenia Gravis Table 2. MGFA clinical classification at onset and at maximal worsen- international standards22 had a beneficial impact on our ing is shown for drug-refractory myasthenia gravis patients according thymoma-associated MG patients outcome. to immunological subgroup. The clinical and immunological characteristics associ- AChR MuSK AChR + Seronegative ated with drug-refractory MG may indicate that distinc- MG MG MuSK MG MG tive immunopathologic pathways or biological mechanisms are involved in the development of drug- MGFA at onset n = 65 n=5 n=1 n=9 I 14 0 0 4 refractory MG. Studying these underlying molecular pro- IIA 12 0 0 3 cesses should be a priority as they may lead to the identi- IIB 12 2 0 0 fication of therapeutic targets that could help treat drug- IIIA 4 1 0 1 refractory MG more efficiently. The anti-CD20 agent IIIB 11 1 0 1 rituximab, for instance, has extensively proven to be IVA 3 0 0 0 highly effective for the treatment of anti-MuSK-positive IVB 7 1 0 0 patients,13–21 as for other IgG4-related diseases.23 Our V 2 0 1 0 MGFA at n = 62 n=5 n=1 n = 10 results regarding rituximab efficacy in treating anti- maximal MuSK-positive patients are in agreement with previously worsening reported studies. Other emerging drugs target important I 4 0 0 2 molecules involved in MG. The terminal complement IIA 4 0 0 3 activation inhibitor eculizumab merits consideration in IIB 4 1 0 1 the treatment of drug-refractory anti-AChR-positive IIIA 6 0 0 3 MG,13,14,24 although we have scarce data about this drug IIIB 19 2 0 0 IVA 6 0 0 1 as it is not still available in our country and the only IVB 12 1 0 0 patient that responded was part of a clinical trial. Other V 7 1 1 0 anti-complement strategies25,26 and neonatal Fc receptor (FcRn) antagonists26,27 are currently on trial but unfortu- MG, myasthenia gravis; MGFA, Myasthenia Gravis Foundation of nately none of the patients received these therapies during America; AChR, acetylcholine receptor; MuSK, muscle-specific tyrosine the study period. The development of these new mole- kinase. cules highlights the importance of studying the molecular pathophysiology underlying disease development and progression. their non-drug-refractory counterparts, specifically in Another important observation from our study is that terms of generalized MG, bulbar symptoms, and life- around 40% of drug-refractory patients did not achieve threatening events during the course of the disease. remission or minimal manifestations MGFA-PIS status at Furthermore, they more frequently needed rescue treat- the end of a long follow-up. And importantly, a signifi- ments with intravenous immunoglobulin and plasma cant percentage of these participants were treatment intol- exchange. erant to some of the drugs received. Fifty percent of The frequency of drug-refractory MG patients was drug-refractory patients had adverse events with one or lower than that reported in previous studies where more of the drugs tested. Some of these side effects were around 10–15% of patients were drug-refractory.9,10 severe and could have increased the disease burden. Also, These differences may be due to the variation of defini- some of the treatments we currently use are potentially tions of drug-refractoriness over time. However, it may teratogenic, a risk that cannot be overlooked when a vast also be because we have learned to treat some subgroups majority of drug-refractory patients are young females. of patients more efficiently in recent years. For instance, This point again supports the need to develop more in our series, anti-MuSK patients diagnosed after ritux- specific, well tolerated drugs to treat MG. imab effectiveness was described were not considered In the present study, the most effective drugs to treat drug-refractory because immediately after prednisone fail- drug-refractory MG patients were rituximab and tacroli- ure they were treated with rituximab rather than other mus and we found the same results when we analyzed sep- immunosuppressive drugs that we now know are rarely arately anti-AChR positive patients. We highlight that two effective.13–21 Previous studies suggested thymoma is of five patients treated with methotrexate achieved remis- more frequent in drug-refractory MG patients9 but we sion, although a recent clinical trial of oral weekly did not find any statistically significant difference com- methotrexate in anti-AChR generalized MG patients pared to the frequency in non-drug-refractory MG showed that it is not a useful drug to spare steroids with patients. Maybe a more precise thymoma staging and a class I level of evidence.28 Regarding thymectomy, drug- more accurate treatment strategy following recent refractory patients were more frequently thymectomized, ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association 127 Drug-Refractory Myasthenia Gravis E. Cort es-Vicente et al. Figure 2. The drug that achieved the best MGFA-PIS status (improved, minimal manifestations, or remission) for each patient is represented in percentages for the total of drug-refractory patients, and broken down based on the immunological profile (anti-acetylcholine receptor-positive patients, anti-muscle-specific tyrosine kinase-positive patients, and seronegative patients). MG, myasthenia gravis; anti-AChR, anti-acetylcholine receptor; anti-MuSK, anti-muscle-specific tyrosine kinase. but they were younger at onset and consequently more at last follow-up. However, we have no specific data about likely to have undergone thymic removal. Furthermore, the clinical response to thymectomy in these patients. The most patients in the study were diagnosed of MG before retrospective nature of the study and the fact that patients the clinical trial that demonstrated the efficacy of thymec- were simultaneously treated with other agents prevented tomy in non-thymomatous anti-AChR positive patients an accurate evaluation. Overall, these results show the was published.29 The lack of such evidence at this stage heterogeneous response of drug-refractory anti-AChR MG may have impacted on the percentage of patients who patients and highlight the importance of the search for were eventually thymectomized. We know that 10 of the treatment response biomarkers. 37 thymectomized drug-refractory patients achieved a Another important finding in our study is that 80% of MGFA-PIS status of remission or minimal manifestations seronegative drug-refractory MG patients did not respond 128 ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association E. Cort es-Vicente et al. Drug-Refractory Myasthenia Gravis Table 3. Immunosuppressor therapies used for the treatment of drug-refractory MG, percentage of withdrawal, reasons for withdrawal, and reported side effects. Immunosuppressor (number of patients) Withdrawal (%) Reasons for withdrawal (%) Side effects Prednisone (84) 18 (21.4) 6 (33.3) inefficacy 1 High blood pressure 6 (33.3) side effects 1 Diabetes mellitus 6 (33.3) improvement or remission 1 High blood pressure + diabetes mellitus 1 Osteopenia 1 Compulsion 1 Weight gain Azathioprine (70) 63 (90) 40 (63.5) inefficacy 5 Hepatotoxicity 22 (34.9) side effects 5 Abdominal pain 1 (1.6) inefficacy and side effects 4 Anemia 3 Allergy 1 Pancytopenia 1 Leucopenia 1 Arthralgia 3 Unknown Mycophenolate Mofetil (57) 43 (75.4) 32 (74.4) inefficacy 2 Abdominal pain 8 (18.6) side effects 2 Hepatotoxicity 3 (7.0) desire for pregnancy 1 Diarrhea 1 Abdominal pain and diarrhea 1 Pancytopenia 1 Unknown Cyclosporine (56) 45 (80.4) 21 (46.7) inefficacy 10 Nephrotoxicity 21 (46.7) side effects 4 Abdominal pain 2 (4.4) inefficacy and side effects 2 High blood pressure and headache 1 (2.2) desire for pregnancy 1 Hepatotoxicity 1 Hypertrichosis 1 Gum hyperplasia 1 Tremor 1 Anemia and leucopenia 2 Unknown Tacrolimus (33) 17 (51.5) 8 (47.1) inefficacy 2 Nausea and vomits 7 (41.2) side effects 1 Skin rash 2 (11.8) remission 1 Alopecia 1 Hyperglycemia 1 Vision loss 1 Unknown Rituximab (40) 35 (87.5) 21 (60.0) inefficacy 1 Psoriasis exacerbation 2 (5.7) inefficacy and side effects 1 Progressive multifocal leukoencephalopathy 13 (37.1) remission Methotrexate (6) 5 (83.3) 2 (40) inefficacy 1 Abdominal pain 1 (20) side effects 2 (40) remission Cyclophosphamide (7) 7 (100) 3 (42.9) inefficacy 1 Toxic organizing pneumonia 1 (14.3) inefficacy and side effects 3 (42.9) remission MG, myasthenia gravis. to any drug used and 90% did not achieve a minimal published findings that also suggested a poorer outcome manifestations or remission MGFA-PIS status. The accu- for seronegative patients.30 In this study, drug-refractory- racy of diagnosis in these patients might be questioned seronegative MG patients received fewer other-than- here, but we should emphasize that all patients included prednisone immunosuppressor agents than anti-AChR in the MG registry had a diagnosis of confirmed MG and MuSK positive patients. Maybe the lack of a detect- based on both clinical features and electrophysiological able antibody or the fact that they had mainly mild forms studies. Moreover, these results are in line with previously of the disease prevented us from adopting a more ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association 129 Drug-Refractory Myasthenia Gravis E. Cort es-Vicente et al. aggressive pharmacological approach. Another hypothesis Casasnovas work on a CSUR (centro, servicio, unidad de is that the unknown underlying physiopathology of referencia) on rare neuromuscular diseases. E. Cortes- seronegative MG prevents us from finding a specific treat-  Vicente, R. Alvarez-Velasco, R. Rojas-Garcia, J. Turon-Sans, ment, as was the case with anti-MuSK positive patients E. Pascual-Go~ ni, E. Gallardo, I. Illa, C. Casasnovas and A. before the antibody was discovered and the efficacy of Ramos-Fransi are members of XUECs (Xarxes d’unitats rituximab was demonstrated.13–21 Research focusing on d’expertesa clınica en malalties minoritaries). finding the antibodies involved in seronegative MG is of high significance. Conflict of Interest Although some of our observations are in accordance with those in previously published studies,9,10 it would be Authors report no conflict of interests. inaccurate to compare results because the definition of drug-refractoriness varies. A main strength of this study is References that it is the first to classify patients based on the current universally accepted definition.8 Furthermore, we used 1. Gilhus NE. Myasthenia gravis. N Engl J Med. standardized, updated information from a large number 2016;375:2570-2581. of patients from 15 hospitals around the country, and the 2. Querol L, Illa I. Myasthenia gravis and the neuromuscular junction. Curr Opin Neurol. 2013;26:459-465. series of drug-refractory MG patients is the widest 3. Meriggioli MN, Sanders DB. Autoimmune myasthenia reported to date. The main limitation is that the sample gravis: emerging clinical and biological heterogeneity. may be biased in terms of disease severity and non- Lancet Neurol. 2009;8:475-490. response to commonly used drugs. This is because data 4. 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Cortes-Vicente E, Alvarez-Velasco R, Segovia S, et al. side effects of the drugs used to treat many drug- Clinical and therapeutic features of myasthenia gravis in refractory MG patients, which was the aim of this article. adults based on age at onset. Neurology. 2020;94(11): An epidemiological study is needed to determine the e1171-e1180. exact prevalence of drug-refractory MG patients.  7. Cortes-Vicente E, Gallardo E, Alvarez-Velasco R, Illa I. Myasthenia gravis treatment updates. Curr Treat Options Conclusions Neurol. 2020;22:24. 8. Sanders DB, Wolfe GI, Benatar M, et al. International In conclusion, we demonstrate that a subgroup of MG consensus guidance for management of myasthenia gravis patients with distinct clinical features is drug-refractory to executive summary. Neurology. 2016;87:419-425. available therapies. Many of these patients never achieve 9. Suh J, Goldstein JM, Nowak RJ. Clinical characteristics of the therapeutic goal and drug side effects are common. refractory myasthenia gravis patients. Yale J Biol Med. Seronegative drug-refractory patients specifically need 2013;86(2):255-260. more effective drugs, as most patients do not respond 10. Rath J, Brunner I, Tomschik M, et al. Frequency and favorably to any treatment. These findings highlight the clinical features of treatment-refractory myasthenia gravis. need for more specific therapies to treat MG. J Neurol. 2020;267(4):1004-1011. 11. Ramos-Fransi A, Rojas-Garcıa R, Segovia S, et al. Myasthenia gravis: descriptive analysis of life-threatening Acknowledgments events in a recent nationwide registry. Eur J Neurol. The authors thank the patients for contributing their data to 2015;22:1056-1061. this registry and Carolyn Newey for language support. E. 12. Jaretzki A, Barohn RJ, Ernstoff RM, et al. Myasthenia  Cortes-Vicente, R. Alvarez-Velasco, R. 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Response of patients with refractory myasthenia gravis to 2016;375(6):511-522. doi:https://doi.org/10.1056/ rituximab: a retrospective study. Ther Adv Neurol Disord. NEJMoa1602489 2011;4:259-266. 30. Tomschik M, Hilger E, Rath J, et al. Subgroup 18. Iorio R, Damato V, Alboini PE, Evoli A. Efficacy and stratification and outcome in recently diagnosed safety of rituximab for myasthenia gravis: a systematic generalized myasthenia gravis. Neurology. 2020;95(10): review and meta-analysis. J Neurol. 2015;262:1115-1119. e1426-e1436. 19. Tandan R, Hehir MK, Waheed W, Howard DB. Rituximab treatment of myasthenia gravis: a systematic review. Muscle Nerve. 2017;56:185-196. Supporting Information 20. Hehir MK, Hobson-Webb LD, Benatar M, et al. Additional supporting information may be found online Rituximab as treatment for anti-MuSK myasthenia gravis: in the Supporting Information section at the end of the multicenter blinded prospective review. Neurology. article. 2017;9:1069-1077. 21. Cortes-Vicente E, Rojas-Garcıa R, Dıaz-Manera J, et al. Figure S1. (A) Percentages of use of immunosuppressive The impact of rituximab infusion protocol on the long- therapies are represented in bars for drug-refractory and term outcome in anti-MuSK myasthenia gravis. Ann Clin non-drug-refractory myasthenia gravis patients. (B) Per- Transl Neurol. 2018;5:710-716. centages of use of immunomodulatory therapies are rep- 22. Lamarca A, Moreno V, Feliu J. Thymoma and thymic resented in bars for drug-refractory and non-drug- carcinoma in the target therapies era. Cancer Treat Rev. refractory myasthenia gravis patients. MG, myasthenia 2013;39(5):413-420. gravis; IVIG, intravenous immunoglobulin; PLEX, plasma 23. Huijbers MG, Querol LA, Niks EH, et al. The expanding exchange. field of IgG4-mediated neurological autoimmune Figure S2. (A) Percentage of Myasthenia Gravis disorders. Eur J Neurol. 2015;22(8):1151-1161. doi:https:// Foundation of America post-intervention status at end of doi.org/10.1111/ene.12758 follow-up are represented in bars for drug-refractory and 24. Howard JF Jr, Utsugisawa K, Benatar M, et al. Safety and non-drug-refractory myasthenia gravis patients. Curly efficacy of eculizumab in anti- acetylcholine receptor brackets show the percentage of drug-refractory and non- antibody- positive refractory generalized myasthenia gravis drug-refractory myasthenia gravis patients that achieved (REGAIN): a phase 3, randomised, double-blind, the treatment goal. (B) Percentage of Myasthenia Gravis placebo-controlled, multicentre study. Lancet Neurol. Foundation of America post-intervention status at end of 2017;16:976-986. follow-up are represented in bars for seronegative, double 25. Howard JF Jr, Nowak RJ, Wolfe GI, et al. Clinical seropositive, anti-muscle-specific tyrosine kinase-positive effects of the self-administered subcutaneous complement and anti-acetylcholine receptor-positive drug-refractory inhibitor zilucoplan in patients with moderate to severe MG patients. MG, myasthenia gravis; CSR, complete generalized myasthenia gravis: results of a phase 2 stable remission; PR, pharmacologic remission; MM, min- randomized, double-blind, placebo-controlled, imal manifestations; I, improvement; U, unchanged; W, multicenter clinical trial. JAMA Neurol. 2020;77(5): worsening; anti-AChR, anti-acetylcholine receptor; Anti- 582-592. MuSK, anti-muscle-specific tyrosine kinase. ª 2021 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association 131