Real-world experience with eculizumab and switching to ravulizumab for generalized myasthenia gravis.

OBJECTIVE: Eculizumab and ravulizumab are complement protein C5 inhibitors, showing efficacy and tolerability for patients with anti-acetylcholine receptor-positive (AChR+) generalized myasthenia gravis (gMG) in phase 3 clinical trials and subsequent analyses. The purpose of the present study was to evaluate the clinical significance of eculizumab and switching to ravulizumab for refractory AChR+ gMG patients in the real-world experience. METHODS: Among the database of Japan MG registry survey 2021, we studied AChR+ gMG patients who received eculizumab. We also evaluated these patients who switched from eculizumab to ravulizumab. Responder was defined as an improvement of at least 3 points in MG-ADL. We performed a questionnaire of preference between eculizumab and ravulizumab. RESULTS: Among 1,106 patients with AChR+ gMG, 36 patients (3%) received eculizumab (female 78%, mean age 56.0 years). Eculizumab was preferentially used in severe and refractory MG patients. The duration of eculizumab treatment was 35 months on average. MG-ADL improved from 9.4 ± 4.9 to 5.9 ± 5.1, and 25 (70%) of the 36 gMG patients were responders. Postintervention status was markedly improved after the eculizumab treatment. Of 13 patients who did not continue eculizumab, 6 showed insufficiencies. Early onset MG was most effective. However, 15 patients switching from eculizumab to ravulizumab kept favorable response and tolerability. Questionnaire surveys showed preference for ravulizumab over eculizumab. INTERPRETATION: Eculizumab and switching to ravulizumab showed to be effective for refractory AChR+ gMG patients in clinical settings.

Taste disorders and alopecia in myasthenia gravis.

BACKGROUND: Non-motor symptoms in myasthenia gravis (MG) are rarely confirmed. Although there are some small cohort studies, a large-systemic survey has not yet been performed. METHODS: We investigated the incidence and clinical characteristics of patients with MG who had taste disorders and alopecia using data of 1710 patients with MG enrolled in the Japan MG Registry 2021. RESULTS: Among them, 104 (6.1%) out of 1692 patients and 138 (8.2%) out of 1688 patients had histories of taste disorders and alopecia, respectively. Among the patients with MG, taste disorders were significantly more common in women, those with severe symptoms, refractory MG, or thymoma-associated MG, and were less common in those with ocular MG. The taste disorders often occurred after the onset of MG and often responded to MG treatments. Alopecia was more common in MG patients with a history of bulbar palsy and thymoma, and it often occurred before the onset of MG and sometimes responded to MG treatments. Multivariate logistic regression analysis revealed taste disturbance was associated with worst quantitative MG score and thymoma-associated MG; and alopecia was associated with thymoma-associated MG. CONCLUSION: Clinicians should be aware of the non-motor symptoms in MG, especially in patients with severe myasthenic symptoms and thymoma-associated MG.

Therapeutic Responses to Efgartigimod for Generalized Myasthenia Gravis in Japan.

Background and Objectives: Efgartigimod, which has been well tolerated and efficacious in individuals with generalized myasthenia gravis (MG), is available in Japan not only for the treatment of anti-acetylcholine receptor-positive (AChR+) but also anti-muscle-specific receptor tyrosine kinase (MuSK+) and seronegative generalized MG. We report details of the use of efgartigimod for generalized MG in clinical practice in Japan. Methods: We included patients with generalized MG in the 2021 survey of Japan Myasthenia Gravis Registry (JAMG-R) study group who received an initial cycle of efgartigimod between May and September 2022. We defined "responders" as patients who achieved a score ≥2 points for MG activities of daily living (MG-ADL) in the first treatment cycle. The MG composite and the Revised scale of the 15-item Myasthenia Gravis-Quality of Life scale (MG-QOL15-r) were also evaluated. Results: Of 1,343 JAMG-R patients, 36 (2.7%) started efgartigimod (female 68%, age 53 years). Their serologic profiles were as follows: AChR+, n = 19 (53%); MuSK+, n = 6 (17%); and seronegative, n = 11 (31%). Twenty-six patients (72%) had refractory MG. There were 81 cycles of efgartigimod during the 26-week observation in 34 patients (average, 2.4 cycles). The mean interval between cycles was 5.9 weeks. A continuous 4-weekly infusion of efgartigimod was performed in 65 (80%) of 81 cycles. In the first cycle, the MG-ADL score of the 34 patients decreased significantly from 10.5 ± 4.3 to 6.9 ± 5.1 (p = 0.003). Similarly, the mean MG composite and MG-QOL15-r decreased from 18.4 ± 13.6 to 11.8 ± 9.6 (p = 0.004) and from 19.2 ± 6.3 to 14.2 ± 8.3 (p = 0.007), respectively. Twenty-one (62%) patients were responders. Therapeutic responses were observed in the subsequent cycles. The duration of effectiveness of efgartigimod was varied among the responders; 4 responders had only a single effective cycle. Significant improvement was observed in the MuSK+ patients. Prednisolone dose of 7 patients was reduced. Our examination of the patients' postintervention status revealed that 6 patients achieved minimal manifestations. COVID-19 occurred in 5 patients. We failed to detect clinical or laboratory findings associated with responders. Discussion: Efgartigimod can be considered for the treatment of patients with generalized MG who do not achieve minimal manifestations, with a broad flexibility of patient selection and treatment schedules.

Clinical features and outcomes of patients with muscle-specific kinase antibody-positive myasthenia gravis in Japan.

This study included 51 patients with muscle-specific kinase antibody-positive myasthenia gravis (MuSK-MG) from a Japanese multicenter survey to examine clinical features and outcomes. Median onset age was 37 years and female predominance was observed. All patients developed generalized symptoms and almost all (50/51) patients had bulbar symptoms. About half of the patients met the criteria for refractory MG. The refractory group had a lower age of onset, higher severity scores, and higher maximum daily doses of oral prednisolone compared to the nonrefractory group. The outcomes for MuSK-MG patients in Japan are not favorable, indicating the need for more aggressive treatment.

Impact of Early Treatment with Intravenous High-Dose Methylprednisolone for Ocular Myasthenia Gravis.

The efficacy of intravenous high-dose methylprednisolone (IVMP) in ocular myasthenia gravis (MG) has not been fully established. This study aimed to elucidate the effects of early intervention with IVMP for achieving the therapeutic targets (minimal manifestations [MM] or MM or better status with prednisolone ≤ 5 mg/day [MM5mg]) in ocular MG. In this observational study, we included a total of 1710 consecutive patients with MG enrolled in the Japan MG Registry in 2021. Of these, 204 patients with ocular MG who received immunotherapy were analyzed. The clinical course and time to first achieve MM or MM5mg after starting immunotherapy were compared between the early IVMP group (treated with IVMP within 3 months of treatment initiation) and the non-early IVMP group. Despite having greater clinical severity before immunotherapy and lower oral prednisolone doses throughout the course, the early IVMP group (n = 55) showed a higher rate of achievement of MM (P = 0.0040, log-rank test; hazard ratio 1.58, 95% confidence interval [CI] 1.13-2.20, P < 0.0001) and MM5mg (P = 0.0005, log-rank test; hazard ratio 1.78, 95% CI 1.27-2.51, P < 0.0001) compared with the non-early IVMP group (n = 149). In conclusion, an early intervention with IVMP is likely to increase the probability of achieving a better long-term outcome and reducing the total dose of corticosteroids in ocular MG.

Effectiveness of early cycles of fast-acting treatment in generalised myasthenia gravis.

BACKGROUND: Early fast-acting treatment (EFT) is the aggressive use of fast-acting therapies such as plasmapheresis, intravenous immunoglobulin and/or intravenous high-dose methylprednisolone (IVMP) from the early phases of treatment. EFT is reportedly beneficial for early achievement of minimal manifestations (MM) or better status with ≤5 mg/day prednisolone (MM5mg), a practical therapeutic target for myasthenia gravis (MG). OBJECTIVE: The current study aimed to clarify which specific EFT regimen is efficacious and the patient characteristics that confer sensitivity to EFT. METHODS: We recruited a total of 1710 consecutive patients with MG who enrolled in the Japan MG Registry for this large-cohort study. Among them, 1066 with generalised MG who had received immunotherapy were analysed. Prognostic background factors were matched in a 1:1 ratio using propensity score matching analysis between patients treated with EFT (n=350) and those treated without EFT (n=350). The clinical course and time to first achieve MM5mg after starting immunotherapy was analysed in relation to treatment combinations and patient characteristics. RESULTS: Kaplan-Meier analyses showed that EFT had a significant effect on the achievement of MM5mg (p<0.0001, log-rank test; HR 1.82, p<0.0001). Notably, EFT was efficacious for any type of MG, and the inclusion of IVMP resulted in earlier and more frequent achievement of MM5mg (p=0.0352, log-rank test; HR 1.46, p=0.0380). In addition, early administration of calcineurin inhibitors also promoted MM5mg achievement. CONCLUSION: Early cycles of intervention with EFT and early use of calcineurin inhibitors provides long-term benefits in terms of achieving therapeutic targets for generalised MG, regardless of clinical subtype.

Reappraisal of Oral Steroid Therapy for Myasthenia Gravis.

Treatment with oral corticosteroids at high doses with an escalation and de-escalation schedule is effective against myasthena gravis (MG). In fact, the use of corticosteroids has led to a reduction in mortality to below 10% after the 1960s. However, long-term use of oral steroids above a certain dosage level is known to cause a number of problems. In 2014, the Japanese clinical guidelines for MG proposed that the first goal in MG treatment (treatment target) should be set at minimal manifestations (MM) with oral prednisolone (PSL) 5 mg/day or below, and that treatment strategies should strive to attain this level as rapidly as possible. In 2015, a multicenter, cross-sectional study revealed that higher PSL dose and longer PSL treatment do not ensure better outcome. In the absence of good response, the PSL dose should be decreased by combining with modalities such as plasma exchange/plasmapheresis and intravenous immunoglobulin (fast-acting treatments). In 2018, we conducted a multicenter, cross-sectional study in a large population of Japanese patients with generalized MG, aiming to elucidate the correlation between oral PSL regimens and achievement of treatment goals. The ORs for low vs. high dose to achieve treatment goals at 1, 2, and 3 years were 10.4, 2.75, and 1.86, respectively, whereas the corresponding ORs for low vs. medium dose were 13.4, 3.99, and 4.92. Early combination with fast-acting therapy (OR 2.19 at 2 years, 2.11 at 3 years) or combination with calcineurin inhibitors (OR 2.09 at 2 years, 2.36 at 3 years) were also positively associated with achieving treatment goals. These results indicate that early combination of low-dose PSL regimens with other therapies is the key for early achievement of treatment goals in generalized MG. However, even with this regimen, ~35% of patients did not achieve the treatment target after 3 years. These results suggest the limitation of the current oral corticosteroid therapy. We need to develop new treatment options to increase the rate of satisfactory outcome.

Rationale for the clinical guidelines for myasthenia gravis in Japan.

According to the 2014 Japanese clinical guidelines for myasthenia gravis, the most important priority in treatment is maintaining patients' health-related quality of life. Therefore, the initial treatment goal is defined as maintaining a postintervention status of minimal manifestations or better (according to the Myasthenia Gravis Foundation of America classification) with an oral prednisolone dose of 5 mg/day or less. Every effort should be made to attain this level as rapidly as possible. To achieve this goal, the guidelines recommend minimizing the oral prednisolone dose, starting calcineurin inhibitors early in the course of treatment, using intravenous methylprednisolone infusion judiciously (often combined with plasma exchange/plasmapheresis or intravenous immunoglobulin), and effectively treating patients with an early, fast-acting treatment strategy. The early, fast-acting treatment strategy enables more frequent and earlier attainment of the initial goal than other strategies. Thymectomy is considered an option for treating nonthymomatous early-onset myasthenia gravis in patients with antiacetylcholine receptor antibodies and thymic hyperplasia in the early stages of the disease.

Oral corticosteroid dosing regimen and long-term prognosis in generalised myasthenia gravis: a multicentre cross-sectional study in Japan.

OBJECTIVE: We examined the correlation between the dosing regimen of oral prednisolone (PSL) and the achievement of minimal manifestation status or better on PSL ≤5 mg/day lasting >6 months (the treatment target) in patients with generalised myasthenia gravis (MG). METHODS: We classified 590 patients with generalised MG into high-dose (n=237), intermediate-dose (n=187) and low-dose (n=166) groups based on the oral PSL dosing regimen, and compared the clinical characteristics, previous treatments other than PSL and prognosis between three groups. The effect of oral PSL dosing regimen on the achievement of the treatment target was followed for 3 years of treatment. RESULTS: To achieve the treatment target, ORs for low-dose versus high-dose regimen were 10.4 (P<0.0001) after 1 year of treatment, 2.75 (P=0.007) after 2 years and 1.86 (P=0.15) after 3 years; and those for low-dose versus intermediate-dose regimen were 13.4 (P<0.0001) after 1 year, 3.99 (P=0.0003) after 2 years and 4.92 (P=0.0004) after 3 years. Early combined use of fast-acting treatment (OR: 2.19 after 2 years, P=0.02; OR: 2.11 after 3 years, P=0.04) or calcineurin inhibitors (OR: 2.09 after 2 years, P=0.03; OR: 2.36 after 3 years, P=0.02) was associated positively with achievement of treatment target. CONCLUSION: A low-dose PSL regimen with early combination of other treatment options may ensure earlier achievement of the treatment target in generalised MG.

Analysis of peripheral B cells and autoantibodies against the anti-nicotinic acetylcholine receptor derived from patients with myasthenia gravis using single-cell manipulation tools.

The majority of patients with myasthenia gravis (MG), an organ-specific autoimmune disease, harbor autoantibodies that attack the nicotinic acetylcholine receptor (nAChR-Abs) at the neuromuscular junction of skeletal muscles, resulting in muscle weakness. Single cell manipulation technologies coupled with genetic engineering are very powerful tools to examine T cell and B cell repertoires and the dynamics of adaptive immunity. These tools have been utilized to develop mAbs in parallel with hybridomas, phage display technologies and B-cell immortalization. By applying a single cell technology and novel high-throughput cell-based binding assays, we identified peripheral B cells that produce pathogenic nAChR-Abs in patients with MG. Although anti-nAChR antibodies produced by individual peripheral B cells generally exhibited low binding affinity for the α-subunit of the nAChR and great sequence diversity, a small fraction of these antibodies bound with high affinity to native-structured nAChRs on cell surfaces. B12L, one such Ab isolated here, competed with a rat Ab (mAb35) for binding to the human nAChR and thus considered to recognize the main immunogenic region (MIR). By evaluating the Ab in in vitro cell-based assays and an in vivo rat passive transfer model, B12L was found to act as a pathogenic Ab in rodents and presumably in humans.These findings suggest that B cells in peripheral blood may impact MG pathogenicity. Our methodology can be applied not only to validate pathogenic Abs as molecular target of MG treatment, but also to discover and analyze Ab production systems in other human diseases.

Social disadvantages associated with myasthenia gravis and its treatment: a multicentre cross-sectional study.

OBJECTIVES: To clarify the social disadvantages associated with myasthenia gravis (MG) and examine associations with its disease and treatment. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: We evaluated 917 consecutive cases of established MG seen at 13 neurological centres in Japan over a short duration. OUTCOME MEASURES: All patients completed a questionnaire on social disadvantages resulting from MG and its treatment and a 15-item MG-specific quality of life scale at study entry. Clinical severity at the worst condition was graded according to the MG Foundation of America classification, and that at the current condition was determined according to the quantitative MG score and MG composite. Maximum dose and duration of dose ≥20 mg/day of oral prednisolone during the disease course were obtained from the patients' medical records. Achievement of the treatment target (minimal manifestation status with prednisolone at ≤5 mg/day) was determined at 1, 2 and 4 years after starting treatment and at study entry. RESULTS: We found that 27.2% of the patients had experienced unemployment, 4.1% had been unwillingly transferred and 35.9% had experienced a decrease in income, 47.1% of whom reported that the decrease was ≥50% of their previous total income. In addition, 49.0% of the patients reported feeling reduced social positivity. Factors promoting social disadvantages were severity of illness, dose and duration of prednisolone, long-term treatment, and a depressive state and change in appearance after treatment with oral steroids. Early achievement of the treatment target was a major inhibiting factor. CONCLUSIONS: Patients with MG often experience unemployment, unwilling job transfers and a decrease in income. In addition, many patients report feeling reduced social positivity. To inhibit the social disadvantages associated with MG and its treatment, greater focus needs to be placed on helping patients with MG resume a normal lifestyle as soon as possible by achieving the treatment target.

Early fast-acting treatment strategy against generalized myasthenia gravis.

INTRODUCTION: In this study we sought to clarify the effects of early fast-acting treatment (EFT) strategies on the time course for achieving the treatment target in generalized myasthenia gravis (MG). METHODS: This retrospective study of 923 consecutive MG patients analyzed 688 generalized MG patients who had received immunotherapy during the disease course. The time to first achieve minimal manifestations (MM) or better while receiving prednisolone at ≤5 mg/day for ≥6 months (MM-or-better-5mg) up to 120 months after starting immunotherapy was compared between EFT and non-EFT patients. RESULTS: Achievement of MM-or-better-5mg was more frequent and earlier in the EFT group (P = 0.0004, Wilcoxon test; P = 0.0001, log-rank test). Multivariate Cox regression analysis calculated a hazard ratio of 1.98 (P < 0.0001) for utilization of EFT. Dosing regimens of oral steroids in EFT produced no differences in the time course. CONCLUSIONS: EFT strategies are advantageous for early achievement of MM-or-better-5mg. Muscle Nerve 55: 794-801, 2017.

Response to treatment of myasthenia gravis according to clinical subtype.

BACKGROUND: We have previously reported using two-step cluster analysis to classify myasthenia gravis (MG) patients into the following five subtypes: ocular MG; thymoma-associated MG; MG with thymic hyperplasia; anti-acetylcholine receptor antibody (AChR-Ab)-negative MG; and AChR-Ab-positive MG without thymic abnormalities. The objectives of the present study were to examine the reproducibility of this five-subtype classification using a new data set of MG patients and to identify additional characteristics of these subtypes, particularly in regard to response to treatment. METHODS: A total of 923 consecutive MG patients underwent two-step cluster analysis for the classification of subtypes. The variables used for classification were sex, age of onset, disease duration, presence of thymoma or thymic hyperplasia, positivity for AChR-Ab or anti-muscle-specific tyrosine kinase antibody, positivity for other concurrent autoantibodies, and disease condition at worst and current. The period from the start of treatment until the achievement of minimal manifestation status (early-stage response) was determined and then compared between subtypes using Kaplan-Meier analysis and the log-rank test. In addition, between subtypes, the rate of the number of patients who maintained minimal manifestations during the study period/that of patients who only achieved the status once (stability of improved status) was compared. RESULTS: As a result of two-step cluster analysis, 923 MG patients were classified into five subtypes as follows: ocular MG (AChR-Ab-positivity, 77%; histogram of onset age, skewed to older age); thymoma-associated MG (100%; normal distribution); MG with thymic hyperplasia (89%; skewed to younger age); AChR-Ab-negative MG (0%; normal distribution); and AChR-Ab-positive MG without thymic abnormalities (100%, skewed to older age). Furthermore, patients classified as ocular MG showed the best early-stage response to treatment and stability of improved status, followed by those classified as thymoma-associated MG and AChR-Ab-positive MG without thymic abnormalities; by contrast, those classified as AChR-Ab-negative MG showed the worst early-stage response to treatment and stability of improved status. CONCLUSIONS: Differences were seen between the five subtypes in demographic characteristics, clinical severity, and therapeutic response. Our five-subtype classification approach would be beneficial not only to elucidate disease subtypes, but also to plan treatment strategies for individual MG patients.

International clinimetric evaluation of the MG-QOL15, resulting in slight revision and subsequent validation of the MG-QOL15r.

INTRODUCTION: The MG-QOL15 is a validated, health-related quality of life (HRQOL) measure for myasthenia gravis (MG). Widespread use of the scale gave us the opportunity to further analyze its clinimetric properties. METHODS: We first performed Rasch analysis on >1,300 15-item Myasthenia Gravis Quality of Life scale (MG-QOL15) completed surveys. Results were discussed during a conference call with specialists and biostatisticians. We decided to revise 3 items and prospectively evaluate the revised scale (MG-QOL15r) using either 3, 4, or 5 responses. Rasch analysis was then performed on >1,300 MG-QOL15r scales. RESULTS: The MGQOL15r performed slightly better than the MG-QOL15. The 3-response option MG-QOL15r demonstrated better clinimetric properties than the 4- or 5-option scales. Relative distributions of item and person location estimates showed good coverage of disease severity. CONCLUSIONS: The MG-QOL15r is now the preferred HRQOL instrument for MG because of improved clinimetrics and ease of use. This revision does not negate previous studies or interpretations of results using the MG-QOL15. Muscle Nerve 54: 1015-1022, 2016.

Association between Glucocorticoid-Induced Osteoporosis and Myasthenia Gravis: A Cross-Sectional Study.

PURPOSE: To investigate the association between glucocorticoid-induced osteoporosis and myasthenia gravis (MG) using a cross-sectional survey in Japan. METHODS: We studied 363 patients with MG (female 68%; mean age, 57 ± 16 years) who were followed at six Japanese centers between April and July 2012. We evaluated the clinical information of MG and fractures, bone markers, and radiological assessment. Quality of life was measured using an MG-specific battery, MG-QOL15. RESULTS: Glucocorticoids were administered in 283 (78%) of 363 MG patients. Eighteen (6%) of 283 MG patients treated with prednisolone had a history of osteoporotic fractures. The duration of glucocorticoid therapy, but not the dose of prednisolone, was associated with the osteoporotic fractures in MG patients. Bone mineral density was significantly decreased in the MG patients with fractures. The multivariate analyses showed that the total quantitative MG score was the only independent factor associated with osteoporotic fractures (OR = 1.30, 95% CI 1.02-1.67, p = 0.03). MG patients who had experienced fractures reported more severe difficulties in activities of daily living. CONCLUSION: Glucocorticoid-induced osteoporosis aggravates quality of life in patients with MG.

Oral corticosteroid therapy and present disease status in myasthenia gravis.

INTRODUCTION: The aim of this study was to elucidate the effectiveness of oral prednisolone (PSL) according to dosing regimen in 472 patients with myasthenia gravis (MG). METHODS: We compared the clinical characteristics and PSL treatment between 226 patients who achieved minimal manifestations (MM) or better and 246 patients who remained improved (I) or worsened, according to the MG Foundation of America postintervention status. RESULTS: Achievement of MM or better at peak PSL dose (odds ratio 12.25, P < 0.0001) and combined use of plasma exchange/plasmapheresis (PE/PP) and/or intravenous immunoglobulin (IVIg) (odds ratio 1.92, P = 0.04) were associated positively, and total PSL dose during the past year (odds ratio 0.17, P = 0.03) was associated negatively with present MM or better status. CONCLUSIONS: Higher PSL dose and longer PSL treatment do not ensure better outcome. In the absence of a good response, the PSL dose should be decreased by combining with modalities such as PE/PP or IVIg.

Insights into the classification of myasthenia gravis.

BACKGROUND AND PURPOSE: Myasthenia gravis (MG) is often categorized into thymoma-associated MG, early-onset MG with onset age <50 years, and late-onset MG with onset age ≥50 years. However, the boundary age of 50 years old between early- and late-onset MG remains controversial, and each category contains further subtypes. We attempted to classify MG from a statistical perspective. METHODS: We analyzed 640 consecutive MG patients using two-step cluster analysis with clinical variables and discrimination analysis, using onset age as a variable. RESULTS: Two-step cluster analyses categorized MG patients into the following five subtypes: ocular MG; MG with thymic hyperplasia (THMG); generalized anti-acetylcholine receptor antibody (AChR-Ab)-negative MG; thymoma-associated MG; and generalized AChR-Ab-positive (SP) MG without thymic abnormalities. Among these 5 subtypes, THMG showed a distribution of onset age skewed toward a younger age (p<0.01), whereas ocular MG and SPMG without thymic abnormalities showed onset age skewed toward an older age (p<0.001 and p<0.0001, respectively). The other 2 subtypes showed normal distributions. THMG appeared as the main component of early-onset MG, and ocular MG and SPMG without thymic abnormalities as the main components of late-onset MG. Discrimination analyses between THMG and ocular MG and/or SPMG without thymic abnormalities demonstrated a boundary age of 45 years old. CONCLUSIONS: From a statistical perspective, the boundary age between early- and late-onset MG is about 45 years old.

Japanese cases of neuromyelitis optica spectrum disorder associated with myasthenia gravis and a review of the literature.

BACKGROUND: The incidence of concurrent myasthenia gravis (MG) and neuromyelitis optica spectrum disorder (NMOSD) is higher than what chance predicts, yet it remains unclear why MG and NMOSD appear concurrently. OBJECTIVE: The purpose of the present study was to examine the clinical features of the concurrence of these diseases. METHODS: Clinical details were analyzed retrospectively. RESULTS: Three (0.5%) out of 631 MG patients had confirmed (n=2) or suspected (n=1) NMOSD. Two of these patients were women. All showed early-onset MG (EOMG) that preceded NMOSD and were positive for acetylcholine receptor antibody (AChR-Ab). Two patients were tested for aquaporin 4 antibody (AQP4-Ab) and were positive. Two patients were treated with a thymectomy that preceded NMOSD. Two patients had decreased frequency of regulatory T (Treg) cells. We identified in the literature 46 patients with both MG and NMOSD. Our results of female predominance, EOMG, MG preceding NMOSD, and positive AChR-Ab are consistent with previous descriptions. CONCLUSIONS: This is the first report to examine the frequency of NMOSD in Japanese patients with MG. The reduction and/or dysfunction of Treg cells may be one cause of NMOSD development in MG.