Epidemiologic evidence for a changing natural history of myasthenia gravis

Epidemiology of myasthenia gravis in France: Incidence, prevalence, and comorbidities based on national healthcare insurance claims data

BACKGROUND

The European literature has reported high variability in the incidence and prevalence rates of myasthenia gravis (MG), but no specific epidemiological data for France have been published. This study aimed to assess the incidence and prevalence rates of myasthenia gravis in France based on data extracted from the French National Health Insurance Claims Database (the SNIIRAM database).

METHODS

We conducted a retrospective repeated cross-sectional population study from 2008 to 2018 using a representative sample of the French population (Échantillon généraliste des bénéficiaires) covered by health insurance. We calculated the incidence, prevalence, and sex ratio of MG and screened for comorbidities associated with MG (standardized to the general population).

RESULTS

In total, 331 MG patients were identified between 2008 and 2018. The average incidence of MG in France was 50 per million person-years, while the mean prevalence was 465 per million people. The female-to-male ratio was 1.33. The Incidence of MG gradually increased from 40years of age for women and 60 for men. Thymoma was present for 5.1% of MG patients and a thymectomy was performed for 4.7%. Thyroid disease was the most prevalent autoimmune comorbidity, affecting approximately 8.5% of cases. MG patients had an increased cancer risk, with a standardized rate ratio of 2.38 (95% CI: 1.64-3.46).

CONCLUSION

The incidence and prevalence rates of MG are significantly higher than those previously reported in the literature and the incidence increases with age. The excess risk of cancer raises concerns for MG patients, in particular, concerning the management of immunosuppressive drugs.

Epidemiology of myasthenia gravis in France: A retrospective claims database study (STAMINA)

BACKGROUND

The objectives of this observational study were to report the incidence and prevalence of myasthenia gravis (MG) in France, describe patients' characteristics and treatment patterns, and estimate mortality.

METHODS

A historical cohort analysis was performed using the French National Health Data System (SNDS) database between 2008 and 2020. Patients with MG were identified based on ICD-10 codes during hospitalization and/or long-term disease (ALD) status, which leads to a 100% reimbursement for healthcare expenses related to MG. The study population was matched to a control group based on age, sex and region of residence.

RESULTS

The overall incidence of MG was estimated at 2.5/100,000 in 2019 and the overall prevalence at 34.2/100,000. The mean age was 58.3 years for incident patients and 58.6 for prevalent patients. Among patients with MG, 57.1% were women. In the first year after identification of MG, acetylcholinesterase inhibitors were the most commonly used treatments (87.0%). Corticosteroids were delivered to 58.3% of patients, intravenous immunoglobulin to 34.4%, and azathioprine to 29.9%. Additionally, 8% of patients underwent thymectomy. The proportions of patients with exacerbations and crises were 59.7% and 13.5% respectively in the first year after MG identification. All-cause mortality was significantly higher in patients with MG compared to matched controls (HR=1.82 (95% CI [1.74;1.90], P<0.0001)).

CONCLUSION

In this study, the incidence and prevalence of MG estimated in France were found to be higher than previously reported. Most exacerbations and crises occurred within the first year after MG identification. MG was associated with increased mortality compared to a control population matched on age, gender, and geographical region.

Epidemiology of myasthenia gravis in the United States

Introduction

Global studies of epidemiology of myasthenia gravis (MG) have pointed to increasing prevalence of this rare autoimmune disorder affecting the neuromuscular synapse; however, no new data for the USA were available for decades. We aimed to estimate the incidence rate and prevalence of MG in a large-scale insured US population.

Methods

We conducted a population-based retrospective cohort study to estimate the annual incidence and prevalence of MG cases in the USA during 2017. Using a previously validated algorithm, we identified cases of MG in two Truven Health MarketScan databases, which during 2017 included a sample of approximately 20 million commercially insured and Medicare recipients, plus 10 million Medicaid recipients. We report crude incidence and prevalence and calculated age-and sex-standardized estimates for the USA based on the 2017 American Community Survey. We estimated the number of adult cases during 2021 by extrapolating from the stratified estimates to the population size from the 2021 American Community Survey.

Results

From the US commercially/Medicare-insured cohort, we calculated an age-and sex-standardized incidence of 68.5 new cases per million person-years with an adjusted prevalence of 316.4 per million. Within the Medicaid-insured population, similar yet slightly lower numbers emerged: the adjusted incidence was 49.7 new cases per million person-years, and the adjusted prevalence rate was 203.7 cases per million. Given our results, we were able to estimate that there were approximately 82,715 US adults living with MG in 2021 (or an estimated 320.2 cases per million adults in the USA). We observed a strong effect of age and sex when stratifying the identified incidence rate and prevalence, with a pattern of female preponderance among the younger age brackets, a male preponderance for older cases in the commercially/Medicare-insured cohort, and the disease incidence and prevalence steadily increasing with age.

Discussion

Our updated US population-based estimates of MG epidemiology demonstrate an increase in the previously reported incidence and prevalence from over 20 years ago, in keeping with developments in westernized, industrialized countries. Notable findings of steadily increasing prevalence with age, driven by robust increases in elderly males, prompts questions for basic-translational research, therapeutics, and public health.

Epidemiology of myasthenia gravis in the province of Ourense (Galicia, Spain)

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune disease affecting nerve transmission at the level of the neuromuscular junction, and typically causes fluctuating muscle weakness. Epidemiological studies show an increase in MG prevalence, particularly among the older population.

OBJECTIVE

We performed a retrospective epidemiological study to determine the incidence and prevalence of MG in the province of Ourense (Galicia, Spain), characterised by population ageing.

MATERIAL AND METHODS

Patients were selected from our clinical neuromuscular diseases database by searching for patients with an active prescription for pyridostigmine bromide. Incidence was estimated for the period 2009-2018. We calculated prevalence at 31/12/2018. According to census data for the province of Ourense, the population on 1/1/2019 was 307 651, of whom 96 544 (31.4%) were aged ≥ 65 years.

RESULTS

We identified 80 cases of MG, with a prevalence rate of 260 cases/1 000 000 population (95% CI, 202.7-316.4), rising to 517.9/1 000 000 population in those aged ≥ 65 (95% CI, 363.2-672.9). Cumulative incidence in the study period was 15.4 cases per 1 000 000 person-years. Early onset (≤ 50 years) was recorded in 29.1% of cases.

CONCLUSION

The prevalence of MG in our health district is one of the highest published figures, and the disease is highly prevalent in the older population.

The Use of the Saccadometer to Identify Saccadic Characteristics in Myasthenia Gravis: A Pilot Study

BACKGROUND

Myasthenia gravis (MG) often presents with ocular signs that mimic other forms of ocular defects, such as isolated cranial nerve palsy. Normal velocity or even hyperfast saccadic eye movements in the presence of deficits of smooth pursuit have been well described in the literature in myasthenic patients. The reason for these paradoxical clinical findings has been reported to be due to increased postsynaptic folding of the fast-twitch fibers responsible for the execution of a saccade which is absent in those fibers responsible for slower, smooth eye movement. Saccadic characteristics therefore offer a point of differential diagnosis between patients suspected of having ocular motility deficits as a result of MG and those caused by other neuropathies. The advent of portable quantitative saccadic assessment means that previously laboratory-based assessments that require specialist equipment and training may now be undertaken clinically, providing a noninvasive test that can aid the differential diagnosis of the condition. The aim of this pilot study was to investigate the feasibility of the saccadometer (Ober Consulting, Poznan, Poland) in detecting the saccadic characteristics associated with myasthenia, specifically normal peak velocity (PV) in a group of patients confirmed with myasthenia.

METHODS

A group of 5 patients with a confirmed diagnosis of MG were recruited from a single site into the study along with 5 age-matched healthy volunteers. All myasthenic patients had ocular signs such as underaction or limitations of motility confirmed through ocular clinical examination. Healthy volunteers were screened for any underlying ocular motility or neurological defects before inclusion within the study. All participants undertook 100 trials of both 10 and 20° amplitude saccades, and mean PV, amplitude, and latency were recorded using the saccadometer for each individual. Overall, mean PV, amplitude, and latency were collated for both myasthenic and healthy control groups for each saccade size and compared.

RESULTS

The mean PV was significantly greater (481 ± 103.5 deg/seconds) for myasthenic patients compared with healthy controls (384 ± 42.8 deg/seconds) (P < 0.05) in 10° saccades. PV was also greater in myasthenics for 20° saccades; however, this difference did not reach statistical significance for patients with MG (547 ± 89.8 deg/seconds vs 477 ± 104.5 deg/seconds) (P = 0.14). The latency of participants with MG was not significantly different from those of age-matched healthy participants in 10° saccades but was significantly different for 20° saccades. There was no difference in amplitude measured between the groups.

CONCLUSIONS

PV for both 10 and 20° saccades was greater in myasthenic patients compared with healthy controls. All myasthenic patients produced normal velocity saccades in the presence of deficits of smooth ocular motility. The results from this small pilot study demonstrate the potential use of the saccadometer in a clinical setting to provide a noninvasive aid in the diagnosis of patients suspected with myasthenia.

Myasthenia Gravis and Thymectomy

Myasthenia gravis (MG) is a rare autoimmune neuromuscular disorder. Though MG was diagnosed four centuries ago, its rational management started in 1930s. In the present era, MG is managed by multimodality care including pharmacological agents, plasmapheresis, intravenous immunoglobulins, and surgical thymectomy. Thymectomy has evolved from open trans-sternal to video-assisted thoracoscopic and robotic thymectomy. In this article, the concise history of MG, its clinical features, diagnosis, and management are described.

The epidemiology of myasthenia gravis

Neuromuscular junction (NMJ) disorders include several dysfunctions that ultimately lead to muscle weakness. Myasthenia gravis (MG) is the most prevalent NMJ disorder with a highly polymorphic clinical presentation and many different faces. Being an autoimmune disease, MG correlates with the presence of detectable antibodies directed against the acetylcholine receptor, muscle-specific kinase, lipoprotein-related protein 4, agrin, titin, and ryanodine in the postsynaptic membrane at the NMJ. MG has become a prototype serving to understand both autoimmunity and the function of the NMJ better. The aim of this review is to synthesize some of the epidemiological data available. Epidemiological data regarding MG are important for postulating hypotheses regarding its etiology and facilitating the description of MG subtypes. Thus, adequate documentation through broad databases is essential. The incidence and prevalence of MG reported around the globe have been rising steadily and consistently over the past decades. Ethnic aspects, gender-related differences, and environmental risk factors have been described, implying that these might contribute to a specific phenotype, further suggesting that MG may be considered an umbrella term that covers several clinical entities.

Epidemiology of myasthenia gravis in the province of Ourense (Galicia, Spain)

INTRODUCTION

Myasthenia gravis (MG) is an autoimmune disease affecting nerve transmission at the level of the neuromuscular junction, and typically causes fluctuating muscle weakness. Epidemiological studies show an increase in MG prevalence, particularly among the older population.

OBJECTIVE

We performed a retrospective epidemiological study to determine the incidence and prevalence of MG in the province of Ourense (Galicia, Spain), characterised by population ageing.

MATERIAL AND METHODS

Patients were selected from our clinical neuromuscular diseases database by searching for patients with an active prescription for pyridostigmine bromide. Incidence was estimated for the period 2009-2018. We calculated prevalence at 31/12/2018. According to census data for the province of Ourense, the population on 1/1/2019 was 307,651, of whom 96,544 (31.4%) were aged ≥ 65 years.

RESULTS

We identified 80 cases of MG, with a prevalence rate of 260 cases/1 000 000 population (95% CI, 202.7-316.4), rising to 517.9/1 000 000 population in those aged ≥ 65 (95% CI, 363.2-672.9). Cumulative incidence in the study period was 15.4 cases per 1 000 000 person-years. Early onset (≤ 50 years) was recorded in 29.1% of cases.

CONCLUSION

The prevalence of MG in our health district is one of the highest published figures, and the disease is highly prevalent in the older population.

Clinical features of LRP4/agrin-antibody-positive myasthenia gravis: A multicenter study

Introduction

Our aim in this study was to identify the prevalence and clinical characteristics of LRP4/agrin‐antibody–positive double‐seronegative myasthenia gravis (DNMG).

Methods

DNMG patients at 16 sites in the United States were tested for LRP4 and agrin antibodies, and the clinical data were collected.

Results

Of 181 DNMG patients, 27 (14.9%) were positive for either low‐density lipoprotein receptor–related protein 4 (LRP4) or agrin antibodies. Twenty‐three DNMG patients (12.7%) were positive for both antibodies. More antibody‐positive patients presented with generalized symptoms (69%) compared with antibody‐negative patients (43%) (P ≤ .02). Antibody‐positive patients’ maximum classification on the Myasthenia Gravis Foundation of America (MGFA) scale was significantly higher than that for antibody‐negative patients (P ≤ .005). Seventy percent of antibody‐positive patients were classified as MGFA class III, IV, or V compared with 39% of antibody‐negative patients. Most LRP4‐ and agrin‐antibody–positive patients (24 of 27, 89%) developed generalized myathenia gravis (MG), but with standard MG treatment 81.5% (22 of 27) improved to MGFA class I or II during a mean follow‐up of 11 years.

Discussion

Antibody‐positive patients had more severe clinical disease than antibody‐negative patients. Most DNMG patients responded to standard therapy regardless of antibody status.

Hospital and healthcare insurance system record-based epidemiological study of myasthenia gravis in southern and northern China

OBJECTIVE

This is the first cross-region epidemiological study of myasthenia gravis (MG) in China. We estimated the incidence, prevalence, and medical costs of MG in southern China and explored the differences between the southern and northern Chinese populations.

METHODS

We collected and analyzed records from 20 hospitals in the southern city, Guangzhou, 13 hospitals in the northern city, Harbin, and two healthcare insurance systems: job based and residence based in Guangzhou during 2000-2017.

RESULTS

(1) The estimated annual incidence of MG was 1.55-3.66 per 100,000, and the estimated prevalence of MG was 2.19-11.07 per 100,000 in southern China based on insurance records. (2) The proportion of hospitalized MG patients in the south-based hospital records was three times as high as that in the north-based hospital records. (3) Female MG prevalence was significantly higher than male MG prevalence in Guangzhou, while the similar gender difference in Harbin was not statistically significant due to higher variation in earlier years. (4) The average expense was $35-42 for each outpatient service and $2526-2673 for each hospitalization expense in the south. (5) Contrary to the increase of insurance-based estimate of MG prevalence, the proportion of hospitalized MG patients did not increase over the years, suggesting rising awareness and utilization of health insurance.

CONCLUSIONS

The southern MG population had a significantly higher prevalence and a lower response threshold to medication than the northern MG population. These results are calling for further investigations on the genetic, cultural, and environmental variations of the Chinese MG populations between north and south.

Incidence, Epidemiology, and Transformation of Ocular Myasthenia Gravis: A Population-Based Study

PURPOSE

To establish the incidence of ocular myasthenia gravis (OMG) as well as identify determinants of transformation to generalized myasthenia gravis (GMG) using a population-based record-linkage system.

DESIGN

Population-based, retrospective cohort study.

METHODS

All adults (≥18 years) diagnosed with myasthenia gravis (MG) from January 1, 1990, through December 31, 2017, were identified using the Rochester Epidemiology Project. Sixty-five patients with MG were identified. Data were collected regarding symptom onset, diagnostic testing results, and conversion from OMG to GMG.

RESULTS

Median follow-up time was 91 months (range 17-333 months). The annual incidence of MG was 2.20/100 000 with a mean age at diagnosis of 59 years (SD=17) and 62% male sex. Thirty-three (51%) of the 65 patients presented with OMG, providing an annual incidence of 1.13/100 000. Eighteen (55%) of the 33 patients presenting with OMG converted to GMG at a median time of 13 months (range 2-180 months). Sixteen (67%) of 24 OMG patients who were seropositive for acetylcholine receptor antibody (AchR Ab) converted to GMG at 5 years compared to 11% (1/9) of those who were seronegative (hazard ratio [HR], 8.2, P = .04). Ten (77%) of 13 OMG patients with a positive single-fiber electromyography (sfEMG) at diagnosis converted to GMG at 5 years, compared with 18% (2/11) of patients who had a negative sfEMG (HR, 5.5, P = .01).

CONCLUSIONS

In our population-based study, 51% (33/65) of patients with MG presented with isolated ocular involvement, with 55% (18/33) of these patients converting to GMG at some point in the course of their disease. Positive sfEMG and AchR Ab seropositivity at the time of diagnosis increased the risk of conversion to GMG.

Benefits of Comprehensive Rehabilitation Therapy in Thymectomy for Myasthenia Gravis: A Propensity Score Matching Analysis

OBJECTIVE

To demonstrate the effectiveness of a comprehensive program of rehabilitation therapy in patients undergoing thymectomy for myasthenia gravis (MG).

DESIGN

From 2005 to 2010, 46 consecutive patients affected by MG underwent a rehabilitation program both before and after thymectomy. We matched each patient with a "control patient" who underwent thymectomy within the period 1999 to 2004 with no preoperative rehabilitation, who had the closest propensity score matching.

RESULTS

All patients but 2 were able to complete the intended program. Eighteen patients (41%) experienced mild fatigue (>25 at MG quantitative score). Propensity score selected a group of 17 patients for the matching process. The group of patients who underwent the rehabilitation program showed significant preoperative improvement associated with a reduced operative risk, a decreased early postoperative morbidity, a lower rate of postoperative intensive care unit needed (12% vs 35%; P = 0.01) and a shorter hospital stay (3 vs 5 days; P = 0.04). After the expected perioperative decline, all major myasthenic outcomes demonstrated a significant faster recovery at 3 months. Complete stable remission did not reveal significant differences.

CONCLUSIONS

Exercise is not necessarily a contraindication in MG, and rehabilitation can be safely performed before and after thymectomy, reducing operative risks and decreasing recovery time.

TO CLAIM CME CREDITS

Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCMECME OBJECTIVES: Upon completion of this article, the reader should be able to do the following: (1) appreciate the benefits of physical therapy in individuals with myasthenia gravis; (2) describe the benefits of physical therapy on postoperative morbidity in myasthenia gravis patients who undergo thymectomy; and (3) incorporate appropriate rehabilitation into the treatment plan of patient with myasthenia gravis.

LEVEL

AdvancedACCREDITATION: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this activity for a maximum of 1.5 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Epidemiology of myasthenia gravis in Northern Portugal: Frequency estimates and clinical epidemiological distribution of cases

INTRODUCTION

In this study we estimated the prevalence, incidence, and mortality of myasthenia gravis (MG) in northern Portugal and characterized the clinical features of the patients identified.

METHODS

We used 2 data sources: clinical records from the hospitals and pyridostigmine prescription registers.

RESULTS

On December 31, 2013, we estimated a point prevalence of 111.7 patients per million population. The highest prevalence was observed in the group >65 years of age, especially in men (288.1 per million). During 2013, we estimated an incidence rate of 6.3 per million per year. Among women, the incidence rate was highest in the 15-49-year age group; in men, incidence increased with age up to 22.1 per million in those >65 years old. The MG-related mortality rate was 0.5 per million.

CONCLUSIONS

These figures are in keeping with similar studies and emphasize the importance of diagnosis and management of MG in elderly populations. Muscle Nerve 54: 413-421, 2016.

Incidence and Prevalence of Myasthenia Gravis in Korea: A Population-Based Study Using the National Health Insurance Claims Database

Background and Purpose

There have been a few national population-based epidemiological studies of myasthenia gravis (MG) with wide variation of incidence and prevalence rates worldwide. Herein we report the first nationwide population-based epidemiological study of MG in Korea.

Methods

We attempted to estimate the incidence and prevalence rates of MG using the Korean National Health Insurance claims database for 2010 to 2013. Cases with MG were defined as those having claim records with a principal diagnosis of MG and the prescription of acetylcholinesterase inhibitors or immunosuppressive agents including corticosteroids and azathioprine within 2 years after the diagnosis. The year 2010 was set as a washout period, such that patients were defined as incident cases if their first records of MG were observed in 2011.

Results

In 2011 there were 1,236 incident cases, and the standardized incidence rate was 2.44 per 100,000 person-years. The standardized prevalence rates were 9.67 and 10.66 per 100,000 persons in 2010 and 2011, respectively. The incidence and prevalence rates peaked in the elderly population aged 60 to 69 years for both sexes.

Conclusions

This is one of the largest national population-based epidemiological studies of MG, and it has confirmed the high incidence and prevalence rates of MG in the elderly population of South Korea.

Myasthenia gravis: a clinical-immunological update

Myasthenia gravis (MG) is the archetypic disorder of both the neuromuscular junction and autoantibody-mediated disease. In most patients, IgG1-dominant antibodies to acetylcholine receptors cause fatigable weakness of skeletal muscles. In the rest, a variable proportion possesses antibodies to muscle-specific tyrosine kinase while the remainder of seronegative MG is being explained through cell-based assays using a receptor-clustering technique and, to a lesser extent, proposed new antigenic targets. The incidence and prevalence of MG are increasing, particularly in the elderly. New treatments are being developed, and results from the randomised controlled trial of thymectomy in non-thymomatous MG, due for release in early 2016, will be of particular clinical value. To help navigate an evidence base of varying quality, practising clinicians may consult new MG guidelines in the fields of pregnancy, ocular and generalised MG (GMG). This review focuses on updates in epidemiology, immunology, therapeutic and clinical aspects of GMG in adults.

Epidemiology of myasthenia gravis in Ontario, Canada

Incidence and prevalence estimates in myasthenia gravis have varied widely. Recent studies based on administrative health data have large sample sizes but lack rigorous validation of MG cases, and have not examined the North American population. Our aim was to explore trends in MG incidence and prevalence for the years 1996-2013 in the province of Ontario, Canada (population 13.5 million). We employed a previously validated algorithm to identify MG cases. Linking with census data allowed for the calculation of crude- and age/sex-standardized incidence and prevalence rates for the years 1996-2013. The regional distribution of MG cases throughout the province was examined. Mean age at the first myasthenia gravis encounter was 60.2 ± 17.1 years. In 2013, there were 3611 prevalent cases in Ontario, and the crude prevalence rate was 32.0/100,000 population. Age- and sex-standardized prevalence rates rose consistently over time from 16.3/100,000 (15.4-17.1) in 1996 to 26.3/100,000 (25.4-27.3) in 2013. Standardized incidence rates remained stable between 1996 (2.7/100,000; 95% CL 2.3-3.0) and 2013 (2.3/100,000; 2.1-2.6). Incidence was highest in younger women and older men, and geographic variation was evident throughout the province. In conclusion, this large epidemiological study shows rising myasthenia gravis prevalence with stable incidence over time, which is likely reflective of patients living longer, possibly due to improved disease treatment. Our findings provide accurate information on the Canadian epidemiology of myasthenia gravis and burden for health care resources planning for the province, respectively.

Clinical profile of patients with myasthenia gravis followed at the University Hospital, Federal University of Minas Gerais

OBJECTIVE

to determine the clinical profile of patients with myasthenia gravis (MG); followed at the Neuromuscular Diseases Clinic of the University Hospital, Federal University of Minas Gerais, Brazil, and to compare it with other Brazilian case series.

METHODS

sociodemographic and clinical data were collected from patients, and a systematic literature review performed, focusing on national studies on the clinical profile of MG patients.

RESULTS

sixty nine patients were enrolled in the study. Fifty five (91%) subjects were female and the mean age (SD) was 37.6 (± 11.4) years. The mean disease duration was 14.1 years. Regarding treatment, prednisone was the most used strategy (64%), followed by the use of azathioprine (43%). There was no difference between thymectomized (42) and non-thymectomized (27) patients regarding disease severity and medication use.

CONCLUSION

clinical and socio-demographic features of this MG sample from a University-based clinic resemble those reported in other Brazilian series and in the international literature.

Canadian Administrative Health Data Can Identify Patients with Myasthenia Gravis

Introduction: Incidence and prevalence estimates for myasthenia gravis (MG) have varied widely, and the ability of administrative health data (AHD) records to accurately identify cases of MG is yet to be ascertained. The goal of the current study was to validate an algorithm to identify patients with MG in Ontario, Canada using AHD - thereby enabling future disease surveillance. Methods: A reference standard population was established using automated key word searching within EMRALD (Electronic Medical Record Administrative data Linked Database) and chart review of potential cases. AHD algorithms were generated and tested against the reference standard. The data was used to calculate MG prevalence rates. Results: There were 123,997 eligible adult patients, and 49 patients had definite MG (forming the reference standard). An algorithm requiring: (1 hospital discharge abstract with MG listed as a reason for hospitalization or a comorbid condition), or (5 outpatient MG visits and 1 relevant diagnostic test, within 1 year), or (3 pyridostigmine prescriptions, within 1 year) identified MG with sensitivity = 81.6%, specificity = 100%, positive predictive value = 80.0% and negative predictive value = 100%. The population prevalence within our cohort was 0.04%. Conclusions: This novel validation method demonstrates the feasibility of using administrative health data to identify patients with myasthenia gravis among the Ontario population.

Antititin antibody in early- and late-onset myasthenia gravis

OBJECTIVES

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies against neuromuscular junction proteins, 85% of patients have antibodies against acetylcholine receptor (AChR-MG). Antititin antibodies are present in a subset of patients with MG. We aimed to determine the value of antititin antibodies as severity markers and thymoma predictors in early- and late-onset MG.

MATERIALS & METHODS

Two-hundred and ninety-five consecutive MG patients (188 F and 107 M) aged 12-89 years (mean 50y) were included. 164 patients had early-onset (EOMG, ≤50 years of age), 131 had late-onset MG (LOMG). Twenty-six patients had thymoma. symptoms, severity graded with MGFA scale, thymus histology, medications, and treatment results were analyzed.

RESULTS

Antititin antibodies were present in 81 (27%) of all patients: 54% of thymoma MG, 0.6% of non-thymomatous EOMG, and 55% of LOMG, with proportion of titin-positive patients increasing linearly from 40% in the 6th to 88% in the 9th decade of life. Titin-positive patients had more bulbar symptoms (P = 0.003). Severity of MG, need for immunosuppression, myasthenic crisis risk or treatment results were not related to its presence. Antititin antibodies had 56% sensitivity, 99% specificity, 90% positive predictive value (PPV), and 95% negative predictive value (NPV) for thymoma diagnosis in EOMG, and 50% sensitivity, 75% specificity, 71% PPV and 55% NPV in LOMG.

CONCLUSIONS

Antititin antibodies have high PPV and NPV for thymoma in EOMG. In MG without thymoma, antititin antibodies can be considered as markers of LOMG, but not of a severe course in our MG cohort.

Increased subsequent risk of myasthenia gravis in children with allergic diseases

Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junction. The initiating factors of MG remain unclear. However, allergy has been regarded as a potential risk factor. We included 410 children with MG diagnosed between 2000 and 2008, as well as 1640 randomly selected controls. The odds ratios of MG were calculated to determine the association between MG and preexisting allergic diseases. The children with allergic diseases were at increased subsequent risk of MG, which was associated with the cumulative effect of the concurrent allergic diseases and the frequency of seeking medical care.

Brazilian cross-cultural translation and adaptation of the "Questionnaire of Life Quality Specific for Myasthenia Gravis - 15 items"

Objective To translate and to perform the cross-cultural adaptation of the “Questionnaire of Life Quality Specific for Myasthenia Gravis - 15 items” (MG-QOL15). Method The original English version of the questionnaire was translated into Portuguese. This version was revised and translated back into English. Later, both English versions were compared and the divergences were corrected in the Portuguese text. At a second stage, ten patients with MG followed at the Neuromuscular Diseases Clinic from the University Hospital, Universidade Federal de Minas Gerais answered the questionnaire. The authors analyzed the difficulties and misunderstandings in the application of the questionnaire. Results The questions 8, 13 and 15 were considered difficult to understand and were modified in the final Portuguese version. Most patients (70%) had a total score above 25, and the statements 3, 8 and 9 showed the highest scores. Conclusion The Brazilian version of the questionnaire MG-QOL15 seems to be a promising tool for the assessment of Brazilian patients with MG.

Different characteristic phenotypes according to antibody in myasthenia gravis

OBJECTIVES

To find the characteristic phenotypes of 3 different types of myasthenia gravis (MG).

METHODS

The clinical and electrophysiological features among 15 cases of muscle-specific kinase antibody positive (MuSK Ab+) MG, 59 cases of double seronegative (DSN) MG, and 161 cases of acetylcholine receptor antibody (AChR Ab)+ MG in the University of Alabama at Birmingham were compared.

RESULTS

AChR Ab was positive in 69% of cases and MuSK Ab in 6% of cases. MuSK Ab+ MG was more common (14%) in African Americans compared with whites (4%). AChR Ab+ MG is characterized by male predominance, later onset, a fewer cases of ocular MG, and a higher association with thymoma. DSN-MG is characterized by a greater prevalence of ocular MG, milder forms of MG with less number of crisis, and fewer abnormalities in the repetitive nerve stimulation test. MuSK Ab+ MG is characterized by younger age at onset, severe and bulbar forms of MG, predominant faciobulbar neck weakness, and a poor response to edrophonium, anticholinesterase, and intravenous immunoglobulin. Long-term outcome showed no difference among 3 types of MG.

CONCLUSIONS

AChR Ab+ MG and DSN-MG are similar, with the exception of less severity in the latter. MuSK Ab+ MG has distinct clinical and electrophysiological features.

Epidemiology of myasthenia gravis in Austria: rising prevalence in an ageing society

OBJECTIVE

The purpose of this study was to investigate recent epidemiological trends of myasthenia gravis (MG) in Austria.

METHODS

We used the national hospital discharge register, which records the discharge diagnoses of all inpatient stays in Austria to calculate the yearly inpatient prevalence of MG from 1992 to 2009 (main or secondary diagnosis of MG). The population prevalence was indirectly estimated. The temporal and geographical variability of the inpatient prevalence was correlated with the number of practicing neurologists.

RESULTS

The inpatient prevalence of 2009 was calculated as 8.0 and the population prevalence as 15.69 (95 % CI 13.16-19.42) per 100,000. We observed a 2.2 fold increase in the inpatient prevalence between 1992 and 2009, which was mainly due to a rise in the number of older patients (³ 50 years). Partly this could be accounted for by an ageing of the population as a whole and a rise in the age of hospitalised patients. However, after adjusting for demographic factors an unexplained average yearly rise of 3.7-3.9 % remained. We found a significant spatial and temporal correlation of MG inpatient prevalence rates with the number of practicing neurologists, which increased over the same period.

CONCLUSIONS

The results from this study support the notion that the prevalence rate of MG in Austria is rising and near the higher end of the wide range discussed in the literature. Our data argue for the importance of specialist neurological care for the diagnosis of this disease.

Updated assessment of the prevalence, spectrum and case definition of autoimmune disease

Autoimmune diseases are heterogeneous with regard to prevalence, manifestations, and pathogenesis. The classification of autoimmune diseases has varied over time. Here, we have compiled a comprehensive up-to-date list of the autoimmune diseases, and have reviewed published literature to estimate their prevalence. We identified 81 autoimmune diseases. The overall estimated prevalence is 4.5%, with 2.7% for males and 6.4% for females. For specific diseases, prevalence ranges from 1% to <1/10(6). Considering all diseases in the class, the most common mean age-of-onset was 40-50 years. This list of autoimmune diseases has also yielded information about autoantigens. Forty-five autoimmune diseases have been associated with well-defined autoantigens. Of the diseases with known autoantigens, 33.3% had highly repetitive sequences, 35.6% had coiled-coil arrangements and 57.8% were associated with cellular membranes, which means that based on these structural motifs alone, autoantigens do not appear to be a random sample of the human proteome. Finally, we identified 19 autoimmune diseases that phenocopy diseases arising from germline mutations in the corresponding autoantigen. Collectively, our findings lead to a tentative proposal for criteria for assigning autoimmune pathogenesis to a particular disease.

Current and emerging treatments for the management of myasthenia gravis

Myasthenia gravis is an autoimmune neuromuscular disorder. There are several treatment options, including symptomatic treatment (acetylcholinesterase inhibitors), short-term immunosuppression (corticosteroids), long-term immunosuppression (azathioprine, cyclosporine, cyclophosphamide, methotrexate, mycophenolate mofetil, rituximab, tacrolimus), rapid acting short-term immunomodulation (intravenous immunoglobulin, plasma exchange), and long-term immunomodulation (thymectomy). This review explores in detail these different treatment options. Potential future treatments are also discussed.

Change in myasthenia gravis epidemiology in Trento, Italy, after twenty years

BACKGROUND

The recent literature suggests that the incidence and prevalence of myasthenia gravis (MG) are changing. We performed a population-based study of MG in the province of Trentino (524,826 inhabitants) and compared the results with those collected 20 years ago.

METHODS

Multiple sources of information (discharge diagnosis, antibody tests and anticholinesterase drugs) were analyzed. Incidence was calculated from 2005 to 2009. Prevalence was calculated on December 31, 2009. Comparison was made with descriptive statistics for 1981-1990 for the identical region.

RESULTS

Incidence and prevalence greatly increased in comparison with 1981-1990 data. The prevalence rate increased from 82.9 (95% confidence interval, CI, 58.4-114.3) in 1990 to 129.6 (95% CI 100.6-164.3) per million population, whereas the average annual incidence increased from 7.4 (95% CI 5-10.4) per million person-years in 1981-1990 to 14.8 (95% CI 10.5-20.3) in 2005-2009. This increase was mainly due to male patients with late-onset MG.

CONCLUSIONS

The study confirms the increase in incidence and prevalence of late-onset MG in the same region 20 years apart. So we should consider MG also as a disease of the elderly.

Myasthenia gravis requiring pyridostigmine treatment in a national population cohort

BACKGROUND

Pyridostigmine is the first drug of choice for patients with myasthenia gravis (MG). The drug is not prescribed regularly to any other patient groups. We aimed to determine the prevalence, incidence and gender-specific characteristics of patients with MG needing drug treatment in a well-defined population cohort.

METHODS

Data were retrieved from the Norwegian Prescription Database (NorPD) 2004-2007, containing information on all dispensed drugs in Norway. The study population comprised 677 recipients of pyridostigmine who met the following inclusion criteria (one or more): (i) More than one prescription 1 January 2004-31 December 2007, (ii) prescription from a specialist in neurology, (iii) prescription for MG being specified in NorPD.

RESULTS

A total of 435 (64%) women and 242 men were included; female:male ratio 1.8:1. Point prevalence (1 January 2008) of symptomatic MG was 131 per million; 92 for men, 170 for women. Seventy-four new users of pyridostigmine were registered in 2007 (42 women, 32 men), i.e. the incidence rate for 2007 being 16 per million; 14 for men, 18 for women. Mean age of incident cases was 59 years; 64 and 55 years, respectively. Prevalence and incidence were significantly higher in the age group ≥ 50 years than < 50 years (P < 0.001), and highest at 70-79 years. Prevalence and incidence did not differ in the five geographical health regions in Norway.

CONCLUSIONS

Reported prevalence and incidence are amongst the highest found in similar studies. This may be explained by optimal case identification, higher incidence of drug requiring MG amongst the elderly, and recurrences of previous MG.

Current and emerging therapies for the treatment of myasthenia gravis

Myasthenia gravis (MG) is an autoimmmune disease in which autoantibodies to different antigens of the neuromuscular junction cause the typical weakness and fatigability. Treatment includes anticholinesterase drugs, immunosuppression, immunomodulation, and thymectomy. The autoimmune response is maintained under control by corticosteroids frequently associated with immunosuppressive drugs, with improvement in the majority of patients. In case of acute exacerbations with bulbar symptoms or repeated relapses, modulation of autoantibody activity by plasmapheresis or intravenous immunoglobulins provides rapid improvement. Recently, techniques removing only circulating immunoglobulins have been developed for the chronic management of treatment-resistant patients. The rationale for thymectomy relies on the central role of the thymus. Despite the lack of controlled studies, thymectomy is recommended as an option to improve the clinical outcome or promote complete remission. New videothoracoscopic techniques have been developed to offer the maximal surgical approach with the minimal invasiveness and hence patient tolerability. The use of biological drugs such as anti-CD20 antibodies is still limited but promising. Studies performed in the animal model of MG demonstrated that several more selective or antigen-specific approaches, ranging from mucosal tolerization to inhibition of complement activity or cellular therapy, might be feasible. Investigation of the transfer of these therapeutic approaches to the human disease will be the challenge for the future.

Myasthenia gravis in Ceará, Brazil: clinical and epidemiological aspects

A retrospective chart review was performed on patients diagnosed as having myasthenia gravis in Ceará State, Brazil and who were followed from October 1981 to June 2009. Clinical and epidemiologic aspects were evaluated. In this work, 122 patients were studied, of whom 85 (69.7%) were females and 37 (30.3%) were males. The disease duration ranged from five months to 50 years (8.9±8.1 years). Age at the first symptoms varied from 0 to 74 years (31.9±14.4 years). The first main symptoms and signs were ptosis, diplopia and limb weakness. Generalized myasthenia was the most common clinical presentation, but 5.1% (n=6) persisted as ocular myasthenia. Thymectomy was performed in 42.6% (n=52) of myasthenic patients. A thymoma was present in 10 patients. Serum acetylcholine receptor (AChR) antibodies were present in 80% (n=20) of specimens tested. The data presented are similar to those of studies performed in other countries.

A systematic review of population based epidemiological studies in Myasthenia Gravis

BACKGROUND

The aim was to collate all myasthenia gravis (MG) epidemiological studies including AChR MG and MuSK MG specific studies. To synthesize data on incidence rate (IR), prevalence rate (PR) and mortality rate (MR) of the condition and investigate the influence of environmental and technical factors on any trends or variation observed.

METHODS

Studies were identified using multiple sources and meta-analysis performed to calculate pooled estimates for IR, PR and MR.

RESULTS

55 studies performed between 1950 and 2007 were included, representing 1.7 billion population-years. For All MG estimated pooled IR (eIR): 5.3 per million person-years (C.I.:4.4, 6.1), range: 1.7 to 21.3; estimated pooled PR: 77.7 per million persons (C.I.:64.0, 94.3), range 15 to 179; MR range 0.1 to 0.9 per millions person-years. AChR MG eIR: 7.3 (C.I.:5.5, 7.8), range: 4.3 to 18.0; MuSK MG IR range: 0.1 to 0.32. However marked variation persisted between populations studied with similar methodology and in similar areas.

CONCLUSIONS

We report marked variation in observed frequencies of MG. We show evidence of increasing frequency of MG with year of study and improved study quality. This probably reflects improved case ascertainment. But other factors must also influence disease onset resulting in the observed variation in IR across geographically and genetically similar populations.

Nationwide population-based epidemiological study of myasthenia gravis in taiwan

BACKGROUND

The purpose of this study is to investigate the epidemiology and medical expenses of myasthenia gravis (MG) in Taiwan.

METHODS

Cases of MG were identified from the National Health Insurance Research Database with corresponding codes of the International Classification of Diseases, ninth revision (ICD-9), from January 2000 to December 2007. Age- and sex-specific incidences were estimated by dividing the incidence number by population data obtained from the Department of Statistics, Ministry of the Interior.

RESULTS

During the study period, 5,211 cases were identified. The incidence ratio of males to females was 0.68. The average annual incidence rate was 2.1/100,000. MG occurred in all age groups with a higher incidence in older individuals and the lowest incidence in the 10- to 14-year-olds for both sexes. Among the 5,211 cases, 615 (12%) had a neoplasm of the thymus. The prevalence increased steadily during the study period from 8.4/100,000 in 2000 to 14.0/ 100,000 in 2007.

CONCLUSIONS

This is the first population-based epidemiological study of MG in Taiwan. The incidence rate and prevalence were higher than in most published studies, especially in old age groups.

Myasthenia gravis in an adolescent patient presenting to the pediatric emergency department

Myasthenia gravis is a rare, chronic, autoimmune disorder characterized by postsynaptic dysfunction at the neuromuscular junction. The disease affects more females than males. We describe the case of a 17-year-old female adolescent with recurrent episodes of dysarthria and dysphagia and a history of aspiration pneumonia. A bedside edrophonium (Tensilon) test in our emergency department confirmed the diagnosis of myasthenia gravis.

Geoepidemiology of myasthenia gravis [corrected]

Myasthenia gravis (MG) is an autoimmune disease that affects the post-synaptic area of the neuromuscular junction. Its hallmark is weakness that worsens with activity. MG incidence is rising in the recent decades, mostly the late onset subtype, which is considered to be due to the aging population or unknown environmental factors. The disease has several subtypes which defer slightly in the clinical characteristics, immunological markers, population distribution and the suitable treatments. The autoimmune nature of the disease is manifested by a decrease in the number of acetylcholine receptors in the muscle receptors which makes the endplate potential to be lower than the threshold needed to activate muscle fiber action potential. In our review we try to find the environmental influence on the disease.

No increased risk of adverse pregnancy outcomes for women with myasthenia gravis: a nationwide population-based study

BACKGROUND

This study aims to examine the risk of adverse pregnancy outcomes [low birthweight (LBW), preterm birth, cesarean sections (CS) and babies born small for gestational age (SGA)] in pregnant women with myasthenia gravis (MG), using a 3-year population-based database, taking characteristics of infant and mother into consideration.

METHODS

This study used two nationwide population-based datasets: the Taiwan National Health Insurance Research Dataset and the Taiwan birth certificate registry. We identified 163 pregnant women with MG during 2001-2003 as the study cohort and 815 randomly selected pregnant women as a comparison cohort. Conditional logistic regression analyses were performed.

RESULTS

The results showed that, although these patterns did not reach a statistically significant level, mothers with MG had higher percentages of LBW (6.8%, vs. 5.6%), SGA (17.8%, vs. 14.1%) and cesarean deliveries (44.8%, vs. 37.4%), except for preterm births (8.1%, vs. 8.1%). After adjusting for highest maternal education level, marital status, family monthly income and infant gender and parity, the odds ratios (OR) of LBW, preterm birth, SGA infants, and cesarean delivery for mothers with MG were 1.19 (95% CI = 0.60-2.38), 1.00 (95% CI = 0.54-1.87), 1.30 (95% CI = 0.83-2.04), and 1.33 (95% CI = 0.94-1.88), respectively, as compared to unaffected mothers.

CONCLUSIONS

We conclude that there were no statistically significant differences in the risk of having preterm, LBW, SGA infants and cesarean deliveries between women with and without MG.

Autoimmune myasthenia gravis: emerging clinical and biological heterogeneity

Acquired myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction in which patients experience fluctuating skeletal muscle weakness that often affects selected muscle groups preferentially. The target of the autoimmune attack in most cases is the skeletal muscle acetylcholine receptor (AChR), but in others, non-AChR components of the neuromuscular junction, such as the muscle-specific receptor tyrosine kinase, are targeted. The pathophysiological result is muscle endplate dysfunction and consequent fatigable muscle weakness. Clinical presentations vary substantially, both for anti-AChR positive and negative MG, and accurate diagnosis and selection of effective treatment depends on recognition of less typical as well as classic disease phenotypes. Accumulating evidence suggests that clinical MG subgroups might respond differently to treatment. In this Review, we provide current information about the epidemiology, immunopathogenesis, clinical presentations, diagnosis, and treatment of MG, including emerging therapeutic strategies.

Racial differences in myasthenia gravis in Alabama

Demographic, clinical, and laboratory features were compared in 235 white and African-American (AA) patients with myasthenia gravis (MG) at the University of Alabama at Birmingham Neuromuscular Disease Clinic from May 2003 to January 2008. Seventy nine percent of patients were white. Acetylcholine receptor antibody was positive in 71% of white patients and in 59% of AA. In patients with seronegative generalized MG, the rate of positive muscle-specific tyrosine kinase antibody (MuSK-Ab) was significantly higher in AA than it was in whites (50% in AA vs. 17% in whites). Ocular MG was seronegative in 75% of AA patients. In AA, MG occurred earlier and more frequently in females, whereas, in whites, disease onset was later and more common in males. Another significant difference was a higher percentage of abnormality on repetitive nerve stimulation in AA. There was also a tendency for more severe forms of MG in AA. There are racial differences in MG between whites and AA in Alabama. These racial differences highlight the need to study biological factors in the pathogenesis of MG and to assess different approaches in diagnosis and treatment.

Ocular myasthenia: diagnostic and treatment recommendations and the evidence base

PURPOSE OF REVIEW

Increasing rigor is being applied to medical decision making, but myasthenia gravis, commonly considered the best understood autoimmune disorder from a pathophysiological basis, lags other disciplines in the evidence base used to make clinical decisions. The review attempts to provide a focused, practical guideline for the diagnosis and treatment of ocular myasthenia within the limits of largely retrospective case series and expert opinion.

RECENT FINDINGS

Confirmation of clinical diagnosis continues to be challenging for ocular myasthenia. Despite the recognition of a new autoantigen, the muscle-specific kinase protein in generalized myasthenia gravis, it has been found to be only rarely identified in ocular myasthenia patients and therefore the majority of patients lack detectable autoantibodies and confirmation of a neuromuscular transmission disorder relies on specialized testing of single-fiber electromyography. The visual compromise of ocular myasthenia responds poorly to nonpharmacological and cholinesterase inhibitor therapy, and although corticosteroids are thought to be extremely effective, their toxicity is poorly defined in ocular myasthenia patients and whether they reduce the risk of development of generalized disease is not known.

SUMMARY

Rigorous clinical trials or large databases with outcome assessments are necessary in order to allow development of rational treatment strategies.

Clinical efficacy and cytokine network-modulating effects of tacrolimus in myasthenia gravis

To clarify the long-term efficacy, safety and the cytokine network-modulating effects of tacrolimus in myasthenia gravis, medical records of 86 newly diagnosed consecutive patients and nine steroid-dependent patients were retrospectively reviewed, and peripheral blood mononuclear cells (PBMC) were cultured for the cytokine profile. Steroid reduction effects were observed by using tacrolimus, and no serious adverse effects were observed. The culture study showed reduced IL-12, IL-17, IFN-gamma, GM-CSF, TNF-alpha and MIP-1beta, and elevated IL-10 in the PBMC from patients who received tacrolimus, which suggests inhibition of T cells and macrophages, and enhancement of type 1 regulatory T cells.

Myasthenia gravis

Myasthenia gravis (MG) is a rare, autoimmune neuromuscular junction disorder. Contemporary prevalence rates approach 1/5,000. MG presents with painless, fluctuating, fatigable weakness involving specific muscle groups. Ocular weakness with asymmetric ptosis and binocular diplopia is the most typical initial presentation, while early or isolated oropharyngeal or limb weakness is less common. The course is variable, and most patients with initial ocular weakness develop bulbar or limb weakness within three years of initial symptom onset. MG results from antibody-mediated, T cell-dependent immunologic attack on the endplate region of the postsynaptic membrane. In patients with fatigable muscle weakness, the diagnosis of MG is supported by: 1. pharmacologic testing with edrophonium chloride that elicits unequivocal improvement in strength; 2. electrophysiologic testing with repetitive nerve stimulation (RNS) studies and/or single-fiber electromyography (SFEMG) that demonstrates a primary postsynaptic neuromuscular junctional disorder; and 3. serologic demonstration of acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK) antibodies. Differential diagnosis includes congenital myasthenic syndromes, Lambert Eaton syndrome, botulism, organophosphate intoxication, mitochondrial disorders involving progressive external ophthalmoplegia, acute inflammatory demyelinating polyradiculoneuropathy (AIDP), motor neuron disease, and brainstem ischemia. Treatment must be individualized, and may include symptomatic treatment with cholinesterase inhibitors and immune modulation with corticosteroids, azathioprine, cyclosporine, and mycophenolate mofetil. Rapid, temporary improvement may be achieved for myasthenic crises and exacerbations with plasma exchange (PEX) or intravenous immunoglobulin (IVIg). Owing to improved diagnostic testing, immunotherapy, and intensive care, the contemporary prognosis is favorable with less than five percent mortality and nearly normal life expectancy.

Available treatment options for the management of Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome is a rare, but reasonably well-understood, antibody-mediated autoimmune disease that is caused by serum auto-antibodies and results in muscle weakness and autonomic dysfunction. One half of the patients have an idiopathic form, the other half a tumour-associated form of the disease. Three randomised trials and a large number of smaller clinical studies have resulted in a number of drugs becoming available for the treatment of Lambert-Eaton myasthenic syndrome. Several drugs are available for the symptomatic treatment of the disease, including guanidine, aminopyridines or acetylcholinesterase inhibitors. Other therapies aim to deplete the serum autoantibodies or to suppress the immune system. For this purpose, immunomodulating strategies, such as intravenous immunoglobulins or plasmapheresis, or several immunosuppressive agents are available. Chemotherapy has successfully ameliorated the course of disease in Lambert-Eaton myasthenic syndrome patients with an underlying tumour.