Epidemiologic evidence for a changing natural history of myasthenia gravis

Myasthenia gravis in a patient with pauciarticular juvenile chronic arthritis

There have been reported cases of children with histories of pauciarticular juvenile chronic arthritis (JCA) later developing myasthenia gravis (MG) as young adults. This is intriguing because it had been considered rare to diagnose a second autoimmune disease in a patient with pauciarticular JCA, unlike in those with adult-onset rheumatoid arthritis. We report a case of MG in a 20-year-old woman with a history of pauciarticular JCA. She presented with bilateral ptosis, weakness, and a history of dysphagia. The diagnosis was confirmed with positive serum acetylcholine receptor antibodies (2000 nm/L) and electromyography showing a decremental response to repetitive muscle stimulation. The patient's inflammatory arthritis was quiescent at diagnosis. The patient underwent a surgical thymectomy and was treated with pyridostigmine, intravenous immunoglobulin, and corticosteroids with a fluctuating clinical course. Previous cases have been reported of MG associated with this subtype of JCA, suggesting a connection in autoimmune pathology. The earlier recognition and management of MG in a patient with pauciarticular JCA presenting with weakness may improve the prognosis of this disease.

Epidemiology of myasthenia gravis with anti-muscle specific kinase antibodies in The Netherlands

The epidemiology of myasthenia gravis subtypes and the frequency of antibodies to muscle-specific kinase (MuSK) was studied in patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies who had an onset of symptoms between 1990 and 2004 in a well-defined region in The Netherlands. The nationwide prevalence and incidence of myasthenia gravis with anti-MuSK antibodies were also studied. MuSK antibodies were found in 22% of patients with generalised myasthenia gravis without anti-acetylcholine receptor antibodies. Nationwide, 35 patients with MuSK myasthenia gravis were identified, yielding a prevalence of 1.9 per million (95% confidence interval (CI) 1.22 to 2.59) and an annual incidence 0.10 per million person-years (95% CI 0.06 to 0.14).

Comparison of the histological and immunohistochemical features of the thymus in young- and elderly-onset myasthenia gravis without thymoma

We performed histological and immunohistochemical analyses of the removed thymuses from 20 elderly (onset age > 60 years) and 23 young (onset age < 40 years) patients with myasthenia gravis (MG) who tested positive for serum anti-acetylcholine receptor (AChR) antibodies, but who did not have associated thymoma. In the elderly group, nine (45%) patients had accumulations of lymphocytes, indicating an atrophied thymus with loss of the basic structure. The elderly MG patients with atrophied thymic tissues had higher titres of anti-AChR antibody (59.6+/-81.0 nmol/L) than those with adipose infiltration of the thymus alone (20.1+/-20.9 nmol/L). In immunohistochemical studies using image analysis, both young patients and elderly patients with atrophied thymic tissues were found to have significantly higher levels of CD20 than age-matched controls (p < 0.005). Atrophied thymic tissues, often seen immunohistochemically in young MG patients, may also be found in elderly patients, particularly in those with high titres of the anti-AChR antibody, even though adipose infiltration is marked in these patients.

Ocular myasthenia: diagnosis, treatment, and pathogenesis

BACKGROUND

Although myasthenia gravis (MG) is often considered the best-understood autoimmune disorder and effective treatments have controlled life-threatening complications, the pathogenesis of ocular myasthenia (OM) remains enigmatic, and its clinical consequences offer therapeutic challenges.

REVIEW SUMMARY

About half of patients with MG present with visual complaints of droopy eyelids or double vision, and many will remain with purely ocular muscle weakness without generalized weakness, defined as OM. OM may be confused with disorders of the brainstem, ocular motor nerves, and eye muscles. Frustrating for the clinician, confirmatory tests such as the edrophonium test, serum acetylcholine receptor antibodies, and standard electrodiagnostic evaluations may fail to positively identify the clinical suspicion of OM. Patients may derive relief from nonpharmacologic interventions and cholinesterase inhibitors, but most will desire better symptom control with corticosteroids or need other immunosuppression. Early corticosteroid therapy may reduce the probability of generalization of the disease. The reasons for ocular muscle involvement by OM include physiologic and cellular properties of the ocular motor system and the unique immunology of OM, which, when better understood, will lead to novel treatments.

CONCLUSIONS

OM is a challenging disorder for the clinician and scientist, with both learning from the other for the betterment of the patient. The future requires answers to why the ocular muscles are so frequently involved by MG, whether the generalization of the disease may be limited by early corticosteroid treatment, and what treatment options may be developed which will improve symptoms without long-term complications.

Causes of death among patients with myasthenia gravis in Norway between 1951 and 2001

OBJECTIVE

This study investigated the causes of death among patients with myasthenia gravis (MG), with emphasis on respiratory tract and cardiac disease.

METHODS

The Norwegian Cause of Death Register contains information on all deaths among Norwegian citizens. In total, 249 deceased patients with MG were identified (1951-2001). These were compared with 1245 controls deceased in the same period and matched for sex and year of birth.

RESULTS

The death certificates of patients with MG had a significantly higher occurrence of respiratory tract disease as cause of death than controls (28.1% v 20.9%, p = 0.012). The difference was most pronounced for male patients, for patients dying between 30 and 69 years of age, and for deaths occurring before 1996. For cardiac disease there was a significantly lower occurrence among patients with MG than among controls at 50-69 years of age, for both men (19.4% v 52.0%, p = 0.001) and women (14.6% v 29.6%, p = 0.036). Age and year of death were important determinants for the causes of death, but could not account for the differences between the patients with MG and controls.

CONCLUSIONS

This study shows that patients with MG dying between 1951 and 1995 had a higher occurrence of respiratory tract disease listed as cause of death than had a matched control group. The lack of difference after 1995 probably reflects improved treatment of MG and its complications. The reduced occurrence of cardiac disease among patients with MG is probably explained by competing factors (respiratory tract disease) causing death.

Myasthénie du sujet âgé : analyse rétrospective de 23 observations

PURPOSE

There is evidence that myasthenia gravis is substantially underdiagnosed in older people, for which diagnosis and treatment may be difficult.

METHOD

We report on a series of 23 cases of myasthenia gravis diagnosed after the age of 65. Diagnosis was ascertained by compatible symptoms, associated with electrophysiological evidence and/or presence of antibodies to the acetylcholine receptor (AchRAb) and/or positive prostigmine test.

RESULTS

Twelve female and 11 male patients were identified, with a mean age of 77 (range: 66-89). Initial symptoms were ocular in 8 cases (35%), bulbar and ocular in 9 cases (39%), generalized in 6 cases (26%). Diagnosis was delayed in many patients (mean delay 31+/-47 months). Prostigmine test was positive in 16 cases (100%), AchRAb were positive in 19/23 cases (83%). Only one thymoma was found. Other diagnoses than myasthenia gravis, mainly stroke, were often considered. Treatment with anticholinesterase drugs, prescribed in all cases, has been able to control symptoms in only 3 cases. Corticosteroids were used in 10 cases, azathioprine or mycophenolate mofetil in 14 cases, intravenous immunoglobulins in 8 cases, and plasma exchanges in 2 cases. Thymectomy was performed on one patient with thymoma. Three patients were hospitalized in intensive care units for several weeks, and 3 patients died from their myasthenia.

CONCLUSION

Diagnosis of myasthenia gravis is often missed or delayed in the elderly, because of a broad differential diagnosis in older people, and because the high incidence of the disease in middle and old age is often overlooked. The outcome of myasthenia gravis in older people is far from simple, and immunomodulation proves to be necessary in most cases. However, quality of life of surviving patients appears good.

Increase in incidence of elderly-onset patients with myasthenia gravis in Nagano Prefecture, Japan

OBJECTIVES

In European countries and the United States the incidence of elderly-onset myasthenia gravis (MG) has recently been increasing. To investigate whether the incidence of the elderly-onset MG has increased in Nagano Prefecture of Japan, we divided the patients into young and elderly groups, and retrospectively examined their incidence.

PATIENTS AND METHODS

On the basis of two-step questionnaires sent to hospitals and the patient list of the intractable disease registration system in Nagano Prefecture we studied 213 MG patients diagnosed between 1982 and 2001. This 20-year period was divided into 4 five-year terms, and the incidence of MG in young- (younger than 65) and elderly-onset (65 or older) groups was investigated separately for each term.

RESULTS

The ratio of the elderly-onset group showed a significantly positive correlation with terms irrespective of associated thymoma (r=0.98, p<0.05). There was a significant difference in the mean onset age among the 4 terms (p<0.005). The standardized incidence of MG gradually increased in both young- and elderly-onset groups as well as in the whole age range. The elderly group showed a particularly high incidence in females (12.01/million/year) and in patients without thymoma (8.78/million/year) in the final five years.

CONCLUSIONS

We confirmed that the incidence of elderly-onset MG has recently been increasing in the Nagano Prefecture. Since the change of the age distribution in this district is almost identical to that of the whole country, the incidence of MG might have been increasing in Japan as a whole, particularly in the elderly population.

Retrospective analyses of clinical features and therapeutic outcomes in thymectomized patients with myasthenia gravis at Shinshu University

OBJECTIVES

Thymectomy has become recognized as an integral element in the treatment of patients with myasthenia gravis (MG). Although the incidence of elderly-onset MG has recently been increasing, there is little data demonstrating the efficacy and complications of thymectomy in this population. To clarify this point, we divided the thymectomized patients with MG into young and elderly groups, and retrospectively examined their clinical features and therapeutic outcomes.

PATIENTS AND METHODS

We reviewed 57 MG patients who had been admitted to our hospital between 1988 and 2002. The patients were classified into young (younger than 60) and elderly (60 or older) groups according to the age of onset, and the therapeutic outcomes of thymectomy were evaluated using myasthenic severity scales and the duration from operation to discharge.

RESULTS

Myasthenic severity scales significantly improved after thymectomy in the elderly group both with (p<0.005) and without thymoma (p<0.05) compared with before. With regard to the duration from thymectomy to discharge, no significant difference could be found between the young and elderly groups, irrespective of associated thymoma. There were no serious complications during and after thymectomy in either the young or the elderly group.

CONCLUSIONS

Despite various possible complications due to aging, thymectomy should be actively considered also in the treatment of elderly MG patients because it can reliably and safely improve myasthenic symptoms in combination with immunosuppressive agents, including corticosteroid.

Clinical evaluation and management of myasthenia gravis

Myasthenia gravis (MG) is a syndrome of fluctuating skeletal muscle weakness that worsens with use and improves with rest. Eye, facial, oropharyngeal, axial, and limb muscles may be involved in varying combinations and degrees of severity. Its etiology is heterogeneous, divided initially between those rare congenital myasthenic syndromes, which are genetic, and the bulk of MG, which is acquired and autoimmune. The autoimmune conditions are divided in turn between those that possess measurable serum acetylcholine receptor (AChR) antibodies and a smaller group that does not. The latter group includes those MG patients who have serum antibodies to muscle-specific tyrosine kinase (MuSK). Therapeutic considerations differ for early-onset MG, late-onset MG, and MG associated with the presence of a thymoma. Most MG patients can be treated effectively, but there is still a need for more specific immunological approaches.

The epidemiology of myasthenia gravis

Population-based studies of the epidemiology of myasthenia gravis (MG) have been conducted for over 50 years. Over that time, there has been a clear trend towards an increase in the reported prevalence of the disease. In recent years, there has also been an interest in determining a reasonably accurate estimate of the number of MG patients in the United States. Current estimates place the prevalence at a high value of about 20 per 100,000. The year 2000 U.S. population estimate is slightly less than 280 million. A crude estimate of the number of MG patients derived from the population estimate and the reported prevalence from selected populations indicates that there are between 53,000 and 59,900 patients in the United States at this time. The age and ethnic distributions in the United States are evolving from those that were present when the majority of the population-based studies were done, and the distribution of severity of the disease may also have changed. Future studies of the epidemiology of MG should take these factors into account, and further research into the economic and quality-of-life impact of the disease in the population is needed.

A population based epidemiological study on myasthenia gravis in Estonia

OBJECTIVE

To describe the occurrence of myasthenia gravis in the Baltic area.

METHODS

Data were obtained from hospital files recorded during the period 1942 to 1996 from neurologists and the patient organisation. Survival data were checked with the Estonian Citizenship and Migration Board. Prevalence was determined on 1 January 1997. A questionnaire on the course of myasthenia gravis was sent to all the prevalent patients.

RESULTS

The size of the population surveyed was 1 462 130. The average annual incidence from 1970 to 1996 was 4.0 per million (women, 5.2; men, 2.6). The point prevalence was 99 per million (women, 133; men 59). The incidence in the younger age group (<50 years) was 3.4 per million (women, 4.8; men, 1.9) and in the older age group (>or=50 years), 5.5 (women, 5.9; men, 4.9). The prevalence ratio was twofold higher in the older age group (p<0.0001)-for men (p = 0.034) as well as for women (p<0.001).

CONCLUSIONS

Prevalence and incidence values of myasthenia gravis from Estonia are similar to those reported in most studies from Europe and north America. However, there seems to be a higher frequency in the elderly (>or=50 years) in Estonia.

Myasthenia gravis (MG): epidemiological data and prognostic factors

Data from 756 myasthenic patients were analyzed for diagnostic criteria, clinical aspects, and therapeutic approaches. The patients were followed up at our institution from 1981 to 2001. Clinical evaluation was performed according to the myasthenia gravis score adopted at our clinic. Clinical features of each patient (comprising demographic, clinical, neurophysiological, immunological, radiological, and surgical data, as well as serial myasthenia gravis scores) were filed in a relational database containing more than 7000 records. Clinical efficacy and variables influencing outcome were assessed by life-table methods and Cox proportional hazards regression analysis. Complete stable remission, as defined by the Task Force of the Medical Scientific Advisory Board of the Myasthenia Gravis Foundation of America, was the end point for good prognosis. Four hundred and ninety-nine patients (66%) were female and 257 (34%) were male. Mean follow-up was 55.1 +/- 48.1 months. Onset of symptoms peaked in the third decade in females, whereas the male distribution was bimodal with peaks in the third and sixth decades. Modality of myasthenia gravis presentation was as follows: ocular, 39.3%; generalized, 28.5%; bulbar, 31.3%; and respiratory, 0.8%. Thymectomy was carried out on 63.7% of our patients by different approaches: (1) transcervical; (2) transsternal; (3) video-thoracoscopic mini-invasive surgery. The last approach has been preferentially used in more recent years and accounted for 62.4% of the thymectomized myasthenia gravis population. Univariate analysis and Kaplan-Meier analysis showed that variables such as sex (female), age at onset (below 40 years), thymectomy, and histological diagnosis of thymic hyperplasia were significantly associated with complete stable remission, whereas on multivariate analysis only age at onset below 40 years and thymectomy were confirmed.

Chiropractic care of a pediatric patient with myasthenia gravis

OBJECTIVE

To describe the chiropractic care of a pediatric patient with complaints associated with myasthenia gravis. Clinical features A 2-year-old girl was provided chiropractic care at the request and consent of her parents for complaints of ptosis and generalized muscle weakness (ie, lethargy), particularly in the lower extremities. Prior to entry into chiropractic management, magnetic resonance imaging of the brain and acetylcholine receptor antibody tests were performed with negative results. However, the Tensilon test was positive and the diagnosis of myasthenia gravis was made by a pediatrician and seconded by a medical neurologist. Intervention and outcome The patient was cared for with contact-specific, high-velocity, low-amplitude adjustments to sites of vertebral subluxation complexes in the upper cervical and sacral spine. The patient's response to care was positive and after 5 months of regular chiropractic treatment her symptoms abated completely.

CONCLUSION

There are indications that patients suffering from disorders "beyond low back pain" as presented in this case report may derive benefits from chiropractic intervention/management.

Treatment of myasthenia gravis: current practice and future directions

Myasthenia gravis is the best understood of the autoimmune diseases and a number of treatments are currently used to produce clinical improvement. However, due to the scarcity of evidence-based and comparative data, there is still no consensus on many therapeutic issues. Even a widely accepted treatment like thymectomy has never been proven effective by a well-designed trial. These are just some of the unanswered questions: What is the best treatment algorithm and safest long-term management of myasthenia gravis? What patients are likely to benefit from thymectomy? How long should myasthenia gravis patients be treated? Is it possible to discontinue immunotherapy once remission has been achieved? What are the risks associated with long-term immunosuppression? In this article, we review current therapeutic strategies and these unresolved questions about myasthenia gravis treatment.

Myasthenia gravis

BACKGROUND

In myasthenia gravis (MG), the prototypic autoimmune disease, antibodies against acetylcholine receptors impair neuromuscular transmission and produce weakness. Although recognized for several hundred years, it has only been over the last three decades that effective treatments have become available for MG.

REVIEW SUMMARY

This review summarizes the principles of normal neuromuscular transmission, the clinical features of MG, and the tests available for its diagnosis. The current treatments for MG are discussed, including possible mechanisms of action and a discussion of potential adverse effects. When available, evidence-based justification for individual treatment options is given, and areas of controversy identified.

CONCLUSIONS

Significant improvements in the diagnosis and management of MG have been made over the last several decades. The available treatments either improve neuromuscular transmission directly, or suppress or modulate the pathogenic immune response in MG. Treatment is highly individualized and must take into account the severity of disease, the presence of other diseases, and the kinetics of response for the available treatments. This requires detailed knowledge of the mechanisms of action and possible adverse effects for each treatment. However, despite an optimistic outlook with modern treatment, the management of MG continues to be plagued by lack of efficacy in some, and significant adverse effects in most MG patients.

Advances in myasthenia gravis

Recent advances in the diagnosis and treatment of acquired myasthenia gravis (MG) are reviewed. Increased awareness about the need for more uniform methods of reporting treatment trials for MG has prompted systematic review of the literature and inspired an effort to develop better classifications and disease-specific outcome measures. New antibodies have been discovered in patients with seronegative MG, possibly defining an immunologically distinct form of the disease. A new immunosuppressant, mycophenolate mofetil, may be an additional and safe option in the treatment of MG. Other work supports the possibility of developing a vaccine against MG suitable for trial in humans.

Myasthenia gravis and Waldenström's macroglobulinemia: a case report and review of the literature

An elderly man with ocular type myasthenia gravis (MG) was found to have monoclonal gammopathy (IgM). Waldenström's macroglobulinemia (WM) was proven later. This is the second case report of MG associated with WM. However, this case is unique due to the presence of anti-acetylcholine receptor (anti-AChR) antibody (IgG). MG is considered to be an autoimmune disease and WM an immunoproliferative disorder. The association of MG and WM is not clear.

Epidemiology of seropositive myasthenia gravis in Greece

OBJECTIVES

To study the epidemiological characteristics of myasthenia gravis in Greece.

METHODS

A population based study was carried out of seropositive myasthenia gravis in Greece for the period from 1 January 1983 to 30 June 1997; 843 patients were studied.

RESULTS

The average annual incidence for the period 1992-7, for which the database is complete, was 7.40/million population/year (women 7.14; men 7.66). On 1 July 1997, there were 740 prevalent cases. The point prevalence rate was 70.63/million (women 81.58; men 59.39). The average overall annual mortality rate in the patients was 0.67/million population (women 0.53; men 0.82), and the mortality rate attributed to myasthenia gravis was 0.43/million population (women 0.41; men 0.45). The average age at onset was 46.50 years (women 40.16; men 54.46), and the mean age of the prevalent patients was 52.58 (women 47.65; men 59.48). The women:men incidence ratio was 1:1.04, and the prevalence ratio was 1.41:1. It is predicted that the prevalence and women: men prevalence ratio would increase if the patient list included all patients with a date of onset before 1983.

CONCLUSIONS

The largest epidemiological study ever performed on myasthenia gravis is presented. The most important epidemiological indexes are provided.

Myasthenia gravis on the Dutch antilles: an epidemiological study

We carried out an epidemiological study on the prevalence and annual incidence of myasthenia gravis on tropical islands Curaçao and Aruba in the period 1980-1995. Twenty-one patients (seven men and 14 women) were identified. The point prevalence increased from 29 per million in 1980 to about 70 per million in 1990-1995; the annual incidence over the total period was 4.7 per million. The female:male ratio was 2:1; purely ocular cases (2/21) comprised 9.5% and thymomas (4/21), 19%. These data are in accordance with most other epidemiological studies in non-tropical areas. No other studies on myasthenia gravis in tropical areas have been reported.

Clinical characteristics and prognosis of myasthenia gravis in older people

OBJECTIVES

To investigate the characteristics of myasthenia gravis (MG) in older people and to evaluate the benefits of immunosuppressive treatments at this age.

BACKGROUND

Myasthenia gravis in older adults has not been extensively studied. In patients with disease onset after the age of 60, treatment mainly relies on medical therapy because thymectomy is generally not performed unless a thymoma is present.

METHODS

Of 837 myasthenic patients followed since 1978, we identified 172 cases with onset after age 60. All patients were treated with anticholinesterases. In the decade from 1978 to 1988, immunosuppressive therapy was performed mainly with corticosteroids (prednisone); since 1989, azathioprine alone or, more often, associated with prednisone, has been increasingly used in MG patients. Long-term outcome was evaluated in 149 cases with follow-up longer than 1 year. Remission, pharmacological remission, and marked improvement with reduction in drug dosage were considered good results.

RESULTS

Patients older than age 60 at onset of the disease were 20.5% of our series, male/female ratio was 1.9, age at onset ranged from 61 to 86 years, 87.2% patients had generalized disease, thymoma was detected in 37 patients (21.5%). Of 149 cases with sufficient follow-up data, 9 were in remission, 111 achieved good results, 3 died of MG, and 120 required immunosuppressive therapy at some time. Sixty-seven patients had been treated with prednisone for 0.5-16 years (mean, 5 years); good results were recorded in 51 patients (76.1%) and severe side effects in 12 (17.9%). Forty-six patients had received combined therapy with prednisone and azathioprine for 1 to 12 years (mean, 3.9 years); good results were recorded in 41 patients (89.1%) and severe side effects in six (19.5%). Seven patients had been treated with azathioprine alone for 1 to 4 years (mean, 2.3 years) with good results in five and with no side effects.

CONCLUSIONS

The prognosis of MG in older people seems to be favorable, although full remission is rare and MG weakness, treatment side effects, and associated thymoma can contribute to mortality rate. In our experience, the combined therapy with prednisone and azathioprine was more effective than prednisone alone, and steroid-related side effects were more frequent than those related to azathioprine.

Different age-related effects of thymectomy in myasthenia gravis: role of thymoma, zinc, thymulin, IL-2 and IL-6

Different age-related immune pathogenetic mechanisms in myasthenia gravis (MG) have been suggested because of restoration after thymectomy (Tx) of altered zinc, thymulin (TH) and T-cell subsets exclusively in early-onset patients (younger <50 years), not in late-onset patients (older >50 years). In this context interleukin-2 (IL-2), interleukin-6 (IL-6) and thymoma are crucial because both involved in MG pathogenesis and correlated with acetylcholine receptors (AchRs) Ab production. Moreover, IL-2 and IL-6 are zinc-dependent, are altered in aging and related with zinc and TH age-dependent declines. Moreover, zinc is relevant for immune efficiency. In order to confirm these different age-related pathogenetic mechanisms further, the role of thymoma, zinc, TH, IL-2 and IL-6 is studied in MG patients with generalized MG with and without thymoma before and 1 month and 1 year after Tx. The high IL-2, IL-6, zinc, and AChR Ab levels observed before Tx are significantly correlated each other in younger MG patients (<50 years) independently by thymoma and in older MG patients (>50 years) with thymoma. No correlations exist in older MG patients without thymoma. Thymulin is not correlated with other parameters considered to be both in younger and older MG patients independently by the thymoma. Thymectomy restores zinc; immune parameters and AChR Ab are exclusively in the younger group, not in the older one. These findings suggest that IL-2 and IL-6, via zinc, rather than TH, may be involved in different age-related pathogenetic mechanisms mainly in early-onset MG. By contrast, thymoma may be involved in MG etiology in late-onset representing, as such, a useful discriminant tool for MG etiology between early and late-onset MG patients. Because autoimmune phenomena may rise in aging, a parallelism with altered immune functions during aging is discussed.

Myasthenia gravis: a population based epidemiological study in Cambridgeshire, England

OBJECTIVES

To perform a comprehensive survey of myasthenia gravis in the county of Cambridgeshire, England, establishing contemporary epidemiological data.

METHODS

Cases were ascertained from multiple sources. Prevalent patients were visited and assessed by means of a standardised questionnaire and examination complemented by review of medical case notes.

RESULTS

One hundred cases were identified in a population of 684000 (prevalence 15 per 100000 population, 95% confidence intervals (95% CIs) 12-18). Thirty eight new diagnoses were made over a five year period providing an incidence of 1.1/100000 population/year. The sex ratio was 2:1 F:M. After a mean follow up of 11.7 years, symptomatic disease was still restricted to ocular muscles in 25 patients. Thirty four of 100 patients underwent thymectomy a mean of 0.8 years after presentation, and a thymoma was present in 12. Highest remission rates were seen in patients presenting with generalised disease who underwent thymectomy but did not have a thymoma (27%). Cosegregation of an additional autoimmune disease occurred in 27 patients and in 24/49 (49%) women with onset<50 years of age.

CONCLUSIONS

This, the second highest reported prevalence for myasthenia, is likely to be the result of optimum case ascertainment, increased disease duration, application of complex diagnostic tests, and the impact of an aging population leading to a relative increase in the prevalence of ocular myasthenia.