Response of thymectomy: clinical and pathological characteristics among seronegative and seropositive myasthenia gravis patients

Poor responses and adverse outcomes of myasthenia gravis after thymectomy: Predicting factors and immunological implications

Myasthenia gravis (MG) has been recognized as a series of heterogeneous but treatable autoimmune conditions. As one of the indispensable therapies, thymectomy can achieve favorable prognosis especially in early-onset generalized MG patients with seropositive acetylcholine receptor antibody. However, poor outcomes, including worsening or relapse of MG, postoperative myasthenic crisis and even post-thymectomy MG, are also observed in certain scenarios. The responses to thymectomy may be associated with the general characteristics of patients, disease conditions of MG, autoantibody profiles, native or ectopic thymic pathologies, surgical-related factors, pharmacotherapy and other adjuvant modalities, and the presence of comorbidities and complications. However, in addition to these variations among individuals, pathological remnants and the abnormal immunological milieu and responses potentially represent major mechanisms that underlie the detrimental neurological outcomes after thymectomy. We underscore these plausible risk factors and discuss the immunological implications therein, which may be conducive to better managing the indications for thymectomy, to avoiding modifiable risk factors of poor responses and adverse outcomes, and to developing post-thymectomy preventive and therapeutic strategies for MG.

Robotic thymectomy for myasthenia gravis surgical techniques and outcomes

Myasthenia gravis (MG) is an autoimmune disorder in which antibodies are produced against post-synaptic acetylcholine receptors, thereby causing impairment of neuromuscular transmission. Diagnosis of MG is confirmed with the AChR antibody test and via an Electromyography. Although medical treatment with acetylcholinesterase inhibitors remains the main treatment of MG, in recent years thymectomy has become an integral part of the treatment algorithm. Numerous factors such as the Patient’s age, presence of AChR antibodies, or MuSK antibody, the severity of disease affect the decision of preforming the thymectomy. Historically thymectomy was preformed via sternotomy associated with significant morbidity. Advancement in the minimally invasive approaches to thymic resection has led to more acceptance of thymectomy in the management of MG. Among these approaches, robotic thymectomy is gaining popularity across the globe due to the unique advantages of the robotic platform like 3D visibility, enhanced dexterity, and wrist like articulating movements of instruments. This has led to less post-operative pain and morbidity; faster recovery and shorter hospital stay. Successful treatment of MG requires a multi-modality approach, which has led to the formation of MG teams in most academic centers, comprising of a specialist neurologist, intensivist, and thoracic surgeon. In this article, we describe the techniques and outcomes of the robotic thymectomy for MG.

[The value of thymectomy in the treatment of non-thymomatous myasthenia gravis]

The value of thymectomy in the treatment of non-thymomatous myasthenia gravis has been controversially discussed. The relatively low incidence and prevalence of this disease, the inconsistent documentation in various studies and the necessity of a long-term follow-up to assess the therapeutic effects has made the generation of valid data difficult. The publication in 2016 of the MGTX trial in the New England Journal of Medicine delivered the first randomized controlled data in which patients aged 18-65 years with generalized myasthenia gravis and positive for acetylcholine receptor antibodies showed a significant benefit after surgical resection of the thymus via median sternotomy. Despite a lack of validation of the advantages of thymectomy by minimally invasive surgery from randomized controlled studies, this technique seems to positively influence the outcome of certain patient groups in a similar way. Video-assisted thoracoscopic surgery (VATS) and robotic-assisted thoracic surgery (RATS) using subxyphoidal and transcervical access routes showed not only esthetic advantages but also showed no relevant inferiority in the influence on clinical outcomes of myasthenia gravis compared to median sternotomy; however, not only the benefits and the esthetic results show differences but also the advantages in the various subtypes of myasthenia gravis show divergent prospects of success with respect to remission. The clinical spectrum of myasthenia is heterogeneous with respect to the occurrence of antibodies, the body region affected and the age of the patient at first diagnosis. Ultimately, thymectomy is an effective causal treatment of myasthenia gravis.

Novel Treatments in Myasthenia Gravis

Myasthenia gravis (MG) is the prototypical autoimmune disorder caused by specific autoantibodies at the neuromuscular junction. Broad-based immunotherapies, such as corticosteroids, azathioprine, mycophenolate, tacrolimus, and cyclosporine, have been effective in controlling symptoms of myasthenia. While being effective in a majority of MG patients many of these immunosuppressive agents are associated with long-term side effects, often intolerable for patients, and take several months to be effective. With advances in translational research and drug development capabilities, more directed therapeutic agents that can alter the future of MG treatment have been developed. This review focuses on the aberrant immunological processes in MG, the novel agents that target them along with the clinical evidence for efficacy and safety. These agents include terminal complement C5 inhibitors, Fc receptor inhibitors, B cell depleting agents (anti CD 19 and 20 and B cell activating factor [BAFF)]inhibitors), proteosome inhibitors, T cells and cytokine based therapies (chimeric antigen receptor T [CART-T] cell therapy), autologous stem cell transplantation, and subcutaneous immunoglobulin (SCIG). Most of these new agents have advantages over conventional immunosuppressive treatment (IST) for MG therapy in terms of faster onset of action, favourable side effect profile and the potential for a sustained and long-term remission.

Autoimmune Pathology in Myasthenia Gravis Disease Subtypes Is Governed by Divergent Mechanisms of Immunopathology

Myasthenia gravis (MG) is a prototypical autoantibody mediated disease. The autoantibodies in MG target structures within the neuromuscular junction (NMJ), thus affecting neuromuscular transmission. The major disease subtypes of autoimmune MG are defined by their antigenic target. The most common target of pathogenic autoantibodies in MG is the nicotinic acetylcholine receptor (AChR), followed by muscle-specific kinase (MuSK) and lipoprotein receptor-related protein 4 (LRP4). MG patients present with similar symptoms independent of the underlying subtype of disease, while the immunopathology is remarkably distinct. Here we highlight these distinct immune mechanisms that describe both the B cell- and autoantibody-mediated pathogenesis by comparing AChR and MuSK MG subtypes. In our discussion of the AChR subtype, we focus on the role of long-lived plasma cells in the production of pathogenic autoantibodies, the IgG1 subclass mediated pathology, and contributions of complement. The similarities underlying the immunopathology of AChR MG and neuromyelitis optica (NMO) are highlighted. In contrast, MuSK MG is caused by autoantibody production by short-lived plasmablasts. MuSK MG autoantibodies are mainly of the IgG4 subclass which can undergo Fab-arm exchange (FAE), a process unique to this subclass. In FAE IgG4, molecules can dissociate into two halves and recombine with other half IgG4 molecules resulting in bispecific antibodies. Similarities between MuSK MG and other IgG4-mediated autoimmune diseases, including pemphigus vulgaris (PV) and chronic inflammatory demyelinating polyneuropathy (CIDP), are highlighted. Finally, the immunological distinctions are emphasized through presentation of biological therapeutics that provide clinical benefit depending on the MG disease subtype.

Thymectomy in Myasthenia Gravis

In recent years, thymectomy has become a widespread procedure in the treatment of myasthenia gravis (MG). Likelihood of remission was highest in preoperative mild disease classification (Osserman classification 1, 2A). In absence of thymoma or hyperplasia, there was no relationship between age and gender in remission with thymectomy. In MG treatment, randomized trials that compare conservative treatment with thymectomy have started, recently. As with non-randomized trials, remission with thymectomy in MG treatment was better than conservative treatment with only medication. There are four major methods for the surgical approach: transcervical, minimally invasive, transsternal, and combined transcervical transsternal thymectomy. Transsternal approach with thymectomy is the accepted standard surgical approach for many years. In recent years, the incidence of thymectomy has been increasing with minimally invasive techniques using thoracoscopic and robotic methods. There are not any randomized, controlled studies which are comparing surgical techniques. However, when comparing non-randomized trials, it is seen that minimally invasive thymectomy approaches give similar results to more aggressive approaches.

Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society

Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4(+) T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and

Two-year outcome of thymectomy with or without immunosuppressive treatment in nonthymomatous myasthenia gravis and its effect on regulatory T cells

BACKGROUND

Myasthenia gravis (MG) is the autoimmune disorder in which the thymus is considered the pathogenic organ. Thymectomy (TE) is a therapeutic option for MG and often ameliorates clinical symptoms.

METHODS

We evaluated clinical features and outcomes after TE in patients without thymoma and the influence of TE with or without concomitant immunotherapy on the CD4(+)CD25(+) regulatory T cell subpopulation of lymphocytes in peripheral blood in defined followed groups of nonthymomatous MG patients.

RESULTS

A total of 46 patients with generalized MG who underwent transsternal TE were identified. Neurologic outcomes after TE were favorable for the majority of patients mainly from the group treated with corticosteroids or combined immunosuppressive treatment. TEs with immunosuppressive treatment in MG patients were associated with increased percentages of CD4(+)CD25(+) cells (p<0.001). No significant change in the postoperative levels of CD4(+)CD25(+) cells was observed in thymectomized patients who preoperatively only received pyridostigmine. Also their clinical response to TE after 2 years of follow-up was worst of all followed groups.

CONCLUSIONS

The exact mechanism by which TE ameliorates symptoms of MG is yet not clear. These observations indicate that increased percentages of CD4(+)CD25(+) T cells in MG may be related to disease stability and that TE and synergistic effect with concomitant, continuing immunotherapy augmented the proportion of CD4(+)CD25(+) T cells. On the basis of our observations TE alone is not enough to increase the number of circulating CD4(+)CD25(+) regulatory T cells and to establish complete stable remission.

Update on juvenile myasthenia gravis

PURPOSE OF REVIEW

Juvenile myasthenia gravis is a relatively rare autoimmune neuromuscular disorder. The pathophysiology of juvenile myasthenia gravis is similar to that of adult myasthenia gravis, though there remain important differences regarding presentation and therapeutic options. We review the pathophysiology, clinical presentation, and treatment options for juvenile myasthenia gravis.

RECENT FINDINGS

Randomized clinical studies of myasthenia gravis have been carried out primarily in adult populations. As juvenile myasthenia gravis is rare, it has been difficult to collect prospective randomized controlled data to evaluate treatment outcomes and efficacy. A recent retrospective series suggests that, as in adult myasthenia gravis, thymectomy is a viable therapeutic option for selected cases of generalized juvenile myasthenia gravis. This is corroborated by the clinical experience of the authors in a referral center with a cohort of patients affected by juvenile myasthenia gravis over a number of years.

SUMMARY

Recent studies illustrate that some, but not all, adult research on myasthenia gravis is applicable to children and adolescents with juvenile myasthenia gravis. Adult research can inform pediatric studies, but should not be regarded as a substitute for dedicated research in those populations.

Overview of myasthenia gravis

Myasthenia gravis is an antibody-mediated disorder of neuromuscular transmission that is characterized by weakness and fatigue of voluntary muscles. Weakness may be ocular, bulbar, or generalized. Diagnostic evaluation of patients consists of bedside assessment, antibody testing, and electrophysiologic studies. Various therapeutic options are available, which consist of anticholinesterase inhibitors for symptomatic management, immunosuppressive agents as maintenance therapy, and thymectomy. Plasmapheresis and intravenous immunoglobulin are used in patients in crisis or those with rapidly worsening or refractory symptoms. In our article, we elaborate on key aspects of the epidemiology, pathogenesis, diagnostic evaluation, and therapeutic options for patients with myasthenia gravis.

Paraneoplastic syndromes of the neuromuscular junction: therapeutic options in myasthenia gravis, lambert-eaton myasthenic syndrome, and neuromyotonia

OPINION STATEMENT

Myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS) and neuromyotonia are neuromuscular transmission disorders occurring with or without associated malignancy. Due to the common antibody-mediated pathophysiology, immunosuppression has an important role in the treatment of each of these disorders. Symptomatic treatment is more variable. Pyridostigmine is first-line treatment in generalized MG. Response seems to be better in patients with acetylcholine receptor (AChR) antibodies than in patients with antibodies against muscle-specific tyrosine kinase (MuSK). Pyridostigmine can be sufficient in mild MG, although most patients need additional immunosuppressive therapy. If so, prednisolone is efficient in the majority of the patients, with a relatively early onset of clinical effect. High drug dosage and treatment duration should be limited as much as possible because of serious corticosteroid-related side effects. As long-term treatment is needed in most patients for sustainable remission, adding non-steroid immunosuppressive drugs should be considered. Their therapeutic response is usually delayed and often takes a period of several months. In the meantime, corticosteroids are continued and doses are tapered down over a period of several months. There are no trials comparing different immunosuppressive drugs. Choice is mainly based on the clinician's familiarity with certain drugs and their side effects, combined with patients' characteristics. Most commonly used is azathioprine. Alternatively, tacrolimus, cyclosporine A, mycophenolate mofetil or rituximab can be used. The use of cyclophosphamide is limited to refractory cases, due to serious side effects. Plasma exchange and intravenous immunoglobulin induce rapid but temporary improvement, and are reserved for severe disease exacerbations because of high costs of treatment. It is recommended that computed tomography (CT) of the thorax is performed in every AChR-positive MG patient, and that patients are referred for thymectomy in case of thymoma. In patients without thymoma, thymectomy can be considered as well, especially in younger, AChR-positive patients with severe disease. However, definite proof of benefit is lacking and an international randomized trial to clarify this topic is currently ongoing. When LEMS is suspected, always search for malignancy, especially small cell lung carcinoma with continued screening up to two years. In paraneoplastic LEMS, cancer treatment usually results in clinical improvement of the myasthenic symptoms. 3,4-Diaminopyridine is first-line symptomatic treatment in LEMS. It is usually well tolerated and effective. When immunosuppressive therapy is needed, the same considerations apply to LEMS as described for MG. Peripheral nerve hyperexcitability in neuromyotonia can be treated with anticonvulsant drugs such as phenytoin, valproic acid or carbamazepine. When response in insufficient, start prednisolone in mild disease and consider the addition of azathioprine. Plasma exchange or intravenous immunoglobulin is indicated in severe neuromyotonia and in patients with neuromyotonia combined with central nervous system symptoms, a clinical picture known as Morvan's syndrome.

Unilateral extended thoracoscopic thymectomy for nontumoral myasthenia gravis--a new standard

Myasthenia gravis (MG) is a heterogeneous disorder with a fluctuating, clinical, pathologic, and immunobiological picture. Today, it is believed that effective treatment of MG must include both immunosuppression and surgery. Thymectomy is recommended by neurologists for patients with nontumoral MG as an option to increase the probability of remission or improvement. Currently, thoracoscopic thymectomy is considered a good alternative to the standard open approach because of its higher rate of acceptance, low morbidity, and high efficacy, as measured by complete stable remission rates. We present a review of the experience of unilateral extended thoracoscopic thymectomy for nontumoral MG, a technique that could became a new standard in the complex management of MG treatment.

Surgical and neurologic outcomes after robotic thymectomy in 100 consecutive patients with myasthenia gravis

OBJECTIVE

Thymectomy is a well-defined therapeutic option for patients with myasthenia gravis; however, controversies still exist about the surgical approach, indication, and timing for surgery. We reviewed our experience reporting surgical and neurologic results after robotic thymectomy in patients with myasthenia gravis.

METHODS

Between 2002 and 2010, 100 patients (74 female and 26 male; median age, 37 years) underwent left-sided robotic thymectomy using the da Vinci robotic system (Intuitive Surgical, Inc, Sunnyvale, Calif). The Myasthenia Gravis Foundation of America classification was adopted for pre- and postoperative evaluation. Preoperative Myasthenia Gravis Foundation of America class was I in 10% of patients, II in 35% of patients, III in 39% of patients, and IV in 16% of patients.

RESULTS

Median operative time was 120 (60-300) minutes. No death or intraoperative complications occurred. Postoperative complications were observed in 6 patients (6%) (bleeding requiring blood transfusions in 3, chylothorax in 1, fever in 1, and myasthenic crisis in 1). Median hospital stay was 3 days (range, 2-14 days). Histologic analysis revealed 76 patients (76%) with hyperplasia, 7 patients (7%) with atrophy, 8 patients (8%) with small thymomas, and 9 patients (9%) with normal thymus; ectopic thymic tissue was found in 26 patients (26%). Clinical follow-up showed a 5-year probability of complete stable remission and overall improvement of 28.5% and 87.5%. Remission was significantly associated with preoperative I to II Myasthenia Gravis Foundation of America class (P = .02). A significant improvement rate was found in Myasthenia Gravis Foundation of America class I to II (P = .03) and AbAchR+ (P = .04). A high percentage of patients interrupted or reduced their medications.

CONCLUSIONS

Robotic thymectomy is a safe and effective procedure. We observed a neurologic benefit in a great number of patients. A better clinical outcome was obtained in patients with early Myasthenia Gravis Foundation of America class.

The predictive value of the presence of different antibodies and thymus pathology to the clinical outcome in patients with generalized myasthenia gravis

OBJECTIVES

To analyze the predictive value of anti-acetylcholine receptor antibodies (anti-AChR Ab) and anti-muscle specific kinase antibodies (anti-MuSK Ab), as well as the thymus pathology to the clinical outcome in patients with generalized myasthenia gravis (MG).

METHODS

We analyzed 138 patients with generalized MG, who were thymectomized and assayed for anti-AChR Ab and anti-MuSK Ab.

RESULTS

Anti-AChR Ab were detected in 84% of patients, while anti-MuSK Ab were present in 36% of the AChR Ab negative patients. Severe forms of the disease were more frequent in MuSK Ab positive, compared to the AChR Ab positive and complete seronegative patients. Thymic lymphoid follicular hyperplasia (LFH) was present in 60%, thymoma in 23%, atrophic thymus in 9% and the normal thymus in 8% of patients. LFH was more frequent among women, while thymoma and atrophic thymus were more frequent in men. The younger patients mainly had LFH and normal thymus, while thymoma and atrophic thymus were more frequent in older patients. The mildest clinical presentation was present in patients with normal thymus, while severe forms of the disease were registered in the patients with thymoma. The AChR Ab positive patients had more often LFH and thymoma, while within MuSK Ab positive patients atrophic thymus was most common.

CONCLUSION

The best disease outcome was observed in patients with normal thymus or LFH with anti-AChR Ab or without both types of antibodies.

Ten-year results of thoracoscopic unilateral extended thymectomy performed in nonthymomatous myasthenia gravis

OBJECTIVE

The aim of this study was to analyze the 10-year results of thoracoscopic unilateral extended thymectomy (TUET) performed in nontumoral myasthenia gravis according to the Myasthenia Gravis Foundation of America recommendations.

BACKGROUND DATA

Thoracoscopic unilateral extended thymectomy has the benefits of a minimally invasive approach. Previous data have shown promising midterm results but long-term results were lacking.

METHODS

Two hundred forty patients with nontumoral myasthenia gravis who underwent surgery between 1999 and 2009 were eligible for the study. The mean follow-up was of 67 months (range: 12-125), 134 patients completed follow-up assessments more than 60 months after TUET.

RESULTS

There were 39 males (16.3%) and 201 females (83.7%), with an age range from 8 to 60 years. The mean preoperative disease duration was 21.5 months. All patients underwent preoperative steroid therapy. Anticholinesterase drugs were required for 123 patients (51.3%), and immunosuppressive drugs were required for 87 (36.3%) patients. The pathologic findings were as follows: normal thymus in 13 patients (5.5%), involuted thymus in 65 patients (27%), and hyperplastic thymus in 162 patients (67.5%). The average weight of the thymus was 110 ± 45 g. Ectopic thymic tissue was found in 147 patients (61.3%). There was no mortality, and morbidity consisted of 12 patients (5%). Complete stable remission was achieved in 61% of the patients, and the cumulative probability of achieving complete stable remission was 0.88 at 10 years.

CONCLUSIONS

With zero mortality, low morbidity, and comparable long-term results to open surgery, TUET can be regarded as the best treatment option for patients undergoing surgery for myasthenia gravis.

Guidelines for treatment of autoimmune neuromuscular transmission disorders

BACKGROUND

Important progress has been made in our understanding of the autoimmune neuromuscular transmission (NMT) disorders; myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS) and neuromyotonia (Isaacs' syndrome).

METHODS

To prepare consensus guidelines for the treatment of the autoimmune NMT disorders, references retrieved from MEDLINE, EMBASE and the Cochrane Library were considered and statements prepared and agreed on by disease experts.

CONCLUSIONS

Anticholinesterase drugs should be given first in the management of MG, but with some caution in patients with MuSK antibodies (good practice point). Plasma exchange is recommended in severe cases to induce remission and in preparation for surgery (recommendation level B). IvIg and plasma exchange are effective for the treatment of MG exacerbations (recommendation level A). For patients with non-thymomatous MG, thymectomy is recommended as an option to increase the probability of remission or improvement (recommendation level B). Once thymoma is diagnosed, thymectomy is indicated irrespective of MG severity (recommendation level A). Oral corticosteroids are first choice drugs when immunosuppressive drugs are necessary (good practice point). When long-term immunosuppression is necessary, azathioprine is recommended to allow tapering the steroids to the lowest possible dose whilst maintaining azathioprine (recommendation level A). 3,4-Diaminopyridine is recommended as symptomatic treatment and IvIG has a positive short-term effect in LEMS (good practice point). Neuromyotonia patients should be treated with an antiepileptic drug that reduces peripheral nerve hyperexcitability (good practice point). For paraneoplastic LEMS and neuromyotonia optimal treatment of the underlying tumour is essential (good practice point). Immunosuppressive treatment of LEMS and neuromyotonia should be similar to MG (good practice point).

Somatostatin receptor scintigraphy in the follow-up of myasthenia gravis

To evaluate the potential value of somatostatin receptor scintigraphy (SRS) using 111In-DTPA (diethylenetriaminepenta acetic acid)-D-Phe1-octreotide (111In-pentetreotide) in patients with recurring or persisting symptoms of myasthenia gravis (MG), 14 consecutive cases with such supplemental receptor imaging during neurological routine follow-up were retrospectively evaluated in this study. All 14 patients underwent SRS in addition to chest computed tomography (CT). Mean follow-up after imaging was 34 months. Eight patients had previous thymectomy, and three patients were referred to surgery after scintigraphy and chest CT. SRS was positive in one of the 14 patients with local recurrence of thymoma and pleural invasion, and negative in the remaining 13 patients. CT was positive for thymoma in three patients, inconclusive in four patients and negative in seven patients. In conclusion, while SRS may be able to detect thymoma lesions including metastases, it seems of limited value in patients with inconspicuous CT findings. Our initial experience fails to point out a benefit of SRS in the management of persisting or recurring MG (with regard to detection of thymic disorders) compared to CT. Whether SRS is useful for differentiating thymoma from non-neoplastic thymic disease may be investigated by larger series. A predominant proportion of patients with unsatisfactory treatment response, however, continue to suffer an unfavourable clinical course despite absent evidence for thymic pathology.

The effectiveness of thymectomy on seronegative generalized myasthenia gravis: comparing with seropositive cases

OBJECTIVES

To investigate the efficacy of thymectomy between patients with seronegative myasthenia gravis (SNMG) and seropositive myasthenia gravis (SPMG).

METHODS

We present here the first Taiwanese retrospective paired cohort study comparing the effectiveness of thymectomy among 16 seronegative and 32 seropositive MG patients after matching for age-of-onset and time-to-thymectomy, and following up over a mean of 35 +/- 20 (7-86) months. Clinical characteristics and complete stable remission (CSR) rates were compared and analyzed between the groups.

RESULTS

There were no major clinical differences between the two groups except for our finding of a lower percentage of SNMG receiving preoperative plasmapheresis or human immunoglobulin than SPMG (31% for SNMG vs 72% for SPMG, P = 0.007). CSR rates calculated using the Kaplan-Meier method were similar in the two groups (38% for SNMG vs 50% for SPMG, P = 0.709). The median time for CSR was 47.4 months for SNMG and 48.2 months for SPMG. Thymic hyperplasia were the most common pathology (69% for SNMG vs 88% for SPMG, P = 0.24). During the follow-up period, we found no group difference on prednisolone or pyridostigmine dosages. Significant postoperative dosage reductions on pyridostigmine, but not on prednisolone, were found in both groups.

CONCLUSIONS

Thymectomy has a comparable response among SNMG and SPMG in our study. Thymic hyperplasia is prevalent in our SNMG patients and thymectomy may also be a therapeutic option to increase the probability of remission or improvement in SNMG. More prospective controlled trial will be helpful in the future.

Guidelines for the treatment of autoimmune neuromuscular transmission disorders

Important progress has been made in our understanding of the cellular and molecular processes underlying the autoimmune neuromuscular transmission (NMT) disorders; myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS) and neuromyotonia (peripheral nerve hyperexcitability; Isaacs syndrome). To prepare consensus guidelines for the treatment of the autoimmune NMT disorders. References retrieved from MEDLINE, EMBASE and the Cochrane Library were considered and statements prepared and agreed on by disease experts and a patient representative. The proposed practical treatment guidelines are agreed upon by the Task Force: (i) Anticholinesterase drugs should be the first drug to be given in the management of MG (good practice point). (ii) Plasma exchange is recommended as a short-term treatment in MG, especially in severe cases to induce remission and in preparation for surgery (level B recommendation). (iii) Intravenous immunoglobulin (IvIg) and plasma exchange are equally effective for the treatment of MG exacerbations (level A Recommendation). (iv) For patients with non-thymomatous autoimmune MG, thymectomy (TE) is recommended as an option to increase the probability of remission or improvement (level B recommendation). (v) Once thymoma is diagnosed TE is indicated irrespective of the severity of MG (level A recommendation). (vi) Oral corticosteroids is a first choice drug when immunosuppressive drugs are necessary in MG (good practice point). (vii) In patients where long-term immunosuppression is necessary, azathioprine is recommended together with steroids to allow tapering the steroids to the lowest possible dose whilst maintaining azathioprine (level A recommendation). (viii) 3,4-diaminopyridine is recommended as symptomatic treatment and IvIg has a positive short-term effect in LEMS (good practice point). (ix) All neuromyotonia patients should be treated symptomatically with an anti-epileptic drug that reduces peripheral nerve hyperexcitability (good practice point). (x) Definitive management of paraneoplastic neuromyotonia and LEMS is treatment of the underlying tumour (good practice point). (xi) For immunosuppressive treatment of LEMS and NMT it is reasonable to adopt treatment procedures by analogy with MG (good practice point).

Seronegative myasthenia gravis: disease severity and prognosis

Around 10-20% of myasthenia gravis (MG) patients do not have acetylcholine receptor (AChR) antibodies (seronegative), of whom some have antibodies to a membrane-linked muscle specific kinase (MuSK). To examine MG severity and long-term prognosis in seronegative MG compared with seropositive MG, and to look specifically at anti-AChR antibody negative and anti-MuSK antibody negative patients. Seventeen consecutive seronegative non-thymomatous MG patients and 34 age and sex matched contemporary seropositive non-thymomatous MG controls were included in a retrospective follow-up study for a total period of 40 years. Clinical criteria were assessed each year, and muscle antibodies were assayed. There was no difference in MG severity between seronegative and seropositive MG. However, when thymectomized patients were excluded from the study at the year of thymectomy, seropositive MG patients had more severe course than seronegative (P < 0.001). One seropositive patient died from MG related respiratory insufficiency. The need for thymectomy in seronegative MG was lower than in seropositive MG. None of the seronegative patients had MuSK antibodies. This study shows that the presence of AChR antibodies in MG patients correlates with a more severe MG. With proper treatment, especially early thymectomy for seropositive MG, the outcome and long-term prognosis is good in patients with and without AChR antibodies.