Studies in myasthenia gravis: effects of thymectomy. Results on 185 patients with nonthymomatous and thymomatous myasthenia gravis, 1941-1969

Review on Toll-Like Receptor Activation in Myasthenia Gravis: Application to the Development of New Experimental Models

Abnormal toll-like receptor (TLR) activation and uncontrolled resolution of inflammation are suspected to play a key role in the development of autoimmune diseases. Acquired myasthenia gravis (MG) is an invalidating neuromuscular disease leading to muscle weaknesses. MG is mainly mediated by anti-acetylcholine receptor (AChR) autoantibodies, and thymic hyperplasia characterized by ectopic germinal centers is a common feature in MG. An abnormal expression of certain TLRs is observed in the thymus of MG patients associated with the overexpression of interferon (IFN)-β, the orchestrator of thymic changes in MG. Experimental models have been developed for numerous autoimmune diseases. These models are induced by animal immunization with a purified antigen solubilized in complete Freund's adjuvant (CFA) containing heat-inactivated mycobacterium tuberculosis (MTB). Sensitization against the antigen is mainly due to the activation of TLR signaling pathways by the pathogen motifs displayed by MTB, and attempts have been made to substitute the use of CFA by TLR agonists. AChR emulsified in CFA is used to induce the classical experimental autoimmune MG model (EAMG). However, the TLR4 activator lipopolysaccharide (LPS) has proved to be efficient to replace MTB and induce a sensitization against purified AChR. Poly(I:C), the well-known TLR3 agonist, is also able by itself to induce MG symptoms in mice associated with early thymic changes as observed in human MG. In this review, we discuss the abnormal expression of TLRs in MG patients and we describe the use of TLR agonists to induce EAMG in comparison with other autoimmune experimental models.

Expression of RAGE and HMGB1 in thymic epithelial tumors, thymic hyperplasia and regular thymic morphology

Recently, a role of the receptor for advanced glycation endproducts (RAGE) in myasthenia gravis was described. RAGE and its ligand high mobility group box 1 (HMGB1) play key roles in autoimmunity and cancer. To test whether these molecules are involved in patients with thymic abnormalities we applied immunohistochemical analysis in 33 cases of thymic epithelial tumors, comprising 27 thymomas and 6 thymic carcinomas, and 21 nonneoplastic thymuses. Both molecules were detected in neoplastic epithelial cells: RAGE staining was most intense in WHO type B2 thymomas and thymic carcinomas (p<0.001). HMGB1 nuclear staining was strongest in A and AB, and gradually less in B1 = B2>B3>thymic carcinoma (p<0.001). Conversely, HMGB1 cytoplasmic staining intensities were as follows: A and AB (none), B1 (strong), B2 (moderate), B3 and thymic carcinoma (weak); (p<0.001). Fetal thymic tissue showed a distinct expression of RAGE and HMGB1 in subcapsular cortical epithelial cells which was found in 50% of myasthenic patients. Furthermore RAGE and HMGB1 were expressed in thymocytes, macrophages, Hassall's corpuscles, thymic medulla, and germinal center cells in myasthenic patients. Immunohistochemistry results were complemented by systemic measurements (immunosorbent assay): serum levels of soluble RAGE were significantly reduced in patients with epithelial tumors (p = 0.008); and in invasive tumors (p = 0.008). Whereas RAGE was equally reduced in thymic hyperplasia and epithelial tumors (p = 0.003), HMGB1 was only elevated in malignancies (p = 0.036). Results were most pronounced in thymic carcinomas. Thus, RAGE and HMGB1 are involved in the (patho-)physiology of thymus, as evidenced by differentiated thymic and systemic expression patterns that may act as diagnostic or therapeutic targets in autoimmune disease and cancer.

Lifetime course of myasthenia gravis

Between 1940 and 2000 a total of 1976 patients with myasthenia gravis (MG) were studied. Diagnosis was made by improvement in weakness after anticholinesterase medication. The historical developments in diagnosis and treatment of MG are reviewed. We analyzed the clinical course of MG as influenced by age, gender, thymectomy, thymomectomy, and the presence of antibodies to acetylcholine receptors (AChR). The clinical course of MG was significantly influenced by age and gender, and these need special attention in managing patients. The most severe level of weakness and high mortality occurred during the first 1 to 2 years of the disease, after which many patients experienced improvement. For treating MG patients the usefulness of thymectomy remains to be proven, and novel drugs need to be developed to increase the number as well as normal functioning of the AChRs and other components of the neuromuscular system.

Effects of cytokines on acetylcholine receptor expression: implications for myasthenia gravis

Myasthenia gravis is an autoimmune disease associated with thymic pathologies, including hyperplasia. In this study, we investigated the processes that may lead to thymic overexpression of the triggering Ag, the acetylcholine receptor (AChR). Using microarray technology, we found that IFN-regulated genes are more highly expressed in these pathological thymic tissues compared with age- and sex-matched normal thymus controls. Therefore, we investigated whether proinflammatory cytokines could locally modify AChR expression in myoid and thymic epithelial cells. We found that AChR transcripts are up-regulated by IFN-gamma, and even more so by IFN-gamma and TNF-alpha, as assessed by real-time RT-PCR, with the alpha-AChR subunit being the most sensitive to this regulation. The expression of AChR protein was increased at the cytoplasmic level in thymic epithelial cells and at the membrane in myoid cells. To examine whether IFN-gamma could influence AChR expression in vivo, we analyzed AChR transcripts in IFN-gamma gene knock-out mice, and found a significant decrease in AChR transcript levels in the thymus but not in the muscle, compared with wild-type mice. However, up-regulation of AChR protein expression was found in the muscles of animals with myasthenic symptoms treated with TNF-alpha. Altogether, these results indicate that proinflammatory cytokines influence the expression of AChR in vitro and in vivo. Because proinflammatory cytokine activity is evidenced in the thymus of myasthenia gravis patients, it could influence AChR expression and thereby contribute to the initiation of the autoimmune anti-AChR response.

Differential estrogen receptor expression in autoimmune myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease associated with thymic hyperplasia and is much more prevalent in women than men. In this study we investigated potential changes in estrogen receptor (ER) expression in thymic hyperplasia. We first quantified by real-time PCR the relative expression of ER alpha and ER beta in normal thymus and found that the ER beta to ER alpha ratio was inverted in thymocytes (8.6 +/- 1.2), compared with thymic epithelial cells (0.18 +/- 0.05). The ER transcript number gradually decreased in thymic epithelial cells during culture, indicating that the thymic environment influences ER expression. CD4+ helper T cells expressed higher level of ERs, compared with CD8+ cells, as assessed by flow cytometry in thymocytes and peripheral blood mononuclear cells. In MG patients, we found an increased expression of ER alpha on thymocytes and both ERs on T cells from peripheral blood mononuclear cells, indicating that the signals provided by thymic and peripheral microenvironments are distinct. Finally, activation of normal thymocytes by proinflammatory cytokines induced increased expression of ERs especially in the CD4+ subset, suggesting that an excess of proinflammatory cytokines could explain the increase of ERs expression on MG lymphocytes. The dysregulation of ER expression in MG lymphocytes could affect the maintenance of the homeostatic conditions and might influence the progression of the autoimmune response.

Childhood ocular myasthenia gravis

PURPOSE

To investigate the clinical manifestations and ocular findings in children with ocular myasthenia gravis (MG) that rarely have been reported in the literature.

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Twenty-four consecutive patients less than 15 years of age with ocular MG treated between June 1988 and July 2001.

METHODS

The medical records of 6 boys and 18 girls with ocular MG were reviewed retrospectively.

MAIN OUTCOME MEASURES

Alternate prism cover and uncover test, examination of ductions and versions, and visual acuity.

RESULTS

Mean age at onset was 38 months. Ptosis was found in 23 patients (96%), strabismus in 21 patients (88%), and amblyopia in 5 patients (21%). Exotropia combined with vertical heterotropia was the most frequent type of strabismus. Ductions were limited in 17 patients (71%), among whom supraduction or infraduction limitations were most frequently observed. Contrary to previous reports, medial rectus underaction was less common than lateral rectus underaction. Manifestations of strabismus and limitation of duction were variable and changed frequently during the follow-up period. The combined use of prednisone and pyridostigmine was found to be the predominant form of maintenance therapy, and ptosis was more responsive to drug therapy than limited ocular motility.

CONCLUSIONS

Children with ocular MG were found to have a high incidence of ptosis (96%) and exotropia and vertical hyperdeviation. Limitation on adduction was less common than that on abduction. First reported incidence of amblyopia (21%) and a relative nonresponsiveness of the limitation of eye movement to treatment were also noted.

Fulminant myasthenia gravis manifested after removal of anterior mediastinal tumor

Myasthenia gravis developed in a 35-year-old man after removal of an encapsulated anterior mediastinal tumor that was preoperatively diagnosed as a teratoma based on a computed tomographic image. Postoperative pathologic diagnosis of the excised tumor was thymoma. The patient was in crisis after the initiation of immunosuppressive treatment. The therapy was changed to immunoadsorbent perfusion therapy because of concurrent severe pneumonia and an extremely high serum concentration of anti-acetylcholine receptor antibodies. Respiratory support was necessary for 2 months after reoperation.

Delayed remission after thymectomy for myasthenia gravis of the purely ocular type

Twenty-two cases of purely ocular myasthenia gravis were reviewed to evaluate the long-term effects of thymectomy. Remission rate increased gradually with time (11.8% at 3 years, 23.1% at 5 years, and 33.3% at 10 years). Analysis of factors influencing remission with time showed that patients with short duration of illness attained remission significantly earlier (p = 0.035 at 5-year follow-up). One of 22 patients with purely ocular myasthenia gravis (4.5%) had disease progression. Because ocular myasthenia gravis often progresses to the generalized type and because duration of illness before operation is one of important factors influencing remission, we conclude that thymectomy in the earlier stages of the disease is the preferred treatment for ocular myasthenia gravis, just as for generalized myasthenia gravis.

Prognostic factors of patients with thymoma

OBJECTIVES

To analyze the prognostic factors influencing the survival of patients with thymoma, clinical characteristics, treatment modalities and survival of patients were evaluated. The efficacy of chemotherapy was also determined.

METHODS

Retrospective study was done on one hundred patients whose diagnosis was confirmed pathologically at Seoul National University Hospital from 1981 to 1994. The staging was carried out according to the Masaoka system. Survival rate was calculated by the Kaplan-Meier method and prognostic factors were analyzed by a multivariate analysis (Weibull model).

RESULTS

The stage of 100 patients was as follows: Stage I-50, II-6, III-27, IV A-10, IV B-7. The overall survival rates at 5 and 10 years after diagnosis were 73.1% and 58.7%, respectively. The 5-year survival differences, according to various prognostic factors, were as follows: 1) Stage: I-92.8%, II-100%, III-71.6%, IVA-25.9% and IVB-32.9% (p = 0.0029). 2) Age: < 60 years-79.5% and > or = 60 years-41.5% (p = 0.0489). 3) Extent of resection: Total patients: complete resection-87.6% and incomplete resection-50.5% (p > 0.05) Stage III: complete resection-66.7% and incomplete resection-75.5% (p > 0.05) 4) Myasthenia gravis: present-71.6% and absent-74.9% (p > 0.05) Seventeen patients were treated with a combination chemotherapy of Cyclophosphamide, Adriamycin and cisplatin(CAP). Two complete responses and seven partial responses (overall response rate of 53%) were observed with a median response duration of fourteen months. Combination chemotherapy with CAP was effective.

CONCLUSIONS

Stage and age were the independent prognostic factors in patients with thymoma. However, the presence of myasthenia gravis or the extent of resection in stage III patients was not associated with the survival time.

Sulfhydryl blocker-induced colitis in the rat: immunological changes in thymus gland and colonic mucosa

The study was designed to examine the changes of thymus in sulfhydryl blocker-induced colitis. We used N-ethylmaleimide (NEM) as sulfhydryl blockers. Fasted male Sprague-Dawley rats were given 3% NEM in 1% methyl cellulose into the colon. N-ethylmaleimide treatment caused severe diarrhoea with bleeding for the first 7 days. At autopsy, adhesions, colon dilatation, and single or multiple erosions and ulcers were observed. Time-course studies revealed that the lesions were most extensive and severe 3 or 7 days after the administration of NEM. Histological examination of colon on the 3rd day after NEM treatment demonstrated mucosal erosion, oedema and extensive infiltration of neutrophils. The mucosal lesions extended into the submucosa and muscle on the 7th day after NEM treatment. Immunohistochemical studies showed that T cells and macrophages were markedly increased in the lamina propria of colonic mucosa. After 3 weeks, the infiltration of chronic inflammatory cells was observed and regeneration of the mucosa was noticed. The thymus gland was significantly decreased in weight and size on the 3rd day after NEM treatment, but the weight loss of thymus gland was regained in 3 weeks. Transient atrophy of thymus gland was noticed in this colitis model. The phenotypes of thymocytes were not influenced by NEM treatment. It is concluded that the thymus abnormalities in human ulcerative colitis are not induced in this animal model and that other chronic models are necessary for the elucidation of the immunological abnormalities, including thymus abnormalities.

Ocular myasthenia: a protean disorder

Ocular myasthenia is a localized form of myasthenia clinically involving only the extraocular, levator palpebrae superioris, and/or orbicularis oculi muscles. Ocular manifestations can masquerade as a variety of ocular motility disorders, including cranial nerve and gaze palsies. A history of variable and fatiguable muscle weakness suggests this diagnosis, which may be confirmed by the edrophonium (Tensilon) test and acetylcholine receptor antibody titer. Anticholinesterases, corticosteroids and other immunosuppressive agents, and other therapeutic modalities, including thymectomy and plasmapheresis, are used in treatment. As the pathophysiology of myasthenia has been elucidated in recent years, newer treatment strategies have evolved, resulting in a much more favorable prognosis than several decades ago. This review provides historical background, pathophysiology, immuno-genetics, diagnostic testing, and treatment options for ocular myasthenia, as well as a discussion of drug-induced myasthenic syndromes.

Tests for juvenile myasthenia gravis: comparative diagnostic yield and prediction of outcome

The clinical picture, family history, laboratory data, treatment modalities, and outcome in 27 juvenile myasthenics seen over a 25-year period are presented. Onset was after 10 years of age in the majority of patients. Half presented with ocular signs, the other half with generalized-onset myasthenia. Half of those with ocular-onset myasthenia progressed to generalized myasthenia. The female-to-male ratio was 3.5:1. Myasthenia gravis was reported in the mother of one patient. Ptosis was the most common presenting sign. It was unilateral at onset in 33% of patients and remained unilateral in 11%. Pharmacologic tests (neostigmine methylsulfate and edrophonium chloride) were positive in 92% of patients. Serology was positive in 63%, whereas repetitive nerve stimulation was positive in 33% when distal nerves were stimulated and in 66% when proximal and distal nerves were stimulated. Seropositivity tended to increase with generalization of the myasthenic process. No statistically significant difference in seropositivity was noted between males and females. Anti-striated muscle antibodies were detected in two patients, neither of whom had thymoma. The yield of repetitive stimulation increased with generalization of the myasthenic process and when proximal nerves were stimulated. No statistically significant difference was noted in the decremental response between seropositive and seronegative patients. The majority of ocular myasthenics were treated with pyridostigmine bromide monotherapy. With generalization of the myasthenic process, other modes of medical and surgical therapies were needed. All patients given corticosteroids ultimately underwent thymectomy. The mean age at presentation and the duration of symptoms at presentation were longer in thymectomized patients than in those without thymectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical study of thymic B cells in myasthenia gravis and ulcerative colitis

The phenotypes of B cells and dendritic cells in human thymus were examined immunohistochemically using various monoclonal antibodies. Normal thymus contained a few B lymphocytes recognized by CD19, CD20, CD22, L26 and LN-2, which were localized in the medulla. These B cells were negative for LN-1, L30 and CD11c (Leu M5). Activated B cells recognized by CD23 (B6) and L29 antibodies were not present in normal thymus. Dendritic cells stained by CD11c were weakly positive for L26 and CD20. There was no difference in the distribution of dendritic cells between normal thymus and thymus from the patients. In the thymus from patients with myasthenia gravis, numerous B cells were demonstrated in the medullary area and lymphoid follicles. Activated B cells were seen mainly in the germinal center of lymphoid follicles and were scarce in the medulla. Many B cells were also found in the medulla and lymphoid follicles of the thymus from patients with ulcerative colitis. However most of those B cells were not activated, even in the lymphoid follicles. These results suggest that thymic B cells may contribute to the induction of immune abnormalities in patients with myasthenia gravis and those with ulcerative colitis, however, the mechanisms by which thymic B cells participate in the pathogenesis of these two diseases would be different.

Remission rate after thymectomy in myasthenia gravis when the bias of immunosuppressive therapy is eliminated

The clinical course of all 86 myasthenia gravis (MG) patients who were thymectomized at Sahlgrenska Hospital between 1955 and 1980 was evaluated in order to estimate what the rate of complete clinical remission (with or without anticholinesterase medication) would be without immunosuppressive (IS) therapy; 19 of 73 patients without thymoma received IS therapy. A suitable way of dissociating the course after thymectomy from the influence of IS therapy is the Markov method. The calculated probability of remission was 0.18, 0.35, 0.43, 0.53 and 0.56 in the 0-1, 2-3, 4-5, 5-10 and more than 10-year periods after thymectomy. A similar result (53 +/- 7%) was obtained by a life-table method with censoring of IS-treated patients when they received such therapy. Time to remission was significantly shorter for patients with age of MG onset before 35 years. Timing of IS therapy after thymectomy is discussed, considering the post-thymectomy remission rate.

The transcervical approach to the superior mediastinum

We describe our experience with the transcervical approach for the surgical treatment of nonthyroidal superior mediastinal masses. With careful patient selection, proper preoperative workup, and proper operative positioning and technique, the entire superior mediastinum may be explored, thus avoiding the significant morbidity associated with the transsternal route. The transcervical approach requires a thorough knowledge of the surgical anatomy. Nine patients underwent transcervical exploration of the superior mediastinum. The indications included parathyroid adenoma, thymoma, congenital cyst, hemangioma, adenocarcinoma, and thymectomy for myasthenia gravis. We specifically discuss the role of thymectomy in the treatment of myasthenia gravis.

A case of myasthenia gravis complicated with hyperthyroidism and thymic hyperplasia in childhood

We report here a case of myasthenia gravis complicated with hyperthyroidism and thymic hyperplasia. The patient was a 13-year-old girl with struma and hyperthyroidism which began at age 12. Two weeks following the initiation of treatment against hyperthyroidism she developed left blepharoptosis, diplopia, and dysphagia, which responded promptly to edrophonium administration. An increase of the anti-acetylcholine receptor antibody was found in the serum. A chest CT showed a large soft tissue mass in front of the ascending aorta, which was proven histopathologically as thymic hyperplasia. The patient underwent an extensive thymectomy and was placed on combination therapy with an anti-thyroid drug, glucocorticosteroid, and an anti-cholinesterase drug. Her symptoms and signs have been well controlled by this treatment. Coexistence of myasthenia gravis, hyperthyroidism, and thymic hyperplasia in childhood have never been documented in literature.

[Myasthenia gravis: clinical and surgical treatment]

The indication for thymectomy in myasthenia gravis still is controversial, and it is uncommon to find in the present days studies comparing conservative treatments, due to the widespread surgical treatment adopted in most centers. We studied 65 cases divided into three groups of patients: (1) 15 thymectomized patients and 50 with conservative treatment; (2) 15 thymectomized patients paired with 15 on conservative treatment; (3) 49 patients treated with corticosteroids against 16 without corticosteroids. These three groups where compared regarding age, age when the symptoms began, disease duration, clinical severity and functional scale, studying remission, stability or worsening of the symptoms and death rate after several years of treatment. It was found a reduction of the symptoms (p < 0.05) in the thymectomized patients of group 1; the remaining parameters of all three groups did not show any statistical significance. These results suggest that the type of treatment did not interfere with evolution of myasthenia gravis in this group of patients.

The characteristics of thymoma with myasthenia gravis: a 28-year experience

Of 134 patients with thymoma, 79 (59%) also had myasthenia gravis (MG). The thymoma with MG differed from that in the absence of MG in the following aspects: The ratio of lymphocytes to epithelial cells in the tumor was larger, the polygonal cell type was more prominent (i.e., in 83% of the MG patients this cell type predominated), and the differentiation of epithelial cells in the tumor was more advanced in the group with MG than in the group without MG. Furthermore, the clinical stage of thymoma was earlier, the recurrence rate was lower, and the survival curve was better in the group with MG than in the group without MG. These findings suggest that the thymoma with MG is less malignant than that without MG.

Myasthenic sera recognize the human acetylcholine receptor bound to thymopoietin

The thymic hormone, thymopoietin (Tpo), from human (HTpo), bovine (BTpo) and from synthetic (sHTpo) origins bound to the acetylcholine receptor (AChR) solubilized by Triton 1.5% from human muscle. This binding was demonstrated either by inhibition of formation of radiolabeled alpha bungarotoxin (alpha Bgt)-AChR complexes measured after precipitation by ammonium sulfate or by a myasthenic serum containing a high concentration of anti-AChR antibodies, or directly by incubating the human AChR with radiolabeled sHTpo or BTpo. The 125I-labeled alpha Bgt-AChR complexes were totally inhibited by 10(-6) M sHTpo or BTpo. The complexes formed by AChR and the radiolabeled Tpo were recognized specifically by sera containing anti-AChR antibodies from myasthenic patients. The active pentapeptide derivative of Tpo, thymopentin, another thymic hormone, thymulin, as well as bovine insulin did not interfere with the specific binding of alpha Bgt to human AChR. Tpo and anti-AChR antibodies could participate together in the inhibition of neuromuscular conduction with Tpo modulating the depressive effect of the antibodies on the neuromuscular junction in myasthenia gravis.

The course of myasthenia gravis and therapies affecting outcome

The course of 1,487 patients with myasthenia gravis followed between 1940 and 1985 for a mean of 18 years provides further evidence that the distribution, severity, and outcome of the disease are determined during the first 1 to 3 (occasionally 5) years after onset, suggesting that injury to acetylcholine receptors occurs mainly during this time. In 14%, the disease remained clinically localized to the extraocular muscles, and in the remaining 86% became generalized, in 87% within a year, with the disease reaching maximum severity within the first year after onset of symptoms in 55%, during the first 3 years in 70%, and during the first 5 years in 85%. Male patients tended to have more rapid progression of disease, higher mortality, and lower rates of remission and improvement than females. From 1940 to 1957, when management relied on anticholinesterase compounds, endotracheal intubation or tracheostomy and negative pressure assisted ventilation for respiratory failure, and thymectomy in 26% of patients and thymomectomy in 8%, 31% of patients with generalized myasthenia gravis died of the disease (29% of these during the first year after onset, 27% during the second and third years, and 17% during the fourth and fifth years), 32% improved, 23% remained unchanged, 10% went into remission, and only 5% were worse during the last year seen than during the worst of the first 3 years (or 5 years in the minority of patients who reached maximum weakness after 3 years). From 1958 to 1965, during which time the management of respiratory failure was improved by positive pressure and volume controlled ventilation and improved intensive care, mortality fell to 14% (p less than 0.005), and a higher proportion remained unchanged (p less than 0.005). From 1966 to 1985, when over half the patients received adrenal cortical steroids, mortality fell to 7% (p less than 0.005) and the proportion who improved rose to 47% (p less than 0.05). Even though the patients who received steroids usually had more severe myasthenia, they had a higher rate of improvement than those who received no steroid, 54% compared to 39% (p less than 0.005). Thymectomy was performed in one-fourth of patients with generalized myasthenia gravis, more frequently in young females and those with more severe weakness, and less often in older males and those with less severe weakness.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of thymectomy in myasthenia gravis

Factors influencing onset of remission in myasthenia gravis were evaluated in 2062 patients, of whom 962 had had thymectomy. Multivariate analysis showed that appearance of early remissions among all patients was significantly and independently influenced by thymectomy, by milder disease, and by absence of coexisting thymomas. Patients with mild generalized symptoms treated with thymectomy reached remission more frequently, even when compared with those with ocular myasthenia treated without surgery. Short duration of disease before thymectomy in mild cases was another factor associated with earlier remissions. Mortality for all patients was significantly and independently influenced by severity of symptoms, age, associated thymomas, and failure to remove the thymus. Patients without thymectomy and with thymomas had, in addition, earlier onset of extrathymic neoplasms. Morbidity after the transcervical approach was minimal. This study demonstrates that early thymectomy by the transcervical approach, when technically feasible, has significant clinical advantages over the transthoracic approach and should be advocated for all patients with myasthenia gravis, including those with ocular disease.

Surgical treatment for myasthenia gravis

A new surgical technique for thymectomy is presented. Three hundred and seventeen patients with myasthenia gravis and 20 with thymomas who had myasthenic symptoms were operated on. The new surgical approach--a small transverse sternotomy--was used in 257 cases (in 240 patients with myasthenia gravis and 17 with thymomas) and conventional median sternotomy in 80. In myasthenic patients small transverse sternotomy enabled radical thymectomy to be performed with an uneventful postoperative course and very good cosmetic results. There were no hospital deaths among patients with myasthenia gravis after thymectomy. The long term results, assessed after 18-24 months, were good: the total remission rate was 39.5%, and there was a great improvement in 48.5% and an improvement in 9%. After thymectomy about 30% of patients received supplementary treatment with prednisone. A correlation between the duration of symptoms and the result of thymectomy was established: the shorter the duration of myasthenia gravis the better the results. In the small group of 20 patients with thymomas two died in hospital. In 12 patients with encapsulated thymic tumours the long term results were similar to those in patients with myasthenia gravis, whereas in patients with infiltrating thymic tumours the results were unsatisfactory.

Increased binding of anti-acetylcholine receptor antibodies to thymic antigen in patients with myasthenia gravis and other autoimmune diseases, as compared to those with myasthenia gravis alone

We compared the binding activity against acetylcholine receptors solubilized from human muscle (AChRM) and human thymus (AChRT), of sera from patients with myasthenia gravis (MG) alone, to those of sera from patients with myasthenia gravis and associated autoimmune diseases (MG AD). The sera of the MG AD group bound relatively better to thymic antigen (86% vs. 62%). This group was found to contain a higher proportion of women over 40 years of age (more than 50% of the group). The expression of a particular AChR antigen in normal human thymus may be one of the factors involved in the pathogenesis of MG, especially when this disease is associated with other autoimmune disorders.

Thymomas. A review of 169 cases, with particular reference to results of surgical treatment

One hundred sixty-five patients with surgically treated thymoma were followed over 28 years; 73% had myasthenia gravis at presentation. Invasiveness was based on macroscopic findings at operation. Postsurgical radiotherapy or chemotherapy were not routinely used. Overall survival was 84%, 79%, and 65% at 3, 5, and 10 years, respectively. Patients with invasive thymoma survived for a shorter period than patients with noninvasive tumors (67% versus 85% at 5 years); when radical excision was possible, no difference was detectable between the two groups. Patients with subtotally resected or only biopsied invasive thymomas survived 59% and 42% at 5 years, respectively. Lymphoepithelial cases had the worst prognosis of the histologic types considered. Myasthenia gravis did not adversely affect survival. Surgery is the basic treatment of thymomas. Macroscopic invasiveness and degree of excision judged by the surgeon have prognostic value and are reliable criteria of malignancy. Radiotherapy and chemotherapy may be effective, but their use should be limited to controlled trials.

Myasthenia gravis: immunohistological heterogeneity in microenvironmental organization of hyperplastic and neoplastic thymuses suggesting different mechanisms of tolerance breakdown

Four samples of thymoma obtained from patients affected by myasthenia gravis have been immunohistologically analysed on cryostat sections using a panel of antisera and monoclonal antibodies specific for antigens which define different stages of intrathymic lymphocyte differentiation and antigens specific for different types of thymic epithelial cells (cortical, medullary). When the thymoma samples were compared to age-matched normal thymuses and hyperplastic thymuses obtained from patients with myasthenia gravis some evident microenvironmental differences could be demonstrated using these reagents. In all the thymoma samples in fact the neoplastic lobules appeared as grossly enlarged cortical-type areas, formed by accumulations of T lymphocytes exhibiting the cortical immature phenotype (TdT+, T6+, etc.) within a network of putatively neoplastic epithelial cells characterized by cortical phenotype as defined by reactivity with various monoclonal antibodies (RFD4-, MR3+). These 'cortical' epithelia showed some abnormal features such as lack or irregular distribution of HLA-DR and enhanced keratin expression. Small areas of 'medullary' differentiation could be observed in 3/4 thymoma samples. In thymic hyperplasia, on the other hand, the cortical areas appeared somewhat compressed (but comparable to those observed in normal age-matched samples) by enlarged medullary areas. The expansion of medullary areas was due to the infiltration of 'peripheral' lymphoid tissue intruding through the extraparenchymal zone and forming organized B and T areas. These observations are discussed in the light of the clinical heterogeneity observed in myasthenia gravis.

Clinical characteristics and prognosis of myasthenia gravis with other autoimmune diseases

Of 277 patients with myasthenia gravis (MG) who underwent thymectomy, including 78 with thymomatous MG, 33 patients had other autoimmune diseases. The clinical characteristics of MG with other autoimmune disease were investigated. Graves's disease and rheumatoid arthritis were the most common autoimmune diseases seen. The association rate of autoimmune disease in patients with thymomatous MG (3.8%) was significantly lower than that in patients with nonthymomatous MG (15.1%). The positive rate for a germinal center in the thymus was significantly higher in patients with other autoimmune disease than in those without such disease. Thymectomy was effective for MG in patients with an associated disease as well as in those without such a complication. The clinical course of the associated autoimmune disease did not seem to be adversely affected by thymectomy. Therefore, thymectomy should be performed in MG patients with other autoimmune disease.

Thymoma and myasthenia gravis in a 4-year-old child. Case report and review of the literature

Thymomas are exceedingly rare in the first 20 years of life, and only a few well-documented cases are present in the literature. Thymomas in adults are commonly associated with other diseases, the most frequent being myasthenia gravis (MG). However, this association has been reported not to occur in childhood. The authors report the case of a 4-year and 10-month-old girl who presented with clinical evidence of MG before thoracotomy and who developed florid MG after thoracotomy for removal of an anterior mediastinal mass later documented to be a thymoma.

Thymectomy for myasthenia gravis: 14-year experience

Forty-eight consecutive patients with myasthenia gravis (MG) attended by generalized weakness were treated by complete thymectomy, performed transsternally in 46 patients and through a left thoracotomy in two with thymomas. There were no operative deaths. A 12-year-old child with fulminating MG died of acute pneumonia shortly after hospital discharge. Of the remaining 47 evaluable patients, thymectomy resulted in complete remission in six, marked improvement with a reduced need for medication in 20, and mild improvement on the same dosage of medication in 18. Neither the age of the patient, nor the histopathology of the excised thymus, nor the postoperative change in acetylcholine receptor antibody titer were found to have a significant influence on the response to thymectomy. If the ten patients who were 20 years of age or younger were excluded, the patients with a shorter duration of MG achieved a better response to operation. The authors conclude that thymectomy is effective treatment for MG, regardless of the age of the patient or the type of thymic pathology.

Myasthenia gravis in elderly patients

The clinical features and the effect of thymectomy were compared between 27 elderly patients (Group 2) and 119 young adult patients (Group 1) with myasthenia gravis (MG). In the elderly group, MG was type I in 3 patients, type IIA in 6, type IIB in 17, and type III in 1; and in the young group, type I in 6, type IIA in 36, type IIB in 73, and type III in 4. The association rate with autoimmune disease in patients without thymoma was 12.5% (1/8) in Group 2 and 21.3% (20/94) in Group 1. Autoimmune diseases were not seen in any patients with thymoma. The clinical stage of thymoma was not significantly different between the two groups. The rates of remission and of palliation at 3 years after thymectomy were 18.2% and 72.7%, respectively, in Group 2 patients with thymoma, 21.4% and 78.6% in Group 1 patients with thymoma, 50% and 100% in Group 2 patients without thymoma, and 50% and 98.1% in Group 1 patients without thymoma.

A molecular hypothesis concerning the pathogenesis of myasthenia gravis

The purine enzyme, adenosine deaminase, is essential for the maturation of lymphocytes, cell growth and normal immune function. Since adenosine deaminase has the highest activity in the thymus and in T lymphocytes, it is hypothesized that a defective or altered enzyme may be a cause of myasthenia gravis, a lymphoid dyscrasia. It is proposed that the alteration is on the non-catalytic portion of adenosine deaminase concerned with the normal immune function of T lymphocytes. Lymphocytes, particularly suppressor T lymphocytes containing a defective adenosine deaminase will function improperly. They will lose their normal immune regulatory function, allowing immunoglobulin-producing B lymphocytes to produce autoantibodies against the nicotinic acetylcholine receptor, with resultant induction and perpetuation of the autoimmune state. In an attempt to compensate for the defect, there may be hypertrophy of the thymus and lymphoid system, with overproduction of a defective adenosine deaminase. Since many of the functions of thymosin, the alleged active principle in thymus are identical to those of adenosine deaminase, it is postulated that thymosin may be a subunit of adenosine deaminase.

Acetylcholine receptor antibody-producing cells in thymus and lymph nodes in myasthenia gravis

Eleven patients with myasthenia gravis (5 with thymoma) were studied and spontaneous production of antibody to acetylcholine receptor (AChR) in vitro was found by thymus cells in 10 (and in all 5 with thymoma) and by lymph node cells in 8 (and in 3 with thymoma). The rate of AChR antibody production by thymus cells was greater than that by lymph node cells (10.7 +/- 11.6 and 1.4 +/- 1.5 fmol/10(6) cells/week, respectively, mean +/- SD, P less than 0.05 by paired t test), although the B-cell population was always smaller in the thymus than in the lymph nodes (9.5 +/- 9.4 and 31 +/- 12.7%, P less than 0.001), suggesting the principal role of the thymus in AChR antibody production. It is suggested that lymph nodes can be one of the main sites of AChR antibody production in myasthenia gravis but the antibody-producing cells may originate in the thymus.

Do true remissions in myasthenia really exist? An electrophysiological study

To answer the question whether true remissions in myasthenia gravis occurred, 20 patients were studied with a history of evident, typical myasthenia but in full clinical remission. Two control groups served as a comparison: one of 10 healthy volunteers and the other of 10 patients with generalized, presently active myasthenia. In 17 of the 20 patients in remission single-fibre EMG (SFEMG) abnormalities were found, indicating some subclinical disturbances of neuromuscular transmission (in 3 cases the results were overtly pathological, in 11 cases moderately pathological, and in 3 cases slightly pathological). The abnormalities found in the remission group were much less distinct than those in the group with clinically symptomatic myasthenia. A case illustrates these findings: a man in full remission following thymoma extirpation in whom the SFEMG revealed subclinical disturbances of the neuromuscular transmission. Three weeks later a full clinical relapse occurred. The results obtained suggest that in the majority of patients the remissions are only apparently complete. A pathological jitter in a patient in remission calls for special attention: the patient must be spared any immunological stimuli such as vaccination, injections of sera, infections etc.; no drugs can be given which may increase the neuromuscular block; an immunosuppressive course of treatment should be considered; prognosis should be reconsidered.

Invasive thymoma with myasthenia gravis

In 261 surgically treated patients with myasthenia gravis (MG), 26 had an invasive thymoma and 49 had a noninvasive thymoma. Invasive thymoma was seen in 41% of thymomatous MG patients older than 40 years of age, and 28% in patients younger than 40 years of age. Of 19 patients who underwent total or subtotal thymothymomectomy accompanied by irradiation (4000 rad), 17 were still alive on an average 6.5 years after surgery. The deterioration of MG by the irradiation was observed in 7 of 20 irradiated cases. Thus, postoperative irradiation is effective but should be done with attention to the deterioration of MG. The prognosis of MG in patients with an invasive thymoma was poorer than that in patients with a noninvasive thymoma.

Effects of preoperative duration of symptoms on patients with myasthenia gravis

In 80 patients with type II nonthymomatous myasthenia gravis who underwent extended thymectomy, we investigated preoperative duration of symptoms, prognosis after thymectomy, immunological findings, and germinal center formation in the thymus. Our findings included the following. First, the palliation rate after thymectomy ranged from 73 to 100% and was independent of the preoperative duration of symptoms. The remission rate was high in patients with a short preoperative duration. Second, the lymphocyte count of peripheral blood decreased as preoperative duration increased. Third, the percentage of positive reactions to purified protein derivative of tuberculin decreased as preoperative duration increased: 100% in the one-year group, 78% in the two-year group, 75% in the three-year group, and 56% in the four-year group. Fourth, the degree of germinal center formation in the thymus was higher in patients with a longer preoperative duration. The correlation between germinal center formation and preoperative duration was significant. Finally, the T-cell population in peripheral blood and immunoglobulin, and antibody to acetylcholine receptor in serum, had no significant relationship with the preoperative duration of myasthenia gravis.

Postoperative respiratory care after transsternal thymectomy in myasthenia gravis. A 3-year experience in 53 patients

During a three-year period, 53 patients with myasthenia gravis underwent transsternal thymectomy by a partial sternum-splitting technique at our institution. This procedure was carried out (1) because an x-ray film or a computed tomography scan had suggested the presence of a thymoma or (2) to manage symptoms of myasthenia gravis. In 41 patients the endotracheal tube was removed in the post-anesthesia recovery room. The remaining 12 patients were extubated in the Respiratory Care Unit--in five, after prolonged mechanical ventilation. From our experience, the only factor useful for predicting the probable need for prolonged postoperative mechanical ventilation is the degree of bulbar involvement. Patients in Osserman classification groups 3 and 4 have an extremely high incidence of postoperative respiratory failure. Consideration should be given to the use of preoperative plasmapheresis in myasthenia gravis patients who have significant bulbar symptoms.

Myasthenia gravis with thymoma: analysis of and postoperative prognosis for 65 patients with thymomatous myasthenia gravis

Sixty-five patients with thymomatous myasthenia gravis were investigated. Thymomas were present in 44% of the male patients and 19% of the female patients with myasthenia gravis. The incidence of thymomatous disease in male patients was higher than in female patients in all age groups. Eighty percent of men more than 50 years old and women more than 60 years old had myasthenia gravis with thymoma. Germinal center formation in the thymus of patients with thymomatous myasthenia gravis was positive in 91% and was high grade. The prognosis for patients undergoing extended thymectomy of thymomatous myasthenia gravis was significantly better than in those having transsternal simple thymectomy, but it was worse than the prognosis for patients with nonthymomatous myasthenia gravis. No increase in the rate of remission or palliation was seen one year after thymectomy. It is concluded that early thymectomy is effective in control of myasthenia gravis in thymomatous myasthenia gravis.

The in vivo effects of corticosteroids on thymocyte subsets in myasthenia gravis

The in vivo effects of corticotherapy on thymocyte subpopulations have been evaluated in patients with myasthenia gravis (MG). Ten patients receiving high-dose, long-term treatment were studied and compared with two control groups (MG untreated patients and normal age-matched subjects). In the treated group, the thymus was generally involuted; the percentage of OKT6+ or OKT4+T8+ thymocytes was profoundly decreased compared to controls. A significant percentage of OKT10 - cells was detected particularly among older patients, suggesting steroid-induced immigration. Conversely the percentage of more mature OKT3+ cells was increased. The balance between OKT4+T8- and OKT4-T8+ cells was unchanged in young patients (less than 40 years old) and increased in the older group. These data show that, as in the mouse, corticosteroids profoundly alter human thymocyte subsets.

Evidence for the presence of immunoreactive acetylcholine receptors on human thymus cells

Triton extracts from thymuses and thymomas from either normal subjects or MG patients specifically bind [125I] alpha-bungarotoxin (alpha Bgt). This binding is saturable (apparent Ks = 5.9 X 10(-9) M) and can be inhibited by cold alpha Bgt, acetylcholine or nicotinic agonists. These results demonstrate the presence on human thymus cells of acetylcholine receptor (ACh.R), 2.8% for normal human thymus in regard of ACh.R concentration in human muscle. Normal human thymic extracts were used as an antigen source in the radioimmunoassay for the detection of anti-ACh.R antibodies in positive MG patients' sera. 72% of these sera were also positive with the thymic antigen. The demonstration of ACh.R in human thymus brings further support to the hypothesis of intrathymic autosensitivity against ACh.R as a major factor in MG pathogenesis.

Thymectomy in myasthenia gravis. A review

The role of thymectomy in the management of myasthenia gravis is reviewed in the light of the published data and of a personal series. The patients in whom the operation is most successful are non thymomatous patients aged between 10 and 40 years with an MG history of less than 3 years. There is no sex prevalence. Lasting improvement may be expected. There are no proven correlations between biological indices like the germinal centers in the thymus and/or AChR antibody titers and the postoperative course of the disease. Complete removal of the thymus seems to be crucial and hence the transsternal approach is preferred. The operation, less effective in patients with thymoma than in those with an active thymus, is nonetheless necessary to in these patients prevent putative damage to surrounding organs from thymoma infiltration. Why thymectomy should be effective in patients with an active thymus and not in those with a thymoma may be revealed by in vitro studies of the interactions between thymic cells and peripheral B cells, now in progress.

Surgical treatment of myasthenia gravis in childhood

Myasthenia gravis is considered to be an autoimmune disorder of neuromuscular transmission. Thymectomy is an effective mode of treatment which produces either remission or stabilization of symptoms especially in young female patients with short duration of disease. The present study, records the experience in ten pediatric patients with early thymectomy done via the transcervical approach. There were no operative deaths or serious complications. Follow-up for a mean of 37 months has shown one to be in complete remission requiring no medication and eight to have improved or stable symptoms. Thymectomy via the transcervical approach is an effective mode of treatment for patients with myasthenia gravis. Since this approach involves a small dissection and avoids sternotomy, the transcervical approach results in a very short postoperative recovery period. It is ideal for those patients not in respiratory failure. It can also be safely done in patients requiring intubation for acute respiratory failure preoperatively.