Thymoma-associated Myasthenia Gravis Research Articles

Incidence of Myasthenia gravis in the Province of Ferrara

Background: The reported annual incidence of myasthenia gravis (MG) ranges from 0.25 to 15 per million. The sex- and age-related pattern of disease incidence is still debated. Methods: An intensive descriptive study was performed in the province of Ferrara (mean population 360,950 people) over the period 1985 through 2000. Results: The average crude annual incidence rate was 2 per 100,000. We confirm a female preponderance in the total population, particularly in the youngest age groups. Conclusions: We observed an early increase in incidence in females, partly due to thymoma-associated MG, while MG without thymoma showed increasing incidence with age nonsignificantly different in the two sexes.

Characterization of the immunoreactivity of anti-interferon alpha antibodies in myasthenia gravis patients. Epitope mapping

Cytokines, such as interferons (IFN), underlie many immunological functions and are increasingly implicated in disease-related symptoms and pathology. In order to study the potential roles of IFN α and its antagonists in autoimmune phenomena, the sera from 89 patients (aged 15–95 years, 65 females) diagnosed as having myasthenia gravis (MG) (2 months to 34 years duration) were tested for the presence of natural anti-IFN α-2b auto-antibodies. Sera were screened for anti-IFN α-2b by a sandwich-type enzyme immunoassay system. Ten (11.2%) and 6 (6.7%) sera were identified that contained positive-competing and non-competing anti-IFN α-2b auto-antibodies, respectively. The MG sera were further analyzed by immunobloting against reduced IFN α-2b and for neutralizing anti-IFN α activity in an antiviral assay cells system. From tested EIA positive-competing sera, 5 were shown to be positive by immunoblot and 6 sera were found to contain neutralizing anti-IFN α-2b. Four of the 6 neutralizing anti-IFN α-2b sera came from patients with thymoma-associated MG. The sera were studied for linear epitope recognition on the IFN α-2b molecule by a solid phase binding assay, in which overlapping peptides homologous with the entire IFN α-2b sequence were separately synthesized on a nitrocellulose sheet. Peptides number 2 (residues 8–21), 3 (15–28), 6 (33–46), 10 (63–76), 15 (98–112), and 21 (141–154) were immunoreactive. Peptide 21 was apparently associated with antiviral activity, although peptide 21 has not been previously described as an immunogenic determinant on the IFN α-2b molecule. These results indicate that neutralizing anti-IFN α-2b is often present in MG, particularly in cases of thymoma-associated MG, and recognize a variety of epitopes on the IFN α-2b molecule, including those involved in its biological activity. Two groups of IFN epitopes were described associated with patient's age but not with diseases evolution.

Clinical and pathologic predictors of outcome in Thymoma-Associated myasthenia gravis

Background Myasthenia gravis is by far the most common paraneoplastic syndrome of thymomas. There is little information regarding the influence of clinical variables and thymoma-associated factors on biologic development of myasthenia gravis. The aim of the study was to determine independent predictors of clinical outcome in thymoma with myasthenia gravis. Methods We studied 108 patients with thymoma-associated myasthenia gravis undergoing removal of the mediastinal mass between 1967 and 2000. Clinical and pathologic variables associated with clinical outcome of myasthenia were assessed by multivariate Cox regression analysis. Results Patients were followed for a mean period of 10 years (9 months to 33 years). A total of 38 patients died (35.2%), in 14 cases (37%) because of myasthenia gravis and in 6 (16%) because of recurrence of thymoma. With respect to clinical outcome of myasthenia gravis, at the end of the follow-up period, the rate of remission was 16% (n = 17). Of the 91 patients in whom remission was not achieved, 55 had no symptoms with immunosuppressive medication and 36 had symptoms with medication. Conclusions In patients with thymoma-associated myasthenia gravis, well-differentiated thymic carcinoma (Müller-Hermelink system), age more than 55 years, and interval from the onset of symptoms to thymectomy of less than 1 year were found to be independent predictors of nonremission of myasthenia gravis after thymectomy.

The role of thymomas in the development of myasthenia gravis.

Thymic pathology occurs in 80-90% of myasthenia gravis patients. Significant associations between different thymic alterations and clinical findings are discussed. To highlight peculiarities in thymoma-associated myasthenia gravis, we briefly review myasthenia gravis associated with thymic lymphofollicular hyperplasia (TFH) and thymic atrophy.

Titin and ryanodine receptor epitopes are expressed in cortical thymoma along with costimulatory molecules

Cortical-type thymomas are associated with myasthenia gravis (MG) in 50% of the cases. MG is caused by antibodies against the acetylcholine receptors (AChR), but additional non-AChR muscle autoantibodies such as those against titin and ryanodine receptor (RyR) are found in up to 95% of MG patients with thymoma. To elucidate the induction of non-AChR autoantibodies in thymoma-associated MG, we studied cortical-type thymomas from seven thymoma MG patients, and sera from six of them. All six had titin antibodies, and four had RyR antibodies. Titin and RyR epitopes were co-expressed along with LFA3 and B7 (BB1) costimulatory molecules on thymoma antigen-presenting cells (APC) in all thymomas. In normal thymus, the staining by anti-titin, anti-RyR, anti-LFA3, and anti-BB1 antibodies was weak and occurred exclusively in the medulla and perivascularly. Our results indicate a primary autosensitization against titin and RyR antigens inside the thymoma. In MG-associated thymoma, the mechanisms involved in the initial autosensitization against titin and RyR are probably similar to those implicated in the autosensitization against AChR. In all cases, there is an overexpression of muscle-like epitopes and costimulatory molecules indicating that the T-cell autoimmunization is actively promoted by the pathogenic microenvironment inside the thymoma.

Epitopes expressed in myasthenia gravis (MG) thymomas are not recognized by patients' T cells or autoantibodies.

Most thymic epithelial tumours that associate with MG express an epitope that resembles the sequence alpha373-380 from the cytoplasmic loop of the acetylcholine receptor (AChR). It has been proposed that sensitization to this linear epitope initiates autoimmunity to the AChR in thymoma-associated MG. We therefore tested whether MG/thymoma patients have T cell responses or antibodies to this region of the AChR. We found no significant recognition of the alpha309-417 region by their thymoma or peripheral blood T cells, or by their serum anti-AChR antibodies. Instead, the T cell epitopes that were recognized, like the previously characterized B cell epitopes, were in the extracellular AChR domain.

Thymomas alter the T-cell subset composition in the blood: a potential mechanism for thymoma-associated autoimmune disease

Thymomas are the only tumors that are proven to generate mature T cells from immature precursors. It is unknown, however, whether intratumorous thymopoiesis has an impact on the peripheral T-cell pool and might thus be related to the high frequency of thymoma-associated myasthenia gravis. This study shows, using fluorescence-activated cell sorting-based analyses and T-cell proliferation assays, that thymopoiesis and T-cell function in thymomas correspond with immunologic alterations in the blood. Specifically, the proportion of circulating CD45RA+CD8+ T cells is significantly increased in patients with thymoma compared with normal controls, in accordance with intratumorous T-cell development that is abnormally skewed toward the CD8+ phenotype. Moreover, it is primarily the proportion of circulating CD45RA+CD8+ T cells that decreases after thymectomy. The results also demonstrate that T cells reactive toward recombinant autoantigens are distributed equally between thymomas and blood, whereas T-cell responses to foreign antigen (ie, tetanus toxoid) are seen only among circulating T cells and not among thymoma-derived T cells. These functional studies support the hypothesis that thymopoiesis occurring within thymomas alters the peripheral T-cell repertoire. Because many thymomas are enriched with autoantigen-specific T cells, a disturbance of circulating T-cell subset composition by export of intratumorous T cells may contribute to paraneoplastic autoimmune disease arising in patients with thymoma.

Thymomas alter the T-cell subset composition in the blood: a potential mechanism for thymoma-associated autoimmune disease

AbstractThymomas are the only tumors that are proven to generate mature T cells from immature precursors. It is unknown, however, whether intratumorous thymopoiesis has an impact on the peripheral T-cell pool and might thus be related to the high frequency of thymoma-associated myasthenia gravis. This study shows, using fluorescence-activated cell sorting-based analyses and T-cell proliferation assays, that thymopoiesis and T-cell function in thymomas correspond with immunologic alterations in the blood. Specifically, the proportion of circulating CD45RA+CD8+ T cells is significantly increased in patients with thymoma compared with normal controls, in accordance with intratumorous T-cell development that is abnormally skewed toward the CD8+ phenotype. Moreover, it is primarily the proportion of circulating CD45RA+CD8+ T cells that decreases after thymectomy. The results also demonstrate that T cells reactive toward recombinant autoantigens are distributed equally between thymomas and blood, whereas T-cell responses to foreign antigen (ie, tetanus toxoid) are seen only among circulating T cells and not among thymoma-derived T cells. These functional studies support the hypothesis that thymopoiesis occurring within thymomas alters the peripheral T-cell repertoire. Because many thymomas are enriched with autoantigen-specific T cells, a disturbance of circulating T-cell subset composition by export of intratumorous T cells may contribute to paraneoplastic autoimmune disease arising in patients with thymoma.

Autoantibodies in thymoma-associated myasthenia gravis with myositis or neuromyotonia.

About 50% of patients with thymoma have paraneoplastic myasthenia gravis (MG). Myositis and myocarditis or neuromyotonia (NMT) will also develop in some. Patients with thymoma-associated MG produce autoantibodies to a variety of neuromuscular antigens, particularly acetylcholine receptor (AChR), titin, skeletal muscle calcium release channel (ryanodine receptor [RyR]), and voltage-gated potassium channels (VGKC). To examine whether neuromuscular autoantibodies in patients with thymoma correlate with specific clinical syndromes. Serum and plasma samples from 19 patients with thymoma-associated MG, of whom 5 had myositis and 6 had NMT, underwent testing for antibodies to AChR, titin, RyR, and VGKC. Antibodies to AChR and titin were found in 19 and 17 patients, respectively. Antibodies to RyR correlated with the presence of myositis (P = .03); they were found in all 5 patients with myositis and in only 1 patient with NMT, but also in 4 of 8 patients with neither disease. Antibodies to VGKC were found in 4 patients with NMT, 1 of 3 patients undergoing testing for myositis, and 2 of 7 patients undergoing testing with neither comorbidity. Presence of RyR antibodies correlated with high levels of titin antibodies. The results appear to distinguish partially between 3 groups of patients with thymoma-associated MG: the first with RyR antibodies and myositis or myocarditis, the second with NMT without RyR antibodies, and the third without RyR antibodies, myositis, or NMT. Differences in the thymoma may underlie these pathologic associations.

Myasthenic Crisis After Resection of an Isolated Metastatic Thymoma of the Cervical Spine

A 73-year-old man presented with cervical cord compression resulting from a metastatic spindle cell thymoma 10 years after undergoing thymectomy for thymoma-associated myasthenia gravis. After being virtually asymptomatic following thymectomy, his myasthenic symptoms returned 3 months after removal of the spinal metastasis, culminating in myasthenic crisis that required immunosuppression and plasma exchange This case shows that isolated, extrathoracic metastases without any mediastinal tumor may occur many years after apparent surgical cure of primary thymoma, and that myasthenia gravis may recur after surgical resection of a thymic metastasis.

Ryanodine receptor gene expression thymomas.

Ryanodine receptor (RyR) antibodies are present in sera of myasthenics with thymoma, and their titer correlates with morbidity and mortality. We investigated whether skeletal muscle RyR expression in thymic tissues could be the source of immune sensitization to the RyR. Skeletal muscle RyR gene expression was investigated using reverse transcription followed by semiquantitative polymerase chain reaction. Hyperplastic and normal thymuses expressed significant levels of RyR, but RyR gene transcripts was statistically less likely in thymomas than in hyperplastic and normal thymus (P < 0.05). The presence of RyR transcripts in thymomas did not correlate with myasthenic manifestations, thymic pathology, or serum RyR antibodies. We conclude that the skeletal muscle RyR in thymoma is not the inciting antigen for immune sensitization to RyR epitopes in thymoma-associated myasthenia gravis.

Ryanodine receptor gene expression thymomas

Ryanodine receptor (RyR) antibodies are present in sera of myasthenics with thymoma, and their titer correlates with morbidity and mortality. We investigated whether skeletal muscle RyR expression in thymic tissues could be the source of immune sensitization to the RyR. Skeletal muscle RyR gene expression was investigated using reverse transcription followed by semiquantitative polymerase chain reaction. Hyperplastic and normal thymuses expressed significant levels of RyR, but RyR gene transcripts was statistically less likely in thymomas than in hyperplastic and normal thymus (P < 0.05). The presence of RyR transcripts in thymomas did not correlate with myasthenic manifestations, thymic pathology, or serum RyR antibodies. We conclude that the skeletal muscle RyR in thymoma is not the inciting antigen for immune sensitization to RyR epitopes in thymoma-associated myasthenia gravis. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1299–1303, 1998.

Nephrotic syndrome developing in association with thymoma and myasthenia gravis

Three patients with thymoma associated myasthenia gravis complicated by the nephrotic syndrome are described. There were two male and one female patients with a mean age at presentation of 55.6 years (27–75). In all cases anti striated‐muscle and acetylcholine‐receptor antibodies were present. Thymectomy was performed 1.4 years (1–3) after diagnosis of myasthenia gravis; histology revealed invasive mixed lymphocytic/epithelial (1), invasive epithelial (1) and non‐invasive lymphocytic/epithelial (1) cell thymoma. All patients were receiving pyridostigmine, prednisolone and azathioprine at the time nephrotic syndrome developed (a mean of 2 years after thymectomy). Renal biopsy demonstrated a minimal change nephropathy alone in all three. Remission following increased steroids occurred in two despite continuing azathioprine. Myasthenic symptoms remained stable throughout. The third patient died 3 weeks after onset of nephrotic syndrome. The cause of the nephrotic syndrome is uncertain, but an immune mechanism, possibly in genetically predisposed individuals, is perhaps most likely.

Pathogenesis of myasthenia gravis.

Various studies over the last 25 years in Man and animal models have revealed many steps in the pathogenesis of myasthenia gravis (MG) which is now considered the classical organ specific, autoantibody mediated and T cell dependent human autoimmune disease. Though not a disease entity, MG is associated with pathological alterations of the thymus in about 80% of cases. These are described here with reference to distinct models of autoimmunization against the acetylcholine receptor (AChR). In MG with thymitis, intrathymic production of AChR-specific autoantibodies is the result of a classical antigen-driven immune reaction that occurs completely inside the thymus and probably involves AChR on myoid cells as the triggering (myasthenogenic) antigen. Genetic factors contribute essentially to the pathogenesis of this form of MG. In thymoma-associated MG genetic factors are probably of marginal significance. Neither intratumour autoantibody production nor T cell activation seem to occur and the AChR is not the myasthenogenic antigen. Instead, abnormal neurofilaments that share epitopes with the AChR and other auto-antigen targets in paraneoplastic MG are expressed in thymomas and may trigger autoantigen-specific, non-tolerogenic T cell selection by molecular mimicry. These data support the hypothesis that initial steps in the pathogenesis of most MG cases take place within abnormal thymic microenvironments, be they inflammatory or neoplastic. Where these initial steps occur in MG cases without thymic pathology is not known. Likewise, the factors involved in the initial triggering of MG remain enigmatic in all MG subtypes.

Detection of bcl-2 and p53 in thymoma: Expression of bcl-2 as a reliable marker of tumor aggressiveness

The distinction between noninvasive and invasive or malignant thymoma has been severely compromised by a lack of objective morphological criteria. A reliable marker of tumor aggressiveness is, therefore, mandatory for predicting the tumor behavior. Forty thymic epithelial tumors, including 5 noninvasive thymomas, 18 invasive thymomas, and 17 thymic carcinomas (Rosai's classification) were investigated for expression of bcl-2 and p53 proteins by immunohistochemistry. The thymic epithelial cells showed positive immunostain for bcl-2 in 0, 7, and 16 of these categories, respectively. Thymic carcinomas had a significantly higher proportion of bcl-2 expression than thymomas ( P < .0001). A significantly higher expression of bcl-2 protein was also shown in thymoma-associated myasthenia gravis ( P < .05). However, p53 showed no correlation with the histological subtypes nor clinical aggressiveness. Bcl-2 expression appeared to be positively correlated with p53 immunoreactivity, but this result was not statistically significant ( P = .07). In conclusion, these data indicate that bcl-2 expression correlates with aggressiveness in thymic epithelial neoplasms.

Anti-ryanodine receptor antibodies in thymoma-associated myasthenia gravis

Anti-ryanodine receptor antibodies in thymoma-associated myasthenia gravis

Severity of thymoma-associated myasthenia gravis is related to the presence of anti-ryanodine receptor antibodies

Severity of thymoma-associated myasthenia gravis is related to the presence of anti-ryanodine receptor antibodies

Ryanodine receptor antibodies related to severity of thymoma associated myasthenia gravis.

Ryanodine receptor (RyR) antibodies are detected in about 50% of patients with myasthenia gravis who have a thymoma. The RyR is a calcium release channel involved in the mechanism of excitation-contraction coupling in striated muscle. In this study the severity of myasthenia gravis assessed by a five point disability score was compared between 12 patients with myasthenia gravis, a thymoma, and RyR antibodies and 10 patients with myasthenia gravis and a thymoma but without such antibodies. Symptoms of myasthenia gravis were significantly more severe in patients with RyR antibodies. The mean (SD) disability scores were 3.7(0.5) in patients with antibodies and 2.7 (0.9) in those without at peak of illness, (p = 0.01) and 3.4(1.4) v 1.6(0.7) at the end of an average observation period of five years (p = 0.002). The number of deaths due to myasthenia gravis was five of 12 RyR antibody positive patients, and none of 10 RyR antibody negative patients (p = 0.04). RyR antibody levels correlated positively with severity of myasthenia gravis. The presence of circulating RyR antibodies seems to be associated with a severe form of thymoma associated myasthenia gravis.

Ryanodine receptor autoantibodies in myasthenia gravis patients with a thymoma.

Sera from patients with myasthenia gravis were examined by Western blot for the presence of antibodies to proteins of the sarcoplasmic reticulum from rabbit skeletal muscle. Fourteen of 30 patients with myasthenia gravis and a thymoma had IgG autoantibodies to the calcium release channel of the sarcoplasmic reticulum (the ryanodine receptor), which plays a crucial role in the mechanism of excitation-contraction coupling in striated muscle. Ryanodine receptor autoantibodies were not detected in any of the 45 sera from patients with myasthenia gravis without a thymoma. Ryanodine receptor autoantibodies may have pathogenetic relevance in thymoma-associated myasthenia gravis.

A striational muscle antigen and myasthenia gravis-associated thymomas share an acetylcholine-receptor epitope.

The coincidence of autoantibodies against the acetylcholine receptor (AChR) and muscle striational antigens (SA) is a characteristic finding in thymoma-associated myasthenia gravis (MG), but their origins are still unresolved. Some common muscle antigens that were shown to be targets of anti-SA autoantibodies in thymoma-associated MG have also been detected in normal or neoplastic thymic epithelial cells, suggesting that the release of (eventually altered) antigens from the thymic tumors could elicit SA autoimmunity. In contrast to this model, we report here that titin, which is a recently reported target of SA autoimmunity, is not expressed in thymomas. In addition, we show that skeletal muscle type-II fibers exhibit a striational immunoreactivity with monoclonal antibody mAb155, which was previously identified to label a very immunogenic cytoplasmic epitope of the AChR and neoplastic epithelial cells of MGassociated thymomas. We conclude from these findings that titin autoimmunity in thymoma-associated MG is either due to a molecular mimicry mechanism involving tumor antigens (other than titin) or is a secondary phenomenon following release of titin from muscle. Based on the common immunoreactivity of the AChR, a striational antigen and thymoma, we suggest as the pathogenetic mechanism of thymoma-associated MGa "circulus vitiosus" in which SA autoimmunity could help maintain the AChR autoimmunity that is primarily elicited by the thymomas.