A tri-modal distribution of age-of-onset in female patients with myasthenia gravis is associated with the gender-related clinical differences.

BACKGROUND: A tri-modal distribution of age-at-onset emerged among females patients with myasthenia gravis (MG) in our database. This finding may be indicative of different gender-based disease mechanisms. METHODS: We retrospectively reviewed the files of 127 MG patients for the clinical, serology and thymus pathology according to their age at disease onset: ≤40 years (early-onset, EOMG), 40-70 years (intermediate-onset, IOMG) and >70 years (late-onset, LOMG). RESULTS: EOMG was more common among females, and IOMG was more common among males. Ocular MG was more common among the male MG patients with an IOMG. Patients with EOMG had lower rates of positive anti-acetylcholine receptor (anti-AChR). IOMG females, but not IOMG males, had lower rates of positive anti-AChR. IOMG and EOMG females had high rates of thymic hyperplasia, while EOMG males had high rates of thymoma. Comorbidity with autoimmune diseases was common among females with IOMG and LOMG. CONCLUSIONS: The prevalence of IOMG was the reason for the trend reversal of MG prevalence between genders. The clinical features of patients with IOMG differed between genders in the rates of positive anti-AChR, follicular hyperplasia of the thymus and comorbidity with autoimmune diseases. This may suggest a different gender-based mechanism of immune intolerance towards AChR and other antigens.

Thymus involvement in early-onset myasthenia gravis.

It has long been established that the thymus plays a central role in autoimmune myasthenia gravis (MG) because of either thymoma or thymic hyperplasia of lymphoproliferative origin. In this review, we discuss thymic changes associated with thymic hyperplasia and their implications in the development of an autoimmune response against the acetylcholine receptor (AChR).The hyperplastic MG thymus displays all the characteristics of tertiary lymphoid organs (TLOs): neoangiogenic processes with high endothelial venule and lymphatic vessel development, chemokine overexpression favoring peripheral cell recruitment, and ectopic germinal center development. As thymic epithelial cells or myoid cells express AChR, a specific antigen presentation can easily occur within the thymus in the presence of recruited peripheral cells, such as B cells and T follicular helper cells. How the thymus turns into a TLO is not known, but local inflammation seems mandatory. Interferon (IFN)-ß is overexpressed in MG thymus and could orchestrate thymic changes associated with MG. Knowledge about how IFN-ß is induced in MG thymus and why its expression is sustained even long after disease onset would be of interest in the future to better understand the etiological and physiopathological mechanisms involved in autoimmune MG.

CD4+ FoxP3+ T regulatory cell subsets in myasthenia gravis patients.

Although myasthenia gravis (MG) is a classic autoantibody-mediated disease, T cells are centrally involved in its pathogenesis. In recent years a number of studies have analyzed the role of CD4+ FoxP3+ regulatory T cells (Treg) in the disease with contradictory results. Here, the generation of Treg was significantly reduced in thymoma as compared to thymic hyperplasia and normal thymus tissue (p=0.0002). In the peripheral blood, Treg subsets classified according to CD49d, HELIOS and CD45RA expression changed after thymectomy and in the long-term course of immunosuppression. Compared to healthy volunteers the frequency of CD45RA+FoxP3low Treg was reduced in MG patients in general (p=0.037) and in particular in patients without immunosuppression (p=0.036). In our study, thymectomy and immunosuppressive treatment were associated with changes in Treg subpopulations. The reduced frequency of CD45RA+FoxP3low Treg we observed in MG patients might play a role in MG pathogenesis.

PD-L1, PD-1, CD4, and CD8 expression in neoplastic and nonneoplastic thymus.

The checkpoint protein programmed cell death ligand-1 protein (PD-L1) binds to its receptor (PD-1) activating the PD-L1/PD-1 pathway, an important therapeutic target. There is limited information regarding PD-L1 and PD-1 expression in thymic lesions. Sections from nonneoplastic thymi (n = 20), thymomas World Health Organization types A, AB, B1, B2, and B3 (n = 38) and thymic squamous cell carcinoma (n = 8) were stained for PD-L1 (clone SP142; Spring BioScience), PD-1 (MRQ22; Cell Marque), CD4 (clone SPO32; Cell Marque), and CD8 (JCB117; Ventana). Immunoreactivity for each antibody was classified as focal or diffuse and scored as follows: 0, negative; 1%-5%, 1+; 6%-20%, 2+; and >20%, 3+. The proportions of cases expressing PD-L1, PD-1, CD4, and C8 at score ≥1+ were compared by diagnosis, using χ2 statistics. PD-L1 was expressed in 90% of nonneoplastic thymi, 92% of thymomas, and 50% of carcinomas, with significantly higher scores (P < .01) in B2 and B3 thymomas and carcinomas than in AB and B1 thymomas; PD-L1 was diffuse in most B2 and B3 thymomas and focal in carcinomas. PD-1 was focally expressed, and mostly with scores 1+, in 55% of nonneoplastic thymi, 63% of thymomas, and 37.5% of carcinomas. CD4+ and CD8+ cells were diffusely distributed with scores 3+ in all lesions other than B3 thymomas and carcinomas. The latter showed CD4+ cells mostly at the interface between neoplastic cells and stroma. PD-L1 and PD-1 are not expressed in similar locations and cellular proportions in thymic lesions, raising a question as to whether the PD-L1/PD-1 pathway is an actionable therapeutic target in these lesions.

Graves' Patient with Thymic Expression of Thyrotropin Receptors and Dynamic Changes in Thymic Hyperplasia Proportional to Graves' Disease Activity.

Thymic hyperplasia is frequently observed in Graves' disease. However, detectable massive enlargement of the thymus is rare, and the mechanism of its formation has remained elusive. This case showed dynamic changes in thymic hyperplasia on serial computed tomography images consistent with changes in serum thyrotropin receptor (TSH-R) antibodies and thyroid hormone levels. Furthermore, the patient's thymic tissues underwent immunohistochemical staining for TSH-R, which demonstrated the presence of thymic TSH-R. The correlation between serum TSH-R antibody levels and thymic hyperplasia sizes and the presence of TSH-R in her thymus suggest that TSH-R antibodies could have a pathogenic role in thymic hyperplasia.

The thymus in autoimmune Myasthenia Gravis: Paradigm for a tertiary lymphoid organ.

In autoimmune Myasthenia Gravis (MG), a neuromuscular disease generally mediated by autoantibodies against the acetylcholine receptor (AChR), the muscle is the target organ of the autoimmune attack, while the thymus seems to be the primary production site of the autoantibodies. In the majority of patients with anti-AChR antibodies, it is characterized by the presence of germinal centers, which contain B cells that produce anti-AChR antibodies. In this review, we summarize recent results regarding neoangiogenic processes, cell infiltration and modified chemokine expression in the MG thymus, which are typical features of secondary lymphoid organs. The structural and functional changes in the MG thymus therefore allow us to declare it to be an archetype for tertiary lymphoid neogenesis providing optimal settings for the interaction between lymphocytes and antigen presenting cells in order to elicit an immune response. We further discuss factors that may have a key role in the transformation of the MG thymus into a tertiary lymphoid organ, such as IFN type I and dsRNA signaling. These factors could also be of importance in other autoimmune diseases, especially those characterized by tertiary lymphoid neogenesis.

Seronegative myasthenia gravis and Graves' disease. Is there a link?

Graves' disease (GD) and myasthenia gravis (MG) are common autoimmune diseases but their coexistence is very rare. They may possibly share the same pathogenetic mechanisms. Recent research has shown the involvement of autoantibodies, lymphocytes, cytokines and chemokines in the pathogenesis of MG and GD. It appears that Th17 cell lineage is involved in autoimmune thyroid disease (AITD) and seems to be key factor in the development of both MG and GD.A 34-year-old male with seronegative myasthenia gravis due to thymic hyperplasia was diagnosed with also GD and opthalmopathy. Several diagnostic and therapeutic issues regarding the relevant literature are discussed.

Comparative clinical features and immune responses after extended thymectomy for myasthenia gravis in patients with atrophic versus hyperplastic thymus.

BACKGROUND: Although extended thymectomy is believed to be suitable for myasthenia gravis (MG) patients with hyperplastic thymus, it is not clear whether surgical treatment is indicated for MG patients with atrophic thymus. We therefore assessed the clinical features and immune responses in 175 MG patients who underwent thymectomy between 1990 and 2004. METHODS: All patients underwent extended thymectomy by the transsternal approach. Clinical features, prognosis, and immune response after extended thymectomy were compared in patients with atrophic and hyperplastic thymuses. RESULTS: Of the 175 patients, 47 had atrophic and 128 had hyperplastic thymuses. Although the median times to complete stable remission of the two groups were similar (4.9 versus 4.8 years; p=0.513), the median time to clinical improvement was significantly longer in patients with atrophic thymus (3.3 versus 2.3 years; p=0.005). Patients with atrophic thymus showed a greater increase in ectopic thymus in the anterior mediastinal adipose tissue. Elevated B-cell activating factor receptor, CD19, and CD21 were observed in both hyperplastic and atrophic thymuses, although serum immunoglobulin G concentration after thymectomy increased more in patients with atrophic than in those with hyperplastic thymus. CONCLUSIONS: Atrophic thymus may contribute to the progression of MG. Patients with MG who have a atrophic thymus show similar postoperative prognosis as those with hyperplastic thymus, suggesting that surgical therapy should also be considered for the former subset.

IL-2 and proteoglycans synergistically induce antigen-specific B-cell responses--a possible immune response in the hyperplastic myasthenia thymus.

To understand developmental mechanisms of effector B-cells in the hyperplastic MG thymus, we have evaluated immunological roles of IL-2 and the 100-kDa haemopoietic biglycan, because the number of their producers increases pathologically there. When these two factors were added to an immune system together, the number of antibody-producing cells was markedly increased in a synergistic fashion. Further, IL-2 and the conditioned medium of myoid cells induced immunoglobulin isotype switches, suggesting that new B-cell stimulatory microenvironments were generated in the hyperplastic thymus. In relation to this, we also discuss a new biological feature, an immunomodulator, of conventional biglycan and decorin.

Clinical features of patients with myasthenia gravis associated with autoimmune diseases.

We investigated the incidence and clinical features of patients with myasthenia gravis (MG) associated with autoimmune diseases. Associated autoimmune diseases were found in 28 of 142 consecutive Japanese MG patients (19.7%), amongst which Graves' disease (7.7%) and Hashimoto's thyroiditis (4.2%) were predominant. The clinical features of MG patients with Graves' disease were different from those of MG patients without autoimmune diseases in terms of age at onset of MG symptoms (35.5 +/- 4.0 years and 49.0 +/- 1.7 years; P < 0.05), positivity for the anti-acetylcholine receptor antibody (44.4% and 89.8%; P < 0.05), and association with thymic hyperplasia (72.7 and 17.9%; P < 0.05). The therapeutic outcome of MG patients with Graves' disease and that of those without autoimmune diseases were not significantly different. Further studies should be performed to investigate whether MG associated with Graves' disease is a distinct subtype of MG.

Antigen-specific T-cell activation in hyperplastic thymus in myasthenia gravis.

In order to determine whether antigen-specific T-cell activation by dendritic cells (DCs) is accelerated in thymuses exhibiting lymphofollicular hyperplasia (TLFH) among patients with early-onset myasthenia gravis (EOMG), we investigated the expression levels of phosphorylated protein kinase C (PKC)theta and the local relationship between the presence of phosphorylated PKCtheta and the homing receptor CD44 or CD83, a marker for mature DCs, in samples taken from EOMG patients with early improvement following thymectomy, in remnant thymuses from late-onset MG patients, and in non-MG control thymuses. Antigen-specific T-cell activation was markedly accelerated in TLFH from EOMG patients. Activated T cells and adjacent DCs appeared to be components of a CD44(high) cell population circulating from the blood to the thymus. Although there is no convincing evidence that thymectomy is of benefit in MG, in some EOMG patients with early improvement following thymectomy, blockade of CD44-associated circulation mechanisms is probably the cause for the early benefits of thymectomy and is a potential alternative to thymectomy.

The distribution of parenchyma, follicles, and lymphocyte subsets in thymus of patients with myasthenia gravis, with special reference to remission after thymectomy.

OBJECTIVE: We sought to examine the distribution of parenchyma, follicles, and lymphocyte subsets in the thymus of patients with myasthenia gravis and to identify determinants of remission after thymectomy. METHODS: Sixty patients with myasthenia gravis who underwent thymectomy were examined. The thymus was divided into upper, middle, and lower parts. The upper part was defined as the superior horn, the lower part as the inferior horn, and the middle part as tissue located between the 2 horns. The percentage of parenchyma was measured morphometrically. The degree of follicular hyperplasia was classified into 5 grades. The densities of CD3+, CD4+, and CD8+ lymphocytes were classified into 5 grades. The remission of myasthenia gravis after thymectomy was examined with those variables in each part of the thymus. RESULTS: The middle part had the highest percentage of parenchyma, the highest grade of follicular hyperplasia, and the highest density of CD3+, CD4+, and CD8+ lymphocytes among the 3 parts (P < .001-.05). The grades of follicular hyperplasia in the middle and lower parts were significantly higher in patients with improvement of myasthenia gravis than in those without (P < .05). The densities of CD3+, CD4+, and CD8+ lymphocytes in the cortex of the middle part were significantly higher in patients with improvement than in those without improvement (P < .01-.05). CONCLUSIONS: The thymus has a heterogeneous distribution of parenchyma, follicles, and lymphocyte subsets. The middle part had the largest parenchyma, the highest grade of follicular hyperplasia, and the highest densities of CD3+, CD4+, and CD8+ lymphocytes among the 3 parts of the thymus. The grade of follicular hyperplasia and the density of these lymphocyte subsets are predictive of improvement in myasthenia gravis after thymectomy.

Microarrays reveal distinct gene signatures in the thymus of seropositive and seronegative myasthenia gravis patients and the role of CC chemokine ligand 21 in thymic hyperplasia.

Myasthenia gravis (MG) is an autoimmune disease mainly caused by antiacetylcholine receptor autoantibodies (seropositive (SP) disease) or by Abs against unknown autoantigenic target(s) (seronegative (SN) disease). Thymectomy is usually beneficial although thymic hyperplasia with ectopic germinal centers is mainly observed in SP MG. To understand the role of thymus in the disease process, we compared the thymic transcriptome of non-MG adults to those of SP patients with a low or high degree of hyperplasia or SN patients. Surprisingly, an overexpression of MHC class II, Ig, and B cell marker genes is observed in SP but also SN MG patients. Moreover, we demonstrate an overexpression of CXCL13 in all MG thymuses leading probably to the generalized B cell infiltration. However, we find different chemotactic properties for MG subgroups and, especially, a specific overexpression of CCL21 in hyperplastic thymuses triggering most likely ectopic germinal center development. Besides, SN patients present a peculiar signature with an abnormal expression of genes involved in muscle development and synaptic transmission, but also genes implicated in host response, suggesting that viral infection might be related to SN MG. Altogether, these results underline differential pathogenic mechanisms in the thymus of SP and SN MG and propose new research areas.

Raised prolactin levels in myasthenia gravis: two case reports and a study of two patient populations.

OBJECTIVES: To describe two patients with myasthenia gravis (MG) and prolactinoma and analyze the associations between MG and prolactin (PRL) levels. DESIGN: Two case reports and a case-control study of PRL levels in 192 patients with MG. PARTICIPANTS: The Immunological Research Laboratory, Center for Molecular Medicine, Department of Medicine and the Department of Neurology, Karolinska Institutet, Stockholm, Sweden; St Petersburg Medical Academy for Postgraduate Studies, and St Petersburg State Medical Pediatric Academy, Russia. RESULTS: Two women with MG and thymic hyperplasia accompanied by prolactinomas are described. The levels of plasma PRL were raised in 101 women with MG, but not in 91 men. There was an association between high PRL levels and high levels of autoantibodies against the acetylcholine receptor. CONCLUSIONS: There is an association of MG with raised levels of PRL in women. PRL has stimulating effects on immune activation and the increased levels might thus be implied in the pathophysiology of MG.

[Thymus CT scan and thymoma associated antibodies in myasthenia gravis with thymoma].

OBJECTIVE: To investigate the clinical significance of the serum anti-titin, anti-ryanodine receptor (RyR) antibody level and thymus CT scan in the diagnosis of myasthenia gravis with thymoma. METHODS: Totally 32 patients with myasthenia gravis who had received thymectomy were included in the study. Abnormalities were shown under CT scan of thymus in all these patients. The relationships were studied among the pathological diagnosis, CT findings, and serum level of thymoma associated antibodies: anti-titin and anti-RyR antibodies. RESULTS: The pathological diagnosis of thymoma was made in 21 patients and thymus hyperplasia in 11 patients after operation. The sensitivity of CT scan in the diagnosis of thymomas was 90.5%, the specificity of serum thymoma associated antibodies in the diagnosis of thymoma was 100%. CONCLUSION: The thymoma-associated antibodies test is helpful in the differential diagnosis of thymomas and thymus hyperplasia; when combined with CT scan, it may achieve high sensitivity in the diagnosis of the thymoma.

Pleiotropic effects of the 8.1 HLA haplotype in patients with autoimmune myasthenia gravis and thymus hyperplasia.

The 8.1 haplotype of the HLA complex has been reproducibly associated with several autoimmune diseases and traits, notably with thymus hyperplasia in patients with acquired generalized myasthenia gravis, an autoantibody-mediated disease directed at the muscle acetylcholine receptor. However, the strong linkage disequilibrium across this haplotype has prevented the identification of the causative locus, termed MYAS1. Here, we localized MYAS1 to a 1.2-Mb genome segment by reconstructing haplotypes and assessing their transmission in 73 simplex families. This segment encompasses the class III and proximal class I regions, between the BAT3 and C3-2-11 markers, therefore unambiguously excluding the class II loci. In addition, a case-control study revealed a very strong association with a core haplotype in this same region following an additive model (P=7 x 10(-11), odds ratio 6.5 for one copy and 42 for two copies of the core haplotype). Finally, we showed that this region is associated with a marked increase in serum titers of anti-acetylcholine receptor autoantibodies (P=8 x 10(-6)). Remarkably, this effect was suppressed by a second locus in cis on the 8.1 haplotype and located toward the class II region. Altogether, these data demonstrate the highly significant but complex effects of the 8.1 haplotype on the phenotype of myasthenia gravis patients and might shed light on its role in other autoimmune diseases.

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

OBJECTIVE: To identify the response to thymectomy in patients with seronegative and seropositive myasthenia gravis (SPMG). We analyzed the associated diseases, thymus histology, and the severity of symptoms between the two groups. MATERIAL AND METHODS - DESIGN: Descriptive, comparative. STUDY UNITS: Fourteen patients with seronegative myasthenia gravis (SNMG) and 57 patients with SPMG who had a thymectomy between 1987 and 1997, with at least 3 years of follow-up. The patients were divided into four groups; (1) Remission, (2) Improvement, (3) No change and (4) Deterioration. RESULTS: Fourteen patients (20%) were seronegative and 57 were seropositive (80%). In the group of patients with SNMG, three patients were in remission (21%), five with improvement (36%), five with no change (36%) and one with worsening (7%). In the group of patients with SPMG, 12 were in remission (21%), 17 with improvement (30%), 25 with no change (44%) and three (5%) with worsening. The patients with SNMG were older, with less associated diseases and with a lower frequency of thymomas. CONCLUSIONS: The response to thymectomy was similar between the two groups. It has been suggested that seronegative patients have a better prognosis, but our results show no differences.

Massive benign thymic hyperplasia in a six-month-old girl: case report.

A 6-month-old girl presented with respiratory symptoms with a large right-sided mediastinal mass noted on diagnostic imaging. Percutaneous biopsy revealed normal thymic tissue. Steroids were administered with no response. Right thoracotomy and complete thymectomy were performed. The specimen weighed approximately eight to ten times normal weight, and histology and flow cytometry revealed normal thymic tissue consistent with benign hyperplasia. The child has remained tumor free for a year since surgery. The rare nature of this tumor leads us to report this case and review the current literature.