Thymectomy and anti-muscle autoantibodies in late-onset myasthenia gravis

Effects of thymectomy on late-onset non-thymomatous myasthenia gravis: systematic review and meta-analysis

BACKGROUND

The effects of thymectomy on late-onset non-thymomatous myasthenia gravis (NTMG) remain controversial. The objective of this study was to conduct a systematic review in order to answer two questions pertinent to late-onset NTMG: (1) do patients with late-onset NTMG experience the same effects from thymectomy as their early-onset counterparts? (2) Compared with conservative treatment, does thymectomy have any benefits for late-onset NTMG patients?

METHODS

We searched the PubMed, EMBASE, and Cochrane Library databases for studies published from January 1, 1950 to March 10, 2021. Outcomes were measured via clinical stable remission/pharmacological remission (CSR/PR) and improvement rates. We used Stata software to analyze the data.

RESULTS

We ultimately included a total of 12 observational articles representing the best evidence answering the questions of our study objective. Of these, nine studies, which included 896 patients overall (766 early-onset and 230 late-onset), compared postoperative outcomes between early- and late-onset NTMG. The remaining three articles, which included 216 patients (75 in the thymectomy group and 141 in the conservative-treatment group), compared thymectomy with conservative treatment for late-onset NTMG. The early- versus late-onset NTMG studies demonstrated that patients in the former category were 1.95× likelier than their late-onset counterparts to achieve clinical remission (odds ratio [OR] 1.95; 95% confidence interval [CI] 1.39-2.73; I2 = 0%). No difference was seen in improvement or remission + improvement rates between these two groups. When comparing thymectomy with conservative treatments in late-onset NTMG patients, neither did we observe any difference in CSR/PR.

CONCLUSION

We found that late-onset NTMG patients had a lower chance of achieving CSR after thymectomy than early-onset patients. Thymectomy in late-onset NTMG also yielded no benefit to CSR or PR compared with conservative treatments. In late-onset NTMG patients, thymectomy should therefore be performed with caution, and the appropriate cutoff between early- and late-onset MG should be further explored in order to tailor and execute the proper therapeutic strategies.

Clinical features of myasthenia gravis in elderly and senile patients

The prevalence of myasthenia gravis is 10-24 cases per 100, 000 population. The debut of the disease is possible at any age: from infancy to old age. In the literature, the definition of “myasthenia gravis with late onset” – at the age of 60 years and older, which is 20-46% of all cases. In this regard, the disease is often combined with a burdened somatic history, which makes it difficult to timely diagnosis and treatment. This group of elderly patients accounts for the majority of diagnostic errors in the diagnosis of myasthenia gravis. This study is devoted to the study of the features of the onset and course of myasthenia gravis in elderly and senile people.

Effect of thymectomy in elderly patients with non-thymomatous generalized myasthenia gravis

Whether thymectomy is beneficial in elderly patients with myasthenia gravis (MG) is unclear. Thus, we assessed whether conducting thymectomy in MG patients aged ≥ 50 years is beneficial. This retrospective cohort study included patients with MG between 1990 and 2018. Thymectomy and control cohorts were selected from among the population of MG patients with an age at onset of ≥ 45 years and elevated concentrations of acetylcholine-receptor antibodies. Patients with evidence of thymic malignancy were excluded. Of these patients, those who underwent thymectomy at the age of ≥ 50 years were designated as the thymectomy group and those who received only medical treatment were designated as the medical treatment group. We compared the Myasthenia Gravis Foundation of America post-intervention status between the thymectomy and medical treatment groups. Landmark analysis was conducted with the landmark set at 24 months. A total of 34 and 105 patients were classified into the thymectomy and medical treatment groups, respectively. Before landmark analysis, the thymectomy group had a higher cumulative incidence of pharmacologic remission (p = 0.009) and complete stable remission (p = 0.022) than the medical treatment group. After landmark analysis, the thymectomy group had a 2.22-fold (95% confidence interval 1.01-4.80) increased chance of achieving pharmacologic remission compared to the medical treatment group after adjustment for age, sex, and disease severity. No significant difference was observed in the rate of relapse after pharmacological remission between the thymectomy (16.7%) and medical treatment groups (21.4%). In conclusion, thymectomy may have a beneficial effect in elderly patients with non-thymomatous generalized MG.

Antititin antibody in early- and late-onset myasthenia gravis

OBJECTIVES

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies against neuromuscular junction proteins, 85% of patients have antibodies against acetylcholine receptor (AChR-MG). Antititin antibodies are present in a subset of patients with MG. We aimed to determine the value of antititin antibodies as severity markers and thymoma predictors in early- and late-onset MG.

MATERIALS & METHODS

Two-hundred and ninety-five consecutive MG patients (188 F and 107 M) aged 12-89 years (mean 50y) were included. 164 patients had early-onset (EOMG, ≤50 years of age), 131 had late-onset MG (LOMG). Twenty-six patients had thymoma. symptoms, severity graded with MGFA scale, thymus histology, medications, and treatment results were analyzed.

RESULTS

Antititin antibodies were present in 81 (27%) of all patients: 54% of thymoma MG, 0.6% of non-thymomatous EOMG, and 55% of LOMG, with proportion of titin-positive patients increasing linearly from 40% in the 6th to 88% in the 9th decade of life. Titin-positive patients had more bulbar symptoms (P = 0.003). Severity of MG, need for immunosuppression, myasthenic crisis risk or treatment results were not related to its presence. Antititin antibodies had 56% sensitivity, 99% specificity, 90% positive predictive value (PPV), and 95% negative predictive value (NPV) for thymoma diagnosis in EOMG, and 50% sensitivity, 75% specificity, 71% PPV and 55% NPV in LOMG.

CONCLUSIONS

Antititin antibodies have high PPV and NPV for thymoma in EOMG. In MG without thymoma, antititin antibodies can be considered as markers of LOMG, but not of a severe course in our MG cohort.

Late-onset myasthenia gravis - CTLA4(low) genotype association and low-for-age thymic output of naïve T cells

Late-onset myasthenia gravis (LOMG) has become the largest MG subgroup, but the underlying pathogenetic mechanisms remain mysterious. Among the few etiological clues are the almost unique serologic parallels between LOMG and thymoma-associated MG (TAMG), notably autoantibodies against acetylcholine receptors, titin, ryanodine receptor, type I interferons or IL-12. This is why we checked LOMG patients for two further peculiar features of TAMG - its associations with the CTLA4(high/gain-of-function) +49A/A genotype and with increased thymic export of naïve T cells into the blood, possibly after defective negative selection in AIRE-deficient thymomas. We analyzed genomic DNA from 116 Caucasian LOMG patients for CTLA4 alleles by PCR/restriction fragment length polymorphism, and blood mononuclear cells for recent thymic emigrants by quantitative PCR for T cell receptor excision circles. In sharp contrast with TAMG, we now find that: i) CTLA4(low) +49G(+) genotypes were more frequent (p = 0.0029) among the 69 LOMG patients with age at onset ≥60 years compared with 172 healthy controls; ii) thymic export of naïve T cells from the non-neoplastic thymuses of 36 LOMG patients was lower (p = 0.0058) at diagnosis than in 77 age-matched controls. These new findings are important because they suggest distinct initiating mechanisms in TAMG and LOMG and hint at aberrant immuno-regulation in the periphery in LOMG. We therefore propose alternate defects in central thymic or peripheral tolerance induction in TAMG and LOMG converging on similar final outcomes. In addition, our data support a 60-year-threshold for onset of 'true LOMG' and an LOMG/early-onset MG overlapping group of patients between 40 and 60.

Prognostic factors and health-related quality of life in ocular Myasthenia Gravis (OMG)

We evaluate the factors predictive of prognosis in 91 Caucasian patients affected by ocular myasthenia gravis (OMG), followed at our Institution during an observational time, ranging from 12 to 240 months. The Myasthenia Gravis Foundation of America (MGFA) clinical classification was used to grade the disease severity. We considered as outcome measures the variation in two subscores, ocular (O-QMG) and nonocular (NO-QMG); the last one reflected bulbar, neck, extremity functions. None of the independent variables evaluated for association with the outcome, as age of onset, type of therapy, length of interval between first and last examinations, and presence of antibodies to acetylcholine receptors (AChR-Abs) significantly affected the evolution of O-QMG and of NO-QMG. Health-related quality of life (HRQol) was assessed in 63 patients. Variations of diplopia or ptosis did not affect significantly physical (PCS) or mental composite subscores (MCS) of the Short-Form Health Survey (SF-36). Human leukocyte antigen (HLA) genotyping was studied to explore whether HLA class I and II allelic distribution differed among MG patients and controls. None of the studied HLA alleles significantly differed between OMG patients and controls. Similarly, none of the alleles with frequencies higher than 15% either in OMG patients or in controls was significantly associated, after Bonferroni correction, with the presence or absence of anti-AChR-Abs in serum.

Thymus pathology observed in the MGTX trial

The MGTX trial is the first prospective, randomized clinical trial that aims to evaluate the impact of extended transsternal thymectomy on myasthenic symptoms, prednisone requirements, and quality of life in patients with nonthymomatous, anti-acetylcholine receptor autoantibody-positive myasthenia gravis (MG). Here, we give an overview of the rationale of thymectomy and the standardized macroscopic and histopathological work-up of thymectomy specimens as fixed in MGTX standard operating procedures, including the grading of thymic lymphofollicular hyperplasia and the morphometric strategy to assess thymic involution.

Muscle autoantibodies in myasthenia gravis: beyond diagnosis?

Myasthenia gravis is an autoimmune disorder of the neuromuscular junction. A number of molecules, including ion channels and other proteins at the neuromuscular junction, may be targeted by autoantibodies leading to abnormal neuromuscular transmission. In approximately 85% of patients, autoantibodies, directed against the postsynaptic nicotinic acetylcholine receptor can be detected in the serum and confirm the diagnosis, but in general, do not precisely predict the degree of weakness or response to therapy. Antibodies to the muscle-specific tyrosine kinase are detected in approximately 50% of generalized myasthenia gravis patients who are seronegative for anti-acetylcholine receptor antibodies, and levels of anti-muscle-specific tyrosine kinase antibodies do appear to correlate with disease severity and treatment response. Antibodies to other muscle antigens may be found in the subsets of myasthenia gravis patients, potentially providing clinically useful diagnostic information, but their utility as relevant biomarkers (measures of disease state or response to treatment) is currently unclear.

The auto-antigen repertoire in myasthenia gravis

Myasthenia Gravis (MG) is an antibody-mediated autoimmune disorder affecting the postsynaptic membrane of the neuromuscular junction (NMJ). MG is characterized by an impaired signal transmission between the motor neuron and the skeletal muscle cell, caused by auto-antibodies directed against NMJ proteins. The auto-antibodies target the nicotinic acetylcholine receptor (nAChR) in about 90% of MG patients. In approximately 5% of MG patients, the muscle specific kinase (MuSK) is the auto-antigen. In the remaining 5% of MG patients, however, antibodies against the nAChR or MuSK are not detectable (idiopathic MG, iMG). Although only the anti-nAChR and anti-MuSK auto-antibodies have been demonstrated to be pathogenic, several other antibodies recognizing self-antigens can also be found in MG patients. Various auto-antibodies associated with thymic abnormalities have been reported, as well as many non-MG-specific auto-antibodies. However, their contribution to the cause, pathology and severity of the disease is still poorly understood. Here, we comprehensively review the reported auto-antibodies in MG patients and discuss their role in the pathology of this autoimmune disease.

Effects of thymectomy on late-onset myasthenia gravis without thymoma

OBJECTIVES

This study aims to investigate whether thymectomy is beneficial for late-onset (>50 years) myasthenia gravis patients with no thymoma, particularly for those with mild generalized weakness.

PATIENTS AND METHODS

A total of 34 patients were included in the study. The clinical course and long-term outcomes over 2 years were reviewed in 20 patients who underwent thymectomy and in 14 without thymectomy.

RESULTS

Of the 34 patients, 20 (59%) underwent thymectomy. Thymectomized patients had more severe disability at entry than non-thymectomized patients, but outcome measures did not significantly differ between the two patient groups. Moreover, subgroup analyses including 22 patients with mild generalized weakness at entry showed that the thymectomized group (n=10) showed a greater percentage of clinical remission (no symptoms; 50% versus 17%; p=0.11) and a lower frequency of the presence of generalized symptoms (30% versus 75%; p<0.05) than the non-thymectomized group (n=12) at the end of follow-up (means 9.6 years after onset).

CONCLUSIONS

Thymectomy is a potentially effective treatment for late onset, non-thymomatous patients with mild generalized myasthenia gravis.

Titin and ryanodine receptor antibodies in myasthenia gravis

Some myasthenia gravis (MG) patients have antibodies against skeletal muscle antigens in addition to the acetylcholine receptor (AChR). Two major antigens for non-AchR antibodies in MG are the Ca(2+) release channel of the sarcoplasmic reticulum, the ryanodine receptor (RyR) and titin, a gigantic filamentous muscle protein essential for muscle structure, function and development. RyR and titin antibodies are found mainly in thymoma MG patients and in a few late-onset MG patients and correlate with a severe MG disease. The presence of titin antibodies, which bind to key regions near the A/I junction and in the central I-band, correlates with myopathy. The immunosuppressant (FK506), which enhances Ca(2+) release from the RyR, seems to have a symptomatic effect on MG patients with RyR antibodies. The RyR antibodies recognize a region near the N-terminus important for channel regulation and inhibit Ca(2+) release in vitro. However, evidence that antibodies against the intracellular antigens RyR and titin are pathogenic in vivo is still missing.

Myasthenia gravis: disease severity and prognosis

OBJECTIVES

To examine myasthenia gravis (MG) severity and long-term prognosis in seronegative, seropositive, and thymoma MG.

MATERIALS AND METHODS

Four series of patients were studied retrospectively. Severity and treatment were assessed each year, and muscle antibodies were assayed.

RESULTS

Seropositive MG patients had a more severe course than seronegative MG patients. MG severity was higher in non-thymectomized compared to thymectomized early-onset MG patients. MG severity did not differ between thymectomized and non-thymectomized late-onset patients. There was no significant difference in MG severity between thymoma and non-thymoma MG patients.

CONCLUSIONS

MG is more severe in seropositive MG patients. With proper treatment, especially early thymectomy, the long-term prognosis is good in seropositive MG patients. The present studies indicate a benefit of thymectomy in early-onset MG, but no dramatic benefit in late-onset MG. Similar MG severity and outcome was seen in thymoma and non-thymoma MG.

Myasthénie du sujet âgé : analyse rétrospective de 23 observations

PURPOSE

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

METHOD

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

RESULTS

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

CONCLUSION

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

Disease severity and outcome in thymoma myasthenia gravis: a long-term observation study

Thymomas occurring in myasthenia gravis (MG) are usually of the cortical subtype and are usually treated by thymectomy. However, the factors that influence MG outcome in thymoma MG patients are not known. In a long-term study, MG severity and treatment was observed in 24 thymoma and 24 non-thymoma MG patients for up to 30 years, and the occurrence of muscle autoantibodies was assayed. The rate of complete stable remission was low and did not differ between the two groups. There was no significant difference in MG severity between thymoma and non-thymoma MG patients at any time during the study. Titin and ryanodine receptor (RyR) antibody occurrence was significantly higher in thymoma MG patients. Four thymoma (all titin and RyR antibody positive) and two non-thymoma (both titin and one RyR antibody positive) MG patients died from MG-related respiratory insufficiency. Seventy percent of thymoma and 75% of non-thymoma MG patients were treated with immunosuppressive drugs. The number of patients who received plasmapheresis did not differ in those who were treated because of acute MG deterioration, irrespective of planned surgery.This study shows equal MG severity and outcome in thymoma and non-thymoma MG, but the presence of RyR antibodies in thymoma MG and titin/RyR in non-thymoma MG indicates a less favorable prognosis.

Myasthenia gravis in individuals over 40

Myasthenia gravis (MG) in individuals over 40 years of age comprises three groups: early-onset MG with prolonged disease duration, late-onset MG with thymoma, and late-onset of nonthymomatous MG. The clinical features do not differ between the three groups, except that early-onset patients with prolonged disease duration usually have a less severe disease. More than 60% of our MG patients are now more than 50 years of age, often with disease onset after age 40. Although 2 out of the 3 patients in Erb's original description had onset of myasthenic symptoms after age 40, this was apparently infrequent in 1879, when the disease was first identified. Onset of MG after age 40 is now common. For example, in our material, 88/184 (47.8%) had onset of MG after age 40. Eighteen (20.5%) had a thymoma. The female:male ratio in the early-onset group was 2.4:1, whereas it was 1:1.1 among those with onset after age 40. There was no human leukocyte antigen association for MG with thymoma. Antibodies to the acetylcholine receptor were detected in 88% of sera from nonthymomatous MG and in 100% of those with late-onset MG with thymoma. Antibodies to titin were found in sera from 85.7% of MG patients with thymoma (all age groups) and in 58% of nonthymomatous MG with late onset and acetylcholine receptor antibodies. Late-onset, nonthymomatous MG comprises two subgroups, one corresponding to delayed early onset and one immunologically similar to that seen in patients with MG and thymoma.

Treatment Principles in the Management of Autoimmune Myasthenia Gravis

The pathogenesis of myasthenia gravis (MG) involves a T cell-directed antibody-mediated autoimmune attack on the nicotinic acetylcholine receptor (AChR) or, occasionally, on other postsynaptic antigens. The antibodies induce their effects through complement-mediated destruction of the postsynaptic endplate membrane with resultant reduction in endplate AChR, and to a lesser degree by increased turnover of endplate AChR or blockade of AChR function. Considerable progress in the treatment of MG has accrued from so-called symptomatic treatments, including improved critical care of seriously ill patients and medications (e.g., cholinesterase inhibitors) increasing the concentration of acetylcholine at the remaining endplate AChRs. Information from other autoimmune diseases and from the response of the normal immune system to invading pathogens supports the view that the course of MG is characterized by exacerbations and remissions. Therefore, the goal in MG treatment is to induce and maintain a remission. This usually involves combinations of short-term and long-term immunosuppressive agents. Selection of the particular combinations of agents in a given patient is guided by the goal of minimizing the cost/benefit ratio of the regimen in an individual patient. In general, the plan involves an initial forceful attack followed by a slow and measured withdrawal.

Three Forms of Immune Myasthenia

We propose a new classification for immune myasthenia based on antibody pattern. The types of immune myasthenia presently characterized by known antibody targets segregate into three groups: type 1, in which the muscle target is the acetylcholine receptor only; type 2, in which titin antibodies are present in addition to acetylcholine receptor antibodies; and type 3, in which muscle-specific kinase antibodies are present in the absence of acetylcholine receptor antibodies. The immune target is unknown in the patients with immune myasthenia not associated with these antibodies. This classification has advantages over the present classifications as regards homogeneity of groups, etiology, mechanism of disease, and prognosis.