Somatostatin receptor scintigraphy in the follow-up of myasthenia gravis

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

Health‐related quality‐of‐life and treatment targets in myasthenia gravis

Introduction: The aim of this study was to determine factors affecting health‐related quality of life (HRQOL) and to propose appropriate treatment targets for patients with myasthenia gravis (MG). Methods: We evaluated 640 consecutive patients with MG seen at 11 neurological centers. Two‐year follow‐up data were obtained for 282 patients. Correlations between detailed clinical factors and the Japanese version of the 15‐item MG‐specific QOL scale score were analyzed. Results: In a cross‐sectional analysis of 640 MG patients, multivariate regression revealed that disease severity, as evaluated by the MG Composite (P < 0.0001), total dose of oral prednisolone during the last year (P = 0.002), and Cushingoid appearance index (P = 0.0004), showed significant negative effects on HRQOL, but the quantitative MG score and current prednisolone dose did not. Conclusions: Achieving minimal manifestations (MM) status or better with prednisolone ≤5 mg/day was found to exert a major positive impact on HRQOL in both the cross‐sectional and 2‐year follow‐up patient samples and can be recommended as a treatment target. Muscle Nerve 50: 493–500, 2014     

Do acetylcholine receptor and striated muscle antibodies predict the presence of thymoma in patients with myasthenia gravis?

Introduction: Acetylcholine receptor (AChR) and striated muscle antibodies (StrAbs) are found frequently in myasthenia gravis (MG) patients with thymoma. In this study we aimed to determine the positive predictive value (PPV) and negative predictive value (NPV) of these antibodies for thymoma in patients with MG. Methods: Antibody findings, thymic histology, and onset age were reviewed for 1141 patients with MG. PPV and NPV of these antibodies for thymoma were determined. Results: The PPV of AChR binding antibodies plus StrAbs was highest (50.0%) with onset before the age of 40 years. The PPV of all antibodies was low (<9%) after age 40. Higher StrAb levels did not increase the PPV. The NPV of AChR binding antibodies was high (99.7%) for all ages. Conclusions: Patients without AChR binding antibody are not likely to have a thymoma. StrAbs and AChR binding antibodies are not diagnostic for thymoma, but in early‐onset MG their presence should raise the clinical suspicion for thymoma. Muscle Nerve 49 : 30–34, 2014     

Paraneoplastic myasthenia gravis: immunological and clinical aspects

Paraneoplastic myasthenia gravis (MG) is accompanied by a neoplasm, usually thymoma. In patients with thymoma and a specific genetic make‐up, the paraneoplastic immune response develops further in thymic remnant or peripheral lymphatic tissue. Paraneoplastic MG and late‐onset MG (age ≥ 50 years) share a similar immunological profile with high titin and ryanodine receptor (RyR) antibody prevalence. This profile is the most important predictor of clinical outcome in paraneoplastic MG. The presence of a thymoma per se does not cause more severe MG. MG severity is linked to the patient’s immunological profile. Paraneoplastic MG causes a distinctive non‐limb symptom profile at MG onset, characterized by bulbar, ocular, neck, and respiratory symptoms. When the diagnosis of paraneoplastic MG is established, the neoplasm should be removed surgically. Pre‐thymectomy plasmapheresis or iv‐IgG should be considered in these patients to minimize post‐thymectomy MG exacerbation risk. Paraneoplastic MG usually continues after thymectomy. The pharmacological treatment of paraneoplastic MG does not differ from non‐paraneoplastic MG, except for tacrolimus that should be considered in difficult cases. Tacrolimus is an immunosuppressant acting specifically in RyR antibody positive patients through enhancing RyR‐related sarcoplasmic calcium release that in theory might be blocked by RyR antibodies, causing symptomatic relief in paraneoplastic MG.     

Mortality in myasthenia gravis: A nationwide population–based follow‐up study in Denmark

Introduction: In previous studies of myasthenia gravis (MG), increased mortality has been reported. The aim of this study was to estimate mortality in patients with acetylcholine receptor antibody–positive (AChR‐Ab–seropositive) MG in a nationwide population–based, long‐term follow‐up study. Methods: All AChR‐Ab–seropositive MG patients, diagnosed between 1985 and 2005, were identified. Defined by age at diagnosis (≤50 or >50 years), patients were classified as having early‐ or late‐onset MG. For comparison, 10 non‐MG individuals from the general population were matched with each patient. All patients and controls were followed until January 1, 2009. Mortality rates and estimated mortality rate ratios (MRRs) were calculated. Results: Of 702 AChR‐Ab–seropositive MG patients, 302 died during follow‐up. Overall mortality was higher for patients with MG (MRR = 1.41, range 1.24–1.60). In late‐onset women and men, the MRRs were 1.64 (1.36–1.99) and 1.22 (1.02–1.46), respectively. Total MRR was highest during the first 5 years after diagnosis. Conclusions: MG diagnosis is still associated with increased mortality. Muscle Nerve 53 : 73–77, 2016     

Thymus imaging in myasthenia gravis: The relevance in clinical practice

Introduction: The ability to distinguish between normal thymus, thymic hyperplasia, and thymoma should aid clinical management and decision making in patients with myasthenia gravis (MG). We sought to determine the accuracy of routine imaging in predicting thymic pathology. Methods: We retrospectively analyzed records of patients with MG from the Oxford Myasthenia Centre registry who had undergone thymectomy. Each patient received 1 radiological diagnosis and 1 histological diagnosis. Results: We included 106 patients. Radiological and histological diagnoses agreed in 73 (68.9%) patients. Sensitivity and specificity, respectively, were calculated for each radiological diagnosis as follows: thymoma 90% and 95.5%, hyperplasia 17.6% and 98.6%, and normal 96.9% and 60.8%. Discussion: Routine chest computed tomography and MRI can effectively identify thymoma. However, they are not reliable tools to differentiate between thymic hyperplasia and normal thymus in patients with MG. Muscle Nerve 58 : 153–156, 2018     

胸腺瘤的病理类型与重症肌无力发病的相关性研究

目的探讨胸腺瘤WHO病理分型与重症肌无力(MG)发病的相关性。方法收集2008-01—2018-12在大连大学附属新华医院住院的101例胸腺瘤患者,均行胸腺扩大切除术治疗,对患者的临床及病理资料分析,并定期术后随访。根据2004版WHO胸腺瘤的病理分型,分析胸腺瘤患者的WHO病理分型与MG发病的相关性。结果121例胸腺瘤患者中,病理类型A型30.77%合并MG,AB型30.00%合并MG,B1型56.52%合并MG,B2型72.00%合并MG,B3型56.52%合并MG,C型28.57%合并MG,差异有统计学意义(P<0.05)。胸腺切除术的疗效A型有效率最高,为100%,其次是B1型,有效率92.31%,AB型有效率77.78%,B2型有效率66.67%,B3型有效率46.15%,C型有效率最差(0),差异有统计学意义(P<0.05)。结论胸腺瘤的病理类型与MG具有相关性;B2型胸腺瘤与其他病理分型相比更易合并MG;胸腺瘤病理恶性程度越高,手术切除治疗MG的效果越差。     

Factors associated with response to calcineurin inhibitors in myasthenia gravis

The objective was to assess which clinical factors of patients with myasthenia gravis (MG) are associated with responsiveness to calcineurin inhibitors (CNIs, cyclosporine and tacrolimus). We retrospectively analyzed the 6‐month effects of CNIs in 62 MG patients. We excluded the influence of other immune treatments and determined factors associated with response to CNIs. The frequency of patients who achieved neither a ≥3‐point reduction in quantitative MG score nor a ≥25% reduction in daily dose of prednisolone (poor responders) reached 35.5% (22/62) and 64.5% (40/62), respectively, compared with patients who achieved at least one of these improvements (responders). Neither dose nor blood concentration of CNIs differed between groups. Multivariate logistic regression analysis revealed time since onset of disease [odds ratio (OR) = 0.85, P = 0.005] and presence of thymoma (OR = 5.56, P = 0.05) as clinical factors that predict response to CNIs. As for MG‐related autoantibody status, an autoantibody against a voltage‐gated potassium channel, Kv1.4, was associated with response (OR = 9.01, P = 0.04) and showed a correlation with the presence of thymoma (P < 0.01). In MG, the early stages of disease and thymoma‐associated MG are responsive to treatment with CNIs. Muscle Nerve, 2010     

Paraneoplastic diseases associated with thymoma

Abstract Background Thymoma is frequently associated with paraneoplastic diseases (PDs), most commonly with myasthenia gravis (MG). This association is thought to depend on thymoma's capacity to produce and export T lymphocytes. Objective (1) To determine the frequency and characteristics of thymoma-associated PDs other than MG; (2) to evaluate T cell maturation in thymomas with and without PDs. Methods We studied 260 patients with thymoma (associated with MG in 228). The occurrence of PDs was monitored together with the tumor outcome. Phenotypic characterization of thymocyte subsets in 14 thymoma samples (7 with and 7 without MG) was performed by FACS. Results A total of 47 PDs was diagnosed in 41/260 patients (15.8 %). Neurological PDs included neuromyotonia, limbic encephalitis, polymyositis, subacute hearing loss, psychosis and sleep disorders. A broad spectrum of nonneurological PDs were observed, among these, hematological and cutaneous diseases prevailed. Like MG, these disorders occurred either in the presence of the thymoma or at different times after thymomectomy; their onset often heralded a tumor recurrence. In thymomas from MG subjects, we found an increased proportion of fully mature CD4 single positive (SP) thymocytes and a reduced frequency of CD4SPCD25⁺ cells; the latter finding may reflect a deficient generation of T regulatory cells, a reduced intratumorous activation of T cells, or both. Conclusions We confirm the strong association of thymoma with PDs. These disorders often occurred in MG patients and their course in relation to thymoma was similar to that of MG. In accordance with previous observations, we found some alterations in the intratumorous production of mature CD4⁺ T cells that could be involved in the pathogenesis of paraneoplastic autoimmunity.     

Respiratory insufficiency from myasthenia gravis and polymyositis due to malignant thymoma triggering Takotsubo syndrome

Abstract

Background: Takotsubo syndrome (TTS) is a non-ischaemic cardiomyopathy with sudden but transient systolic dysfunction. TTS mimics myocardial infarction clinically, chemically, and electrocardiographically but echocardiography typically shows apical ballooning and coronary angiography is normal. TTS has not been reported in a patient with myasthenia gravis (MG) and polymyositis due to a malignant thymoma.

Case report: Two weeks prior to admission, a 76-year-old female developed dysarthria, chronic coughing and disabling myalgias of the entire musculature. Since there was hyper-CKemia and elevated troponin, myocardial infarction was suspected. During swallowing of the antithrombotic medication on admission, she experienced apnoea, requiring cardio-pulmonary resuscitation with intubation and mechanical ventilation. Further diagnostic work-up precluded coronary heart disease but revealed TTS. Upon neurologic work-up, MG and polymyositis were diagnosed but the response to cholinergic drugs and plasmapheresis was poor. TTS was attributed to stress and anxiety from MG-associated respiratory insufficiency. The further course was complicated by recurrent supraventricular bradyarrhythmias and respiratory insufficiency. Upon thoracic CT a thymoma was suspected. Two months after admission, the mediastinal tumour was resected and malignant thymoma WHO BII infiltrating the mediastinum (modified Masaoka-Koga II/2) was diagnosed.

Conclusions: This case shows that TTS may be triggered by stress from respiratory insufficiency during a myasthenic crisis, MG may be associated with polymyositis, cholinergic medication may trigger bradyarrhythmias, and cholinergic drugs and plasmapheresis may exhibit a poor effect if malignant thymoma and polymyositis are present.     

Do titin and cytokine antibodies in MG patients predict thymoma or thymoma recurrence?

BACKGROUND: Patients with MG often have other autoantibodies in addition to those against the acetylcholine receptor (AChR). It has been suggested that antibodies to the muscle protein titin may be diagnostic of a thymoma, but they have also been found in patients with late-onset MG. Antibodies to certain cytokines have also been detected in patients with MG and thymoma, and it is not clear whether these antibodies could be more useful clinically. The authors measured antibodies against titin and the cytokines interferon alpha (IFNalpha) and interleukin 12 (IL12) in patients with MG and thymoma or thymoma recurrence, and in patients with MG but without thymoma presenting before (early-onset MG) or after (late-onset MG) 40 years of age. METHOD: Levels of titin, IFNalpha, and IL12 antibodies were determined by radioimmunoassay in 191 patients with MG and 82 controls. RESULTS: As previously reported, titin antibodies were uncommon in patients with early-onset MG. However, in patients with late-onset MG, titin antibodies had similar prevalence and levels to those in patients with MG and thymoma, although the antibodies were uncommon in patients between 40 and 60 years of age presenting without a tumor. By contrast, cytokine antibodies were more common in patients with thymoma than in patients without thymoma, and cytokine antibodies typically increased substantially if the thymoma recurred. CONCLUSIONS: Measurement of titin antibodies has limited use in predicting the presence of a tumor, unless the patient is less than 60 years of age, but measurement of IFNalpha and IL12 antibodies may be helpful in identifying patients with a thymoma recurrence, particularly when mediastinal imaging is equivocal.     

West nile virus infection and myasthenia gravis

Introduction: Viruses are commonly cited as triggers for autoimmune disease. It is unclear if West Nile virus (WNV) initiates autoimmunity. Methods: We describe 6 cases of myasthenia gravis (MG) that developed several months after WNV infection. All patients had serologically confirmed WNV neuroinvasive disease. None had evidence of MG before WNV. Results: All patients had stable neurological deficits when they developed new symptoms of MG 3 to 7 months after WNV infection. However, residual deficits from WNV confounded or delayed MG diagnosis. All patients had elevated acetylcholine receptor (AChR) antibodies, and 1 had thymoma. Treatment varied, but 4 patients required acetylcholinesterase inhibitors, multiple immunosuppressive drugs, and intravenous immune globulin or plasmapheresis for recurrent MG crises. Conclusions: The pathogenic mechanism of MG following WNV remains uncertain. We hypothesize that WNV‐triggered autoimmunity breaks immunological self‐tolerance to initiate MG, possibly through molecular mimicry between virus antigens and AChR subunits or other autoimmune mechanisms. Muscle Nerve 49 : 26–29, 2014     

Translation and validation of the arabic version of the revised 15‐item myasthenia gravis quality‐of‐life questionnaire

Introduction: We sought to translate, culturally adapt, and assess the Arabic version of the 15‐item myasthenia gravis quality‐of‐life revised scale (MGQOL15R). Methods: We assessed reliability with Cronbach α; reproducibility with intraclass correlation coefficient (ICC); validity with Spearman correlations for myasthenia gravis (MG)‐specific activities of daily living (MG‐ADL), MG composite (MGC) score, and MG manual muscle test (MG‐MMT) and with MGQOL15R in patients with different disease severity through the Kruskal–Wallis test; and sensitivity to change with Wilcoxon signed‐rank test. Results: In 65 enrolled patients, the mean MGQOL15R score was 10.84 ± 8.11 (α = 0.94, ICC = 0.95). The correlation coefficients between MGQOL15R and MGC, MG‐ADL, and MG‐MMT scores were 0.75, 0.75, and 0.74, respectively (P < 0.001). MGQOL15R scores were significantly higher (worse) in patients with more severe disease at baseline and significantly lower (better) in improved patients at follow‐up. Discussion: The Arabic version of MGQOL15R is valid, reliable, stable, and sensitive to changes. Muscle Nerve 57 : 581–585, 2018     

“Jerky” dystonia in children: Spectrum of phenotypes and genetic testing

Hyperkinetic dystonia is characterized by phasic, tremulous, and “jerky” movements in addition to twisting postures. We studied longitudinally 23 index patients with hyperkinetic dystonia from a quaternary pediatric movement disorder clinic in Ireland. Four clinical categories emerged: (1) Eight patients were diagnosed with myoclonus‐dystonia, of whom seven carried heterozygous epsilon sarcoglycan (SGCE) mutations, including a novel deletion of exon 10. Gait disorder, unsteadiness, or frequent falls before 18 months were detected in all SGCE mutation carriers, whereas the typical neck‐predominant presentation developed only years later. (2) One patient classified as benign hereditary chorea, because jerks were choreiform and continuous rather than action‐induced, carried a heterozygous stop mutation of the TITF‐1 gene (Y114X, exon 2). (3) Three mutation‐negative patients were grouped as “myoclonic dystonia” with jerks only in the body regions affected by dystonia. (4) Eleven patients presented with a novel combination of dystonia and low amplitude poly‐mini myoclonus of the upper limbs and pectoral muscles (D‐PMM). In early childhood up to 3 years of age, an initial presentation with predominant gait impairment with only subtle jerks should prompt consideration of SGCE mutation analysis in addition to testing for DYT1 mutations. A causative gene for D‐PMM remains to be identified. © 2008 Movement Disorder Society     

A case of more than 20 years survival with glioblastoma,and development of cavernous angioma as a delayed complication of radiotherapy

Glioblastoma (GBM) is the most common malignant CNS neoplasm, the prognosis of which remains poor even after multidisciplinary treatment. The 5‐year overall survival rate of GBM is less than 10% and has remained unchanged for more than 50 years. Because GBM patients rarely survive over a decade, only very few cases of delayed complications caused by therapy have been reported. Here, we report the case of a 24‐year‐old man who is still alive 21 years after surgical resection and chemoradiotherapy for GBM. This patient developed a cavernous angioma 19 years after the initial surgery as a delayed complication of radiotherapy. The diagnosis of the initial tumor was confirmed by histopathological review, which indicated that the tumor had immunohistochemical and genetic profiles consistent with GBM. Long‐term survival in the case of this GBM patient likely resulted from a combination of factors, including hypermethylation of the MGMT (O⁶‐methyl guanine methyl transferase) CpG island, young age at diagnosis, good performance status, and complete surgical resection of the tumor. To the best of our knowledge, this case report describes one of the longest‐surviving GBM patients and is the first on radiation‐induced cavernous angioma in a GBM patient.     

Muscle strength and fatigue in newly diagnosed patients with myasthenia gravis

Introduction: Dynamometry is increasingly used as an objective measurement of muscle strength in neurological diseases. No study has applied dynamometry in untreated newly diagnosed patients with myasthenia gravis (MG). Methods: Isometric muscle strength at the shoulder, knee, and ankle was determined in 21 MG patients before and after initial anti‐myasthenic treatment. Isometric strength was compared with MG evaluation scales. Results: Muscle strength was reduced for knee extensors and shoulder abductors but normal for ankle extensors. Isometric muscle strength did not correlate significantly with manual muscle testing (MG Composite). Dynamometry revealed improved muscle strength of up to 50% (median 17%; range ‐1.8–49.8) despite no change in the MG Composite score. Conclusions: Dynamometry appears to be a more sensitive method of identifying changes in limb strength than MG evaluation scales. This supports the use of dynamometry in MG patients, especially for evaluation of the effect of anti‐myasthenic treatment. Muscle Nerve 54 : 709–714, 2016     

Correlation between “hourglass‐like fascicular constriction” and idiopathic anterior interosseous nerve palsy

Introduction: In recent operative cases of anterior interosseous nerve palsy (AINP), hourglass‐like fascicular constrictions have been reported. We prospectively investigated the ultrasonographic history of these lesions to better understand the role of this lesion in AINP. Methods: Seven patients who were diagnosed with idiopathic AINP based on classic clinical findings and had hourglass‐like fascicular constrictions found on ultrasonography were included. All but 1 patient selected surgery, and we followed up all patients clinically and with ultrasonography. Results: In the 5 patients treated surgically in whom paralysis recovered to a level greater than M4, postoperative ultrasonography revealed less constriction. The other patient experienced little recovery after surgery, and the severe constriction remained. In a conservatively treated patient, the paralysis recovered completely, and upon ultrasonography, the constriction had lessened. Conclusions: Although the mechanism is still unknown, hourglass‐like fascicular constriction lessened with relief of motor weakness both in operatively and conservatively treated patients. Muscle Nerve 55 : 508–512, 2017     

CLINICAl AND IMMUNOPATHOLOGICAL.OGICAI. STUDY ON THE THYMUS IN MYASTHENIA GRAVIS

Objective Directing towards the thymus and emphasizing mainly on the clinical and immunopathofogical study to probe its actior of the diagnosis,treatmeant and pathogcnesis cfmyasthema gravis(MG). Results tnd Dicusslons I .Diagnosis of MG with thymus pathologic lesions: I.MG with thymus hyetplasta It was shown by midstemum. CT scanning Germinal center arises from B ceil was determined by immunohistologic stain(Tol 5 marked); 2MG with thymoma It usualy occures at midaged man and apt to relapses on myasthenic crises. Positive rate of serum CAE-Ab(anti-citric acid extract antibody of human skeletal musie) was used tc find small thymoma early Rabbit Anti-serum against human CAE was labeled to determine thymoma AgNOR(argyrophilic stain of nuclear organizer region)was used to differentiate bemgn and maligant thymoma .As Muller-Hermlink' s classfication.thymoma of cortical type occurred more common and reliable to infiltration Ⅱ Treatment of MG with thymus pathoiogic lestons Except for symptomatic treatment with anti-acytlecholine drugs.MPSS or CTX intravenous perfusion had effect to relieve the myasthenic cnsis Using thymus radiation therapy to 134 cases, the complete remission and remarkable improvement rates were 66.5%.Rhe long-term effect followed up was rather stable. Using percutanous paracentesis into thymus gland for intervention treatment to 13 cases, all of them showed effect within one week.10 cases followed up more than 3 years,9 cases were complete remission or remarkable improvement Thymectmy is still a basic therapy for MG.In 102 cases with thymectomy,the complete remission and remarkable improvement rates were 59.8%,mortanty was 176%.Continual observation of CAE-Ab could contribute to determine the pateint' s prognosis,9 patients in severe condition followed up within 3 years,their serum CAE-Ab antibody titers persisted at high lever,3 Of them died,but 7 patients followed up within I year,those of their serum antibodies decreased quickly,5 cases of them got complle remission. Asides the question whether being thymectomied or not operate.it seems that treatment should direct towards the thymus,had better to take corresponding treatment early,indivually and from time to time and use each trcatment correctly under strict monitor to make effort for heigh effcct;It also needs futher following up and creating new therapy for to raise long-term effect Ⅲ .Thymus for the pathogenises of MG: 1.Thymus and skeletal muscie both exist nAchR common antigen; 2.T-cells play the crucial role in MG autoimmune response,they form the complex of TCR-nAchR MHC ,and become the basis of immune resconsibillity in MG; 3.Thymus epithelium cells and thymocytes make interaction abnormally to response again, st foreign antigen(as virus infection);and result in autoimmune response for self-antigen owing to lose immunotolerance. 4 Thymoma epithelium cells exist different inheritance susceptibilities,the alamine at position 57(Ala 57) of HLA - DO β gene expressing is more signiticant association with Chinese MG patients with thymoma.     

A case of myasthenia gravis appearing after thymomectomy: with histopathological investigation]

We report a 64-years old man who had myasthenia gravis (MG) appearing after surgical removal of thymoma. His thymoma was not removed completely due to adhesion with other organs. Histopathologicaly, the thymoma was an invasive and predominantly epithelial type. CD45RO positive cells increased in the thymus. After five months of thymectomy, he received radiation therapy because the remaining tumor grew up slightly. The radiation was effective, and the recurrence of tumor has never been detected after that. However, nine months after the surgery, he noticed ptosis and double vision, and he was diagnosed as MG because of positive serum anti-AchR antibody and positive Tensilon test. He received oral prednisolone, and he has kept a good condition. Previous reports have shown that an extensive thymectomy tends to reduce the incidence of post-operative MG. In our case, the remaining thymoma might increase the risk of MG. And the removed thymus might contain an unknown regulatory factor that could inhibit a development of MG. The risk factor for development of post-operative MG should be investigated in future.