Ryanodine receptor antibodies are associated with severe myasthenia gravis

Sera from 32 thymoma patients, 29 of them with myasthenia gravis (MG), were tested for the presence of circulating antibodies to the ryanodine receptor (RyR) in Western blot RyR is a channel protein essential for the excitation-contraction coupling in skeletal muscle. MG severity was scored according to the Osserman classification during 1–17 years of follow-up (mean 7 years). Fifteen patients (14 MG and 1 non-MG) were RyR-antibody positive. RyR-positive patients had a significantly higher frequency of invasive thymomas (p = 0.01), and also a more severe MG than RyR-antibody negative patients (p = 0.04). The use of immunosuppressive drugs at latest follow-up was more frequent in RyR-antibody positive than in RyR-antibody negative patients (p = 0.02). Thus the presence of RyR-antibodies in thymoma patients is associated with a more severe disease and can be used as a prognostic marker.     

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.     

重症肌无力患者胸腺瘤内Titin、Ryanodine受体表位表达

目的 研究重症肌无力（MG）患者血清连接素抗体（Titin—ab）和Ryanodine受体抗体（RyR—ab）的水平，并探讨胸腺瘤内Titin、RyR表位的表达。方法 应用ELISA法检测62例MG患者血清中Titin—ab、RyR—ab水平，以45例非MG的其他神经系统疾病患者和50名健康志愿者为对照组，采用免疫组织化学技术，对19例合并胸腺异常者[9例MG合并胸腺瘤（MGT）、6例MG合并胸腺增生（MGH）、2例MG合并胸腺萎缩（MGA）以及2例非MG胸腺癌（NMGTC）]的冰冻胸腺组织进行Titin、RyR染色。结果ELISA法显示，MG患者Titin—ab总阳性率为35．5％（22／62），其中以MGT组阳性率最高（82．3％，14／17）；而RyR—ab阳性率为24．2％（15／62），也以MGT组阳性率最高（76．5％，13／17）。9例MGT的肿瘤上皮细胞中有7例存在Titin表位的膜表达和胞质内表达，有6例存在RyR表位的膜表达；而MGH组、MGA组、NMGTC组和对照组均无阳性表达。结论 Titin—ab和RyR—ab主要见于MGT患者。MGT肿瘤上皮细胞存在Titin、RyR表位的表达。MGT患者体内Titin—ab和RyR—ab很可能是胸腺瘤内微环境的改变激活Titin、RyR特异性T细胞，致敏Titin、RyR表位使其发生自身鱼疳反廊的结果．     

Penicillamine-induced myasthenia gravis associated with antibodies to acetylcholine receptor

A woman with rheumatoid arthritis was treated with penicillamine and developed myasthenia gravis. This drug-induced disease was associated with characteristic autoantibodies to acetycholine receptor. After discontinuing the drug, her symptoms improved and the antibody titers fell. Penicillamine is now being used much more frequently in the treatment of rheumatoid arthritis and it is likely that this complication will become more prevalent.     

Acetylcholine receptor antibodies in myasthenia gravis

A multivariate statistical analysis of levels of serum acetylcholine receptor antibody (AChR Ab) obtained from 197 patients with various clinical forms of myasthenia gravis (MG) was performed. Elevated AChR Ab levels are specific for MG, but normal AChR Ab levels do not rule out MG. Patients in remission or with purely ocular MG had the lowest incidence of elevation of serum AChR Ab levels, while patients with generalized, severe MG, particularly in the presence of thymoma, tended to have the greatest antibody elevations. Corticosteroids depressed AChR Ab levels, but thymectomy did not exert a consistent effect on antibody levels within a 24- to 30-month postoperative period. The relatively low 55% positivity of antibody elevations in all 197 patients probably reflects the use of heterologous (rat) AChR.     

Giant cell polymyositis associated with myasthenia gravis and thymoma

We report a case of a 40-year-old woman who developed generalized muscle weakness over a period of 2 months. Physical examination revealed palpable masses in her arms and hands. Serum creatine kinase levels were elevated. Electromyography showed myopathic changes and 3 Hz repetitive nerve stimulation revealed a decremental pattern on repetitive nerve stimulation. Muscle MRI demonstrated increased signal intensity in the biceps brachii on T1-weighted images. Chest CT scan showed a mediastinal mass suggestive of thymoma. Muscle biopsy revealed giant cell polymyositis. The patient was treated with cholinesterase inhibitors and corticosteroids with improvement of strength, and subsequently underwent thymectomy followed by radiotherapy.     

Acetylcholine-receptor-like protein from human thymoma associated with myasthenia gravis

Summary Cobrotoxin-binding protein was isolated by affinity chromatography from human thymoma which had been surgically removed from patients with myasthenia gravis. The protein was composed of polypeptides with a molecular mass of 40, 51, 65, and 74 kilodaltons as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl-sulphate. Isoelectric focusing of the protein gave pI values of 5.2–5.6 and 11. This is the first report of the isolation of the protein from human thymoma. These findings suggest that the cobrotoxin-binding protein from human thymoma patients with myasthenia gravis has subunits similar to those of fish electric organs or mammalian muscles.     

Paraneoplastic encephalitis associated with myasthenia gravis and malignant thymoma

We present a patient with type B2 thymoma (World Health Organization Thymoma Classification) with the complications of anti-muscle acetylcholine receptor antibody-positive myasthenia gravis and anti-voltage-gated potassium channel antibodies associated with paraneoplastic encephalitis. A timing difference between the onset of these neurological disorders and a dissociation of clinical symptoms was observed during the disease. This report alerts clinicians that long-term follow-up is needed where patients have a residual thymoma and attention should be paid to other concomitant autoimmune disorders.     

Stiff-persons' syndrome associated with thymoma and subsequent myasthenia gravis

We report the first case of stiff-persons' (-man) syndrome in the setting of a histologically proven thymoma. Muscular hyperactivity was abolished under general anesthesia and the symptoms of stiffness resolved after thymectomy and three courses of intravenous immunoglobulins. After thymectomy, the patient developed ocular myasthenia gravis which later resolved spontaneously. We suggest that thymoma be sought for in cases with neuromuscular hyperactivity syndromes. Myasthenia gravis may develop subsequently in these cases. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 493–498, 1997     

Anti-MuSK antibodies: correlation with myasthenia gravis severity

The authors measured anti-muscle-specific tyrosine kinase (anti-MuSK) antibodies (Abs) in 83 serum samples from 40 patients and evaluated their correlation with myasthenia gravis severity and treatment response. Ab concentrations were often reduced by immunosuppression but not after thymectomy. Both in individual cases and in the whole population, a correlation between Ab levels and disease severity was found.     

Ryanodine receptor antibodies in myasthenia gravis: epitope mapping and effect on calcium release in vitro

Patients with myasthenia gravis can have antibodies against skeletal muscle ryanodine receptor (Ry1), the sarcoplasmic reticulum calcium-release channel, which plays a crucial role in excitation-contraction coupling. We have screened a panel of overlapping Ry1 fusion proteins with Ry1 antibody-containing myasthenia gravis sera to identify the main immunogenic region. The pc2 Ry1 fusion protein representing a Ry1 region close to the N-terminus (residues 799-1172) was identified as the main immunogenic region for the antibodies. The binding kinetics of the Ry1 antibodies to the pc2 Ry1 fusion protein were tested using an optical biosensor. Ry1 antibodies in the IgG fraction from sera of patients with myasthenia gravis bound with high affinity and with a stoichiometry of 1:1. The functional effect of these Ry1 antibodies was tested in an in vitro Ca2+-release assay. The Ry1 antibodies induced a twofold increase of the half-maximal concentration for 4-Cl-m-cresol-induced Ca2+ release from terminal cisternae vesicles but had no effect on V(max). The effect on 4-Cl-m-cresol-induced Ca2+ release was specific, as preincubation of the active IgG fraction with the pc2 Ry1 fusion protein abolished the inhibition. These data suggest that the Ry1 sequence defined by residues 799-1172 is involved in the regulation of Ry1 function, and that this regulation could be functionally affected in vivo in patients with myasthenia gravis.     

Childhood-onset myasthenia gravis with thymoma

Juvenile myasthenia gravis is an acquired, autoimmune disease occurring before age 16 years. Thymoma is exceedingly rare in children, especially in association with juvenile myasthenia gravis. We describe a 14-year-old boy with juvenile myasthenia gravis and thymoma. He presented with difficulties chewing and swallowing, nasal speech, and fluctuating weakness of the leg muscles. Neurologic examination revealed masticatory and bulbar muscle weakness with nasal speech, proximal muscle weakness, fatigability of the arms and legs, and distal muscle weakness of the legs. A diagnosis of juvenile myasthenia gravis was confirmed by a positive neostigmine test, a decremental response on repetitive nerve stimulation, and increased titers of serum anti-acetylcholine receptor antibodies. The patient received anticholinesterases, corticosteroids, azathioprine, and thymectomy. A pathohistologic analysis of the thymus gland indicated thymoma, Masaoka grade II. After 2 years of an unstable disease course, remission was achieved. Because only 10 cases of thymoma-associated myasthenia gravis are described in the pediatric population, this report offers an important contribution to a better understanding of this rare association.     

Characterization of the nicotinic acetylcholine receptor antibodies after an unexpected increase of antibody titer in thymoma associated myasthenia gravis patients

Two thymoma-associated myasthenia gravis patients with chronic well-controlled disease but an unexpected increase in anti-nAChR autoantibodies titer are reported. The specificity of anti-nAChR autoantibodies directed against extracellular parts of the receptor was studied in order to investigate the discrepancy between clinical and immunological status. Analysis of the anti-nAChR autoantibodies recognizing the extracellular parts of the nAChR revealed that when the concentration of anti-nAChR autoantibodies titer increased both patients had non-anti-α1 autoantibodies. Since the clinical profile of both patients remained unchanged, the increase of non-anti-α1 autoantibodies did not affect the 2 patients’ disease progression. Thus, immunotherapy modification due to an increase of anti-nAChR autoantibodies titer could be erroneous and potentially harmful.     

Anti-presynaptic membrane receptor antibodies in myasthenia gravis

Myasthenia gravis (MG) is considered as an autoimmune disease of neuromuscular junction resulting from antibodies directed to acetylcholine receptors (AChR). We describe the use of beta-bungarotoxin (beta-BuTx) and alpha-bungarotoxin (alpha-BuTx) to capture their corresponding proteins from preparation of crude human muscle receptor. beta-BuTx binds to presynaptic membrane receptor (PsmR) of the whole receptor fraction, while alpha-BuTx binds to AchR. The captured proteins were used as antigen in ELISA to detect antibodies to PsmR and to AchR in sera from 82 Chinese patients with MG and in controls. In MG, antibodies to PsmR only were detected in 13%, to AchR only in 11% and both to PsmR and AchR in 54%. Only 3 of 50 patients with other neurological diseases and none of 50 healthy subjects had these antibodies. Specificity tests for antibodies showed that the detection systems which we used are specific and confident. No correlation was found between antibody levels and clinical status. The significance of the PsmR antibodies in the pathogenesis of MG is unknown. We suggest that myasthenia gravis is not only due to damage of the postsynaptic membrane, but of presynaptic structures as well.     

Thymoma-associated myasthenia gravis without acetylcholine receptor antibodies

Patients with myasthenia gravis and thymoma usually present antibodies to the acetylcholine receptor (AchR-Ab). Only two cases of thymoma-associated myasthenia gravis without AchR-Ab have been previously reported. We describe a case of seronegative thymoma-associated myasthenia gravis as a further evidence of the variability of myasthenia gravis in terms of antibody profile and thymic pathological findings.     

Subacute motor neuronopathy associated with myasthenia gravis and thymoma]

We reported a 63-year-old woman, suffered from myasthenia gravis with thymoma who later developed subacute motor neuronopathy after thymectomy. She noticed distally dominant muscle weakness and atrophy of bilateral upper extremities without sensory loss 4 month after thymomectomy. Her muscle weakness did not improve by intravenous administration of anti-cholinesterase (Tensilon test). Electrophysiological examinations showed no decremental response of examined muscles during repetitive nerve stimulation, nor motor nerve conduction block nor demyelination of affected peripheral nerves. Laboratory study demonstrated positive anti-acetylcholine receptor, anti-nuclear and SS-A antibodies. On immunohistochemistry, the patient's sera positively stained human and rat anterior horn cell cytoplasm as well as axoplasm of spinal white matter and root nerve axon, suggesting the presence of anti-axon antibody, possibly against neurofilament or tubulin components. The biopsied muscle specimen showed neurogenic muscle changes, but with no evidence of vasculitis nor cellular infiltration. Therapeutic trial of plasmapheresis was effective for her muscle weakness. Further recovery of weakness and muscle atrophy of hand muscles was obtained by combined therapy of intravenous and oral corticosteroid administration and plasmapheresis. These clinical, electrophysiological and histological findings suggested that antibodies against neuronal component might be responsible for her motor neuronopathy associated with myasthenia gravis. The findings of our case study may support the idea that some cases of motor neuron disease are caused by auto-immune mechanism.