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      Thymolipoma-associated Myasthenia Gravis with High Titer of Anti-MuSKAb: A Case Report

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          Abstract

          Myasthenia gravis (MG) is a neuromuscular junction disorder caused by pathogenic autoantibodies to some parts of the post-synaptic muscle endplates. About 85% of generalized MG patients have autoantibodies against post-synaptic acetyl-choline receptors (AChR). From the 10-15% of the remaining patients, 45-50% are positive for Muscle Specific Tyrosine Kinase-Antibody (MuSK-Ab). It is believed that the thymus has a critical role in the pathogenesis of the disease with AChR-Ab, specially in patients with thymic abnormalities. In contrast, the role of thymus gland in MG with anti-MuSK-Ab is not clearly obvious. Patients with this antibody virtually have normal or only minimal follicular hyperplastic thymus. The presence of anti-MuSK Ab in a thymolipomatous (an uncommon tumor of thymus) MG is an atypical and new finding of MG because of not only thymolipoma but the presence of anti-MuSK antibodies which makes this case different from the previous reports of the antibodies-associated MG. Here, we present a young woman with thymolipoma and MG (a very uncommon kind of tumor-associated MG) and high level of anti-MuSK-Ab.

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          Most cited references13

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          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.
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            Myasthenia Gravis: A Review

            Acquired myasthenia gravis is a relatively uncommon disorder, with prevalence rates that have increased to about 20 per 100,000 in the US population. This autoimmune disease is characterized by muscle weakness that fluctuates, worsening with exertion, and improving with rest. In about two-thirds of the patients, the involvement of extrinsic ocular muscle presents as the initial symptom, usually progressing to involve other bulbar muscles and limb musculature, resulting in generalized myasthenia gravis. Although the cause of the disorder is unknown, the role of circulating antibodies directed against the nicotinic acetylcholine receptor in its pathogenesis is well established. As this disorder is highly treatable, prompt recognition is crucial. During the past decade, significant progress has been made in our understanding of the disease, leading to new treatment modalities and a significant reduction in morbidity and mortality.
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              Update on muscle-specific tyrosine kinase antibody positive myasthenia gravis.

              Important concepts regarding the pathogenesis, clinical features, diagnosis and treatment of muscle-specific tyrosine kinase (MuSK) antibody positive myasthenia gravis will be reviewed. Special attention will be paid to clinical phenotypes and treatment, particularly encouraging responses that have been reported to rituximab. Worldwide studies confirm three major phenotypes in MuSK antibody positive myasthenia gravis (MMG) patients: indistinguishable from acetylcholine receptor antibody positive patients, prominent faciopharyngeal weakness, usually with marked muscle atrophy, and relatively isolated neck extensor and respiratory weakness. MMG predominates in women and weakness is typically more severe, with more frequent respiratory crises than non-MuSK myasthenia gravis. Patients with sub-acute bulbar, shoulder, and neck weakness pose unique challenges in terms of differential diagnosis and electrodiagnosis. Electrodiagnostic studies evaluating for disorders of neuromuscular transmission should focus on proximal limb and facial muscles, as well as clinically weak muscles. The response to acetylcholinesterase inhibitors is often disappointing. Long-term outcomes appear favorable though patients typically require more aggressive immunosuppression. Uncontrolled observations report encouraging results with rituximab in the treatment of refractory MMG. The role of thymectomy in the management of these patients remains uncertain. MuSK antibody positive patients represent a unique subset of myasthenia gravis. Identification of these patients has important diagnostic and disease management implications.
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                Author and article information

                Journal
                Int J Mol Cell Med
                Int J Mol Cell Med
                IJMCM
                International Journal of Molecular and Cellular Medicine
                Babol University of Medical Sciences (Babol, Iran )
                2251-9637
                2251-9645
                Winter 2019
                28 June 2016
                : 8
                : 1
                : 90-93
                Affiliations
                [1 ] Clinical Neurology Research Center, Department of Neurology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
                [2 ] Medical Imaging Research Center, Department of Radiology, Shiraz University of Medical Sciences, Shiraz, Iran.
                [3 ] Department of Pediatric Medicine, Shiraz University of Medical Sciences, Shiraz, Iran.
                Author notes
                [* ]Corresponding author: Clinical Neurology Research Center, Department of Neurology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran Email: poursadegh@sums.ac.ir
                Article
                10.22088/IJMCM.BUMS.8.1.90
                7073264
                32195208
                ed5ba232-c769-4033-bb7f-a690172697c2

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License, ( http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 5 March 2019
                : 15 June 2019
                Categories
                Case Report

                myasthenia gravis,thymolipoma,anti-acetylcholine receptor antibody,anti-muscle specific tyrosine kinase- antibody

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