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INTRODUCTION

Myasthenia gravis (MG) is an autoimmune disease mediated by anti–acetylcholine receptor (AChr) antibodies directed against the AChr region of the postsynaptic membrane. Blocking and accelerated degradation of acetylcholine receptors lead to impaired neuromuscular transmission and muscle weakness.1 MG has a predilection for the ocular and bulbar muscles, but generalized proximal muscle weakness is also common. Fatigable weakness is the hallmark of MG, and the disorder is diagnosed by clinical presentation, abnormal single-fiber electromyography, repetitive nerve stimulation tests, and elevated ACh and/or anti-MuSK antibodies. Abnormalities of the thymus gland are commonly found in these patients. Of MG patients, 10% to 15% have thymoma. Lymphoid thymic hyperplasia is present in about 70%.2 Significant data support an immunopathologic role of the thymus in the development of autoimmune MG.3

ROLE OF SURGICAL THERAPY

The beneficial role of surgery for patients with MG was first described before the middle of the past century.4 Further clinical reports of the benefits of the thymectomy led to the acceptance of this procedure for patients with generalized MG as a standard of practice. Nonetheless, controversies surrounding the role of thymectomy in the treatment of MG abound in the literature. The role of thymectomy can be questioned because no randomized, controlled trials comparing the best medical therapy and surgery exist. Changes in intensive care unit (ICU) care and ventilatory support, as well as the introduction of immunosuppressive therapy, also have improved the clinical course of the disease and outcomes. Furthermore, the debate persists because patient selection and methods of analysis of results vary from center to center. Regardless, surgery is currently considered to increase the likelihood of improvement.5 Retrospective studies suggest that patients undergoing thymectomy have higher remission rates than those who are treated medically.6

In a review, the likelihood of improvement, defined as medication-free remission, lack of symptoms on medication, or improvement on medication, was two times higher among patients undergoing surgery compared with patients managed medically.5 The median improvement rates were as follows: total remission 25%, asymptomatic with medication 39%, and clinically improved 70%. The benefits of thymectomy are often delayed, with 25% achieving remission in the first year, 40% by the end of the second year, and 55% in the third year.7

An important trial was recently completed examining the role of surgical resection in myasthenia gravis. This trial studied thymectomy for non-thymomatous MG in patients receiving prednisone therapy. This was an international, multicenter, randomized, single-blind (rater-blinded) trial to determine whether extended transsternal thymectomy combined with a standardized prednisone protocol would be superior to prednisone alone after 3 years, with respect to lessening myasthenic weakness, lowering the total dose of prednisone, and enhancing quality of life. The authors claimed that transsternal thymectomy was chosen because it provides “reproducible resection of the maximal amount of thymic tissue with low morbidity and a limited risk of phrenic nerve injury.”

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