158: Transcervical Thymectomy

Introduction

Myasthenia gravis (MG) is an autoimmune disease mediated by anti-acetylcholine receptor antibodies (AChrab) directed against the acetylcholine receptor region of the post-synaptic 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 the 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 exist to support an immunopathological 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 are abound in the literature. The role of thymectomy can be questioned because no randomized, controlled trials comparing the best medical therapy and surgery exist. The changes in intensive care unit (ICU) care, ventilatory support, and the introduction of immunosuppressive therapy also have improved the clinical course of this disease and outcomes. Furthermore, the debate persists because of 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, asymptomatic on medication, or improved on medication, was two times higher among patients undergoing surgery compared to patients managed medically.⁵ The median improvement rates were 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 These results, however, suggest that other factors in addition to surgery may contribute significantly to the improvement observed after surgery. Currently, an international randomized multicenter study comparing transsternal thymectomy to medical treatment is enrolling patients. It appears that this study has had difficulty enrolling patients, with current evidence favoring thymectomy for generalized, nonthymomatous MG, and also by other less invasive routes.

Surgical Options

The point of debate in the surgical treatment of MG has been the preferred surgical approach. Some centers recommend maximal thymectomy (the Jaretzki approach; transsternal + transcervical) to eliminate the gland and possible extra-anatomical thymic tissue as well,^8...