Chapter 134

The most common indication for thymectomy is myasthenia gravis (MG). MG is an autoimmune disorder caused by anti-acetylcholine receptor antibodies that reduce the number of available acetylcholine receptors at the neuromuscular end plate. Clinically, this results in muscle weakness and muscle fatigability. The exact role of the thymus in the pathogenesis of this disease remains poorly understood. Nevertheless, observations made by Blalock1 over 50 years ago suggest that surgical thymectomy can induce remission. Unfortunately, precise preoperative selection criteria for patients likely to achieve remission have not been defined. Likewise, the extent of operation required, whether radical or simple thymectomy, has not been established.

This chapter outlines the transcervical approach to thymectomy. This approach is used most frequently for patients with autoimmune, nonthymomatous MG. Recently, however, some groups have expanded the use of this technique to other anterior mediastinal abnormalities, such as intrathymic parathyroid adenomas.2 This chapter emphasizes patient selection, operative technique, and the advantages of the transcervical technique over more radical transsternal thymic resection. Because the procedure is performed most commonly on patients with MG, special attention is directed toward the care and management of this challenging disease.

### Patient Selection

The diagnosis of MG is suspected on clinical grounds. The muscle groups involved and their fatigability with repetitive exercise vary greatly from one patient to another. The diagnosis is confirmed by a neurologist on the basis of a positive Tensilon test, the presence of acetylcholine receptor antibodies, or characteristic electromyographic responses. It is important to classify patients on initial surgical evaluation to permit meaningful standardized measures of postoperative outcomes. In this regard, the Myasthenia Gravis Foundation of America Clinical Classification and Score for disease severity has been developed.3 Patients should be classified preoperatively according to the expanded quantitative MG scheme with the assistance of a neurologist.

Those considered for thymectomy must be medically optimized; surgical thymectomy is not a treatment for acute exacerbations of MG. The goal of thymectomy in MG, by any approach, is the long-term induction of remission. In this regard, close collaboration with a neurologist is required. Preoperative optimization can include the use of cholinesterase inhibitors, immunosuppressives, plasmapheresis, and IV immunoglobulin. Only patients who are medically stable can be considered for thymectomy. The practice guideline from the American Academy of Neurology states: “For patients with non-thymomatous autoimmune MG, thymectomy is recommended as an option to increase the probability of remission or improvement.”4 Thus, once medically optimized, all patients with MG, regardless of the severity of disease, should be considered for thymectomy by a qualified thoracic surgeon.

### Preoperative Assessment

All patients have a CT scan of the chest to evaluate for thymoma. In our practice, patients with nonthymomatous autoimmune MG are evaluated for transcervical thymectomy. Those with contraindications to this approach, including the presence of thymoma, are considered for transsternal resection (see Chap. 136). We obtain the preoperative forced ...

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