It is only recently that an adequate randomized trial by Wolfe and colleagues has affirmed the usefulness of thymectomy. Beyond the demonstration of effect of the procedure over 3 years when coupled with alternate day prednisone compared to alternate day prednisone alone, certain of the outcomes of the trial were instructive but tentative due to the small number of patients enrolled: medical complications were lower in the surgical group as a result of reduced requirement for prednisone and immunosuppressive drugs, and the effects of the operation were clearer in women than in men. Viewing the Kaplan-Meier curves of that trial, it appears broadly that the effect of thymectomy was maximal at approximately 6 months and remained stable thereafter.
A suprasternal approach for removal of the gland has been developed and results in less postoperative pain and morbidity than occurs with a transsternal thoracotomy but the transsternal operation may be preferable because it assures a more complete removal of thymic tissue. Thymectomy is best performed in a hospital where there is close collaboration between the thoracic surgeon and the neurologist. If the patient is weak preoperatively, a course of plasma exchange or immune globulin may be given preceding the surgical procedure. Large “stress doses” of corticosteroids seem to be unnecessary in most patients who have been taking these medications chronically. After operation, respiratory assistance must be available if needed. Neostigmine intramuscularly may be given every 3 to 6 h postoperatively. Usually the dose requirement is about 75 percent of that taken before surgery. As improvement occurs, oral medications are resumed as remission is not anticipated for many months or longer as noted above.
Thymectomy may also be a safe and effective treatment in elderly patients with myasthenia. In 12 such individuals, Olanow and associates reported complete remission in 9 and clinical improvement in the remainder. The improvement in older patients is less convincing than it is in the younger group, in part because the thymus is atrophic. Nonetheless, some of our patients who were older than age 60 years did benefit. The abovementioned clinical trial did not include patients over age 65 years.
Removal of the thymus gland is also indicated in practically all patients in whom thymoma is detected by CT of the chest. The tumor can be locally invasive but rarely metastasizes. The operative approach is through the anterior thorax, with adequate exposure to remove all the tumor tissue. If the tumor cannot be removed completely, the remaining tissue should be treated with focused radiation. Local spread and lymph node invasion have been treated with combinations of chemotherapy including cisplatin, but it is not very satisfactory. Park and colleagues concluded from a large retrospective study of metastatic cases that chemotherapy offers some benefit in terms of survival, but this remains controversial.
Despite this endorsement of thymectomy for generalized myasthenia, it has remained an unproven therapy by a modern trial and attempts to recruit patients for such an endeavor have been difficult.
A rapid and severe deterioration of the myasthenia, termed myasthenic crisis, can bring the patient to the brink of respiratory failure in a matter of hours. A respiratory infection or excessive use of sedative medications or drugs with a potential for blocking neuromuscular transmission may precede the myasthenic crisis. We have encountered numerous cases in which oropharyngeal weakness has led to aspiration pneumonia, which, in turn, precipitated a crisis. Just as often, a precipitating event is not evident. Rarely, a respiratory arrest is the first manifestation of crisis. Such events may occur at any time after the diagnosis of myasthenia, but half are evident within 12 to 18 months. In an early but still salient experience with 53 patients in myasthenic crisis at the Columbia-Presbyterian Medical Center, pneumonia was the most frequent precipitating event, but no cause could be determined in almost one-third of cases (Thomas et al).