Extended Thymectomy for Myasthenia Gravis Patients: A 20-Year Review

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Background

Since 1973 we have performed extended thymectomy for myasthenia gravis because of the presence of thymic tissue in the anterior mediastinal fatty tissue. Follow-up results were reviewed and influencing factors were investigated.

Methods

Three hundred seventy-five patients with myasthenia gravis (286 nonthymomatous and 89 thymomatous) who have undergone extended thymectomies were reviewed. The status of the patients was evaluated as follows: A (remission), B (improvement), C (no change), D (deterioration), E (death due to myasthenia gravis). Evaluation was performed at 3 and 6 months, and at 1, 3, 5, 10, 15, and 20 years. The effectiveness of the operation was estimated by the remission rate (RR = A/Total number of patients evaluated) and the palliation rate (PR = A + B/Total number of patients evaluated) at each point.

Results

Remission rates of the nonthymomatous patients were 15.2% (3 months), 15.9% (6 months), 22.4% (1 year), 36.9% (3 years), 45.8% (5 years), 55.7% (10 years), 67.2% (15 years), and 50.0% (20 years). Remission rates in the thymomatous patients were 13.6% (3 months), 17.5% (6 months), 27.5% (1 year), 32.4% (3 years), 23.0% (5 years), 30.0% (10 years), 31.8% (15 years), and 37.5% (20 years). Absence of thymoma, younger age, and short duration of the disease were favorable prognostic factors. Thymec-tomy was effective also in patients with ocular myasthenia gravis. Preoperative steroid administration did not improve the outcome.

Conclusions

Extended thymectomy is an excellent operative procedure for myasthenia gravis in both nonthymomatous and thymomatous patients.

Section snippets

Material and Methods

Three hundred eighty-four patients with MG (286 non-thymomatous and 98 thymomatous) were operated on in the First Department of Surgery of Osaka University and in the Second Department of Surgery of Nagoya City University from 1973 to 1993. In these, all of the nonthy-momatous patients underwent extended thymectomy. On the other hand, only 89 patients in the thymomatous group underwent extended thymectomy with total resection of thymoma. The stages of thymomas according to Masaoka and colleagues

Patient Characteristics

The age distribution is shown in Table 2. In the nonthy-momatous group, a peak in the 20- to 40-year-old group was found. The mean age was 35.0 years: men, 38.3 years, and women, 33.9 years. The sex distribution revealed predominance in women. On the other hand, the mean age of the thymomatous patients was 44.0 years: men, 43.1 years, and women, 45.1 years. The sex distribution was equivalent.

The severity of disease was classified by our MG classification system [3]: type I, MG limited to

Comment

We have performed “extended thymectomy” as a standard procedure for treatment of MG since 1973. In 1981, the results of this procedure were compared with those of the transsternal simple thymectomy, and the transcervical simple thymectomy [5]. “Simple thymectomy” means thymectomy without adipose tissue resection. In that article, we showed that the results of extended thymectomy are superior to those of the other procedures. Furthermore, we found that reoperations after ineffective cervical

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