Prevalence of ectopic thymic tissue in myasthenia gravis and its clinical significance.

Forty patients with myasthenia gravis underwent maximal thymectomy. Complete histologic study findings were available for 38 patients. The prevalence of ectopic thymic tissue was 39.5% (15 of 38). On the basis of the presence or absence of ectopic thymic tissue, patients were divided into two groups: group I had ectopic thymic tissue and group II had no ectopic thymic tissue. Male/female ratio was almost equal (1.1:1) in group I, whereas in group II the ratio was 1:2.8. The duration of the disease was less than 1 year in 80% of group I and 47.8% of group II patients (p = 0.05). Furthermore, ectopic thymic tissue (group I) was associated with poor outcome of operation (p = 0.003). Only 2 (13.3%) of 15 patients in group I had complete remission as compared with 11 (47.8%) of 23 patients in group II. Thus it appears that the presence of ectopic thymic tissue not only modifies some of the clinical parameters of myasthenia gravis, but also could serve as a prognostic factor in predicting the outcome of operation.