Computerized tomography in the evaluation of myasthenia gravis.

Thymomas occur in 10% to 15% of patients with myasthenia gravis. Since not all patients are referred for thymectomy, a test that could reliably predict the presence or absence of a thymoma would be of great assistance in the management of these patients. We studied all patients referred for thymectomy at Walter Reed Army Medical Center from 1983 to 1989. Complete records were available for 13 patients. Computerized tomography (CT) correctly predicted the presence of a thymoma in one patient and falsely predicted a thymoma in a patient with a thymic cyst; it accurately predicted the absence of a thymoma in the remaining 11 patients. The sensitivity of CT scanning was 100%, the specificity was 92%, and the accuracy was 92%, results that are in agreement with previously published data. Compared to conventional chest roentgenography, CT scanning provided a more precise anatomic localization, and accurately predicted local invasion. We recommend a CT scan of the mediastinum in all patients with myasthenia gravis to avoid delayed diagnosis of thymoma in patients who normally would not be referred for thymectomy.