The Thymoma and Thymic Hyperplasia in Myasthenia Gravis with Observations on the General Pathology

Abstract

Since the comprehensive study by Bell in 1917 no systematic treatise on the thymic tumors of myasthenia gravis has appeared. It might be expected that the past twenty years would have added the records of many more cases to the literature and have extended our knowledge of the pathological anatomy of myasthenia gravis and the associated thymic tumors. On the contrary but few cases with autopsy findings have been reported and our conceptions concerning the morbid anatomy of this disease are much the same as they were in 1917. In the period from 1901, the year in which Weigert published the record of the first case of myasthenia gravis with an associated thymus tumor, to 1917, Bell found published reports of 56 autopsied cases of this disease. He wrote: “The thymus was described as enlarged in seventeen of these cases; and in ten others it contained a tumor. Therefore some form of thymic involvement seems to occur in nearly half the cases of myasthenia gravis.” Since 1917 the records of 6 more autopsies have been published and 5 of these showed thymic lesions. Of the 4 cases to be reported here, 2 had thymic lesions which were recognized. I am of the opinion that pathologic changes may be found in the thymus in cases of myasthenia gravis in direct ratio to the care with which they are sought. Thus, prior to 1901, when Weigert first called attention to the association, the presence of changes in the thymus had been completely overlooked. In 1912 Starr reviewed 250 cases of myasthenia gravis, including cases reported prior to 1901 in which the thymus was probably not carefully investigated. His figures showed thymus involvement in only 28 per cent of the cases, while Bell9s analysis of 56 autopsies between 1901 and 1917 yielded an incidence of thymic involvement in 50 per cent. With the addition of our 4 cases and the 6 reported elsewhere since 1917 the incidence of thymic lesions remains at 50 per cent. This figure probably expresses the frequency of grossly recognizable lesions of the thymus. It seems quite possible, however, that thymic lesions which have produced little or no macroscopic alteration of the suprapericardial tissue may have been overlooked in some of the reported cases. In the first place, as will be pointed out later on, the thymic lesion may not be recognizable without a microscopic examination. In the second place the thymic region in the post-adolescent ages is frequently passed over in the routine necropsy with the most cursory inspection. These facts have doubtless combined to lower the figure which expresses the frequency of reported lesions of the thymus.