Abstract
Histhlogical characteristics of the thymic tissues in the patients with myasthenia gravis (MG) have been believed to be in the follicular hyperplasia of the thymic tissues or in the thymoma tissues. In this study, both histological and histometrical analyses on non-neoplastic thymi and thymomas of 65 MG patients and of 12 non-MG patients were performed.
All of the investigated thymi of MG patients showed lymph follicular formations in the thymic tissue. The volume ratio of the residual thymic tissue, which was measured by a point-count method, was decreased along with aging. On the other hand, the lymph follicles did not show any remarkable aging involution. The entire thymic tissue related to the pathogenesis of MG, may not have the age involution. On the contrary, the fact that hyperplasia of the lymph follicle has no relationship with aging, may suggests the role of lymph follicle in pathogenesis of MG.
In cases having germinal centers, follicular vasculature showed similar type to those in the lymph follicles of lymph nodes. That was, the arteriolar system merged in the lymph follicle immediately after its divergence, then passed over to multiple postcapillary venules around the follicles and returned to small veins of vascular stroma of the thymus. It become clear in the histological findings that these follicles were located and grown up in these vascular stroma of the thymus. There were distinct limiting membrane were locally interrupted or dispersed in all MG cases.
In the cases studied the thymoma tissues in MG and in non-MG showed no histological differences. However, the peripheral residual thymic tissues in the thymoma in cases of MG revealed similar histopathological changes as in the non-neoplastic thymus of MG.
From all the data described, it may be suggested that lymph follicular formation in the thymic tissue of neoplastic and non-neoplastic MG gives rise to a kind of reconstruction of the kind of reconstruction of the vascular structures in the thymus, and some focal interruption or dispersion of the limiting membrane. It is concluded that a kind of reconstruction of thymic vascular structures may be one of the most characteristic findings in the nonneoplastic and thymomatous thymic tissues in the myasthenia gravis patients.
