Abnormal basement membrane structures in autoimmune thyroid disease

Thyroidectomy specimens of 8 patients with focal thyroiditis, 7 with diffuse thyroiditis, 13 with Graves' disease and 5 with nodular goiter were investigated by electron microscopy for changes in the follicular basement membrane. Five different types of abnormal basement membrane structures (ABMS), analogous to the ones described in the glomerular basement membrane, were found. Type 1 ABMS were present in all diagnostic groups and seemed to be nonspecific. Type 2 ABMS, thought to represent immune complex deposits, were frequently present in patients with focal or diffuse thyroiditis and in patients with Graves' disease, but could not be demonstrated in thyroidectomy specimens of patients with nodular goiter. The occurrence of type 2 ABMS in both focal and diffuse thyroiditis suggests a common etiology of these two morphologic entities. ABMS types 3, 4, and 5 could not be detected in nodular goiter but were seen in various amounts in all other diagnostic groups. The origin of these structures remains to be explained.