Immunohistochemical and ultrastructural study of subacute thyroiditis, with special reference to multinucleated giant cells.

Twenty-four cases of subacute thyroiditis were examined immunohistochemically and ultrastructurally, with special attention being directed to the multinucleated giant cells that characterize the lesions of this condition. Immunohistochemical study revealed that 99 per cent of the giant cells contained lysozyme, 82 per cent contained vimentin, 66 per cent contained alpha 1-antitrypsin, and 61 per cent contained thyroxine. Only 17 per cent contained thyroglobulin, 5 per cent contained keratin, 16 per cent contained epithelial membrane antigen, and 4 per cent contained leukocyte common antigen. Mononuclear cells infiltrating the follicular spaces showed a staining pattern similar to that of the multinucleated giant cells. Desquamated follicular epithelial cells were strongly positive for thyroglobulin and thyroxine, while regenerated epithelia that formed small follicles were positive for thyroglobulin but negative for thyroxine. Electron microscopic examination of cell ultrastructure revealed that most multinucleated giant cells had structures identical with those of infiltrating mononuclear cells, particularly with histiocytes, and that giant cells were formed by mononuclear cell fusion. These findings indicate the majority of multinucleated giant cells in subacute thyroiditis are derived from mononuclear-histiocyte cells.