Histopathologic and ultrastructural study of extraocular muscles in thyroid associated ophthalmopathy

Objective To investigate histopathologic and ultrastructural changes of extraocular muscles(EOM) in thyroid associated ophthalmopathy(TAO).Methods Twelve EOM specimens from 11 patients with TAO were observed.Each of the specimen was stained with HE and observed by light microscope,and then was sectioned with ultrathin method and observed by transmission electronic microscope.Results Under the light microscope,sarcoplasm coagulation,granular degeneration,vacuolization and necrosis were found in the extraocular muscular cells.Under the electronic microscope,there were disturbance and disappearance of the Z line in part of muscular fibers and various degrees of sarcoplasmic reticulum dilatation,myofilament lysis and destruction with formation of vacuoles.In severe cases,the muscular cells could be completely destroyed and phagocytosed by macrophages,fibrosis occurred and myofibroblasts were found in some cases.Conclusion The extraocular muscles in TAO are destroyed at various degrees,and the muscular cells may be the target cells in TAO.