Thyroid Associated Ophthalmopathy:CT Imaging Of Extraocular Muscle Coronal Area And Subtypes Analysis

Objective Both extraocular muscle (EM) and orbital fat are involved inthyroid associated ophthalmopathy (TAO). Orbital imaging for TAO is important fordiagnosis and management of the disease. The aim of this essay is to analysis ofextraocular muscle coronal area(EMA) in thyroid associated ophthalmopathy (TAO)and its clinical significance and describe different TAO subtypes.Method This is a retrospective study.By using commercial software with asegmentation technique, we calculated from computed tomography (CT) scan EMAin42patients with TAO and20control subjects. Enlargement of superior, lateral,inferior, and medial EMA and total EMA were selected.The relationship between total EMA and clinical activity Score (CAS)，exophthalmos, intraocular pressure(IOP), corrected visual acuity were alsomeasured.According to total EMA and proptosis, we divided the TAO patients into4groups: group Ⅰ: no increase in EM or in orbit fat(OF); group Ⅱ: only OF increase;group Ⅲ: only EM increase; group Ⅳ: both EM and OF increase.Result The coronal area of inferior rectus, lateral rectus, superior rectus,medial rectus and total EMA were significantly larger in patients with TAO than thecontrol subjects（p＜0.001，p=0.033，p＜0.001，p＜0.001，p＜0.001).We foundthat the inferior rectus and the superior muscle group were most often involved byTAO (60.71%,58.33%,separately）, followed by the medial rectus(40.48%）, andfinally the lateral rectus(25%）. Clinical Activity Score(CAS), corrected visualacuity and IOP were significantly correlated to the total EMA in TAOpatients(r=0.791，p＜0.001; r=-0.658，p＜0.001; r=0.454，p=0.019,separately). Foursubtypes of TAO could be distinguished: Group Ⅰ, no OF and EM incrase；Group Ⅱ,only OF increase（21.4%）; Group Ⅲ,only EM incrase（23.8%）; Group Ⅳ,bothOFand EM incras（e54.8%）. The patients of group Ⅱ were younger than the subjectsof group Ⅲ and Ⅳ(p＜0.001）.CAS of group Ⅱ patients were less than4scores,andall of them were at inactive stage and had no visual acuity loss. Most of them had theexperence of management of radioiodine-131. CAS of group Ⅲ and Ⅳ wassignificantly higher than group Ⅱ, and corrected visual acuity was lower than groupⅡ.Conclusion We described a simple and accurate method that uses commercialsoftware to determine the cross section areas of EM. With these measurements weobserved EMA enlargement in TAO. Total EMA, as a marker of GO evolution, was correlated to the activity of disease and could distinguish the subtpyes ofTAO.OF increase was found to be related to younger age, female and the experenceof radioiodine-131. Most of them were related bilateral orbit with no diplopia and atinactivity of disease. EM increase were related to more severe disease with orwithout single orbit.