Role of diffusion tensor imaging of extra ocular muscles and orbital fat in Graves’s ophthalmopathy and relation to disease activity

Graves’ ophthalmopathy (GO) is one of the most common autoimmune inflammatory disorders affecting the orbit that characterized by swelling of extra ocular muscles (EOMs) and expansion of the orbital fat. Diffusion tensor imaging (DTI) could assess the microstructural integrity of tissue. We aimed at this study to assess the role of DTI in the evaluation of EOMs and orbital fat in GO and identify the relationship with disease activity. Case–control study included 40 patients diagnosed as Graves’ disease (20 active and 20 inactive) and 10 health control subjects underwent DTI. Low fraction anisotropy (FA) and high mean diffusivity (MD) of inferior rectus (IR), medial rectus (MR) and orbital fat in GO versus healthy control (HC), while high FA and high MD in active group versus inactive group. In order to differentiate between GO and HC; FA cutoff point of IR, MR& orbital fat were 0.46, 0.45 and 0.26 with sensitivity 98.8%,98.8% and 93.8% and specificity 95.0%, 95.0% and 85%, respectively. MD cutoff point for IR, MR and orbital fat 1.24, 1.27 and 1.275 with sensitivity 97.5%, 98.8% and 98.8% and specificity 95.0%, 95% and 95%, respectively. To differentiate between active and inactive GO; FA cutoff point of IR, MR and orbital fat were 0.35, 0.36 and 0.22 respectively with sensitivity 80.0%, 82.5% and 72.5% and specificity 95.0%, 85.0% and 65.0%, respectively. MD cutoff point for IR, MR and orbital fat were 1.58, 1.63 and 1.54 respectively with sensitivity 90.0%, 97.5% and 85.0%, and specificity 90.0%, 80.0% and 62.5%, respectively. DTI parameters (FA and MD) of EOMs and orbital fat are considered as crucial radiological biomarkers for diagnosis of GO and could quantitatively differentiate active form inactive disease.