Abstract: Objective To investigate the classification of thyroid associated ophthalmopathy(TAO)subtypes by single photon emission computed tomography(SPECT)/computed tomography(CT) image analysis of ^99mTC-diethylenetriaminepentaacetic acid (DTPA), and to evaluate its role in activity assessment of TAO by calculating imaging agent uptake rate(UR).Methods An analysis was conducted on 205 patients who were diagnosed with TAO.According to ^99mTC-DTPA orbital SPECT/CT image analysis, TAO patients were divided into two types: type I was mainly retrobulbar lesions, type Ⅱ was mainly periorbital lesions. The clinical indexes were compared and the relationship between the uptake rate of imaging agents and clinical activity scores (CAS) were analyzed. Results The uptake rate of retrobulbar region (URR) of type Ⅰ TAO was significantly higher than that of type Ⅱ TAO, while the uptake rate of periorbital region (URP) of type Ⅱ TAO was higher. The difference was statistically significant (P<0.001). Type I and Ⅱ had significant differences in gender(P=0.001),age (P<0.001), CAS (P<0.001), diplopia scores (P<0.001)and thyrotropin receptor antibody(TRAb)(P=0.004). In type Ⅱ TAO, UR was correlated with the CAS(r=0.407,P<0.001).Receiver operating characteristic curve(ROC) curve analysis showed that the sensitivity of the type1 Ⅱ TAO when UR≥1.596 to judge the disease was active, the sensitivity is 68.4%, the specificity is 64.3%,and the clinical application value was limited. TRAb was correlated with CAS (r =0.215,P=0.007), but the correlation was weak.Conclusion ^99mTC-DTPA orbital SPECT/CT can provide an objective basis for the classification of patients with TAO, but it is not ideal for the evaluation of activity.

Key words: thyroid associated ophthalmopathy(TAO), subtypes, ^99mTC-diethylenetriaminepentaaceticacid, single photon emission computed tomography/computed tomography, clinical activity scores(CAS)