[The application of ⁹⁹Tc^m-DTPA orbital SPECT/CT in staging evaluation of thyroid associated ophthalmopathy]

Objective: To explore the application value of ⁹⁹Tc^m-diethylenetriaminepentaacetic acid (DTPA) orbital single photon emission computed tomography/computed tomography (SPECT/CT) in staging evaluation of thyroid associated ophthalmopathy (TAO). Methods: A case-control study. A total of 40 patients with binocular TAO were recruited from May 2019 to December 2019 in the Second Hospital of Dalian Medical University. According to the clinical activity score (CAS) standard, 40 TAO patients were divided into the active group (15 cases) and the inactive group (25 cases), and 10 healthy volunteers were recruited as the control group. All subjects underwent ⁹⁹Tc^m-DTPA orbital SPECT/CT examination, and each subject's CAS, reading results and maximum standardized uptake value (SUVmax) were recorded. The Kruskal-Walis H test was used for the CAS comparison among the three groups. The analysis of variance was used for the SUVmax comparison among the three groups. The comparison between CAS and SUVmax before and after treatment was performed by paired samples Wilcoxon signed rank test and paired-sample t test, and Spearman correlation analysis was performed between SUVmax and CAS. The Kappa test was used to check the consistency between the reading result and CAS's judgment of TAO activity. The receiver operating characteristic curve was used to analyze the diagnostic value of the reading results and SUVmax for TAO. Results: The age difference among the three groups was not statistically significant, and the gender difference was not statistically significant (all P>0.05). The difference in CAS among the three groups was statistically significant (H=39.894; P<0.01). Patients with active TAO showed abnormal concentration and enhancement of nuclides in the orbital tissue, and the uptake of radionuclides was significantly increased, while patients with inactive TAO had a slight increase, and healthy volunteers had no significant or only mild uptake. The SUVmax of the active group (2.24±0.47) was highest, and that of the inactive group (1.57±0.43) was higher than the healthy control group (0.67±0.22). After pairwise comparison, there were statistical differences between groups (all P<0.05). According to Spearman correlation analysis, the SUVmax of all TAO patients was linearly, positively correlated with their CAS (r=0.753; P<0.05). In assessing the clinical activity of TAO, the reading results were consistent with CAS (Kappa value=0.737; P<0.05). Taking the reading results as the standard, the area under the receiver operating characteristic curve (AUC) of SUVmax was 0.992, and the threshold of SUVmax to distinguish between active and inactive periods was 1.850, with a sensitivity of 86.70% and a specificity of 76.00%. Taking CAS results as the standard, the AUC of SUVmax was 0.853, and the threshold of SUVmax to distinguish between active and inactive periods was 1.850, with a sensitivity of 100.00% and a specificity of 87.50%. Five patients had inconsistent SUVmax and CAS. The CAS was ≥3, but the orbits did not show any inflammatory lesions in two of them; the CAS was<3, but the orbits showed inflammatory lesions in three of them. Thirteen active TAO patients with ⁹⁹Tc^m-DTPA orbital SPECT/CT showing significant accumulation of nuclides were given hormone shock therapy 12 times. After treatment, the CAS 2.00 (2.00) was lower than the pre-treatment 3.00 (1.50) score, and the difference was statistically significant (Z=-3.100, P<0.01). The SUVmax after treatment (1.60±0.20) was lower than the pre-treatment value (2.17±0.34), and the difference was statistically significant (t=10.197, P<0.01). Conclusion: ⁹⁹Tc^m-DTPA orbital SPECT/CT can relatively accurately determine the state of orbital inflammation in patients with TAO, and can be used as a useful supplement to evaluate the clinical activity of TAO, helping to guide clinical treatment. (Chin J Ophthalmol, 2021, 57: 830-836).