## 3 Results  
Thyroid elastography measurements using strain elastography were performed on 74 subjects, 52/74 (70.3%) diagnosed with CAT, and 22/74 (29.7%) without thyroid pathology. A total of 22 (29.8%) subjects had a family history of CAT, 3 (4%) had other autoimmune pathology, and 7 (9.5%) of non-autoimmune thyroid disease. Reliable measurements were obtained in 74/74 subjects (100%). In both groups, the percentage of the female gender was over 70%, compared to the male gender, under 30%. There were no differences between the two groups regarding weight or height. The mean TSH value for the CAT group was  
Figure 2: Strain elastography (**left**) and grey-scale ultrasound (US) (**right**) of a girl, age 16 with no thyroid pathology. The yellow circle A is the local region of interest (ROI) on the thyroid tissue; the yellow circle B is the local ROI on the sternocleidomastoid muscle adjacent to the thyroid. Strain ratio (SR) = 0.69. 2.65 \(\pm\) 1.17, while, for the control group, it was 3.28 \(\pm\) 1.08 (\(p\) = 0.0901). The mean Ft4 value for healthy children was 13.58 \(\pm\) 1.56, while, for the CAT group, it was 14.20 \(\pm\) 1.53 (\(p\) = 0.1175). The main characteristics of the subjects included are summarized in Table 1.  
SR was performed on both thyroid lobes, and no differences were found between the mean values obtained in the left lobe compared to the right lobe for the subjects included in the CAT subgroup (1.20 \(\pm\) 0.31 vs. 1.18 \(\pm\) 0.27; \(p\) = 0.7264), nor in healthy subjects (0.66 \(\pm\) 0.19 vs. 0.70 \(\pm\) 0.24; \(p\) = 0.5432), as presented in Figure 3.  
The mean thyroid stiffness (TS) values were significantly higher for children with CAT compared to the healthy controls (1.19 \(\pm\) 0.25 vs. 0.68 \(\pm\) 0.2; \(p\) < 0.0001) (Table 2). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Children with CAT** & **Healthy Children** & **\(p\) Value** \\  & \(n\) = 52** & \(n\) = 22 & \\ \hline Age (years) & 12.66 \(\pm\) 3.31 & 12.77 \(\pm\) 2.92 & 0.8929 \\ \hline Gender (\%) & & & \\ Female & 73.1\% (38/52) & 77.3\% (17/22) & 0.9307 \\ Male & 26.9\% (14/52) & 22.7\% (5/22) & 0.9307 \\ \hline Weight (kg) & 48.35 \(\pm\) 18.65 & 41.31 \(\pm\) 7.22 & 0.0913 \\ \hline Height (cm) & 149.73 \(\pm\) 16.49 & 146.72 \(\pm\) 10.73 & 0.4339 \\ \hline BSA (m\({}^{2}\)) & 1.40 \(\pm\) 0.33 & 1.29 \(\pm\) 0.15 & 0.1393 \\ \hline TSH & 2.65\(\pm\) 1.17 & 3.28 \(\pm\) 1.08 & 0.0901 \\ \hline FT4 & 14.20 \(\pm\) 1.53 & 13.58 \(\pm\) 1.56 & 0.1175 \\ \hline ATPO & 400 [24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36] & \textless{}0.0001 \\ \hline ATG & 125.5 [1.3–2380] & 14.6 [2.9–45] & \textless{}0.0001 \\ \hline Thyroid volume (Mean \(\pm\) SD) & 14.71 \(\pm\) 6.42 & 9.04 \(\pm\) 3.03 & 0.0002 \\ \hline \hline \end{tabular}  
CAT—chronic autoimmune thyroiditis; BSA—Body Surface Area; TSH—hybrid stimulating hormone; FT4—free thyroxine; ATPO—Anti-thyroid peroxidase antibodies; ATG—Anti-thyroglobulin antibodies; SR—Strain Ratio; SR-ITL—Left thyroid lobe SR; SR-RTL—Right thyroid lobe SR.  
\end{table} 
Table 1: Main characteristics of the study group. Figure 3: Box-and-whisker distribution plots comparing SR mean values, SR-LTL, and SR-RTL, respectively in the two subgroups (healthy subjects vs. subjects with CAT). In children with CAT, no difference between the mean SR values related to gender were observed (1.19 \(\pm\) 0.24 for females vs. 1.20 \(\pm\) 0.30 for males; \(p\) = 0.9014). The optimal cut-off value defined as the highest sum of sensitivity (Se) and specificity (Sp) determined using the mean RS values for predicting the presence of CAT in children was \(>\)0.9 (AUROC--0.90, Se--84.62%, CI 95%: 71.9-93.2; Sp--95.45%, CI 95%: 77.2-99.9; PPV--97.8% and NPV--72.4%) as illustrated in Figure 4.  
Regarding substitution therapy, 75% (39/52) of the children in the CAT group were receiving LT 4 replacementtherapy.