*2.3.1 Hashimoto thyroiditis*

Being a common pathology, HT has been studied in detail. In recent years, the elastographic differences between this type of thyroid damage and other diffuse thyroid pathologies have also been studied. A group of Japanese researchers included in a study 229 subjects, healthy controls and patients diagnosed with CAT. The shear-wave velocity (SWV) was measured, and significant differences were observed between

**Figure 2.** *Normal thyroid tissue—2D SWE.*

the two groups (2.47 ± 0.57 m/s for CAT vs. 1.59 ± 0.41 m/s for the control group; *p* < 0.001). The area under the receiver operating characteristics (AUROC) for CAT was 0.899 and the SWV cut-off value was 1.96 m/s. Statistical analysis revealed 87.4% sensitivity (Se), 78.7% specificity (Sp), 74.2% positive predictive value (PPV), 94% negative predictive value (NPV), and 85.1% diagnostic accuracy. No correlation was found between SWV and ATG antibodies (Spearman's *ρ* = 0.101), but a weak positive correlation was found between SWV and ATPO antibodies (Spearman's correlation coefficient = 0.311) [44].

Similar results were found in a study conducted in Turkey on 50 patients diagnosed with CAT and 40 control subjects. Significant differences were found between the SWV of the two groups (2.56 ± 0.3 m/s vs. 1.63 ± 0.12 ms; *p* < 0.001). A higher cut-off value was found, 2.42 m/s, but lower Se (77%) and Sp (71%). The diagnostic accuracy was 87%, 92% PPV, 81% NPV, and AUROC 0.84 [45]. Differences between thyroid stiffness in normal healthy thyroid compared with HT were also found in a study that compared the mean maximum SWV values (2.36 ± 0.22 m/s vs. 2.08 ± 0.34 m/s; *p* = 0.001). The mean minimum SWV were not statistically different (1.83 ± 0.20 m/s in HT group vs. 1.84 ± 0.3 m/s; *p* = 0.884 > 0.5) [46].

Rahatli et al. compared SWV in three groups of patients: HT, GD, and control subjects. Significant differences were found in SWV (2.5 ± 0.2 m/s for HT group, 2.71 ± 0.22 m/s for GD group and 1.92 ± 0.14 m/s for healthy subjects; *p* < 0.001) [47].

Kara et al. conducted a study on 74 HT patients and 75 healthy controls. They propose cut-off value of 2.15 m/s (Se 85.1%, Sp 78.7%, PPV 79.7%, NPV 84.2%, and diagnostic accuracy 81.8%) and 2.45 kPa (Se 82.4%, Sp 81.3%, PPV 81.3%, NV 82.4%, and diagnostic accuracy 81.8%). The mean values of the elastic index were 25.01 ± 10.53 kPa and 2.70 ± 0.53 m/s for the HT group and 12.49 ± 3.23 kPa and 1.94 ± 0.23 m/s for the control group. A positive correlation was found between SWE values and ATG antibodies. No significant correlation was found between SWE values and ATPO antibodies [48].

Other studies have also observed differences in thyroid stiffness. Ruchala et al. studied groups of patients diagnosed with CAT, SAT, GD, and healthy controls and significant differences were found. The mean values for the CAT group were 36.15 ± 18.7 kPa, higher than values for the control group (16.18 ± 5.4 kPa), *p* < 0.0001 (**Figure 3**) [49].

#### *2.3.2 Graves' disease*

Thyroid stiffness was evaluated in a study to compare tissue elasticity in patients diagnosed with GD compared to healthy controls. The study group consisted of 51 patients with GD and 54 volunteers for the control group. The median SWE values were significantly higher compared to those of the control group (17.34 kPa and 2.28 m/s vs. 12.05 kPa and 1.92 m/s; *p* < 0.001 in both comparisons). The cut-off values were 14.5 k Pa (Se 100%, Sp 72.2%, and AUROC 0.931) and 2.15 m/s (Se85.7%, Sp 74.1%, and AUROC 0.888). The SWE values were not correlated with the age of the subject or the duration of the disease. Also, no correlation was found between SWE values and autoantibodies levels (*p* > 0.05). A negative correlation was found between SWE values and TSH values. Between fT3, fT4 levels, and SWE values were found a strong positive correlation [50].

Another study conducted in China on 207 subjects, 45 healthy volunteers and 162 patients with GD concluded that SWE is a useful tool in diagnosing GD. The control group SWE values were significantly lower than those in the GD group. Mean,

#### *Shear-Wave Elastography in Diffuse Thyroid Diseases DOI: http://dx.doi.org/10.5772/intechopen.102636*

minimum, and maximum values were recorded for each subject. The mean values for the control group were 8.4 ± 2.4 kPa (min); 14.3 ± 2.7 kPa (mean), and 22.1 ± 5.4 kPa (max). GD group values were 10.7 ± 6.4 kPa (min); 17.6 ± 6.4 kPa (mean), and 25.6 ± 10.6 kPa (max); *p* < 0.001. The cut-off value was 15.45 kPa (AUROC 0.656, Se 56.8%, and Sp 71.1%). In contradiction with the previously mentioned study, Li et al. found a positive correlation between SWE values and the duration of the disease, and antibodies serum levels and no correlation between SWE values and fT3, fT4, and THS [51].

Another study published in 2019 evaluated the usefulness of SWE in differentiating thyroid autoimmune diseases. In the GD group, the mean SWV was 2.61 ± 0.32 m/s (range 2.1–3.21 m/s) while in HT group, the mean SWV was 2.85 ± 0.52 m/s (range 2.31–3.82 m/s). The mean SWV value for the control group was 1.75 ± 0.37 m/s (range 1.24–2.36 m/s). The mean values for HT and GD groups were significantly higher than the control group (*p* < 0.01). However, the mean SWV values were higher in the HT group compared to the GD group [52], contrary to the results of the study conducted by Rahatli et al. where higher stiffness was in GD compared to HT [47]. Several studies reported that SWE is not suitable for differentiating GD and CAT even though, both have significantly higher values than the normal thyroid tissue (**Figure 4**) [52–55].

**Figure 5.** *SWE in subacute thyroiditis.*

**Figure 6.** *Radiation-induced thyroiditis.*

## *2.3.3 Subacute thyroiditis*

Given the difference in prevalence, studies on subacute thyroiditis are fewer. Ruchala et al. comparatively studied different types of diffuse thyroid damage, including subacute thyroiditis. This study was included two patients with acute thyroiditis, 18 with SAT, 18 with CAT, and 40 healthy controls. Patients diagnosed with SAT were evaluated three times: at baseline, at 4 weeks follow-up and 10 weeks after diagnosing and treatment initiation. There were significant differences between the three measurements: 214.26 ± 32.5 kPa at the baseline, 45.92 ± 17.4 kPa at 4 weeks and 21.65 ± 5.3 kPa at 10 weeks. The thyroid stiffness was significantly higher at baseline in SAT compared to CAT (36.15 ± 18.7 kPa) or healthy control group (16.18 ± 5.4 kPa). Undertreatment, the values were restored close to normal. The SWE values for the two patients with acute thyroiditis equaled 216.6 and 241 kPa and after treatment, it decreased to 17.93 and 85.384 kPa. All evaluated categories had higher stiffness levels than healthy thyroid (*p* < 0.0001) (**Figure 5**) [49].

Liu et al. also studied thyroid stiffness in SAT. The mean SWE values were 118.01 ± 51.02 kPa. However, the time of measurement is not mentioned, only the fact that all SAT patients had hyperthyroidism at the moment of evaluation. The AUROC for differentiating SAT from CAT was 0.989. The AUROC for distinguishing SAT from GD was 0.975 [54].

Both mentioned studies concluded SWE utility in diagnosing SAT and differentiating it from CAT and GD (**Figure 6**).

To the best of our knowledge, no specific papers have been published regarding shear-wave elastography in postpartum thyroiditis or other diffuse thyroid pathologies.
