This study confirms that the SWV of the thyroid glands with autoimmune thyroiditis (both GD and HT) is higher than normal glands, and the SWV increases with the degree of fibrosis. Although the SWV differs between the GD and the HT, there is overlap in velocities between the two groups.
The ARFI is an emerging technique providing information about tissue stiffness. It contains two modes, VTI and VTQ. They provide the information about tissue elasticity qualitatively and quantitatively, respectively.
Stiffness or elasticity is an important physical parameter of biological tissue; in GD, elasticity is increased due to diffuse hypertrophy and hyperplasia of follicular cells, colloid depletion, and lymphoid infiltration as well as hypervascularity. On the other hand, lymphocytic infiltration and fibrosis occurring in the thyroid gland of HT increase the stiffness of the thyroid tissue. Correspondingly, in the current study, the mean SWVs in the GD and HT groups were significantly higher than that in the control group (p < 0.001); this objective index might make the sonographer more confident in making developmental trauma disorder diagnosis. Nevertheless, our findings showed that although there was statistically significant difference between the SWVs in both HT and GD, there was marked overlapping between the two groups, making differentiation between the two groups unreliable.
In the current study, the mean SWV was 2.61 ± 0.32 m/s in the GD group (range: 2.1–3.21 m/s), 2.85 ± 0.52 m/s in the HT group (range: 2.31–3.82 m/s), and 1.75 ± 0.37 m/s in the control group (range: 1.24–2.36 m/s). The higher elasticity in diffuse thyroid disease is in agreement with previous studies. Two studies using strain ratios done by Ruchala et al. and Menzilcioglu et al. found higher strain ratios in diffuse thyroid disease than control group and were compatible with our study. Hekimoglu et al. found SWV in control group (1.63 ± 0.12 m/s) which is close to our results (1.75 ± 0.37 m/s) and they found significantly higher velocity in the group of chronic autoimmune thyroiditis than the control group. Furthermore, Fukuhara et al. compared SWVs between patients with CAT and a healthy control group using SWE by ARFI. They found that the mean SWV in patients with CAT was 2.47 ± 0.57 m/s, which was significantly higher than that in the control group (1.59 ± 0.41 m/s). All these studies were in agreement with the current study that the SWV of the patient group (HT + GD) is significantly higher than that of the control group.
The higher SWV in HT than GD is not in agreement with two previous reports. Sporea et al. compared the SWV among 29 patients with GD, 22 patients with CAT, and 23 control subjects and found a significantly higher SWV in the GD than in the CAT group (2.82 ± 0.47 vs. 2.49 ± 0.48 m/s, respectively). Furthermore, Rahatli et al. in a study included 30 patients with HT and 22 patients with GD found patients with GD had significantly higher shear wave velocities than those with HT (p < 0.001). The difference between the results of current study and these two studies may be due to difference in number of the patients, and the fact that most of patients with HT included in the study was in chronic stage. On the other hand, our study is in agreement with previous study by Du et al., who in a study included 74 patients with diffuse thyroid disease and 30 normal controls found higher SWV in HT than GD groups (2.72 ± 1.52 m/s, vs. 2.14 ± 0.31 m/s), but they reported the difference as statistically insignificant.
Liu et al. recently reported that the SWV is not suitable for differentiation between chronic thyroiditis and GD, and this assumption was confirmed by our study due to marked overlapping between the two groups. In the current study, the SWV was higher in treated GD than non-treated GD and there was a significant difference between chronic HT and early HT. The cause of the marked overlapping observed in our study probably related to the presence of cases with non-treated GD and early HT, both of them have similar SWV.
Kim et al. in a prospective study found that real-time thyroid US is useful in differentiating diffuse thyroid disease from normal thyroid parenchyma. In the current study, grayscale ultrasound proved accurate in differentiation between normal thyroid tissue and patients with HT or GD. However, regarding differentiation between HT and GD, there was a significant overlap between the sonographic pictures, with only coarse texture and nodularity were significantly more common in HT than GD. In the current study, we studied each ultrasound sign separately for the differentiation between HT and GD and found that most specific sign for diagnosing HT was nodularity (97.87%) and the most sensitive sign was coarse echotexture (81.54%). No sign had high sensitivity and specificity. These results are similar to the study by Pishdad et al. who reported that sonography had a high specificity (90.6%) but low sensitivity (47.1% and 45.2%) in the diagnosis and differentiation of GD and HT. Furthermore, Tabur et al. found that sonography has high specificity (90%) and low sensitivity (35%) in the diagnosis of thyroiditis. Furthermore, in the current study, coarse echotexture as a sign of HT had a sensitivity of 81.54%, a result similar to those of Patel et al., who found that diffuse heterogeneity had a sensitivity of 88.2% in the diagnosis of HT.
Furthermore, we tried to correlate the SWV and the different sonographic signs. High velocities were seen in lobes with coarse echotexture, nodularity, and fine septations (p < 0.05, < 0.01, and < 0.01, respectively). The presence of these signs may correlate with the degree of fibrosis. Our results are similar to those of Kandemirli et al. who in a study included that 85 patients found high elasticity values in that thyroid glands with marked hypoechoic, septations, and pseudonodular appearance.
In the current study, the color Doppler ultrasound showed a sensitivity of 91.8% and a specificity of 56.92% in the differentiation between HT and GD. The low specificity is due to the fact that 28 patients (43.1%) with HT showed hypervascularity (Pattern II), but the Pattern III was seen only in patients with GD. Increased vascularity in HT was previously reported.[33,34] Ceylan et al. reported hypervascularity in 85% of their patients with HT. The presence of HT with hypervascularity leads to the low specificity of CDF in differentiation between HT and GD.
A limitation of this study is that biopsy and/or pathological specimens were not available for all patients; we relied mainly on the clinical and laboratory findings. The HT group and GD were unequal, with a larger number of early and chronic HT. No inter- and intra-observer data were tried. The last to mention is that only the GD and HT patients were involved. Other types of diffuse thyroid disease were not included in the study.