Relationship between Thyroid Gland Echogenicity and Its Function in Pediatric Patients with Hashimoto's Thyroiditis

Study Methodology and Population

A total of 86 patients aged 4–18 years (86% girls; average age 11.1 years) who were diagnosed with Hashimoto's thyroiditis between 2006 and 2016 were included in this retrospective study. The ultrasound findings (echogenicity) of the thyroid gland, serum levels of free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone (TSH), antimicrosomal (anti-TPO) and antithyroglobulin (anti-TG) antibodies were evaluated. Some patients also underwent fine-needle aspiration biopsy (FNAB; n = 1), core cut biopsy (n = 2), or surgical intervention for follicular adenoma (n = 1) or papillary carcinoma (n = 7) of the thyroid gland.

Overt hypothyroidism was defined as a decrease in fT4 concentration and an increase in TSH concentration (> 20 mU/l). Subclinical hypothyroidism was defined as an increase in TSH concentration with no decrease in fT4 concentration.  

Based on thyroid gland echogenicity in ultrasound examinations, the findings were classified into four grades:

• G1 – diffusely enlarged TG with normal echogenicity
• G2 – hypoechoic foci (< 1/3), otherwise TG with normal echogenicity
• G3 – enlarged TG with diffuse, but mild hypoechogenicity
• G4 – enlarged TG with significant hypoechogenicity

Results

A total of 27 (31.4%), 22 (25.6%), 19 (22.1%), and 18 (20.9%) patients were classified in grades G1–G4 based on the ultrasound findings. Among patients with overt hypothyroidism, 91.7% were classified in grades G3 and G4. Conversely, 97.8% of patients with subclinical hypothyroidism or euthyroidism were classified in grades G1 and G2.

In grades G1 and G2, there were only 1 (3.7%) and 2 (9.1%) cases of overt hypothyroidism, respectively. Subclinical hypothyroidism was diagnosed in 15 (55.1%) and 11 (40.7%) patients, euthyroidism in 11 (40.7%) and 5 (22.7%), and hyperthyroidism in only 2 (9.1%) patients classified in grade G2.  

In the group classified as G3 based on the ultrasound findings of the thyroid gland, there were 15 (78.9%) patients with overt hypothyroidism, 3 (15.8%) with hyperthyroidism, and only 1 (5.3%) with subclinical hypothyroidism.

All patients classified in grade G4 had overt hypothyroidism.

Generally, patients with a higher described grade (hypoechogenicity) had thyroid gland hypofunction. The grade increased with the TSH titer, while an opposite trend was observed in the case of fT4 (p < 0.001).

The anti-TPO titer was determined in 84 patients, but no correlation with thyroid gland echogenicity was observed.

Discussion and Conclusion

Thyroid gland hypoechogenicity is an ultrasound finding in pediatric patients noticeable not only in overt but also in subclinical hypothyroidism. Thus, an early sign of thyroid function failure may be the finding of TG hypoechogenicity on ultrasound in addition to increased TSH concentration in the blood.  

The risk of progression from subclinical to overt hypothyroidism is very difficult to estimate. However, a greater risk is likely in patients with reduced or heterogeneous TG echogenicity on ultrasound and elevated anti-TPO levels.

Since this was a retrospective study with a relatively small number of included subjects, further research involving more pediatric patients will certainly be warranted in the future.  

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Source:

Jeong S. H., Hong H. S., Lee J. Y. The association between thyroid echogenity and thyroid function in pediatric and adolescent Hashimoto’s thyroiditis. Medicine (Baltimore) 2019; 98 (14): 1–5, doi: 10.1097/MD.0000000000015055.