Seronegative phenotype in a pediatric population with Hashimoto's thyroiditis

The aim was to verify in a pediatric population with Hashimoto's thyroiditis whether there is a relationship between antithyroid antibodies and inflammatory status on thyroid ultrasound and thyroid function.

A total of 154 children and adolescents, aged 4 to 18 years, diagnosed with Hashimoto's thyroiditis with normal body weight were followed up for 1 year.

Patients with only antiperoxidase antibodies presented with higher TSH levels than subjects with only antithyroglobulin antibodies (p 0.027) but with similar FT4 levels and thyroid score. Prevalence of seronegative Hashimoto's thyroiditis in this cohort was 12.3% (19/154). At diagnosis, the seronegative group presented with lower prevalence of overt hypothyroidism, symptoms of hypothyroidism, and thyroid score, meaning less severe thyroid involvement. In contrast, similar TSH and FT4 values were found at diagnosis and during follow-up in both the seronegative and seropositive groups. A comparison between patients with seronegative Hashimoto's thyroiditis and an overweight/obese antibody-negative population, who presented superimposable altered parenchymal pattern on thyroid ultrasound without circulating antithyroid antibodies, presented similar clinical data.

We report for the first time in the literature that seronegative Hashimoto's thyroiditis in the pediatric age group has a less severe pattern. The seronegative group presents similar characteristics to those of overweight/obese children and adolescents with ultrasound changes, but, according to the established knowledge, the latter condition is reversible and does not need follow-up examinations.