Recovery from Atrophic Autoimmune Thyroiditis in a Child: Thyroid Stimulation-Blocking Antibody as a Prognostic Marker.

Introduction: Atrophic autoimmune thyroiditis (AAT) is a form of autoimmune hypothyroidism characterized by the absence of a goiter. Thyroid stimulation-blocking antibody (TSBAb) has been detected in a subset of pediatric AAT cases. Although the disappearance of TSBAb has been related with the recovery of thyroid function in adult AAT cases, similar outcomes have not been documented in pediatric cases.

Case presentation: A 2-year-old Japanese boy presented for evaluation of stunted growth from 1 year 10 months of age. Tests for congenital hypothyroidism were negative on newborn screening, and he had no significant medical history. However, he showed symptoms of hypothyroidism (inactiveness, hair loss, dry skin), and primary hypothyroidism was confirmed by blood test (serum TSH level, 818 mU/L; serum free T4 level, <0.40 ng/dL). The patient exhibited a unique antibody profile: positive for TSH receptor antibody (TRAb) and TSBAb and negative for anti-thyroglobulin antibody (TgAb) and anti-peroxidase antibody (TPOAb). He was treated with levothyroxine, after which his growth was normalized. During the 8-year follow-up, the patient's TSBAb levels decreased, allowing for the discontinuation of levothyroxine therapy.

Conclusion: We reported the case of a 2-year-old boy diagnosed with AAT who presented with a characteristic antibody profile, negative for TgAb and TPOAb, but positive for TRAb and TSBAb. During 8 years of follow-up, TSBAb seroconversion to negative was observed, leading to treatment discontinuation at age 10 years. This case suggests that monitoring of TSBAb after a diagnosis of AAT may be used to determine treatment discontinuation even in children.