Case Report: Primary Hypothyroidism Caused by Autoimmune Thyroiditis in Infancy Requires Early Intervention

Abstract

Abstract Background: Primary hypothyroidism due to autoimmune thyroiditis is extremely rare in infants, especially under the age of 3 years. For infants, hypothyroidism is most commonly congenital, originating from thyroid dysgenesis with an absent, ectopic, or hypoplastic thyroid gland (1 in 4,000 live births). If left untreated, it can lead to permanent neurodevelopmental deficits. In this report, we describe a male infant who was diagnosed with Hashimoto thyroiditis at 18 months of life, providing a learning example to aid in recognition of this rare disease and enable timely intervention. Clinical Case:Patient was a 2,765 gram, appropriate for gestational age, male born at term with hypospadias of the penis (surgical correction at 11 months). Patient passed meconium in the first 24 hours of life. During the first few months of life, patient developed constipation. Patient had amblyopia necessitating eye patching and began to wear eye glasses at 18 months of life. Patient’s linear and weight growth were within normal limits. Patient had normal motor development, however had language development delay. No known family history of thyroid disease. Screening labs performed at 17-months of age showed abnormal thyroid function: elevated TSH at 14.86 µIU/mL (ref: 0.45 - 4.50 µIU/mL) and normal free T4 level at 1.24 ng/dL (ref: 0.85-1.75 ng/dL). Repeat testing at 18 months of age continued to show elevated TSH at 6.18 µIU/mL (ref: 0.64 - 4.00 µIU/mL), normal free T4 at 1.07 ng/dL (ref: 0.88 - 2.03 ng/dL), and elevated thyroid peroxidase (TPO) antibodies at 163 IU/ml (ref: <35 IU/ml). At 21 months of age, patient was initiated on L-thyroxine therapy for elevation of TSH (9.570 µIU/mL; ref: 0.64 - 4.00 µIU/mL) and free T4 was normal (1.03ng/dL; ref: 0.88 - 2.03 ng/dL). Notably, the newborn screen for hypothyroidism was within normal limits, suggesting chronic autoimmune thyroiditis instead of congenital thyroid dysgenesis. Conclusions: This case report provides insights into autoimmune thyroiditis in infancy, which, although especially rare under age 3 years, should be considered in infants who present with autoimmunity or abnormal thyroid testing. In the neonatal period, infants’ immune systems are learning to discriminate requirements for self-tolerance versus protection against pathogens and may be more prone to infections. Although autoimmunity in this stage of development is uncommon, there can be breakthroughs in tolerance, as seen in this case. In addition to this patient, two other infants were seen with elevated TPO antibodies, diagnosed at 17 and 31 months old, with similar clinical trends. There remains a need for additional studies providing further insights into autoimmunity in infancy. Importantly, this case illustrates that, when infants have abnormal thyroid levels (with or without other autoimmune conditions), consideration should be made for anti-thyroid antibody testing.