Elevated thyroid stimulating hormone in a neonate: Drug induced or disease?

Dyshormonogenesis is an uncommon cause of congenital hypothyroidism. The most common abnormality is absent or insufficient thyroid peroxidase enzyme. Maternal intake of antithyroid drug can also lead to elevated thyroid stimulating hormone (TSH) in a neonate, albeit the scenario is temporary. We report one such interesting case where a clinically euthyroid neonate borne to a mother on antithyroid drug presents on 12(th) day of life with reports of elevated TSH and increased tracer uptake in 99mTc thyroid scan. Disproportionately high TSH in comparison to low maternal antithyroid drug dosage and further elevation of TSH after stopping mother's antithyroid drugs ruled out maternal antithyroid drug-induced congenital hypothyroidism in the baby. Early institution of therapy in these patients can prevent mental retardation and other features of hypothyroidism.