pediatrics
Hypothyroidism in Infants and Children
Treatment
Thyroid hormone replacement In most treated infants, motor and intellectual development is normal. (See also the American Thyroid Association Task Force on Thyroid Hormone Replacement's2014 guidelines for the treatment of hypothyroidism.) Most cases of congenital hypothyroidism require lifelong thyroid hormone replacement. However, if the initial TSH level is < 40 mU/L, an organic basis is not established, and the disease is thought to be transient (based on a lack of dose increase since infancy), clinicians may try stopping therapy after age 3 years, at which time the trial poses no danger to the developing central nervous system. If the TSH rises once therapy is stopped (typically allowing about 6 to 8 weeks off treatment) and the free T4 or T4 is low, permanent congenital hypothyroidism is confirmed and treatment should be restarted. Thyroxine-binding globulin deficiency, detected by screening that relies primarily on total serum T4 measurement, does not require treatment because affected infants have normal free T4 and TSH levels and are thus euthyroid. Treatment withlevothyroxineis indicated for children with a TSH level > 10 mU/L. Older children who have only slight elevations in TSH (typically between 5 mU/L and10 mU/L) and normal free T4 levels are considered to have subclinical hypothyroidism. There is controversy regarding treatment of patients with subclinical hypothyroidism. Subclinical hypothyroidism does not typically cause any symptoms. Treatment can be considered if patients have a goiter, positive thyroid antibodies, or hyperlipidemia. If not treated, thyroid function should be monitored every 6 to 12 months for a period of time to make sure function does not worsen. In congenital hypothyroidism,treatment withlevothyroxine10 to 15 mcg/kg orally once a day must be started immediately and be closely monitored. This dosage is intended to rapidly (within 2 weeks) bring the serum T4 level into the upper half of the normal range for age (between 10 mcg/dL [129 nmol/L] and 15 mcg/dL[193 nmol/L]) and promptly (within 4 weeks) reduce the TSH. In acquired hypothyroidism,the usual starting dosage oflevothyroxineis based on body surface area (100 mcg/m2orally once a day) or on age and weight as follows: For ages 1 to 3 years: 4 to 6 mcg/kg once a day For ages 3 to 10 years: 3 to 5 mcg/kg once a day For ages 10 to 16 years: 2 to 4 mcg/kg once a day For ages ≥ 17 years: 1.6 mcg/kg once a day For both forms of hypothyroidism, the dose is titrated to maintain serum T4 and TSH levels within the normal range for age. Levothyroxineis typically given in tablet form because of the inconsistent delivery of compounded liquid formulations prepared by individual pharmacists. Tablets can be crushed, mixed with a small amount (1 to 2 mL) of water, breast milk, or non–soy-based formula, and given orally by syringe. The absorption oflevothyroxinemay be decreased if it is given with soy formula, iron, or calcium. Commercial oral liquid formulations are available for children of any age and are available as single-dose ampules in different strengths or as 100-mL bottles with the dose selected by syringe volume. To date, there is limited experience with these newer liquid formulations in congenital hypothyroidism, and it is unclear whether dosing is the same as for crushed tablets. Iflevothyroxinemust be given intravenously, 75% of the oral dose should be used. Although T3 is the biologically active thyroid hormone,levothyroxine(T4) is usually given and it is not necessary to use T3 because the majority of brain T3 arises through enzyme conversion of T4 to T3. Children are monitored more frequently during the first few years of life: Every 1 to 2 months during the 1st 6 months Every 3 to 4 months between age 6 months and 3 years Every 6 to 12 months from age 3 years to the end of growth Older children can be monitored more frequently if there are concerns about adherence. After a dose adjustment in older children, TSH and free T4 levels are measured in 6 to 8 weeks. 