The standard treatment for TSH deficiency or primary hypothyroidism is levothyroxine replacement therapy (Fig. 5.1 2 d). Thyroid hormone replacement can precipitate clinical decompensation in patients with unrecognized adrenal insufficiency, because levothyroxine treatment may improve the metabolic clearance of cortisol. Thus, it is necessary to evaluate patients for adrenal insufficiency and, if this condition is present, treat it with hydrocortisone before initiating thyroid hormone therapy. In patients who also have ACTH deficiency, we usually initiate cortisol replacement three days before beginning thyroid hormone therapy.
The typical thyroid hormone replacement dose for infants under three years of age and for healthy children and adolescents with TSH less than 30 mU/l is levothyroxine 3 mcg/kg orally every morning. Children over three years of age who have TSH greater than 30 mU/l, or about whom there are concerns regarding medical stability, can begin levothyroxine at a low-dose (0.75mcg/kg by mouth every morning)
and increase it by 0.75 mcg/kg per day each month to permit a gradual physiologic and psychological adjustment to the new metabolic state. Thyroid hormone concentrations should be measured after four weeks of therapy, due to the fact that levothyroxine has a long half-life (5-6 days).
Unlike primary hypothyroidism, it is not useful to monitor TSH in patients with central hypothyroidism. In a prospective study of 37 patients with central hypothyroidism, free T4 and free T3 were monitored during therapy and adjusted to achieve free T4 in the midnormal range without free T3 elevation and without symptoms of hypothyroidism or hyperthyroidism .We usually adjust thyroid hormone replacement therapy in patients with central hypothyroidism to maintain the level of free T4 just above the middle of the normal range (for example, free T4 of 1.4-1.6 ng/dl if the normal range is 0.781.85 ng/dl).
Was this article helpful?