326 EFFECTS OF THYROID HORMONE THERAPY IN CONGENITAL HYPOTHYROIDISM (CH)

Abstract

Among 15 infants with CH, 6 were identified in our screening program with an elevated cord TSH ( > 100 μU/ml) and low T₄ (< 5 μg/dl), and placed on thyroid hormone therapy within the first month of life. Within 4 weeks of therapy their serum TSH was suppressed below 12 μU/ml either by treatment with T₄ alone or T₃ and T₄ combination therapy. An additional 9 infants not involved in a screening program were identified by clinical symptoms and referred for evaluation. Three infants were initially treated with 25 μg qd of T₃, and serum TSH was < 12 μU/ml in all within 4 weeks. However, among 5 of 6 infants treated with T₄ alone, the TSH did not suppress below 12 μU/ml until ≥ 3 months of therapy.

During therapy in the 7 infants treated with T₄ alone, serial reverse T₃ (rT₃) determinations revealed peak concentrations (106 ± 13.8 ng/dl, mean ± SEM) simultaneous with the initial suppression of TSH to normal and significantly greater than the rT₃ levels just prior to suppression of TSH (66.7 ± 15 ng/dl, p<.001 by paired t test) and following TSH suppression (83.8 ± 16 ng/dl, p<.05). In summary, 1) T₄ alone is adequate therapy for CH identified early by screening programs, but is associated with delayed TSH suppression in infants diagnosed on the basis of clinical symptomatology alone. 2) The peak rT₃ levels associated with the initial TSH suppression suggest an increase in the monodeiodinacion of T₄ to rT₃, or decreased clearance of rT₃ which may indicate the development of intracellular euthyroidism.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD