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      Multivariate Analysis on Factors Affecting Suppression of Thyroid-Stimulating Hormone in Treated Congenital Hypothyroidism

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          Abstract

          Aims: To determine the factors which influence the suppression of thyroid-stimulating hormone (TSH) in infants with congenital hypothyroidism (CH) following treatment. Methods: We examined retrospectively the patterns of thyroid function tests from diagnosis to 3 years of age in 140 infants diagnosed with CH from screening. Patients were classified into 3 groups: athyreosis, ectopia and presumed dyshormonogenesis on the basis of thyroid scans. Adequate TSH suppression was defined as plasma TSH concentration <6 mU/l. The factors affecting the suppression of TSH at 6 months and 1 year of age which were evaluated were: initial confirmatory plasma TSH, initial plasma thyroxine (T4), mean age of starting treatment with L-T4, dose of L-T4 at diagnosis, 6 weeks, 3 months and 6 months, and aetiology of the congenital hypothyroidism. Variables were then entered in a stepwise logistic regression model for TSH suppression at 6 months and 1 year of age. Results: All infants had radionuclide scans prior to treatment: athyreosis (n = 39), ectopia (n = 78) and dyshormonogenesis (n = 23). 58% of patients had persistently raised TSH at 6 months of age while 31% of patients had a persistently raised TSH at 1 year of age. There was a significant delay in the normalisation of plasma TSH in athyreosis and ectopia groups compared with dyshormonogenesis. Multiple regression analysis for TSH suppression at 6 months of age found plasma T4 levels and aetiology of CH as independent factors affecting the timing of TSH suppression. Aetiology of CH was the only independent factor affecting TSH suppression at 1 year of age. Conclusion: At 6 months of age, plasma T4 levels at 6 weeks and 3 months, and aetiology of CH were independent factors affecting timing of TSH suppression. However, by 1 year of age, the aetiology of CH was the only independent factor affecting suppression of TSH.

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          Most cited references18

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          Congenital hypothyroidism: etiologies, diagnosis, and management.

          Congenital hypothyroidism is a common preventable cause of mental retardation. The overall incidence is approximately 1:4000; females are affected about twice as often as males. Approximately 85% of cases are sporadic, while 15% are hereditary. The most common sporadic etiology is thyroid dysgenesis, with ectopic glands more common than aplasia or hypoplasia. While the pathogenesis of dysgenesis is largely unknown, some cases are now discovered to be the result of mutations in the transcription factors PAX-8 and TTF-2. Loss of function mutations in the thyrotropin (TSH) receptor have been demonstrated to cause some familial forms of athyreosis. The most common hereditary etiology is the inborn errors of thyroxine (T4) synthesis. Recent mutations have been described in the genes coding for the sodium/iodide symporter, thyroid peroxidase (TPO), and thyroglobulin. Transplacental passage of a maternal thyrotropin receptor blocking antibody (TRB-Ab) causes a transient form of familial congenital hypothyroidism. The vast majority of infants are now diagnosed after detection through newborn screening programs using a primary T4-backup TSH or primary TSH test. Screening test results must be confirmed by serum thyroid function tests. Thyroid scintigraphy, using 99mTc or 123I, is the most accurate diagnostic test to detect thyroid dysgenesis or one of the inborn errors of T4 synthesis. Thyroid sonography is nearly as accurate, but it may miss some cases of ectopic glands. If maternal antibody-mediated hypothyroidism is suspected, measurement of maternal and/or neonatal TRB-Ab will confirm the diagnosis. The goals of treatment are to raise the serum T4 as rapidly as possible into the normal range, adjust the levothyroxine dose with growth to keep the serum T4 (or free T4) in the upper half of the normal range and the TSH normal, and maintain normal growth and development while avoiding overtreatment. An initial starting dose of 10-15 microg/kg per day is recommended; this dose will decrease on a weight basis over time. Serum T4 (or free T4) and TSH should be monitored every 1-2 months in the first year of life and every 2-3 months in the second and third years.
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            Long-term effects of L-thyroxine therapy for congenital hypothyroidism.

            To study the effects of initial and concurrent dose levels of L-thyroxine on ability and behavior in children with congenital hypothyroidism. An existing database, involving a large cohort of children with congenital hypothyroidism detected by neonatal screening, was analyzed retrospectively. There were 94 children: 89 were assessed at age 7 years for intelligence and selective cognitive abilities, and 87 at age 8 years for behavior, achievement, and selective abilities. Subjects were stratified by median split into low and high starting dose groups. The high-dose group performed better on indexes of intelligence, verbal ability, and memory but had more behavior problems reflecting increased anxiety, social withdrawal, and poorer concentration. The dose of L-thyroxine at age 8 years was negatively correlated with memory task performance. A higher starting dose of L-thyroxine is beneficial for subsequent intellectual outcome in children with congenital hypothyroidism but may be associated with internalizing behavior problems.
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              Initial treatment dose of L-thyroxine in congenital hypothyroidism.

              To determine the optimal initial treatment dose of L-thyroxine in congenital hypothyroidism (CH) by evaluating the time course of rise of thyroxine (T(4)) and free T(4) concentrations into an established "target range" and normalization of thyroid-stimulating hormone (TSH) and to reevaluate the "target range" for T(4) and free T(4) concentrations during the first 2 weeks of CH treatment. Infants of birth weight 3 to 4 kg with CH (n = 47) detected by newborn screening were randomly assigned into three L-thyroxine treatment dose arms: 37.5 microg/day (group 1); 62.5 microg/day for 3 days, then 37.5 microg/day (group 2); and 50 microg/day (group 3). Serum T(4), free T(4), triiodothyronine (T(3)), free T(3), and TSH were measured before treatment and at 3 days and 1, 2, 4, 8, and 12 weeks after treatment. T(4) and free T(4) concentrations increased into the target range (10 to 16 microg/dL) by 3 days of therapy in infants in groups 2 and 3 and by 1 week in group 1; 50 microg/day (average 14.5 microg/kg/day) provided the most rapid normalization of TSH by 2 weeks. With the use of linear regression analysis of T(4) versus TSH or free T(4) versus TSH plots, the intercept at the lower range of normal for TSH (1.7 mU/L) showed T(4) = 19.5 microg/dL and free T(4) = 5.23 ng/dL. Initial dosing of 50 microg/day (12-17 microg/kg per day) raised serum T(4) and free T(4) concentrations to target range by 3 days and normalized TSH by 2 weeks of therapy. We recommend consideration of a somewhat higher "target range" of 10 to 18 microg/dL for T(4) and 2 to 5.0 ng/dL for free T(4) during the first 2 weeks of L-thyroxine treatment. After 2 weeks of treatment, the target range drops to 10 to 16 microg/dL for T(4) and 1.6 to 2.2 for free T(4).
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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                1663-2818
                1663-2826
                2004
                November 2004
                22 November 2004
                : 62
                : 5
                : 245-251
                Affiliations
                Endocrinology Department, Royal Liverpool Children’s Hospital Alder Hey, Liverpool, UK
                Article
                81628 Horm Res 2004;62:245–251
                10.1159/000081628
                15499223
                3e121239-2563-4736-b31f-66f2a8aa3bba
                © 2004 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 31 March 2004
                : 25 August 2004
                Page count
                Tables: 8, References: 27, Pages: 7
                Categories
                Original Paper

                Endocrinology & Diabetes,Neurology,Nutrition & Dietetics,Sexual medicine,Internal medicine,Pharmacology & Pharmaceutical medicine
                Thyroid-stimulating hormone,Aetiology,Congenital hypothyroidism

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