Factors involved in the rate of fall of thyroid stimulating hormone in treated hypothyroidism

A novel therapeutic paradigm to treat congenital hypothyroidism

OBJECTIVE

To determine the effectiveness of a novel therapeutic paradigm to treat congenital hypothyroidism (CH) incorporating variable initial doses of L-T4 based on the underlying aetiology and frequent monitoring, up to 2 years of age.

DESIGN

Retrospective cohort study.

PATIENTS

Infants with primary CH diagnosed by newborn screening.

MEASUREMENTS

Treatment with L-T4 suspension initiated at 10, 12 and 15 microg/kg/day for dyshormonogenesis, ectopia and athyreosis, respectively. Serum TSH and free T4 (FT4) levels monitored weekly during the first 4 weeks, at 6 weeks, thereafter monthly during the first 2 years. Dose changes were made to keep FT4 level in upper half of the normal range.

RESULTS

Sixty-nine infants; 17 had dyshormonogenesis, 35 ectopia and 17 athyreosis. Seventy-eight percent of subjects normalized FT4 levels within 7 days of treatment and 100% within 14 days. TSH levels normalized in 26% of infants within 7 days and in 92% by 21 days. Supraphysiological levels of FT4 were noted in 28% of infants, for a maximum of 2 weeks. 48% infants needed one dose adjustment and 30% needed at least two in the first month. In 52 infants over the first 2 years, mean FT4 levels were consistently in the upper half of the normal range. Two or more dose adjustments every 3 months were made 57 times in the first year as compared to 19 times in the second year.

CONCLUSIONS

A variable initial dose paradigm based on aetiology with frequent testing and using T4 suspension rapidly normalizes FT4 levels without producing persistent hyperthyroxinaemia.

Persistently raised thyroid stimulating hormone in adequately treated congenital hypothyroidism on long-term follow-up

AIM

To determine the percentage of patients with inappropriate secretion of TSH (ISTSH) in a large cohort of patients with congenital hypothyroidism (CH), and to examine a probable influence of the pretreatment T4 or TSH levels and the etiology of CH on ISTSH by describing the clinical features of these patients.

PATIENTS AND METHODS

We retrospectively examined the records, including anthropometric data, clinical findings, and thyroid function tests (TFT), of 500 children diagnosed with CH. Inclusion criteria of ISTSH were appropriate doses of L-T4, improvement of clinical findings, normalization of serum total T4 levels and persistently high TSH concentrations. A group of patients who demonstrated adequate suppression of TSH (<6 mU/l) with therapy among 500 CH patients were chosen randomly as a control group. Both groups were compared with regard to the etiology of CH, and TFT at baseline and during the treatment period.

RESULTS

Overall, 27 (5.4%) out of the 500 patients with CH had ISTSH. Nine patients (1.8%) with ISTHS did not show TSH normalization during the follow-up period. Four out of 27 patients with ISTSH had organic lesions (three empty sella, one corpus callosum agenesis) on cranial imaging. No statistically significant difference was found between the groups for etiological classification. The pretreatment T4 and TSH levels in ISTHS and control groups were not significantly different.

CONCLUSIONS

Our results suggest that a minority (5.4%) of adequately treated children with CH have persistently raised TSH levels. The delay in normalization of TSH is not related to pretreatment T4 and TSH values or the etiology of CH.

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

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.

Children with congenital hypothyroidism are at risk of adult obesity due to early adiposity rebound

OBJECTIVE

There is some evidence that children with congenital hypothyroidism (CH) are heavier than their reference population. There are few data on adults with CH. The timing of adiposity rebound (AR) in childhood has been shown to have strong correlations with adult obesity. Our aims were to study the timing of AR and factors affecting AR in children with CH.

PATIENTS AND METHODS

The timing of AR was examined in a retrospective study of children with CH with growth data at least up to 5 years of age. The proportion of children with CH who reached AR by 37 months and by 49 months of age were compared with healthy children and children with acute lymphoblastic leukaemia (ALL) described in the literature. Correlation of timing of AR with body mass index (BMI) standard deviation score (SDS) at 10 years, initial severity of hypothyroidism and age at normalization of TSH were examined. Multiple logistic regression was used to identify independent factors associated with BMI > or = 20 (overweight) at 10 years of age.

RESULTS

The study included 53 children (34 females and 19 males). AR had occurred by 37 months in 37.7% children with CH, in 42.7% children treated for ALL (CH vs. ALL, P = 0.58) and in 4.5% healthy British children (CH vs. normal, P < 0.0001). We found that 54.7% children with CH had reached AR compared with 21.4% of normal children (CH vs. normal, P < 0.0001) by the age of 49 months. Timing of AR showed significant negative correlation with BMI SDS at 10 years (r = -0.487, P = 0.01). There were no significant relationships between timing of AR and initial thyroid function or age at normalization of TSH. Multiple logistic regression analysis identified age at AR as an independent factor associated with BMI > or = 20 at 10 years of age (P = 0.04).

CONCLUSIONS

Children with CH showed significantly earlier AR compared to normal British children. This showed significant negative correlation with BMI SDS at 10 years. AR in CH does not appear to be directly related to the initial severity of hypothyroidism or to treatment factors.

Persistence of mild hyperthyrotropinemia after discontinuation of three-year course of low-dose L-thyroxine therapy in infants with borderline hypothyroidism

Treatment plan for neonates with borderline hypothyroidism (persistent hyperthyrotropinemia with normothyroxinemia) has not been established. In this study, changes in thyroid function after discontinuation of low-dose L-thyroxine (L-T4) supplement in infants with the condition were evaluated. Fourteen infants with hyperthyrotropinemia at neonatal screening had repeated hyperthyrotropinemia (> 8 mU/L) with normothyroxinemia. TSH response was exaggerated at TRH testing. The subjects were treated with low-dose L-T4 (3 to 9 microg/kg/day) for 2.2 to 6 years, and euthyroid status was maintained. After discontinuation of therapy, mild hyperthyrotropinemia persisted up to 24 months, while serum FT4 remained within the lower half of the normal range. TSH response to TRH stimulation, which tended to be exaggerated 1 month after discontinuation, became lower 6 to 12 months later. RAIU and thyroid scintigraphy were normal in all subjects. No patient developed hypothyroxinemia, although mild elevation of TSH lasted rather long after discontinuation of low-dose L-T4 therapy. Administration of L-T4 was not resumed provided the subjects were followed at regular interval. Further long-term investigation is needed to define whether re-administration is necessary or not.

Dynamics of the plasma concentrations of TSH, FT4 and T3 following thyroxine supplementation in congenital hypothyroidism

OBJECTIVE

The dynamics of the plasma concentrations of various diagnostic determinants of thyroid function were analysed in children with congenital hypothyroidism (CH) after the start of T4 supplementation. The description of the biochemical dynamics of TSH and free T4 (FT4) during the first period of thyroxine treatment is important to depict the practical outlines of the initial dosage of T4 and dosage adjustments for newborns with variable forms of CH.

DESIGN

A retrospective analysis was performed of frequent plasma TSH, total T4 (T4), FT4 and total T3 (T3) measurements in 30 CH neonates during the first weeks of treatment, treated with initial daily T4 dosages ranging from 4.8 to 11.1 microg/kg.

RESULTS

A 50% reduction in the initial plasma TSH concentration was achieved after 3-4 days of treatment, independent of CH severity. At a median of 32 days after the start of T4 supplementation, plasma TSH ranged between 0.4 and 4.0 mU/l. The mean interval needed for FT4 to reach the age-related normal values (12-29 pmol/l) was 3 days. The increase in plasma T3 concentrations levelled off within a few days, when T4 reached concentrations of around 100 nmol/l.

CONCLUSIONS

Plasma T3 and FT4 concentrations reach the normal range a few days after thyroxine treatment is started. By contrast, normalization of plasma TSH concentration takes several weeks. At the time that plasma TSH is normalized, CH neonates show a higher range of plasma FT4 concentrations than the normal range. When TSH normalization is the goal of treatment in CH, the target range for plasma FT4 during treatment in the first months needs to be adapted. During the first month of treatment the plasma TSH concentration is not helpful in assessing the proper T4 supplementation dosage. Once plasma TSH has reached normal values, it becomes a reliable determinant in addition to plasma FT4.