Diagnostic and predictive value of ultrasound and isotope thyroid scanning, alone and in combination, in infants referred with thyroid-stimulating hormone elevation on newborn screening

Outcomes of lowered newborn screening thresholds for congenital hypothyroidism

BACKGROUND

Newborn screening (NBS) has largely eliminated the physical and neurodevelopmental effects of untreated congenital hypothyroidism (CH). Many countries, including Australia, have progressively lowered NBS bloodspot thyroid-stimulating hormone (b-TSH) thresholds. The impact of these changes is still unclear.

OBJECTIVES

To evaluate the performance of CH NBS following the reduction of b-TSH thresholds in New South Wales (NSW) and the Australian Capital Territory (ACT), Australia, from 15 to 8 mIU/L, and to determine the clinical outcomes of cases detected by these thresholds.

METHODS

NBS data of 346 849 infants born in NSW/ACT, Australia from 1 November, 2016-1 March, 2020 inclusive were analysed. A clinical audit was conducted on infants with a preliminary diagnosis of CH born between 1 January, 2016-1 December, 2020 inclusive.

RESULTS

The lowered b-TSH threshold (≥8 mIU/L, ~99.5th centile) detected 1668 infants (0.48%), representing an eight-fold increase in recall rate, of whom 212 of 1668 (12.7%) commenced thyroxine treatment. Of these 212 infants, 62 (29.2%) (including eight cases with a preliminary diagnosis of thyroid dysgenesis) had an initial b-TSH 8-14.9 mIU/L. The positive predictive value for a preliminary diagnosis of CH decreased from 74.3% to 12.8% with the lowered threshold. Proportionally, more pre-term infants received a preliminary CH diagnosis on screening with the lower threshold (16.1% of 62) than with the higher threshold (8.0% of 150).

CONCLUSION

Clinically relevant CH was detected using the lowered threshold, albeit at the cost of an eight-fold increase in recall rate. Further clinical and economic studies are required to determine whether benefits of lowered screening thresholds outweigh potential harms from false-positive results on infants, their families and NBS programs.

Congenital Hypothyroidism: Screening and Management

ABSTRACT

Untreated congenital hypothyroidism (CH) leads to intellectual disabilities. Prompt diagnosis by newborn screening (NBS) leading to early and adequate treatment results in grossly normal neurocognitive outcomes in adulthood. However, NBS for hypothyroidism is not yet established in all countries globally. Seventy percent of neonates worldwide do not undergo NBS.The initial treatment of CH is levothyroxine, 10 to 15 mcg/kg daily. The goals of treatment are to maintain consistent euthyroidism with normal thyroid-stimulating hormone and free thyroxine in the upper half of the age-specific reference range during the first 3 years of life. Controversy remains regarding detection of thyroid dysfunction and optimal management of special populations, including preterm or low-birth weight infants and infants with transient or mild CH, trisomy 21, or central hypothyroidism.Newborn screening alone is not sufficient to prevent adverse outcomes from CH in a pediatric population. In addition to NBS, the management of CH requires timely confirmation of the diagnosis, accurate interpretation of thyroid function testing, effective treatment, and consistent follow-up. Physicians need to consider hypothyroidism in the face of clinical symptoms, even if NBS thyroid test results are normal. When clinical symptoms and signs of hypothyroidism are present (such as large posterior fontanelle, large tongue, umbilical hernia, prolonged jaundice, constipation, lethargy, and/or hypothermia), measurement of serum thyroid-stimulating hormone and free thyroxine is indicated, regardless of NBS results.

Infants Diagnosed with Athyreosis on Scintigraphy May Have a Gland Present on Ultrasound and Have Transient Congenital Hypothyroidism

Scintigraphy using technetium-99m (99mTc) is the gold standard for imaging the thyroid gland in infants with congenital hypothyroidism (CHT) and is the most reliable method of diagnosing an ectopic thyroid gland. One of the limitations of scintigraphy is the possibility that no uptake is detected despite the presence of thyroid tissue, leading to the spurious diagnosis of athyreosis. Thyroid ultrasound is a useful adjunct to detect thyroid tissue in the absence of 99mTc uptake.

AIMS

We aimed to describe the incidence of sonographically detectable in situ thyroid glands in infants scintigraphically diagnosed with athyreosis using 99mTc and to describe the clinical characteristics and natural history in these infants.

METHODS

The newborn screening records of all infants diagnosed with CHT between 2007 and 2016 were reviewed. Those diagnosed with CHT and athyreosis confirmed on scintigraphy were invited to attend a thyroid ultrasound.

RESULTS

Of the 488 infants diagnosed with CHT during the study period, 18/73 (24.6%) infants with absent uptake on scintigraphy had thyroid tissue visualised on ultrasound (3 hypoplastic thyroid glands and 15 eutopic glands). The median serum thyroid-stimulating hormone (TSH) concentration at diagnosis was significantly lower than that in infants with confirmed athyreosis (no gland on ultrasound and no uptake on scintigraphy) (74 vs. 270 mU/L), and median free T4 concentration at diagnosis was higher (11.9 vs. 3.9 pmol/L). Six of 10 (60%) infants with no uptake on scintigraphy but a eutopic gland on ultrasound had transient CHT.

CONCLUSION

Absent uptake on scintigraphy in infants with CHT does not rule out a eutopic gland, especially in infants with less elevated TSH concentrations. Clinically, adding thyroid ultrasound to the diagnostic evaluation of infants who have athyreosis on scintigraphy may avoid committing some infants with presumed athyreosis to lifelong levothyroxine treatment.

Congenital Hypothyroidism: Space-Time Clustering of Thyroid Dysgenesis Indicates a Role for Environmental Factors in Disease Etiology

Background: The etiology of most cases of congenital hypothyroidism (CHT) due to thyroid dysgenesis (DG) is unknown. If transient environmental factors can impact on thyroid gland development, then clustering of cases in time and/or space may occur, and this would be more likely in thyroid DG than dyshormonogenesis (DHG). Methods: The newborn screening program for CHT in Scotland is linked to a central database that includes case details such as postcode. The etiology of CHT is investigated in many cases of CHT using scintigraphy and/or ultrasonography. We looked for evidence of a change in CHT incidence with year of birth and according to season of the year. We then undertook space-time clustering analysis (using a method based on K-functions, with nearest neighbor thresholds) of CHT in Scotland between 1979 and 2015. We also looked for evidence of overall changes associated with sex and area-based birth density. Results: Of 531 cases with CHT during the study period, 290 cases had been categorized as DG (n = 229) or DHG (n = 61) following more detailed investigation. The incidence of CHT increased with year of birth and was in part linked to changing methodology, but there was no seasonality. There was no evidence of overall space-time clustering (p = 0.06), but there was evidence of clustering in babies with DG (p = 0.007). This picture appeared to be most closely linked to underlying thyroid gland hypoplasia rather than thyroid gland agenesis or ectopia. There was significant space-time clustering for both males and females, but clustering was restricted to lesser birth density areas. There was also evidence of clustering for unknown cases (p < 0.001). Clustering of these cases was restricted to females but was present for cases from both greater and lesser birth density areas. There was no evidence of clustering in cases of DHG. Conclusions: These data suggest that an unidentified environmental factor or factors may be involved in the etiology of thyroid DG in Scotland. The variation in CHT incidence observed internationally may reflect environmental as well as genetic factors.

Determination of thyroid volume in infants with suspected congenital hypothyroidism-the limitations of both subjective and objective evaluation

Objective:

To compare two methods of assessing gland size on thyroid ultrasound in newborn infants with suspected congenital hypothyroidism (CH).

Methods:

Images from infants with eutopic glands referred between 2007 and 2013 were evaluated blind by two sets of observers. Subjective gland size was categorised as small, borderline-small, normal, borderline-large and large. Objective gland volume, calculated as the sum of each lobe using the prolate ellipsoid formula (length x width x depth x π/6), was put into corresponding categories: <0.8, 0.81–1.0, 1.1– <2.2, 2.2–2.4 and >2.4 ml, derived from normative Scottish data.

Results:

Of 36 infants, permanent CH was present in 17, transient CH in 17, status uncertain in 2. Mean (SD) intraobserver error for thyroid volume measurement was 0.11 (0.23) ml [8.3%]. Subjective assessment by two observers was discordant in only four (10.8%) infants. However, subjective vs objective evaluation was discordant in 14 (39%). Eight (three permanent, five transient CH) had large glands subjectively but normal glands objectively; and six (four transient CH) had normal glands subjectively but small glands objectively. The former infants all showed a single flattened curve to the anterior thyroid margin, giving an impression of bulkiness. Gland shape was normal in the latter infants.

Conclusion:

Neither subjective nor objective evaluation predicts permanent vs transient CH. Altered gland shape may confound both methods, and undermine use of the conventional formula for measuring lobe volume.

Advances in knowledge:

Until more refined methods are available for assessing thyroid size, both subjective and objective evaluation are recommended in CH.

Permanent vs Transient Congenital Hypothyroidism: Assessment of Predictive Variables

OBJECTIVE

To assess clinical variables, including early thyroid scintigraphy, in predicting the outcome (permanent vs transient) in term infants with congenital hypothyroidism (CH).

METHODS

In a retrospective study, 142 full-term infants with CH diagnosed between 2000 and 2012 were categorized into three groups: agenesis/ectopic thyroid and permanent CH; eutopic thyroid and permanent CH; and eutopic thyroid and transient CH. All underwent early thyroid scintigraphy and were under regular follow-up in our tertiary Pediatric Endocrine Institute.

RESULTS

Thyroid scan showed agenesis/ectopic thyroid in 58 (41%) and eutopic thyroid in 84 (59%) infants. Imaging findings were similar in eutopic-permanent and eutopic-transient groups. At initial evaluation, TSH levels were higher in the agenesis/ectopic group than in the eutopic-permanent and eutopic-transient groups (71.5 ± 11.2 mIU/L vs 49.1 ± 27.9 mIU/L and 42.5 ± 29.1 mIU/L, respectively; P < 0.001). Higher l-T4 doses were required from the third month in the agenesis/ectopic than in the eutopic-permanent group (P < 0.001) and from the sixth month in the eutopic-permanent than in the eutopic-transient group (P < 0.01). Initial TSH >63.5 mU/L (P < 0.001) and l-T4 dose >4.6 μg/kg/d at age >6 months (P < 0.001) were found to be predictors for an agenesis/ectopic gland using receiver operating characteristic analysis, as was an l-T4 dose >2.2 μg/kg/d at age >6 months (P < 0.01) for permanent CH in patients with a eutopic gland.

CONCLUSIONS

Although early thyroid scintigraphy is reliable in predicting permanent CH when detecting agenesis or ectopic gland, it cannot differentiate between permanent and transient CH in cases with a eutopic thyroid. Confirmatory TSH at diagnosis and the l-T4 dose through treatment may better distinguish between permanent and transient CH.

Ultrasound Measurements of Thyroid Gland Volume at 36 Weeks' Corrected Gestational Age in Extremely Preterm Infants Born before 28 Weeks' Gestation

BACKGROUND

Thyroid ultrasound is a non-invasive imaging tool and provides good evaluation of thyroid anatomy, location, vascularisation, and echogenicity. The aim of this study was to assess thyroid function and thyroid volume in extremely preterm infants born before 28 weeks' gestation evaluated at 36 weeks' corrected gestational age (CGA) compared to term infants' normative data in the literature.

DESIGN

In this largest prospective UK study of extremely premature infants born at less than 28 weeks' gestation, thyroid volume measurement was assessed at 36 weeks' CGA. Fifty-five extremely preterm infants (28 males) who were born before 28 weeks' gestation were recruited to the study. All infants had ultrasound assessment of the thyroid gland at 36 weeks' CGA. We also prospectively measured thyroid stimulating hormone (TSH) and free thyroxine (FT4) in all infants at the time of recruitment (within 5 days of birth), at days 14, 21, and 28, and at 36 weeks' CGA.

RESULTS

The mean thyroid volume was measured at 0.57 mL (SD ±0.18). There was no association between mean thyroid volume and thyroid function (TSH or FT4). No associations were found between mean thyroid volume and gestation or birth weight in these infants.

CONCLUSIONS

Our findings provide a reference range with a mean thyroid volume of 0.57 mL (SD ±0.18) in this extremely preterm age group if less than 28 weeks' gestation. Thyroid volume at birth can vary from country to country due to variations in iodine intake as well as gestational age.

Permanent congenital hypothyroidism with blood spot thyroid stimulating hormone <10 mU/L

BACKGROUND

The UK recommended lower threshold for neonatal blood spot thyroid stimulating hormone (TSH) screening for congenital hypothyroidism (CHT) is 10.0 mU/L. Some laboratories use lower thresholds. This will lead to referral of mildly or unaffected infants but some will require thyroxine therapy.

METHODS

Laboratory referrals with a first or repeat capillary TSH between 8.0 and <10.0 mU/L were identified (January 2004 to March 2014). The outcome of these cases was examined.

RESULTS

26 infants had one or more blood spot TSH values between 8.0 and 9.99 mU/L; 65% had transient elevated neonatal TSH while one is awaiting diagnostic challenge. The remaining eight (31%) have permanent CHT; three with dyshormonogenesis, two with thyroid ectopia and the others met the criteria for definite CHT. Two out of three with dyshormonogenesis presented with decompensated hypothyroidism.

CONCLUSIONS

Infants with permanent and occasionally severe CHT may have a screening TSH below the UK recommended lower cut-off.

Congenital Hypothyroidism: Long-Term Experience with Early and High Levothyroxine Dosage

AIM

To assess the management and outcome of the congenital hypothyroidism (CH) patients followed at our institution since the introduction of systemic neonatal screening for CH.

STUDY DESIGN

The records of 139 CH patients referred to our center between 1978 and 2014 were retrospectively reviewed. Biochemical and imaging data at diagnosis, initial treatment and growth were analyzed.

RESULTS

111 patients had thyroid dysgenesis (64 ectopy, 46 athyreosis and 1 hypoplasia) and 28 patients had a gland in situ (17 dyshormonogenesis/goiter and 11 normal-sized gland). Levothyroxine treatment was initiated at a median age of 11 days with a mean dose of 11.4 µg/kg/day. Compared to those with ectopy, patients with athyreosis had higher thyroid-stimulating hormone (TSH) and lower thyroxine at diagnosis as well as more delayed bone maturation. Between 1978 and 2014, we observed earlier treatment and earlier TSH normalization. Birth auxology was slightly above the mean of the reference population. Growth at 1 and 6 years and school progression at 11 years were similar to those of the reference population.

CONCLUSION

Ectopy is the commonest cause of CH. Children with CH treated early with a mean levothyroxine dose of 11.4 µg/kg/day had a median TSH of 3.07 mU/l at 1 month of age and normal growth.

How well does the capillary thyroid-stimulating hormone test for newborn thyroid screening predict the venous free thyroxine level?

OBJECTIVES

To determine, in newborn infants referred with elevated capillary thyroid-stimulating hormone (TSH), a threshold below which a frankly subnormal venous free thyroxine (fT4) level of <10 pmol/L is unlikely, so that treatment with levo-thyroxine (L-T4) might be deferred until venous thyroid function tests (TFTs) become available.

SUBJECTS AND METHODS

All infants referred in Scotland since 1979 with capillary TSH elevation were studied, with particular focus on infants screened using the AutoDELFIA assay between 2002 and 2013.

RESULTS

Of the 321 infants referred with capillary TSH elevation using AutoDELFIA, 35 were excluded (fT4/TSH unavailable (12), venous sample either preceding or >10 days after capillary sampling (13, 10)), leaving 286 eligible for analysis (208 definite/probable hypothyroidism, 61 transient TSH elevation, 17 of uncertain thyroid status). Capillary TSH and venous T4 were strongly correlated (Spearman's rank correlation coefficient -0.707355). The optimal capillary TSH threshold for predicting a venous fT4 of <10 pmol/L was found to be >40 mU/L (90.3% sensitivity and 65.9% specificity compared with 90.25% and 59.1% for >35 mU/L and 88.3% and 68.2% for >45 mU/L). 93 infants (32.5%) had capillary TSH ≤40 mU/L at referral of whom 15 (9.7%) had venous fT4 <10 pmol/L, comprising seven with true congenital hypothyroidism, five with transient TSH elevation and three with uncertain status, two of whom died.

CONCLUSION

For infants in whom capillary TSH is ≤40 mU/L, it is reasonable to defer L-T4 treatment until venous TFT results are known provided that the latter become available quickly.

Thyroid Imaging in Infants

Congenital hypothyroidism is the most common preventable cause of mental retardation. It is important to know the cause of each patient's thyroid dysfunction to foresee the course of therapy and outcomes. Imaging methods, such as ultrasound and thyroid scan, help determine the anatomy and function of the thyroid gland. Although thyroid scan is considered superior in detecting ectopic thyroid tissue, ultrasound is able to detect the presence of thyroid tissue not otherwise visualized in 15% of patients.

Use of Tc-99 m thyroid scans in borderline congenital hypothyroidism

BACKGROUND

Mild or borderline congenital hypothyroidism [often referred to as mild neonatal hyperthyrotropinemia (MNH)] is characterized by an abnormal newborn screen (NBS), followed by mildly elevated TSH and normal FT4 on confirmatory testing. This condition is increasingly observed, but data regarding optimal management are limited.

OBJECTIVE

Examine the use of routine technetium thyroid scanning (TS) in the management of MNH.

METHODS

Retrospective study of infants with MNH between 2000 and 2011. We assessed the clinical course of infants with MNH according to TS results; as a comparator, infants with classic congenital hypothyroidism (CH) were analysed in parallel.

RESULTS

We identified 69 infants (52% boys) with MNH and 164 (34% boys) with classic CH. TS results were divided into four subgroups: no uptake in 7% of MNH vs 24% of classic CH (P < 0·01), decreased uptake/anatomical abnormalities in 39% vs 46% (p = NS), increased uptake in 35% vs 26% (p = NS) and normal uptake in 19% vs 4% (P < 0·01). In MNH, neither NBS-TSH, confirmatory TSH and FT4, mean LT-4 treatment doses and number of dose escalations, nor post-treatment FT4 and TSH differed among the four subgroups. In contrast, clinical features in infants with classic CH differed among the subgroups. Among MNH infants who reached 3 years of age, trial-off treatment was successful in 6 of 11 (55%) with no apparent difference in success rates among TS subgroups.

CONCLUSIONS

The information provided by TS during evaluation of MNH does not predict clinical course; obtaining these scans in infants with MNH may not be an effective use of healthcare resources.

The changing epidemiology of congenital hypothyroidism: fact or artifact?

Screening increases prevalence estimates for most diseases and congenital hypothyroidism (CH) is no exception, affecting one in 6700 children by clinical ascertainment and one in 3500 in the first surveys of systematic biochemical screening of newborns. Importantly, screening has resulted in the disappearance of intellectual disability due to CH. A further doubling in prevalence estimates has recently been reported, mostly accounted for by changes in screening algorithms; accordingly, the prevalence of overt CH has remained stable. Population-based registries that distinguish confirmed diagnoses from positive screening results have proved invaluable. These registries should include: etiology of CH based on imaging, ideally technetium scintigraphy; ethnicity; socio-educational data; input from the screening laboratories and pediatric endocrinologists. Efforts should now be directed at increasing the proportion of the world's newborns screened for overt CH (currently 30%) and at determining if neonates with mild hyperthyrotropinemia also benefit from early treatment.