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Congenital Hypothyroidism - early assessment and management

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Objective

This guideline is intended to assist with the diagnostic work-up and management of infants with congenital hypothyroidism. It is based on current literature, international guidelines and local experience. Within the Auckland region, infants with congenital hypothyroidism are usually managed by the Starship Endocrine Service.

Background

The early detection and treatment of congenital hypothyroidism (CH) prevents intellectual disability and optimises growth and developmental outcomes. The majority of cases will be detected by newborn screening. In New Zealand, an elevated level of thyroid stimulating hormone (TSH) on a dried blood-spot sample collected at 48 hours of age is used to screen for CH.

However, it is not possible to detect all cases through screening and it is important that clinicians remain vigilant about possible missed cases. Whilst TSH based screening has high sensitivity for primary hypothyroidism (thyroid origin, raised TSH), it will not detect central hypothyroidism (pituitary and/or hypothalamic deficiency, TSH low or normal). CH screening is also less reliable in preterm or very unwell infants and in multiple births1,2.

The New Zealand incidence of primary CH is 1:2500-3000, with 20-25 new cases detected each year. In recent years, approximately 40% of cases are due to thyroid dysgenesis (athyreosis or an ectopic gland) and 40% due to dyshormonogenesis. A smaller proportion has unclear aetiology (no scan or a complex clinical picture) or transient disease (due to maternal thyroid antibodies/anti-thyroid drugs or iodine deficiency/excess).

Principles of management

  • Early detection and prompt initiation of thyroxine replacement can prevent severe cognitive impairment and growth failure.
  • Affected infants require close monitoring over the first 2 years of life to maintain euthyroidism.
  • Over-treatment is as deleterious as under-treatment.
  • Treatment should target age-appropriate biochemical reference ranges.
  • Primary CH may be permanent or transient depending on the cause; imaging studies help to determine aetiology.

Evaluation

Infants should be assessed as soon as possible, generally within 48 hours of notification.

History and Examination

  • Maternal: diet (especially high/low iodine), medications (including seaweed tea, a commonly used lactation agent in the Korean population), auto-immune disease or history of thyroid surgery.
  • Familial thyroid dysfunction (e.g. any CH, thyroid hormone resistance).
  • Baby: symptoms and signs of CH (including jaundice, goitre, growth parameters) and a careful examination for features of other congenital problems (especially cardiac).

Biochemistry

  • Serum thyroid function tests (venous or capillary), consisting of TSH and free T4 (FT4).
  • Plasma bilirubin if indicated.
  • Maternal and infant TSH receptor antibodies where there is a positive maternal history of autoimmune thyroid disease.
  • Consider serum thyroglobulin (unrecordable values suggest athyreosis or a thyroglobulin synthesis defect and very high levels dyshormonogenesis).

Imaging studies

  • Thyroid imaging is recommended (scintiscan and/or ultrasound as available), but should not delay the initiation of treatment3,4.
  • Thyroid scintigraphy facilitates the detection of anatomic abnormalities and measures global thyroid function as reflected by radionuclide uptake and will usually provide clear-cut diagnostic information that assists with counselling and treatment.
    • The ADHB nuclear medicine department uses intravenous or subcutaneous technecium-99m (20 MBq). Absorbed radiation is very low, equivalent to 2-3 chest x-rays or a 10h commercial flight5.
    • Whilst scintiscans are currently only available in major centres, they are informative while the TSH remains elevated and can usually be deferred for 1-2 weeks after starting therapy.
    • Caution re: apparent athyreosis. Reduced uptake (e.g. due to maternal TSH receptor blocking antibodies or late scan on treatment) can be misdiagnosed as athyreosis and should therefore be interpreted within clinical context. Ultrasound and thyroglobulin levels may assist.
  • Thyroid ultrasound is widely available but highly observer-dependant during infancy. Although diagnostic accuracy is improved with the use of colour Doppler, ectopic thyroids are detected less reliably as compared with scintigraphy6.

Counselling

Parents of infants with CH are naturally very apprehensive, but can usually be reassured of a favourable prognosis and the expectation of normal intelligence. New Zealand outcome data has demonstrated that affected children (including those with severe CH) detected by newborn screening and managed with the combination of initial high dose therapy and close monitoring can be expected to achieve the same IQ scores as their siblings7. Conversely, delayed diagnosis and treatment may lead to reduced IQ and periods of over-treatment are associated with attention deficits8,9. Note that, in some cases, CNS abnormalities can occur independent of biochemical hypothyroidism (e.g. CH due to TTF1 or PAX8 mutations) so we suggest caution in counselling that the child will definitely have normal neurodevelopment.

Thyroid dysgenesis (an ectopic gland or athyreosis) is very unlikely to recur in subsequent pregnancies. However, permanent thyroid dyshormonogenesis has an autosomal recessive pattern of inheritance, with a 1:4 chance that future siblings will be affected. (see Information for Families)

Treatment

Thyroxine should be started as soon as CH is confirmed on TFTs. Treatment is indicated if serum FT4 concentration is below age norms, and should be considered where FT4 is normal but TSH >20 mU/l3.

  • The initial treatment goal is to rapidly normalise FT4 and can be achieved with a standard loading dose of 10 mcg/kg/d thyroxine10.
  • N.B. high starting doses of 15 mcg/kg/d lead to a high incidence of transient hyperthyroidism, and are no longer advocated locally.
  • It is expected that serum TFTs will be repeated after 1 week of treatment and should be used to guide further dosing.
  • A normal/near normal FT4 after 1 week of treatment should prompt a dose reduction of 20-30% in order to avoid subsequent over-treatment.
  • TSH levels typically take a further 1-2 weeks to normalise and are not the initial treatment target.
  • The replacement dose of thyroxine decreases over the 1st months of life, to a usual required dose of 5 mcg/kg/day between ages 6m-2y.

Treatment decisions in very mild or borderline cases can be difficult and should be made in conjunction with a paediatric endocrinologist. Serial TFTs off treatment or commencement of thyroxine at a low dose (5 mcg/kg/day) may be appropriate. Note that mild rises in TSH can be associated with other conditions such as Trisomy 21, Williams syndrome and Albrights hereditary osteodystrophy.

Thyroxine suspensions made up by a pharmacy at a standard concentration of 15 mcg/ml are stable for 10 days10. Use of a standard (15 mcg/ml) strength helps to avoid dosing errors. Pharmaceutically produced suspensions facilitate reliable dosing and dose changes but also commit families to picking up new supplies each week. Suspensions must also be refrigerated and shaken well before administration. Alternatively, thyroxine tablets can be crushed by families and administered via small spoon, either in a few ml of water or breast milk.

Monitoring

Intensive follow-up is recommended during the first 2 years of life3, 10. Frequent biochemical monitoring minimises the duration of periods of under or over-treatment and helps with growth-related dose changes.

Local experience supports a schedule of weekly TFTs for the 1st six weeks and then monthly until 1 year of age and 2-3 monthly in the 2nd year10.

  • Serum FT4 concentrations increase significantly following a dose of thyroxine. Monitoring tests should ideally be taken >4 hours after a dose.
  • The treatment goals are to maintain FT4 in the upper third of the age-specific reference range (or just above this), and TSH within the normal range.
  • Suppressed TSH indicates over-treatment and should prompt dose reduction. Generally dose reduction equates to a similar reduction in FT4 (e.g. a 10% reduction in dose causes a 10% reduction in FT4)
  • Elevated TSH indicates under-treatment, commonly because of growth or missed doses, and should prompt enquiry about compliance. Specific foods (soy, fibre) and medications (iron, calcium) may also inhibit intestinal absorption of thyroxine.

3-monthly clinical review is recommended during the first 3 years of life, with particular emphasis on growth and development.

Transient hypothyroidism

Thyroid re-evaluation is indicated for children with suspected transient CH. This includes those with an in-situ thyroid gland or in whom no initial imaging was performed (particularly babies that were preterm or sick at the time of referral). Those with thyroid dysgenesis (agenesis or an ectopic gland) have permanent disease by definition. However, consider re-evaluation of children with apparent athyreosis who have not required substantial dose increase with age (as the differential diagnosis includes a late scan with alternative aetiology, TSH receptor defects or maternal blocking antibodies).

Thyroid re-evaluation is usually performed age 2-3 years, after brain myelination is complete, and usually involves withdrawal of thyroxine replacement for 2-4 weeks. At this point, an elevated serum TSH (>10 mIU/l) implies permanent disease3.

Information for families

References

  1. Bijarnia S, Wilcken B, Wiley V. Newborn screening for congenital hypothyroidism in very-low-birth-weight babies: the need for a second test. J Inherit Metab Dis 2011; 43: 827-833.
  2. Azam A, Cutfield W, Mouat F et al. Missed congenital hypothyroidism in an identical twin. J Paediatr Child Health 2012; 48: 936-38.
  3. Leger J, Olivieri A, Donaldson M et al. European society for paediatric endocrinology consensus guidelines on screening, diagnosis and management of congenital hypothyroidism. Horm Res Paediatr 2014; 81: 80-103.
  4. Rose S, Brown R. Update on newborn screening and therapy for congenital hypothyroidism. Pediatrics 2006; 117:2290-2302.
  5. Schoen E, Clapp W, To T, et al. The key role of newborn thyroid scintigraphy with isotopic iodine (123I) in defining and managing congenital hypothyroidism. Pediatrics 2004; 114(6): e683-688.
  6. Lucas-Herald A, Jones J, Attaie M, et al. 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. J Pediatr 2014; 164: 846-854.
  7. Albert B, Heather N, Derraik J et al. Neurodevelopmental and body composition outcomes in children with congenital hypothyroidism treated with high-dose initial replacement and close monitoring. J Clin Endocrinol Metab 2013; 98: 3663-3670.
  8. Bioleau P, Bain P, Rives S. Earlier onset of treatment or increment in LT4 dose in screened congenital hypothyroidism: which is the more important factor for IQ at 7 years? Horm Res 2004; 61: 228-233.
  9. Alvarez M, Iglesias F, Rodriguez-Sanchez A et al. Episodes of overtreatment during the first six months in children with congenital hypothyroidism and their relationships with sustained attention and inhibitory control at school age. Horm Res Paediatr 2010; 74: 114-120.
  10. Mathai S, Cutfield W, Gunn A et al. A novel therapeutic paradigm to treat congenital hypothyroidism. Clin Endocrinol 2008; 69: 142-47. 

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Document Control

  • Date last published: 22 February 2017
  • Document type: Clinical Guideline
  • Services responsible: Paediatric Endocrinology
  • Author(s): Natasha Heather, Paul Hofman
  • Owner: Natasha Heather
  • Editor: Greg Williams
  • Review frequency: 2 years

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