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Thyroid Disorders


Congenital Hypothyroidism – Monitoring Thyroid Function in Infants Sharon Straussman1


and Lynne L Levitsky2


1. Fellow in Pediatric Endocrinology; 2. Chief, Pediatric Endocrine Unit and Associate Professor of Pediatrics, Massachusetts General Hospital, Harvard Medical School


Abstract


Guidelines for monitoring thyroid function in congenital hypothyroidism (CH) are published by the American Academy of Pediatrics, the European Society for Paediatric Endocrinology and the UK Newborn Screening Programme Centre. The fact that the recommendations are not uniform reflects management uncertainty. In addition, clinical care may not always be informed by these guidelines. Recent studies suggest that more frequent monitoring is indicated in some infants. Monitoring to identify delayed thyroid stimulating hormone (TSH) rise is indicated in pre-term, low birth weight and sick full-term newborns. Monitoring thyroid function in infants with CH monthly after normalisation of TSH until six months of age, and every one to two months between six and 12 months of age, will decrease exposure to suboptimal thyroid hormone levels. Assessment for permanency of hypothyroidism should be done only in children in which there is likelihood of resolution and not earlier than three years of age. In some instances, when TSH elevations persist after normalisation of the free thyroxine, it may be reasonable to try combined therapy with triiodothyronine.


Keywords


Congenital hypothyroidism, thyroid function, delayed thyroid stimulating hormone (TSH) rise, thyroid hormone therapy, persistent TSH elevation


Disclosure: The authors have no conflicts of interest to declare. Received: 3 August 2011 Accepted: 26 September 2011 Citation: European Endocrinology, 2012;8(1):53–6 Correspondence: Lynne L Levitsky, Pediatric Endocrine Unit, Massachusetts General Hospital, 5th Floor, 175 Cambridge Street, Boston, MA 02114, US. E: LLevitsky@partners.org


Congenital hypothyroidism (CH) screening was introduced in 1974 and has become common practice, preventing the devastating neurological and developmental outcomes of untreated CH. Thyroid hormones are essential for normal brain development during early years. It is uniformly agreed that screening programmes are essential for early identification and treatment, and that adequate thyroxine (T4) dosing both initially and during the first three years of life correlates with good outcomes.1–3


There is, however, controversy regarding the


timing of repeat thyroid function tests (TFTs) after the initial screen, as well as the frequency of monitoring required to optimise the outcomes of children diagnosed with CH who are being treated. This paper discusses current monitoring guidelines and reviews recent studies suggesting the need for changing these guidelines.


Incidence of Congenital Hypothyroidism Before the use of newborn screening programmes was widespread, the reported incidence of CH was 1:7,000–1:10,000. As expected, the CH incidence rate increased significantly – to approximately 1:4000 – after the introduction of screening programmes.4


Another significant


increase in reported incidence has occurred during the last two decades. It is unclear whether this increase is the result of increased detection or a true increase in incidence due to a change in unidentified risk factors.


One possible reason for the higher reported incidence of CH is the change in screening methods and cut-offs used for its diagnosis. The use of a thyroid stimulating hormone (TSH) assay for initial screening


© TOUCH BRIEFINGS 2012


To further characterise this recent increased incidence, a cohort of children in Massachusetts during the low incidence period (1991–1994, incidence of 1:3010) was compared with a cohort of children during the high incidence period (2001–2004, incidence of 1:1660). Screening was performed with T4 and subsequent TSH on selected specimens. The severity of CH was determined as follows: initial TSH level ≥100 milliunits per litre (mU/l) = severe CH; and initial TSH level <100 mU/l but ≥20 mU/l = mild CH. Initial TSH level <20 mU/l with subsequent abnormal TSH was termed ‘delayed TSH rise’. Clinical and laboratory follow-up determined whether CH was permanent or transient. The increased incidence of CH was attributed to an increase in mild cases and delayed cases, with no increase in severe hypothyroidism. There was no difference in the proportion of transient cases. The conclusion was that the rising incidence of CH in Massachusetts was attributable to enhanced detection, rather than to an absolute increase in numbers.6


Many clinicians question the need for treatment in children with mild CH and delayed TSH rise. In the Massachusetts study, none of the


53


is associated with a reported CH incidence higher by 24 % than that reported by laboratories using a T4 assay.5


During the 1990s, many


laboratories switched to an initial TSH testing method, possibly contributing to the higher current measured incidence of CH. A recent paper by Hertzberg and colleagues, however, concluded that there was indeed an increased incidence rate, even after adjusting for the screening methodologies and parameters.5


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