Year : 2013 | Volume
: 10 | Issue : 4 | Page : 7--8
Neonatal thyroid dysfunction-lessons from Indian experience
Pulliangudi G Sundararaman
Department of Medical Endocrinology, No. 5, Anna Avenue, Adyar, Chennai, India
Pulliangudi G Sundararaman
Department of Medical Endocrinology, No. 5, Anna Avenue, Adyar, Chennai - 600020
Neonatal thyroid dysfunction is quite common in India. The clinical presentation is very subtle and can be captured by neonatal thyroid screening. Neonatal screening paves a better way in detecting and preventing neuro-cognitive insult. In India lack of a national policy, field staff and certified lab; screening programme is not carried out effectively. Managing thyroid disorder in neonates and in children poses unique difficulties. Hypothyroidism can be transient, hence to be reassessed. Neonatal thyrotoxicosis is not commonly seen.
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Sundararaman PG. Neonatal thyroid dysfunction-lessons from Indian experience.Thyroid Res Pract 2013;10:7-8
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Sundararaman PG. Neonatal thyroid dysfunction-lessons from Indian experience. Thyroid Res Pract [serial online] 2013 [cited 2020 Sep 20 ];10:7-8
Available from: http://www.thetrp.net/text.asp?2013/10/4/7/106804
Among the various paediatric endocrine problems, thyroid disorders are the most common. In India, 1-4% of the population is mentally retarded and amongst them congenital hypothyroidism is one of the most preventable cause of mental retardation. Congenital hypothyroidism relates to thyroid dysfunction present at birth. It includes disorders ranging from absence of the thyroid gland to transient hypothyroxinemia of prematurity.
A variety of mechanisms play a role in producing hypothyroidism at birth. Three transcription factors, TTF-1, TTF-2, and PAX8 are important for thyroid gland morphogenesis and differentiation. These factors are found to influence thyroid hormone production and are responsible for the synthesis of thyroglobulin and thyroid peroxidase.
Any defect in thyroid embryogenesis and functional maturation can lead to congenital hypothyroidism. About 75% of congenital hypothyroidism is found to be due to thyroid gland dysgenesis. In a hospital based observational study done by Nair et al. Transient hypothyroidism was seen in 50% patients.
Other aetiologies of congenital hypothyroidism include iodine deficiency, defects in steps of thyroid hormone synthesis, thyroglobulin deficiency and transient neonatal hypothyroidism due to various causes.
Worldwide the prevalence of congenital hypothyroidism approximates to 1:3500-1:4000 live births. The exact incidence of congenital hypothyroidism in India is not known. A screening of 36,000 newborns in Chennai as part of a study conducted by Indian council for medical research has revealed that 1.6 in every thousand births had congenital hypothyroidism that results in stunted growth and low intelligence quotient. Newborn screening conducted in 18,300 neonates in Andhra Pradesh reported a prevalence of 1 in 1,700 live births. In another study from North India, revealed a prevalence of 1 in 3,400.
The neonatal thyroid screening programs conducted worldwide and early initiation of thyroxine therapy have reduced intellectual deficits significantly. Recent literatures insist new born screening at multiple interval periods. Initiation of treatment with thyroxine within 2 weeks of age can normalise cognitive development. Only 5-10% of children detected with a screening program can be diagnosed clinically. Most of the infants detected on screening are asymptomatic in the first few weeks of life, thus making screening programs prudent for early diagnosis and early initiation of treatment so as to prevent or minimize intellectual impairment and neuropsychological damage. Failure to establish diagnosis and institute therapy during the first few weeks can lead to significant impairment in the neurodevelopment.
At present, there is no national screening program for congenital hypothyroidism. The ideal time for screening would be within 30 min of birth (cord blood testing) but this will not reflect metabolic status of neonate in true sense. In view of thyrotropin surge after birth, it is highly recommended that CH testing is done between 2-4 days of age by a heel prick sample. Screening programme in India is thwarted by lack of certified lab, field staff to co-ordinate and cost incurred.
Levels of TSH more than 20 mIU/ml or T4 levels below 6 mg/dl in a full term infant should arouse suspicion and need to be rechecked within a week. During infancy, TSH levels up to 10 mIU/ml are considered normal provided serum T4 levels are in normal range. Thyroid test results in neonates must be reported with gestation and age specific reference intervals. TSH beyond infancy is maintained in the usual 0.3-5 μIU/ml. However, additional tests to determine the aetiology of CH like Thyroid scintigraphy, Ultrasonography etc. should also be carried in order to determine whether the condition is transient, permanent or due to genetic causes.
A study conducted by Reddy et al. at Thirupathi has reported that 59% congenital hypothyroid patients had congenital malformations in the form of cardiac malformations in 29% and neural tube defects in 41%. Hence it is important to assess the co morbidities associated with congenital hypothyroidism so as to improve the outcome. In all congenital hypothyroid infants, the parents must be screened for thyroid dysfunction.
The goal of therapy is to normalize T4 within 2 weeks and TSH within 1 month for which an initial dosage of 10-15 mcg/kg of levothyroxine has been recommended. It must also be noted that all congenital hypothyroidism are not permanent. All children diagnosed with congenital hypothyroidism require re-evaluation at the age of 3, as thyroxine can be withdrawn safely without interruption to normal brain development, to assess for permanence of congenital hypothyroidism. This is done by stopping the drug for 30 days and re-evaluating thyroid status. If the child remains euthyroid, then thyroxine may be stopped safely as it is a child with transient hypothyroidism. If thyroid profile is abnormal and USG reveals absence of gland, then thyroxine needs to be continued owing to permanence of the condition. Growth rate, adult height and the neurodevelopment outcome in children with CH started on thyroid hormone treatment early, is normal or near-normal.
Management issues in congenital hypothyroid must thoroughly be scrutinised in our country such as delay in instituting the treatment, adequacy of the therapy, adherence to the therapy, availability of proper medication, switching over to native medicine, mixing thyroxine with iron syrup and soya milk, stopping thyroxine during travel and acute illness.
Neonatal thyrotoxicosis is rare. Transient neonatal hyperthyroidism is the more common form of neonatal hyperthyroidism and occurs in 1-2% of the offspring of mother. The transplacental passage of maternal TRSAB plays a key role in the pathogenesis of this disease hence mothers must be screened for TRSAB.
Screening thyroid dysfunction in neonates, iodination of salt will solve lot of misery and morbidity in children and adult life; unless this is taken up as universal programme in India the puzzle will persist.
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