Etiological Profile, Targeted Levothyroxine Dosing and Impact of Partial Newborn Screening in Congenital Hypothyroidism-A Single Centre Experience.

Background:Congenital hypothyroidism (CH) is the most common cause of preventable intellectual disability. Newborn screening (NBS) for CH has been in vogue in many parts of the world since 1970, but despite its well-known benefits, many developing countries including India have not been able to establish universal NBS for CH till date. Objective:The aim of this study was to review the clinical aspects of congenital hypothyroidism in a tertiary care university referral teaching hospital, focusing on aetiology of CH, predictors of permanence, optimal targeted dose strategies based on aetiology and the effect of newborn screening on the time to diagnosis. Material and Methods:The electronic medical records of 233 children with CH referred to our centre between January 2009 and December 2019 were analysed. A partial NBS was established in the state in 2012. Results:Dyshormonogenesis (57.5%) was the most common aetiology of CH. The incidence of transient CH in children with a gland in situ (GIS) was 35%. Levothyroxine (LT-4) dose of >2.75 μg/kg/day (sensitivity 76.5, specificity 72), >2.15 μg/kg/day (sensitivity 82.4, specificity 61.9) and >1.85 μg/kg/day (sensitivity 76.5, specificity 61.9) at years 1, 2 and 3, respectively, were predictors of permanent CH. An initial LT-4 dose ≥8 μg/kg was sufficient and very seldom led to undertreatment in children with dyshormonogenesis. On the contrary, even doses ≥13 mcg/kg/day led to frequent undertreatment in children with thyroid dysgenesis. After the introduction of newborn screening, the median age at diagnosis came down from 45 days (IQR 14-180 days) to ten days (IQR 3-12 days). Conclusion:Targeted dosing based on aetiology of CH may be more appropriate to optimise outcomes. The time to diagnosis of CH reduced significantly after the adoption of even a partial NBS program highlighting the urgent need for implementation of the same in resource poor settings.