Congenital hypothyroidism: current perspectives

Abstract

Congenital hypothyroidism (CH), the most common pediatric endocrine disorder with an estimated prevalence of 1:2,000 to 1:4,000, is an under-recognized problem in countries without routine newborn screening (NBS) programs. Thyroid dysgenesis (TD) is the most com- mon cause of primary CH accounting for approximately 85% of all cases; most of the remaining patients have dyshormonogenesis. Transient CH and CH with eutopic gland, are increasingly being identified after introduction of routine NBS. The clinical features of CH are often subtle resulting in delayed diagnosis and eventually poor intellectual outcome. In developed countries, detection by NBS and early initiation of treatment has largely eliminated the intellectual dis- ability caused by this disorder. The lower screening thyroid stimulating hormone (TSH) cutoff and changes in birth demographics in some countries have been associated with an increase in the reported incidence of CH. However, the additional cases detected by the lower TSH cutoff tend to have either milder or transient hypothyroidism. Diagnosis of CH is made on the basis of serum concentrations of TSH and thyroxine (T4). Thyroid ultrasound, radionuclide scintigraphy, serum thyroglobulin (TG) levels and specific genetic tests help ascertaining the exact etiological diagnosis. Non-availability of later tests should not deter the pediatrician from initiation of treat- ment. Age at initiation of treatment and starting dose of levothyroxine are critical factors that determine the long-term outcome. Higher doses of levothyroxine at 10–15 μg/kg/day are required in infants, with titration based on T4 and TSH levels, which are repeated frequently. Coexistence of other congenital anomalies in children with CH adds to the morbidity. Approximately 70% of babies worldwide are not born in an area with an established NBS program and hence are not detected and treated early. Consequently, the economic burden of mental retardation due to CH remains a significant public health challenge in countries without NBS. The health burden owing to CH continues to be high even in countries with well-developed NBS.