Diagnostic WorkUp of Congenital Hypothyroidism

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A positive newborn screening result calls for immediate diagnostic work-up. Information on maternal medication or morbidity should be obtained to assess the infant's prenatal thyroid status. Clinical examination should be performed to document signs and symptoms of CH and possible associated malformations. There is an increased risk for other congenital anomalies (8.4%), including cardiovascular, musculoskeletal and CNS malformations [3].

Confirmatory serum measurements of TSH and T4 are required, along with thyroid hormone binding proteins and serum free T4. In cases of maternal autoimmune thyroid disorder, assessment of TSHR blocking antibodies may indicate a transient form of CH. Thyroglobulin levels tend to be high in dyshormonogenesis and low in thyroid agenesis. Thyroid ultrasonography and/or thyroid scan are considered optional for management of CH [1] but are necessary to clarify the underlying source of CH, to distinguish between thyroid aplasia, ectopy or inborn errors of T4 synthesis. Testing thyroid function in first degree relatives may be informative because of the variable penetrance of inherited CH. Measurement of iodine or iodotyrosines in urine are helpful if iodine exposure, iodine deficiency or recycling defects are considered.

It is clinically important to distinguish permanent or transient forms of CH. If imaging studies reveal ectopic or absent thyroid tissue, hypothyroidism is probably permanent. If initial TSH is below 50mU/l and there is no increase after the neonatal period, at 3 years of age discontinuation of L-T4 may be considered [1]. If TSH increases after 1 month discontinuation, permanent hypothyroidism is probable, and L-T4 treatment must be resumed. Regular follow-up visits are essential to ensure optimal growth and development including auditory and visual abilities and neuropsychological skills.

In recent years genetic studies have revealed a variety of molecular defects underlying CH. In the clinical management of patients with CH, however, genetic testing is currently not yet recommended on a routine basis.

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