Factors Distinguishing between Transient and Permanent Hypothyroidism in Patients Diagnosed as Congenital Hypothyroidism by Newborn Screening

Hong, Su Young; Chung, Hye Rim; Lee, Seong Yong; Shin, Choong Ho; Yang, Sei Won

Abstract

PURPOSE
Since the introduction of newborn screening, the detection rate of transient hypothyroidism has been increased. Therefore, we aimed to reevaluate the prevalences of congenital hypothyroidism according to etiology and to evaluate the clinical characteristics to differentiate between transient and permanent hypothyroidism before L-thyroxine withdrawal to avoid unnecessary prolonged treatment.
METHODS
We retrospectively reviewed medical records of 25 male and 46 female patients diagnosed as congenital hypothyroidism by newborn screening from 1992 to 2002. We performed thyroid function test such as T3, TSH and total T4 before 1997, and free T4 from 1997.
RESULTS
Since the introduction of newborn screening, the prevalences of permanent congenital and transient hypothyroidism were 53.5% and 46.5%, respectively. Thyroid dysgenesis was more common in females (males 3, females 22, P<0.05). Among 58 patients, who were not confirmed as thyroid dysgenesis at L-thyroxine therapy, the proportion of transient and permanent hypothyroidism were 32 (55.2%) and 26 (44.8%) respectively. There were no significant differences in free T4, total T4, TSH levels at initial diagnosis between transient and permanent hypothyroidism patients. Permanent hypothyroidism patients could not withdraw L-thyroxine during the first 3 years. Among 32 patients with transient hypothyroidism, 30, 23, and 17 patients continued L-thyroxine therapy at 1, 2, and 3 years of age, respectively. The mean duration of L-thyroxine therapy was 26.4+/-11.8 months. The dose of L-thyroxine had been significantly decreased since 6 months of age in the patients with transient hypothyroidism (P<0.05). The patients with thyroid aplasia received the highest dose of L-thyroxine from 6 to 36 months of age (P<0.05). Among 13 patients who were confirmed as thyroid dysgenesis at L-thyroxine therapy, 12 patients were confirmed as permanent hypothyroidism, while one patient, who was diagnosed as thyroid aplasia by thyroid scan, revealed normal thyroid gland and could be ceased thyroid hormone therapy at 3 years of age.
CONCLUSION
We could not differentiate between transient and permanent hypothyroidism by free T4, total T4 and TSH levels at the initial diagnosis. We could diagnose as permanent hypothyroidism in patients with thyroid dysgenesis and with higher or appropriate L-thyroxine doses for weight to maintain euthyroid during follow-up. We therefore suggest that diagnostic test maybe done before 3 years of age in some patients who had the histories of suspecting transient hypothyroidism and significantly low L-thyroxine doses for weight.