Changes in thyroid volume during the course of treatment of congenital primary hypothyroidism with an in situ thyroid gland

OBJECTIVES: Changes in thyroid volume (TV) during the course of treatment of primary congenital hypothyroidism (CH) have not been fully elucidated. This study aimed to evaluate changes in TV according to etiology and their impact on treatment withdrawal rates. METHODS: CH. RESULTS: At diagnosis, thyroid ultrasound showed normal volume (64.3 %, n=133), hyperplastic (16.9 %, n=35), and hypoplastic (4.8 %, n=10) glands. In hyperplastic cases, median TV decreased significantly from 4.08 SDS (2.00-22.63) to 0.55 SDS (-1.68-8.52) over 3 years (p<0.0001), while hypoplastic glands showed an increase from -2.25 SDS (-2.75-2.00) to -1.05 SDS (-2.50-0.70) (p=0.005). No significant change was observed in normal volume patients [-0.42 SDS (-1.93-1.87) vs. -0.23 SDS (-2.36-5.16), p=0.305]. Transient CH rates differed by morphology (60.9 , 48.6, and 20 %, respectively; p=0.025). At 3 years, 70 % (n=7) of initially hypoplastic glands reached normal volume, with a treatment withdrawal rate of 28.6 %. CONCLUSIONS: In this study, which is the first to evaluate TV changes during the course of CH treatment, a significant decrease in TV SDS was found in patients with hyperplasia, whereas a significant increase was observed in those with hypoplasia. Despite initial hyperplasia or hypoplasia, TV could normalize over time, and treatment withdrawal was possible even in these groups.