Endocrine Abstracts

JOINT2486

Introduction: Congenital hypothyroidism (CH), a leading cause of preventable intellectual disability in children, can be identified early in life through newborn screening (NBS) programs. This study aims to analyze the clinical and biochemical characteristics of CH patients and identify predictive factors for transient CH (T-CH) in children diagnosed through NBS.

Methods: This retrospective study included a total of 322 term neonates (M/F=163/159) diagnosed through NBS and initiated on levothyroxine therapy between 2006 and 2020. Patients were classified as thyroid dysgenesis (TD) or gland in situ (GIS) (dyshormonogenesis, DH) based on ultrasonography. Exclusion criteria included T-CH due to maternal factors, prematurity; syndromic and central CH. Cases with T-CH and permanent CH (P-CH) were compared based on gender, baseline thyroid hormone levels, and levothyroxine dosage at presentation and during follow-up (at 6 months, 1 year, 2 and 3 years). P-CH was diagnosed in patients whose TSH>10 μIU/ml following the discontinuation of levothyroxine therapy after at least 3 years of follow-up. Predictive factors for T-CH were identified.

Results: Among the cases, 22.7% (n=73) were categorized as TD, and 77.3% (n=249) as DH. Overall, 60.2% (n=194) of the patients were identified as having T-CH, while 39.8% (n=128) were classified in the P-CH group. Ultrasonography revealed thyroid agenesis in the majority (53.4%, n=39) of cases in the TD group. Screening TSH levels, initial venous TSH levels, initial treatment doses, and treatment doses at 6 months, and at 1, 2, and 3 years were significantly higher in the TD group (P=0.001 for all except the initial treatment dose, P=0.006). In DH group, after re-evaluation, 55 patients (23%) required restarting levothyroxine treatment and were diagnosed of P-CH. Among DH cases, mean heel blood TSH levels were significantly higher in the P-CH group (50.4±30.7 mIU/l) compared to the T-CH group (28.2±20.4 mIU/l) (P=0.001). Furthermore, in the P-CH group, treatment doses at the 1st, 2nd, and 3rd years were significantly higher than in the T-CH group (P<0.001 for all). ROC analysis identified levothyroxine dose thresholds for predicting T-CH as 2.1, 1.9, and 1.5 mg/kg/day at 1, 2, and 3 years, respectively.

Conclusion: This study identifies levothyroxine dose thresholds during first 3 years of life, to distinguish transient and permanent CH. Systematic re-evaluation, especially in DH cases at 3 years or even earlier, is crucial for minimizing unnecessary treatments and optimizing long-term follow-up plans. These findings support a tailored approach to CH management.

Key words: Congenital hypothyroidism, Newborn screening, Transient congenital hypothyroidism