Subclinical Hypothyroidism in Children: Natural History, Risk Factors, and Outcomes

Background: Subclinical hypothyroidism (SH) is defined by elevated thyroid-stimulating hormone (TSH) with normal thyroid hormone levels and typically presents without specific symptoms in children. Although treatment criteria exist, predictors of progression and treatment need remain uncertain. Objective: To evaluate the natural course of mild SH, identify clinical conditions associated with elevated TSH, determine predictors of progression requiring levothyroxine, and assess growth outcomes. Methods: Records of 111 children (3 months-18 years) with mild SH (TSH 5-10 mIU/L on ≥ 2 measurements) and ≥ 6 months of follow-up were retrospectively reviewed. Demographic, biochemical, anthropometric, etiological, and imaging data were analyzed. Children were categorized as idiopathic or as having associated clinical factors (autoimmune thyroiditis, iodine imbalance, obesity, or medication use). Outcomes were classified as euthyroid, persistent SH, or requiring treatment. Results: During follow-up, 45 children (40.5%) became euthyroid, 49 (44.2%) remained subclinically hypothyroid, and 17 (15.3%) required levothyroxine. Idiopathic cases showed the most favorable course, with only 8.6% requiring therapy. Hashimoto's thyroiditis (HT) was the strongest predictor of progression (42.1% vs. 9.8% in non-HT). A baseline TSH > 7.5 mIU/L increased treatment likelihood by ~3.5-fold. Growth parameters remained within normal limits, with no deterioration in untreated children. Conclusions: Mild pediatric SH is generally benign and self-limited, particularly in idiopathic cases. HT and higher baseline TSH levels are key predictors of progression, while growth remains stable. Management should be individualized based on underlying conditions, TSH severity, and autoimmune status.