Short- to medium-term follow-up of normoponderal children and adolescents with subclinical hypothyroidism: a retrospective study of the last 15 years.

Objectives: Subclinical hypothyroidism (SCH) is defined by elevated thyroid-stimulating hormone (TSH) levels (>5 mUI/L) and normal total and free thyroxine levels (fT4). There is ongoing debate over whether mild SCH should be treated. This study aims to assess the clinical course of normoponderal pediatric patients with SCH.

Methods: Retrospective study, involving normoponderal children and adolescents with SCH, followed at the Pediatrics Department of Hospital de Braga, from December 2007 to December 2022.

Results: We identified 47 children and adolescents with confirmed SCH. No sex predominance was found. The median age at diagnosis was 11 years. Most cases were idiopathic (59.6 %) and diagnosed during puberty (57.5 %). The majority (46.8 %) experienced spontaneous remission, while 38.3 % required levothyroxine (LT) therapy. Discharged patients were followed for a median of 25 months. No significant differences were seen in body mass index z-score, fT4 levels, heart rate, blood pressure, or lipid parameters. Significant differences were found in TSH levels and LT dosage. Thyroid peroxidase antibody (TPOAb) positivity was significantly correlated with SCH's natural history. Although initial TSH levels were not significantly associated with SCH's natural course, they predict treatment need. Individuals with initial TSH levels >6.47 mUI/L were more likely to require therapy. In the third year of follow-up, a significant strong negative correlation was found between TSH levels and high-density lipoprotein cholesterol.

Conclusions: SCH was self-limiting and benign in most cases. TPOAb positivity was a predictor of SCH's natural history, and the need for treatment was predicted by initial TSH levels.