Evaluation of the etiology of subclinical hypothyroidism in children.

OBJECTIVES: Subclinical hypothyroidism (SH) is defined by normal free triiodothyronine (fT3) and free thyroxine (fT4) levels, elevated thyroid-stimulating hormone levels, and the absence of overt clinical signs of hypothyroidism. The natural course of SH is influenced by the underlying etiology. The purpose of this study was to evaluate the etiologic causes of SH.

METHODS: A total of 135 patients aged 1-18 years, diagnosed with SH by at least two analytical measurements, were included in the study. The anthropometric measurements, demographic characteristics, and laboratory findings of the patients were determined. A comparison was conducted between patients with Hashimoto's thyroiditis and patients with non-autoimmune etiology.

RESULTS: The median age was 9.7 (6.5) years, and 82 of the 135 patients were female. The most prevalent etiology was idiopathic, affecting 39 (28.9 %) patients. This was followed by obesity, which was identified in 21 (15.6 %) patients. Hashimoto's thyroiditis was the third most common cause, accounting for 18 (13.3 %) patients. In patients with Hashimoto's disease, fT4 levels were significantly lower, and the rate of initiation of LT4 treatment was higher than in patients with other etiologies. A heterozygous variation in the TSH receptor (TSHR) gene was detected in six patients.

CONCLUSIONS: In our study, idiopathic cases were the most frequently identified in the etiology of SH. It is important to determine whether there is autoimmune thyroiditis. In cases of idiopathic SH, it is recommended to perform TSHR gene analysis, particularly in the presence of positive family history and newborn screening results. This approach will help elucidate the underlying etiology.