Effect of the normalization of TSH and free T4 on lipid profile in a pediatric population with primary hypothyroidism

Hypothyroidism has been associated with dyslipidemia. Its treatment with levothyroxine has shown a positive effect on the lipid profile in adults, however, there is a lack of data on the pediatric population. Objective: to evaluate the effect of the thyroid profile normalization on the lipid profile in children with primary hypothyroidism. Patients and Method: Retrospective study in children aged from 6 to 16 years, with diagnosis of primary hypothyroidism due to Hashimoto's thyroiditis, in treatment with levothyroxine, and who had an evaluation of serum lipids before and during their treatment. The lipid profile was evaluated in 2 stages: the first one referred to as "before levothyroxine treatment" (at the diagnosis of primary hypothyroidism) and the second one referred to as " thyroid profile normalization" (when normalization of Thyroid-stimulating hormone [TSH] and free T4 [FT4] was achieved during levothyroxine treatment). Sociodemographic and anthropometric data were recorded. The lipid profile evaluation consisted of the serum determination of total cholesterol (TC), high-density cholesterol (HDL-C), and TG. The phenotype of dyslipidemias was determined according to the Fredrickson's classification. Results: 72 patients were included (61% women; age 11.5 +/- 2.9 years), out of which 58.3% (n = 42) presented pre-treatment dyslipidemia. In hypothyroid state, it was evident the correlation of TSH with TC (r = 0.36; p = 0.002), LDL-C (r = 0.46; p = 0.01), and HDL-C (r = -0.33; p = 0.004). The thyroid profile normalization showed the reduction of TC [184 mg/dL (IQR 92-322) vs 147 mg/dL (IQR 92-283); p = 0.05], LDL-C [99 mg/dL (IQR 44-232) vs 82 mg/dL (IQR 41-168); p = 0.02], TG [113 mg/dL (IQR 50-483) vs 88 mg/dL (IQR 16-343); p = 0.03], and the frequency of dyslipidemia [58.3% vs 22.2%; p = 0.001), as well as the TC correction with TG (r = 0.35; p = 0.02) and LDL-C (r = 0.88; p = 0.01). Persistent dyslipidemia was associated with obesity (r = 0.27; p = 0.02), overweight (r = 0.58; p = 0.001), and pre-treatment dyslipidemia (r = 0.53; p = 0.001). Conclusions: There is an association between TSH, TC, LDL-C, and HDL-C in hypothyroidism. When the thyroid profile was normalized, there was a reduction of TC, TG, LDLC, and dyslipidemia frequency. Persistent dyslipidemia was associated with obesity, overweight, and pre-treatment dyslipidemia.