T4 plus T3 treatment in children with hypothyroidism and inappropriately elevated thyroid-stimulating hormone despite...

Area of Science:

• Pediatric Endocrinology
• Thyroid Hormone Replacement Therapy

Background:

• Congenital hypothyroidism (CH) requires lifelong thyroid hormone replacement.
• Levothyroxine (L-T4) monotherapy can lead to persistent high thyroid-stimulating hormone (TSH) levels despite normal serum thyroxine (T4).
• This 'inappropriate hyperthyrotropinemia' may indicate inadequate T3 action at the pituitary level.

Purpose of the Study:

• To investigate the efficacy of adding triiodothyronine (T3) to L-T4 treatment in children with CH and persistent hyperthyrotropinemia.
• To determine if combination therapy can normalize TSH levels without inducing hyperthyroidism.

Main Methods:

• A cohort of 10 children with CH and persistently elevated TSH on L-T4 were switched to a combination therapy (T3+L-T4).
• The combination therapy involved 50% of the usual L-T4 dose and T3 in a 4:1 ratio, titrated to normalize TSH.
• Patients were monitored for thyroid hormone levels, biochemical markers, and vital signs for 1 year.

Main Results:

• Combination T3+L-T4 therapy achieved euthyrotropinemia (normal TSH) at a mean of 7 months.
• Serum T4 and free T4 (fT4) levels were lower, while T3 levels were higher on combination therapy compared to L-T4 alone.
• LDL-cholesterol decreased and alkaline phosphatase (ALP) increased during combination therapy; vital signs remained stable.

Conclusions:

• Combination T3+L-T4 therapy effectively normalizes TSH in children with CH and inappropriate hyperthyrotropinemia.
• This treatment approach achieves euthyrotropinemia without inducing clinical hyperthyroidism.
• The findings support the hypothesis that reduced pituitary T3 levels impair negative feedback, leading to persistent hyperthyrotropinemia on L-T4 monotherapy.