The association between thyroid hormone balance and thyroid volume in patients with Hashimoto thyroiditis

Area of Science:

• Endocrinology and Metabolism
• Thyroidology
• Autoimmune Diseases

Background:

• Thyroid hormone profiles, specifically the free triiodothyronine (FT3)/free thyroxine (FT4) ratio, vary between patients with different thyroid conditions.
• Hashimoto thyroiditis (HT) is a common autoimmune thyroid disease characterized by thyroid gland inflammation and potential goiter formation.
• Understanding thyroid hormone dynamics in relation to thyroid volume (TV) is crucial for managing HT patients.

Purpose of the Study:

• To investigate the relationship between thyroid volume (TV) and thyroid hormone status, particularly the FT3/FT4 ratio, in euthyroid Hashimoto thyroiditis (HT) patients.
• To compare thyroid hormone levels and FT3/FT4 ratios in HT patients with varying degrees of goiter against control subjects.
• To assess the impact of levothyroxine (LT4) treatment on thyroid hormone levels and FT3/FT4 ratios in HT patients with large goiters.

Main Methods:

• Retrospective analysis of 2,603 untreated euthyroid HT patients and 1,554 control subjects.
• Patients were categorized into four groups based on thyroid volume (TV): normal, slight goiter, moderate goiter, and large goiter.
• Baseline laboratory data, including FT3, FT4, and thyroid autoantibodies, were compared; correlation analysis was performed between FT3/FT4 ratio and TV.

Main Results:

• HT patients with moderate and large goiters exhibited significantly higher serum FT3 levels compared to controls.
• All HT patient groups showed lower serum FT4 levels than controls.
• A significant positive correlation was found between the FT3/FT4 ratio and TV in HT patients, independent of age, sex, BMI, TgAb, and TSH levels. Levothyroxine (LT4) treatment reduced FT3 levels and FT3/FT4 ratios.

Conclusions:

• Euthyroid Hashimoto thyroiditis patients with increased thyroid volume tend to have higher serum FT3, lower FT4, and consequently, higher FT3/FT4 ratios.
• Elevated deiodinase activity is suggested as a potential mechanism influencing thyroid hormone balance in HT patients with enlarged thyroid glands.
• Levothyroxine therapy can modulate these thyroid hormone ratios, highlighting the complex interplay between thyroid size, hormone metabolism, and treatment in HT.