Growth hormone/insulin-like growth factor axis in patients with subclinical thyroid dysfunction

Area of Science:

• Endocrinology
• Thyroidology
• Growth Hormone Axis

Background:

• Subclinical thyroid dysfunction, characterized by abnormal thyroid-stimulating hormone (TSH) levels with normal free thyroxine (FT4) and free triiodothyronine (FT3), may impact other endocrine axes.
• The growth hormone-insulin-like growth factor (GH-IGF) axis plays a crucial role in growth and metabolism.
• Understanding the GH-IGF axis in subclinical thyroid states is important for comprehensive patient management.

Purpose of the Study:

• To evaluate serum concentrations of growth hormone (GH), insulin-like growth factor-I (IGF-I), and insulin-like growth factor-binding protein-3 (IGFBP-3) in patients with subclinical thyroid dysfunction.
• To compare these levels before and after normalization of thyroid function.
• To determine if subclinical hyperthyroidism or hypothyroidism differentially affects the GH-IGF axis.

Main Methods:

• Serum concentrations of TSH, FT4, FT3, GH, insulin, IGF-I, and IGFBP-3 were measured in 51 patients with subclinical hypothyroidism, 30 with subclinical hyperthyroidism, and 37 healthy controls.
• Measurements were taken before and after treatment aimed at normalizing thyroid function using levothyroxine (LT4) or antithyroid drugs.
• Statistical analysis compared levels between groups and before/after treatment.

Main Results:

• Baseline GH levels were similar across all groups.
• Serum IGF-I levels were significantly lower in patients with subclinical hypothyroidism compared to controls.
• Following treatment, IGF-I levels increased in subclinical hypothyroid patients but remained unchanged in subclinical hyperthyroid patients. GH and IGFBP-3 levels were unaffected by treatment.

Conclusions:

• The GH-IGF axis is affected in subclinical hypothyroidism, evidenced by altered IGF-I levels.
• Subclinical hyperthyroidism does not appear to significantly impact the GH-IGF axis.
• Levothyroxine replacement therapy can normalize GH-IGF axis abnormalities in subclinical hypothyroidism, suggesting its importance in managing these patients.