Comparison of pathophysiology in subclinical hyperthyroidism with different etiologies

Area of Science:

• Endocrinology
• Thyroidology
• Metabolic Research

Background:

• Subclinical hyperthyroidism (SHyper) is characterized by normal free thyroxine (fT4) and free triiodothyronine (fT3) with suppressed thyroid-stimulating hormone (TSH).
• Previous research has examined endogenous SHyper and TSH suppression therapy separately, but direct comparisons are lacking.

Purpose of the Study:

• To compare the physiological effects of endogenous subclinical hyperthyroidism with those of TSH suppression therapy in athyreotic patients.
• To investigate thyroid hormone profiles and peripheral indicators of thyrotoxicosis in both groups and healthy controls.

Main Methods:

• A comparative study involving 540 untreated endogenous SHyper patients and 1,024 athyreotic patients on levothyroxine TSH suppression therapy.
• Analysis of thyroid hormone levels (fT4, fT3), TSH, alkaline phosphatase (ALP), creatinine (Cre), and pulse rate.

Main Results:

• Endogenous SHyper patients had higher fT4 and fT3 levels and more peripheral signs of thyrotoxicosis than healthy controls.
• Athyreotic patients on TSH suppression therapy showed thyrotoxicosis signs only with strongly suppressed TSH.
• Endogenous SHyper patients had higher fT3 and more thyrotoxicosis signs (ALP, pulse rate) than athyreotic patients, especially with strong TSH suppression.

Conclusions:

• Endogenous SHyper and TSH suppression therapy exert distinct effects on target organ function.
• Athyreotic patients with mildly suppressed TSH levels on TSH suppression therapy are not thyrotoxic, despite similar thyroid hormone profiles to thyrotoxic states.