The relationship between serum triiodothyronine and thyroxine concentrations in hyperthyroidism

Area of Science:

• Endocrinology
• Thyroidology

Background:

• Relapses of hyperthyroidism after medical therapy are common in toxic nodular goiter.
• A high triiodothyronine (T3) to thyroxine (T4) ratio has been suggested to predict hyperthyroidism relapse in toxic diffuse goiter.

Purpose of the Study:

• To investigate the relationship between T3 and T4 ratios in untreated toxic diffuse goiters and toxic nodular goiters.
• To determine if the T3/T4 ratio can predict relapse of hyperthyroidism after medical treatment.

Main Methods:

• Compared T3/T4 ratios in patients with toxic diffuse goiters (n=46) and toxic nodular goiters (n=12).
• Analyzed T3/T4 ratios in toxic diffuse goiter patients who achieved remission (n=10) versus those who relapsed (n=10) at baseline, 4, and 8 weeks.
• Compared both groups to normal controls (n=16).

Main Results:

• No significant difference in T3/T4 ratios was found between untreated toxic diffuse and toxic nodular goiters.
• Both toxic goiter groups showed significantly higher T3/T4 ratios compared to normal controls.
• No significant differences in T3/T4 ratios were observed between patients with toxic diffuse goiter who relapsed or remained in remission.

Conclusions:

• The T3/T4 ratio is not a useful marker for distinguishing between diffuse and multinodular toxic goiters.
• The T3/T4 ratio does not reliably predict the prognosis of hyperthyroidism after medical treatment.
• A very high T3/T4 ratio (>60 nmol/mumol) after 8 weeks of treatment was associated with recurrence in 3 patients.