Factors predicting hypothyroidism in long-term follow-up after 131I therapy

Area of Science:

• Endocrinology
• Nuclear Medicine
• Thyroidology

Background:

• Radioiodine therapy is a common treatment for hyperthyroidism.
• Long-term monitoring is essential to detect potential complications like hypothyroidism.
• Predicting the development of hypothyroidism post-treatment is crucial for patient management.

Purpose of the Study:

• To investigate the long-term incidence of hypothyroidism after radioiodine treatment for hyperthyroidism.
• To identify clinical and biochemical predictors of developing hypothyroidism.
• To evaluate the utility of serum TSH, FT4I, FT3I, cholesterol, and physical examination in predicting hypothyroidism.

Main Methods:

• A 10-year prospective study of 187 patients treated with radioiodine for hyperthyroidism.
• Regular monitoring of thyroid function tests, including serum TSH and FT4I.
• Assessment of clinical factors such as thyroid size, nodularity, autoantibodies, and physical changes.

Main Results:

• 43% of patients developed hypothyroidism within 10 years.
• Elevated serum TSH (100% sensitivity) and low FT4I (94% sensitivity) were strong indicators of hypothyroidism.
• Predictive value was lower for TSH in euthyroid patients (61%) and FT4I (78%). Initial large or nodular thyroids and absence of autoantibodies correlated with lower hypothyroidism incidence.

Conclusions:

• Serum TSH and FT4I are the most reliable biochemical predictors for long-term hypothyroidism after radioiodine therapy.
• Clinical assessment remains important, but biochemical markers offer superior predictive power.
• A continued, albeit slower, increase in hypothyroidism incidence is expected in the long term.